Three Most Common Mistakes Made by Geothermal Designers


If you’re new to the geothermal heat pump industry, read the Geothermal 101 Reading list. It has free tools and articles on geothermal design and installation, and sales and marketing best practices.

Working in the ground source heat pump (GSHP) industry, especially in a small company where you are asked to take on the role of salesman and designer, you will find yourself answering the same questions with each new customer.  Get used to it.  If you work in the industry long enough, you will be asked every question under the sun.  How will this system heat my home when the soil temperatures are only 50 degrees?  What if I want to keep it warmer in my house?  Do I need to buy an air conditioner too?  How does a heat pump work?  The list goes on and on.

The truth is, the average homeowner doesn’t understand how their central air conditioner works (or the refrigerator in their kitchen for that matter).  They just know it works.  When you mention the term “geothermal heat pump” or “ground source heat pump” to your prospective customer, all of a sudden you find yourself in uncharted territory.  Then the questions begin.

Homeowners ask these questions because they want to understand what they are getting for their extra dollar.  You are asking them to spend a lot more of their hard earned money than they would have to spend on a conventional heating and cooling system.  Because of the price tag, the homeowner will ask questions to get comfortable with the idea of purchasing such a system, that they aren’t buying into some new fad that will be here and gone before they know it.  Most importantly, they want to get the sense that you know what you are talking about and that they can trust you with their money, especially when they are spending it on something they don’t completely understand.  These systems are a complete unknown to a vast majority of people, although that is changing.

Even if you are able to land the big sale, an improperly designed or installed system can be huge detriment to your company (and to our small industry as a whole).  Most experienced contractors and designers have made their mistakes, learned from them and moved on.  But everyone needs to start somewhere.  An expert in anything was a beginner in that subject at one point in time.  This article is intended for those who are just starting out.

In my opinion, three of the biggest mistakes that a new designer can make are

  1. Underestimating the importance of accurate peak heating and cooling load calculations
  2. Not giving proper consideration to the many options that are available and
  3. Overcomplicating matters.

Let’s look at number one right now.

Underestimating the importance of accurate load calculations

If you’re involved in this industry in any way, you already know that the biggest hurdle we must overcome is the up-front cost associated with GSHP systems.  Because of this, we need to be accurate when sizing and selecting equipment.

It is not uncommon to see a natural gas-fired furnace with a 60,000 Btu/hr output rating down in the mechanical room when a mere 30,000 Btu/hr heating output is required.  The thing is, it really doesn’t cost that much extra to install a furnace that is twice the size it needs to be.

The price difference between putting a 30,000 Btu/hr furnace and a 60,000 Btu/hr furnace is probably a few hundred dollars.  Because of this, it is common practice to size conventional HVAC equipment based on rule of thumb principles.  Such principles minimize the amount of up-front time and investment on the part of the contractor to size and select the equipment while still being able to install a system that will serve its purpose.

If you install a 5-ton unit coupled with a “5-ton” ground heat exchanger where only 2.5 tons is required, the installation cost will be much higher than necessary.  Severe heat pump oversizing can cause a number of issues related to comfort, efficiency and equipment life expectancy, but the main concern is the fact that the customer will be paying much more for the system than necessary, which will dramatically affect the payback period on their investment.

Even if you’re able to sell a grossly oversized system, you might say, “No big deal, I was able to sell a larger system than necessary.  My bottom line looks pretty good”.  But when the homeowner realizes they aren’t as comfortable as they were hoping for and they aren’t recouping their initial investment as quickly as they were promised, they’ll tell their friends that geothermal isn’t all it’s cracked up to be.  The same goes for severely undersized systems.

Properly sizing equipment to deliver maximum performance and occupant comfort while keeping costs in check is the only way to keep our industry moving in the right direction.  The importance of high quality and great value cannot be stressed enough.  If you stick to the principles of proper system design, it’s unlikely that you’ll ever be the cheapest bidder but I guarantee that many homeowners will choose quality over price.  It is your job to inform them of the value you bring to the table that the other guys don’t.

If you liked this post, subscribe for more (it's free)

About Ryan Carda

Ryan Carda is a Mechanical Engineer at GeoPro, Inc. and is a co-founder of Geo-Connections, Inc. He is a co-author of 'Design and Installation of Residential and Light Commercial GSHP Systems', developed in cooperation with the International Ground Source Heat Pump Association (IGSHPA).
This entry was posted in Building Efficiency and tagged , , , . Bookmark the permalink.
  • Pingback: The Third Most Common Mistake Made Designing Geothermal Heat Pump Systems | HeatSpring Magazine

  • Eric Schardein

    Doing a thorough/optimum heat loss heat gain calculation is not easy…especially if the home is existing. Crawling around verifying insulation values, that can be affected by workmanship and the passage of time, is not an exact science. Infiltration rates are another underestimated source of heating and cooling loads…and, hard to measure. The same can be said for designing loops is questionable soil.
    But, I agree, that these are very important details that need our closest attention.
    Eric Schardein

  • Brian Hayden


    I completely agree, it’s not easy at all. I think the point of Ryan’s article is to showcase that although it’s difficult to create exact calculations its SO critical to geothermal sizing that you should spend more time on it then a normal manual J for a tradition heating system.

    Have you been putting in a lot of geothermal systems lately?


  • Garth Gibson


    You’re correct in emphasizing that a geothermal system design requires a greater degree of scrutiny of the heat loss/gain accuracy. Fortunately, in any reasonably competitive situation, the well oversized design is eliminated by simple economics, too big is also typically too expensive. The crux of the question then is “properly sized” vs “too small”. In a competitive situation, without proper justification by the contractor, the “too small” may win. So again the contractor needs to go the extra mile in his/her sales proposal (ie – not just a quote), just as they have to endeavor to do a better Manual J.

  • Chris Williams


    Great point! Is there any way contractors can educate consumers or create a bid so they don’t loose against someone who is bidding a project that is just too small?

    Just a small note, Ryan Carda wrote the post, not Brian Hayden.


    • Garth Gibson

      Ryan, Brian and Chris;

      I think I have everyone covered this time….

      My reference to a sales proposal instead of just a quote (model number of unit and price tag) would encompass a copy of your Manual J, your site survey, company brochure and then the output of any commercial or manufacturer software that helps design systems and calculates operating costs. By giving a specific “snapshot” of what will happen if they install a geothermal system in their home, they can make an educated decision about the investment. It will certainly elevate you over the guy who just sends a “quote”. Again, it’s a little more work for a geo sale, but would you buy a Cadillac on the basis of an invoice sheet?

  • Ryan Carda

    Great point Garth. I think we can all agree that much more time and effort goes into selling these systems compared to