Building Efficiency

Articles and resources on building envelope efficiency

Troubleshooting Condensing Boilers in Hydronic Systems – What is the System Doing?

This a guest post from Roy Collver. Roy is a condensing boiler expert. Here’s what John Siegenthaler, author of “Modern Hydronic Heating,” says about Roy’s work: “When I have a detailed question about the inner operation of a modulating / condensing boiler, Roy Collver is the first person I contact. The investment in Roy’s HeatSpring course is a fraction of the cost of a single mod/con boiler, but it will teach you concepts, procedures, and details that will return that investment many times over.”

Learn from Roy

  • Free. Roy is teaching a two-part free course on how to sell mod-con boilers. The second live lecture is happening on Wednesday, July 30th. Sign up for the free mod-con course here.
  • Paid: Roy Collver teaches an advanced 5-week course on mastering condensing boiler design in hydronic systems with the folks at HeatSpring. If you need to increase your skills and confidence around selling, quoting, designing, setting up controls, or troubleshooting condensing boilers in new construction or retrofit applications, this course is for you. Each session is capped at 50 students, but there are 30 discounted seats. Get your discount and sign up for Condensing Boilers in Hydronic Systems.

Enter Roy…

Understanding the Simple Basics

Cold weather is never too far away in most parts of North America. Be ready when it hits, and review the basics of hydronic system operation so you can quickly locate the problems that always come up. When you approach an operational hydronic system it will exhibit one of the following six states. Quickly understanding what you are dealing with will greatly reduce head-scratching time and point you in the right direction. Standing slack-jawed in front of a boiler with no clear path to determining what is wrong is very uncomfortable and a waste of time. Confidence is a key factor in successful troubleshooting, and to be able to indicate to a customer what the BASIC problem is right away buys you time to be able to work the problem, find out the SPECIFIC cause, and fix it. Using this guide as a quick reference should help speed the troubleshooting process along.

Hydronic systems are all about Delta T (the difference in temperature between the heating fluid, the system components and the surrounding air and objects). Heat always travels to cold, and if heat is not added to the heat transfer fluid (usually water), the fluid and all of the components in the system will eventually cool down to the temperature of the surroundings.



The boiler is on and the hot combustion gases create a large Delta T between the combustion chamber and the water in the surrounding heat exchanger. Because heat travels to cold, the water heats up. The circulation pump moves the hot water through the distribution piping to the terminal units. The terminal units heat up and a Delta T develops between the hot terminal units and the colder air. The air will get warmer at the expense of the water, which cools slightly. The cooler water circulates back through the system back to the boiler where it is heated up again. If the heat going into the boiler is more than the system can use, the water will continue to get hotter until the boiler cycles off on its operating control. The temperature difference between the water leaving the boiler and the water returning to the boiler will be “normal” for the system (usually 15°F to 40°F depending on the load and system design).

noflowThe boiler is on, adding heat to the water, but for some reason the hot water is not circulating through the distribution piping to the terminal units. The terminal units will cool down to the temperature of their surroundings and a “no heat” condition will result. The water in the boiler will continue to get hotter until the boiler cycles off on its operating control or internal high limit control. The supply and return piping near the boiler will be close to the same temperature.



The boiler is on, adding heat to the water, but the hot water is not circulating fast enough through the system. The first terminal unit may become warm, but because the water is moving so slowly, all of the usable heat is transferred out of it before it gets very far. The last terminal units do not become warm enough to heat the space and a “not enough heat” condition will result. The water in the boiler will continue to get hotter until the boiler cycles off on its operating control or internal high limit control. There will be a large Delta T between the water leaving the boiler and the water returning to the boiler. (The supply will be a bit hotter than normal, but the return will be much colder than normal.)


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[Free Floor Plan] 10 Ways Passive House Design is Different Than Normal Home Design

If you want to download the floor plan, please scroll to the bottom of the article.

This is a guest post by Mike Duclos. Mike is founder of The DEAP Energy Group, a firm providing a wide variety of deep energy retrofit, zero net energy, and Passive House related consulting services. Mike has real-world experience with the design, construction, certification, and delivered performance measurement of Passive House, and is a Certified Passive House Consultant. Mike will be teaching a 6-week course on Passive House Design as part of NESEA’s Building Energy Master Series that will teach builders, architects, and engineers the fundamentals of Passive House design. In the class you’ll design your own passive house and get it reviewed by Mike using “PHPP Lite.” The class is capped at 50 students with 30 discounted seats. Sign up for the Passive House Design training here. 

Passive House Design vs Normal Home Design

Passive House is a hot topic, and we get a lot of questions about how to design and model these homes. Most people are familiar with design principles for “normal” residential homes, so we wanted to provide a sample as-built for an actual Passive House with a number of comments on how its design is different from traditional construction.

A Real Passive House Design

passive house plans

Here are 10 Key Design Features That are Different From Normal Residential Home Design

  1. The long elevation of the home faces close to due South, providing more wall area for windows.
  2. Home is positioned on lot so views are to the South so that the larger South window area is used to advantage for both the view and solar gain.
  3. Room layout centers around a ‘great room’ comprised of a living and kitchen/dining area for entertaining a modest number of people in 1152-square-foot home.
  4. Master bedroom receives sun from the East and South; the other front bedroom receives sun from the South and West.
  5. Point source heating efficacy is optimized by use of a central great room in which a single, 9 KBTU/hr  ductless mini-split is used for all space conditioning.
  6. Bathroom door is located immediately below ductless mini-split, for best localized space conditioning.
  7. Mechanicals are located between bathroom and kitchen sink, minimizing delay to hot water and stranding of hot water after a draw. Solar DHW tank can contribute 300-500 BTU/hr next to the bathroom door.
  8. Glazing is maximized on the South elevation, minimized on East and especially West to help manage overheating , and is minimized on the North to minimize space heating losses.
  9. South elevation has one entry door which is glazed to take advantage of the view and the sun.
  10. Mudroom on the North is the entrance used on a daily basis by occupants.

Download the Sample Passive Home Design

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Robert Bean + HeatSpring = Integrated HVAC Engineering Training

The way a building functions represents an incredibly complex intersection of numerous fields, including architecture, design, engineering, environmental and health sciences, and construction. As each field evolves, it becomes increasingly necessary, but also difficult, to understand how they are interrelated. If you find yourself looking for a way to marshal the knowledge from each of these fields into a comprehensive and  comprehensible framework, look no further: “Integrated HVAC Engineering: Mastering Comfort, Health, and Efficiency” is a multidisciplinary online design course based on thirty years of data and experience. The course goes beyond ASHRAE and LEED standards to the heart of HVAC engineering: integrating comfort, health, and efficiency to the maximum benefit of the building occupants.

The course is capped at 50 with 30 discounted seats available. View a full course outline for Integrated HVAC Engineering: Mastering Comfort, Health, and Efficiency

The course is taught by Robert Bean, R.E.T., P.L.(Eng.), a registered engineering technologist in building construction and a professional licensee in mechanical engineering. Robert is president of Indoor Climate Consulting Inc. and director of He is a volunteer instructor for the ASHRAE Learning Institute and serves ASHRAE TC’s 6.1, 6.5, 7.4 and SSPC 55 Thermal Environmental Conditions for Human Occupancy. He is a special expert on IAPMO’s new Uniform Solar Energy and Hydronics Code committee.

This integrated design course, based on thirty plus years of data-driven experience, goes beyond ASHRAE and LEED standards to the heart of HVAC engineering. ASHRAE 55 addresses comfort. ASHRAE 62 addresses ventilation. ASHRAE 90 and 189 address efficiency. LEED and others attempt to address the entire universe. You cannot understand these dogmatic systems without truly understanding first how to integrate comfort, health, and efficiency to the maximum benefit of the building occupants. This course is crafted for the select few who thirst for comprehensive knowledge. Those who desire a deeper understanding of the fundamental principles of designing great indoor environments, buildings, and HVAC systems. Includes numerous field-ready calculators and design tools. Scroll down this page for the course outline.

This course is for working design practitioners (who may be a recent graduates from architectural, mechanical engineering, or interior design programs) as well as those from the manufacturing, distribution, contracting, and inspection professions. Experienced professionals who may want to expand their knowledge of building science, indoor environmental quality, systems controls, radiant heating and cooling, and fluid hydraulics will also benefit from the program. This course will help students understand the principles behind: ASHRAE Standards 55, 62, 90, 189, ASHRAE Guidelines 10 and 24; and IEA Annex 37, 49 and 59.

Graduates of the class will be able to:

  • Assess materials of construction, buildings and systems from a thermal comfort, indoor air quality, energy, eXergy, entropy, efficiency and efficacy perspective.

  • Assess buildings from a durability perspective.

  • Understand how building enclosures act and serve as a filter, sponge and capacitor.

  • Make enclosure recommendations to improve IEQ whilst conserving energy and maximizing eXergy efficiency.

  • Explain thermal comfort and indoor air quality from a human physiology perspective and communicate how the outdoor and indoor environments affect occupants in subjective and non subjective ways.

  • Assess and recommend HVAC systems based on characteristics which enable acceptable IEQ, and maximum energy efficiency using less heat of a lower temperature in heating and of a higher temperature in cooling.

  • Use heat transfer principles to define loads and operating conditions for building and HVAC systems

  • Explain effectiveness coefficients for temperatures used in HVAC systems.

  • Explain the characteristics of different heat terminal units and the associated percentile splits in heat transfer mechanisms (radiation, conduction, convection).

  • Assess the difference between the safe, acceptable, good, bad and ugly in mechanical rooms and systems.

  • Describe the various components, sub assemblies and systems in radiant based hybrid HVAC systems.

  • Convert heating and cooling loads into flows; select pipe and ducts based on velocity and pressures, and determine differential pressure requirements in the distribution system.

  • Assess control valve selection and perform a control circuit pressure authority calculation.

  • Assess fluid and operating characteristics and size expansion tanks and air separators.

  • Select circulators and pressure control options based on system head losses.

  • Explain control theory and approaches including non-electric and electronic using PI, PID and fuzzy logic.

  • Design a radiant-based hybrid HVAC system for a reversible surface (heat/cool) in parallel with a dedicated outdoor air system for dehumidification, deodorization and decontamination of incoming air.

  • Perform thermal comfort calculations to comply with ASHRAE Standard 55.

This is a unique and incredibly valuable opportunity to become Robert’s student for 10 weeks and learn from his decades of experience. He’ll provide all the resources you need to understand integrated hybrid HVAC design and answer all the questions that come up along the way. In the final week of the course, you’ll submit a capstone project that incorporates everything you’ve learned. This will include running thermal comfort calculations and designing a radiant-based hybrid HVAC system with a dedicated outdoor air system (DOAS).

In the capstone project, students will:

  1. Perform thermal comfort calculations.

  2. Design a radiant-based HVAC system with a dedicated outdoor air system (DOAS).

  3. Make recommendations to improve IEQ and energy efficiency through architectural, building, and interior systems.

The course is capped at 50 with 30 discounted seats available. View a full course outline for Integrated HVAC Engineering: Mastering Comfort, Health, and Efficiency

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NESEA, Mike Duclos and HeatSpring Launch Passive House Design Training

If you’re a professional in the building industry, you’ve probably heard of the growing Passive House movement. You may even be familiar with the basic principles. If you have clients who want to apply the Passive House standard to an actual project, and you’re looking for a crash course to get yourself up to speed on the basics, “Passive House Design” is the perfect solution. This new course in HeatSpring and NESEA’s Building Energy Masters Series is designed as a solid introduction to the knowledge and skills you’ll need for Passive House construction or consulting work.

The course starts on September 22nd. The course is capped at 50 students and we’re providing 30 discounted seats. Click here to read more about the course and reserve one of thirty discounted seats.

This intensive, six-week course is taught by Mike Duclos, a founder of The DEAP Energy Group, a firm providing a wide variety of deep energy retrofit, zero net energy, and Passive House related consulting services. Mike has real world experience with the design, construction, certification and delivered performance measurement of Passive House, and is a Certified Passive House Consultant.

Mike’s course covers the history of Passive House design, a detailed explanation of the Passive House standard and how to meet its requirements, the social and environmental context, energy modeling and the Passive House Planning Package (PHPP), and real-world examples of buildings constructed to the Passive House standard. And that’s all in the first week!

Subsequent weeks delve deeper into the application of the Passive House standard on real-world projects. Sample floor plans and a variety of design tools and calculators are included. Students who complete the course will design a simple Passive House “lite” using a simplified version of the PHPP.

The material and exercises will challenge you theoretically and practically, but Mike will be there every step of the way to provide insights and direction through the course discussion board.

Graduates of Passive House Design will walk away with:

  1. A detailed understanding of the history and hidden challenges of very low energy home design and different approaches that have been used successfully.
  2. A simplified version of the PHPP designed as a basic introduction to Passive House modeling and to provide quantitative feedback on key architectural design decisions critical to a successful Passive House design—without all of the labor-intensive detail required by the full PHPP.
  3.  A capstone project: Successful design of a home using the simplified PHPP to get a taste of meeting some of the most difficult challenges of Passive House: Space Heat Demand and Primary Energy.

About Mike Duclos

Mike Duclos is a principal and founder of The DEAP Energy Group, LLC, a consultancy providing a wide variety of Deep Energy Retrofit, Zero Net Energy and Passive House related consulting services. Mike was an energy consultant on the Transformations, Inc. Zero Energy Challenge entry, and has worked on a variety of Zero Net Energy, DER and Passive House projects, including two National Grid DER projects which qualified for the ACI Thousand Homes Challenge, Option B, the first National Grid DER to achieve Net Zero Energy operation, and the first EnerPHit certified home in the USA. Mike is a HERS Rater with Mass. New Construction program specializing in Tier III design and certification, a Building Science Certified Infrared Thermographer, a Certified Passive House Consultant responsible for the design and certification of the second Passive House in Massachusetts, holds a BS in Electrical Engineering from UMass Lowell, and has two patents.

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5 Keys for Greening Commercial Roofs

Dr. Jim Hoff currently serves as vice president of research for the Center for Environmental Innovation in Roofing in Washington, D.C., and president of TEGNOS Research Inc., a consulting organization dedicated to expanding understanding of the building envelope. He’s also the instructor of the upcoming “Commercial Roofing Boot Camp” — an advanced online design course that has been approved by RCI for 20 continuing education hours and by the American Institute of Architects (AIA) for 20 Learning Units.

In this interview, Dr. Hoff responded to readers’ most common questions about environmentally friendly, green, and sustainable roof systems.

Question 1: When I talk to building owners and architects who want a LEED building, the only thing they want to know about the roof is whether or not it’s white because white roofs get a LEED credit. Isn’t this a very shortsighted way to design and spec a roof?

Dr. Hoff: Yes, it is very shortsighted; and I’ll be the first to admit that changing the narrow focus on white roofs supported by the LEED heat island credit is very difficult. Probably the best tool available to improve the discussion about roof surface color is the RoofPoint program developed by the Center for Environmental Innovation in Roofing. RoofPoint recognizes the “greenness” of roofs using twenty three different credits, and only one of these credits addresses roof surface color. And even the roof surface color credit in RoofPoint allows the use of darker roofs in the coldest climates and also provides for other cool roof alternatives such as ballast in all climate zones. It’s a great program to help educate building owners and help demonstrate that you can be a valuable expert on the best in sustainable roofing practices.

Question 2: How can I go about integrating green into my business?

Dr. Hoff: I think it’s important to integrate green into your business in three basic ways. First, focus on one or two sustainable roofing strategies that could provide real value for your customers. As an example, if you reroof a lot of warehouses for a local developer, consider integrating daylighting – or skylights – into your roofing proposals. There are many excellent design tools available to help you get started, and the payback is very good, especially if you can integrate the skylights into the lighting controls. For businesses with high hot water needs, such as laundries, car washes, etc., rooftop solar thermal can also be a profitable add-on to the next reroofing project.

Next, look for ways to get your employees involved. Is there a company-wide policy regarding recycling? Do you emphasize that worker safety is just as green as any other green practice – after all green is fundamentally about people.

Finally, combine the one or two green sales strategies and green employee policies and start to reach out to the community. Instead of buying uniforms for a local ball team, consider what you could do to help your community save energy and reduce waste – and when you do it will only help promote your own green practices and increase your reputation as a sustainable business.

Question 3: I like green as in sustainable, but I also like green as in profit. How can I turn sustainable practices into the kind of green my bank accepts for deposit?

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5+ Trends that will Drive the Growth of the Hydronic Industry in the Next 3 Years: A 30-Minute Conversion with John Siegenthaler

hydronic heating

There are a variety of forces changing the dynamics of the hydronic heating and renewable thermal industries that were not happening five years ago. While hydronic distribution is still attractive for similar technical reasons that it was five years ago—comfort, air quality, etc.— there are a host of new trends that can have the ability to increase the adoption of hydronics if we can utilize them correctly.

Here’s a quick list of some new trends

  1. We’re lobbying for production based renewable thermal incentives in Massachusetts. Similar actions are being looked at in New York, Maine, and Connecticut. Read about the Massachusetts Clean Heat Bill here. Note, we got this bill out of committee two weeks ago. If you’re in Massachusetts and would like to help with this, email me at If we pass it, this will increase the demand for renewable thermal heat sources and hydronics can be an amazing way to distribute these low temperature heat sources.
  2. Biomass pellets are increasing in adoption because the MMBTU cost is half that of oil. Read more on the BTEC report here. 
  3. Heat pump technology continues to advance with impressive gains on the air source side (both air to air and air to water). Read more about ASHPs + Zero Net Energy Homes here. While hydronic professionals don’t care much about air to air heat pumps, the ability of air to water heat pumps to provide cool water opens up radiant cooling possibilities in the residential market.
  4. GSHPs have not seen a substantial increase in adoption due in large part to the fact that there’s no way of actually verifying in-field performance over a long period of time. This substantially increases perceived risk to property owners that might want to invest in the technology. Real time monitoring for GSHPs is now very cheap and effective, reducing the risk for homeowners to invest in the technology by making it possible to verify that the system is operating as promised, all the time. Read more about Lessons Learned from 100,000+ Hours of Real Time Geo Monitoring Data here. 
  5. ASTM is in the process of finalizing a standard on BTU metering that will help with policy (see bullet 1) of production-based incentives for renewable thermal technologies and much more that we’ll get into during the interview.

When you look at these trends, it’s clear that the hydronic industry has a lot to look forward to. All of these major industry shifts have the ability to increase demand for hydronic distribution systems in residential and commercial applications, for both new construction and retrofits.

In this 30-minute discussion, I talk with John Siegenthaler to see what he sees driving growth in the hydronics industry over the next 3 years. John is a hydronic expert. He teaches Mastering Hydronic System Design and wrote the industry textbook on the subject as well.

If you’re looking to grow the hydronic side of your business or enter the market in the next year or two, you need to listen to this interview. It will provide a special understanding of the industry developments that are on the horizon. Understanding these trends will allow you to take advantage of them. And by take advantage, I mean increase sales.

Here are the key points that we talked about. See below for a full list of items that you’ll learn when listening to the whole interview.

  1. Low temperature heat sources and renewable sources
  2. Single thermal mass systems
  3. Radiant cooling
  4. BTU metering
  5. How technology is changing design best practices

Listen to the Entire Interview 

In this interview, you will learn: 

  • Why John sees low temperature heat sources and renewables driving the adoption of hydronics as the distribution system.
  • Why worldwide low temperature hydronics has moved to 120 degree water temperature as a maximum water temperature under full load.
  • Why low temperature keeps the distribution system compatible with renewable sources.
  • Why you need to learn about hydronic technology if you’re interested in renewable heat sources like solar thermal, heat pumps, and biomass. Ductless heat pump systems are gaining popularity in cold climates like Maine.
  • The difference between the design advice that John is providing today versus 8 years ago and why technology is driving that change.
  • How advances in technology are tangibly impacting the day-to-day operations of professionals in the field.
  • How radiant walls and ceiling can be used with low-temperature applications and  still get great performance.
  • How to use fin-tube baseboards in low water temperature design.
  • Why a large majority of contractors aren’t even aware of what an air to water heat pump is.
  • The key things that John thinks every engineer and contractor needs to understand about heat pumps, including why they’re a renewable source of heat.
  • How heat pumps open up the hydronic industry to cooling, which has been an issue for industry growth for a long time.
  • Why the decreasing costs of solar PV and zero net energy design is driving the adoption of heat pump technology in the hydronic industry.
  • Why smaller duct size, small fans, shorter builders, and lower installation and operating costs is driving the adoption of commercial radiant cooling.
  • Why not being able to easily and cheaply monitor dew point is slowing the adoption of radiant cooling in the residential market.
  • John’s advice for hydronic contractors who want to start doing radiant cooling, working with heat pumps and low mass radiant ceilings.
  •  Why radiant ceilings might start growing FASTER than radiant floors in the coming years.
  • Why John sees single thermal mass system growing in the residential market by reducing installation costs and simplifying system design.
  • The impact of technology on hydronic best practice design and installation.
  • How ECM pumps are substantially reducing operating cost at least 50%.
  • The impact that the new ASTM ANSI BTU metering standard will have on the design and installation of systems in the hydronics market by removing risk for engineering teams.
  • How BTU metering will encourage conservation.
  • Why BTU metering will make district heating more common.
  • How John sees Zero Net Energy and passive house impacting the hydronic industry and the potential role for hydronics
  • The best applications for hydronics within highly efficient buildings.

Questions? What did I get right or miss?

  • If you have any questions or comment about the interview, please leave them in the comment section
  • What trends did I get right?
  • For the contractors, engineers, and architects working with clients every day, what are you seeing in the market?
  • What trend did we miss that you’re seeing?

Want to Learn More?

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Learn How to Calculate the Heat Loss for a Zero Net Energy Home, For Free

Can you answer this question?


No? Perhaps you need the tool below.

 Zero Net Energy Home Heat Loss Calculator

Learn how to Calculate Heat Loss

Click here to sign up for a free test drive of the “Zero Net Energy Homes” course, get the  heat loss calculator, and learn how to calculate the heat loss for a Zero Net Energy home.

In the past 18 months, Marc Rosenbaum has trained 150 professionals how to design zero net energy homes, and the results have been phenomenal. For the capstone project, students submit full designs for zero net energy homes including energy models and floor layouts, which get personally reviewed by Marc. Click here to see two of the capstone projects for yourself.

Students love the high-quality, detailed content; the interaction with Marc and the other students; the tools that can immediately be applied in practice, making them incredibly valuable; and, most of all, the price. You can learn all these skills for under $1,000. An in-person version of this course would cost well over $5,000 (when factoring in travel, hotels, and loss of work time), and you wouldn’t get to delve into the subjects as deeply due to time constraints.

Why is calculating heat gain/loss of a structure so important?

Building a home with an extremely low heat loss is the basis for a well designed, cost effective Zero Net Energy Home. In order to design a home with a low heating and cooling load, you must be able to understand how  design elements of the shell, wall construction, and window and door quantity and placement will impact the heat gain or loss of the building. In this test drive, you will get the video lessons, reading lessons, a free tool, and an assignment to calculate the heat loss of a sample building.

There are three main drivers of energy use in a residential home after it has been built: the heating and cooling load, hot water use, and appliances.

While efficient equipment and closely-monitored energy consumption can substantially decrease the energy used in hot water production and appliances, it’s critical to consider the quality of the shell. The shell of the home is the basis for designing the HVAC system that will determine the heating loads, but it’s also the place where a lot of design decisions will be made based on the client’s desires and tastes, which will impact building and operating costs.

Why are we offering the free test drive?

Think of the test drive like auditing a college course. In the first day or two, you can usually tell if you’re going to like the teacher, the content, the format, and goals of the class. This is exactly how this test drive works.

We created the test drive for two main reasons:

  1. We want to spread this information. Even if you never sign up for the full course, the reading assignments, one hour of video, and free tool will be extremely useful to you.
  2. It will show you how the online course structure works. We’ve worked really hard to make our online courses facilitate real human-to-human interaction, provide amazing content, and lay the content out in a way that’s easy to learn. However, providing extremely high-quality learning experiences for very technical subjects online is still new, so some students are understandably skeptical. The purpose of the test drive is to put any doubts to rest.

What’s included? 

zero net energy homes sample content

  • One hour of sample content
  • Two quizzes to make sure you learned the material
  • One Free Tool: Marc’s Heat Loss Calculator
  • One homework assignment

What will you learn in the test drive?

The goal of the test drive is to get students comfortable with the online course setting and showcase the excellent content.

Everyone needs to understand how to accurately (and quickly) determine what the heat loss of a potential home design is going to be. In the test drive, you will be provided everything you need to calculate the heat loss of a Zero Net Energy building, and you’ll have a homework assignment to test your knowledge and compare it against the right answer.

 Click here to sign up for a free test drive of the “Zero Net Energy Homes” course

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Free Hydronic Design Video From John Siegenthaler

This ten minute video is all about fittings. Fittings can be an afterthought, but they are a critical component for designing a high-performing hydronic heating system. In this video, John Siegenthaler outlines the universe of fittings, and even tells you which fittings you should avoid when designing a hydronic system.

This video comes from John’s ‘Hydronics Master Class’ – an advanced training for hydronic system designers. Click here to learn more about the Hydronics Master Class.

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Free 26 Minute Lesson on Performing Heat Loss Calculations for Net Zero Energy Homes

Calculating heat loss, and designing for minimal heat loss, is absolutely critical to designing and building net zero energy home or to passive house standards.

Watch this 26 minute video lesson, from Marc Rosenbaum’s Zero Net Energy Homes course to learn about how to design buildings with minimal heat loss. If you need to learn how to design Zero Net Energy Homes, here are a few great resources.

  1. Click here to sign up for Marc’s course ”Net Zero Energy Homes” and design a zero net energy home in 6 weeks
  2. Click here to test drive Marc’s course for free and learn how to calculate the heat loss for a Zero Net Energy Home with a free heat loss calculator and an hour of video lessons.
  3. Click here to read a case study of 8 net zero energy homes designed by Marc’s company, South Mountain Company

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Full Case Study of 8 Net Zero Energy Homes

The following post is a case study of 8 Net Zero Energy Homes that were designed by South Mountain Company (SMC). SMC’s Marc Rosenbaum is teaching a class on Net Zero Energy Design that will give you all of the information and tools (Marc’s own custom made tools) to design Net Zero energy homes. The capstone project will be for you to submit a full design, including floor plans, energy models, shell designs, for a net zero energy home. Your design will receive feedback from Marc. Why is this awesome? Because it will provide you all the information you need to design future projects.

  1. Click here if you want to see students past capstone projects for the Zero Net Energy Homes course.
  2. Click here to watch a 26 minute video lesson calculating heat loss for net zero energy homes.
  3. Click here to sign up for the “Zero Net Energy Home” course.

If you’d like to download the case study, please enter your information below.

Copyright Odds and Ends

This article is the copyrighted property of South Mountain Company, Inc. West Tisbury, MA. It was represented with permission.

Please do not publish in entirety, in part, or quote, without express written permission. For permission, please contact John Abrams at


The eight houses are grouped around a central pedestrian green with parking at the perimeter. All houses received LEED Platinum designation and all have permanent affordability restrictions. Each owner purchased the house and ground leases the property from the Island Housing Trust, a community land trust. One of the homes was constructed by Habitat for Humanity with technical assistance and guidance from South Mountain Company during the construction process. Half of the houses are three bedroom units of 1,447 sf and half are two bedroom units of 1,251 sf, all with full basements. The main living area and upstairs bedrooms and bath are identical in the two house types; the third bedroom is a north extension of the two bedroom plan. Designed and built to be net zero possible, they are all-electric homes with a 5.04 kW Sunpower solar electric (PV) array. They were occupied on June 1st 2010.

At the time, South Mountain announced the following contest to the new owners: each household that was able to go from June 1, 2010 thru May 31, 2011 at net zero energy use (or less!) would be awarded a year’s membership in the local Community Supported Agriculture (CSA) farm (Whippoorwill Farm) or a $400 gift certificate at a local fish market, the Net Result. After one year, two households have achieved zero annual net energy – using less energy than the PV array has generated. Two other households were very close: within ~1,100 kWh of reaching net zero.


The houses are superinsulated and have unobstructed southern orientation. Basements are within the thermal envelope, with R-20 walls and sub-slab insulation. Above-grade walls are R-31, roofs are R-50, (note, these are effective R values for the entire assembly) windows are triple glazed Thermotech with two layers low-e and argon fill, (south facing windows are coated with Energy Advantage low-e with a SHGC of 0.62, all others are 0.48) and the blower door results range from 117 to 184 CFM50 for the seven SMC homes and 236 CFM50 for the Habitat home. This is with no mechanical openings taped off and with the heat recovery ventilator running. These are superb numbers.

Heating and cooling is provided by a Daikin single zone minisplit heat pump (RXS24 DVJU) with a wall cassette in the main living area. Supplemental heating is provided by ceiling-mounted Enerjoy electric radiant ceiling panels. The houses are designed such that the single point source of heat – the heat pump – should be able to provide all the required heating, as long as the doors to the bedrooms are left open to allow heating by natural convection. The radiant panels allow heating in the event of a doors-closed operation, or to provide supplemental heating in extreme cold conditions.

Ventilation is provided by a constantly-operating Fantech 704 heat recovery ventilator. This unit draws about 30-35W and exhausts 25 CFM from each bathroom and supplies 15 CFM to each bedroom (in the case of the two bedroom unit, 15 CFM is also supplied to the living area.)

Domestic hot water (DHW) is supplied by a 50 gallon Marathon electric water heater. This tank is polybutylene lined and is insulated with two-and-a-half inches of closed cell foam.


In addition to the standard utility electric meter, each home has sub-metering of major components. They are:

  • Minisplit heat pump
  • Electric radiant panels
  • DHW
  • PV inverter output
  • Water to the DHW tank

These sub-meters allow measurement of energy used for heating, cooling, DHW, and plug loads/lighting/ventilation, as well as the energy generated by the PV system. The meters are read monthly by Matt Coffey, who bought one of the homes and liked it so much, he now works at South Mountain as an architect.


The homes face very close to due south and have essentially full solar access. The Massachusetts Clean Energy Center (MA CEC) PV production calculator for these arrays estimates an annual output of 6,247 kWh. The average output of the eight systems was 6,873 kWh, nine percent higher than the estimate. We don’t know how much of this is due to better-than average solar insolation and how much is due to the premium SunPower product. Production exceeded the estimate for ten of the months, and fell short for two months. Figure 1 shows the estimated vs. actual monthly production:


A key insight here is that estimates are only estimates – they are based on typical conditions and a set of assumptions. For example, the MA CEC production calculator uses Boston weather data, and we don’t know whether MV has more or less sun on average than Boston. The calculator assumes a DC to AC derate factor of 0.77, an industry standard, and Sunpower asserts that a higher value, 0.82, is the correct input for their product. Changing the derate factor from 0.77 to 0.82 yields an annual production estimate of 6,652 kWh, which is within two percent of the actual output of the eight systems. A second key insight is that monthly weather variations will typically exceed the annual weather variations. March 2011 production was close to twenty percent higher than the estimated value – it’s reasonable to assume that March was indeed sunnier than normal. May production was eight percent lower than estimated, so perhaps May was less sunny than normal (it sure seemed soggier…).

One home had the anomalous instance of a young child turning the exterior AC disconnect off during the latter portion of June 2010. It remained off for awhile before being discovered, causing that household to harvest only 279 kWh that month, as compared to an average from the other seven homes of 630 kWh. A key insight is that looking at monthly data means we catch these unique issues before they amount to much – one can imagine, in normal circumstances, that no one might catch that error for months if ever.

Variation in PV production from house to house is small. This is shown in Figure 2 below:

net zero energy design

Lowest production is seen at houses 2, 3, and 8, and highest at houses 5 and 6. How much of this is variation is equipment performance and how much is light shading or off-south orientation is not clear.

Figure 3 shows the Google satellite view of the houses:

zero net energy home design

Lowest production is in the one house that has installed a satellite dish on the open portion of the roof adjacent to the PV array. It’s not clear how much, if at all, this dish shades the array.


The production of the PV array sets the total annual energy budget that a household can use if zero net energy is the goal.

Figure 4 shows the total annual energy usage of each home compared with the average PV production:


The figure shows that two households achieved zero annual net energy, and an additional two households had energy consumption that was within twenty percent of the PV production. Figure 5 shows the breakdown of total annual energy use by end use:


There is a lot of information in this figure. The meter that logs heat pump energy usage is covering usage for both heating and cooling. In the data analysis, I made the simplifying assumption that June, July, August and September usage was cooling, and all other usage was for heating. Lights and appliances usage is calculated for each household by subtracting the usage of the heat pump, the electric radiant panels, and the DHW heater from the total energy usage.

Key insights harvested from Figure 5 include:

  • Cooling energy is small, yet it varies by a factor of twenty-six to one. It’s clearly discretionary energy – some folks use it, others hardly at all.
  • With the exception of one house, heat pump energy is relatively even. The electric radiant panel energy ,however, varies by a factor of fourteen to one. Since the panels are much less efficient than the heat pump, it is in the occupants’ financial interest to minimize panel energy, but it may not be in their comfort interest to do so.
  • Heating energy varies by a factor of two to one. If the highest and lowest usages are discarded (as in Olympic judging) the variation is much tighter – the next highest is thirty-five percent higher than the next lowest, and only thirty-eight percent higher than the lowest. The highest usage is fifty-two percent higher than the next higher usage. Do folks here leave the windows open? Do they keep the house warmer than others do? In this house, the panel energy is more than twice the amount used by panels in the next highest house – the heat pump energy used is second to lowest, so I don’t think that the heat pump is faulty, but perhaps it is worth checking after speaking with the occupants about their experience.
  • DHW energy varies by a factor of 2.4 to one. This type of energy usage is much more linked to number of occupants than heating and cooling (see below)
  • In all but one household, DHW energy exceeds heating energy (see Figure 6 below). This is what happens in low energy use houses using heat pumps and electric resistance for DHW. It is clear to me that the next available investment in energy savings in these homes would be either solar thermal or a heat pump water heater!
  • Plug and lighting loads vary by a factor of two to one. Although it is reasonable to expect that these loads increase somewhat with number of occupants, the second lowest users are a household of two adults and one infant.
  • Heating and cooling energy – that which is most reflective of the efforts of the design and construction process – is a small percentage of the total energy usage. As Andy Shapiro says, there is no such thing as a net zero house, only net zero families. Occupant choice matters hugely. See Figure 7. The two net zero households have the highest percentage of total energy as heating energy, because their DHW and plug/lighting usages are smaller, yet even in these cases the heating energy is less than one third of the total.

net zero energy - heating vs dhw


net zero energy design  - annual heating as a % of total heating


There was not a large variation in air tightness amongst this sample of buildings. One might expect heating energy to be correlated with air tightness. Figure 8 shows this data. The correlation is present, but weak. The leakiest house is also the one that has the highest heating energy, yet it is still an impressively tight house, and proportionally the heating use seems much higher than the others compared to how much leakier the house is.

heating energy vs cfm50

One might expect a higher energy usage per square foot of floor area in the three bedroom homes, due to the disproportionally increased shell area of the third bedroom, which is a first floor ell.

Figure 9 shows that this appears to not be the case, especially if one discards the highest heating use house.

net zero energy home design - water use

What is a clear trend is the proportion of electric radiant panel usage in the two vs. three bedroom homes. Figure 10 shows that the three bedroom homes used significantly more panel energy. Panel energy is likely to increase when interior doors to the bedrooms are closed, hindering natural convective transfer of warm air from the main space, where the heat pump is located. Possible reasons include:

  • The third bedroom might be used as the master bedroom and the door to the bedroom might be closed more than the doors to the upstairs bedrooms are in the two bedroom houses.
  • The three bedroom houses have more occupants on average, so perhaps the doors in general are more often closed for privacy reasons.
  • The third bedroom has more heat loss than the upper bedrooms in relation to the heat gain from both natural convection and conduction through shared interior walls and floors, so perhaps people feel cooler in the third bedroom.

net zero energy - annual heating energy

Another key insight from this data is that our energy modeling is reasonably robust. With a combined (heat pumps and radiant panel guesstimate) Coefficient of Performance (COP) of 2.25 we modeled the two bedroom house as using 1,810 kWh/year for heating, and the four two bedroom houses averaged 1,587 kWh/year, twelve percent lower than predicted. The three bedroom homes averaged 2,030 kWh/year for heating, and if the high user is discarded, the number is 1,728 kWh/year, or nine percent higher than the two bedroom units.

Figure 11 shows the monthly usage of both the heat pump and the electrical radiant panels for heating.

net zero energy home heat pump usage


One expects some types of energy usage to scale more with number of occupants than other types. A house doesn’t need more heat due to more occupants, and in fact, the internal gains associated with more occupants can drive heating energy down. The home with the highest light and appliance energy usage had the lowest heating usage, but this was not a general trend. DHW energy used and energy used for lights, appliances, and entertainment is a function both of number of occupants and the choices they make. Figure 12 shows annual total energy usage vs. number of occupants:


The net zero households have one and three occupants. The four households with four occupants have a total energy usage that varies by a factor of 1.5 to one. One household with four occupants uses slightly less energy than the two houses with two occupants.

Figure 13 shows light and appliance energy usage vs. number of occupants


A key insight is that lights, appliances, and entertainment energy usage is perhaps the most discretionary of all, and this chart shows the lowest usage by a household of three, and that the households of two and four have a similar average usage. Amongst the households of four, this category of energy usage varies 1.5 to one.

DHW usage also varies significantly in gallons of DHW used daily per occupant.

The range here is a factor of three to one, as shown in Figure 14:

dhw to occupants - net zero energy design

Age of the occupants must matter – there is the stereotype of the thirty minute teenage shower. There are also other factors – how much a household prepares their own food, how active they are, whether most of them are bald and therefore can take quick showers (like me!).


We are fortunate to have water meters on the inlet to the DHW tanks, as well as the kWh meters. This has permitted us to look at how much energy is being used per gallon to heat water. In Figure 15, the energy per gallon is plotted against gallons of DHW used daily. It is expected that the standby losses off the DHW tank would be close to constant no matter how much DHW is used, and that lower DHW users would use more energy per gallon than high users. In fact, this appears to be untrue, with the exception of one household. Perhaps the temperature setpoint of the

DHW tank is higher in this household. Overall, the DHW systems are using an average of 0.21 kWh/gallon of DHW. If the temperature rise averages 70F in the tank, this is a system efficiency of 81%. If the rise is 80F, the efficiency is 93%.

kWh to gallons


It is interesting to look at which months households were electricity exporters and which months they needed to import a net quantity of energy from the grid. Every household achieved at least one month where they were a net exporter. All households were net importers in the four coldest and cloudiest months. As a neighborhood, the total annual net import was 13,680 kWh.

Figure 16 shows this information:

monthly energy use

Figure 17 below shows the monthly output of the eight PV systems. The minimum is in November and December and the maximum is in July, although March was an excellent month. The short bar in June on one house is the result of the young child throwing the AC disconnect off, as mentioned.

solar pv production - net zero energy home

Figure 18 shows monthly total energy usage of the eight households. As expected, it peaks in the winter heating season.

monthly electric use - net zero energy home design

Figure 19 below shows the energy into the minisplit air source heat pumps. I’ve assumed that energy input during June through September is cooling and all else is heating. Heating peaks in January, the coldest month in most years, and cooling peaks in July, which had the most hot and humid weather.

heat pump electric use - net zero energy home design

Figure 20 shows the monthly energy input to the electric radiant ceiling panels. A similar January peak is evident, and the dramatically higher usage by one household of these heaters stands out.

radiant ceiling panels - zero net energy design

Lights and appliances, shown below in Figure 21, vary by household but are only mildly winter peaking, which makes sense, as all heating energy is captured in the heat pump and radiant panel graphs, unlike fossil fueled equipment, which uses electricity as well as fossil fuel and therefore increases winter electrical usage. Peaks here likely represent increased lighting, and perhaps more time spent indoors using entertainment equipment in the winter.


The next three figures, 22 through 24, are related to DHW. In the first, gallons of DHW per month are shown. Some households are remarkably consistent in their usage month to month, others vary noticeably. It’s possible that the number of occupants changes.



Not surprisingly, the energy used to heat water follows the quantity of water heated rather closely!

Electricity use per gallon of DHW is relatively even across the households, although one of the two households that used the least DHW is using substantially more energy per gallon than other households. We should check to see if this household’s DHW tank is set at a higher temperature than other households.

The next figure (24) demonstrates that the energy used to heat water per gallon increases as the weather gets colder, and lags the coldest air temperature, as the ground cools more slowly than the air as fall and winter occur, and heats more slowly in the spring.




We are very fortunate to have this sample of low energy housing so close by and so well-equipped with good metering. The unusual numbers of monitoring meters – carefully and consistently read – makes this kind of detailed analysis possible. The summary of all the key insights contained in the complete report is that “there are no zero-energy houses, only zero-energy families.” But there are a number of key lessons that we can use to make our future projects even better, and there are a number of key lines of inquiry and questions raised by this data that we can use to learn still more about high-performance housing.

We are pleased with these results. This is a superb example of housing that is “truly affordable forever.” The real value of these homes will become apparent over time, as they require little or no expenditures for rising energy costs and will incur very low maintenance costs. The owners of these homes have built-in “risk protection” that few other homeowners do. We hope the data we have gathered and the lessons we have learned will help others in the important pursuit of high performance housing for the 21st century.

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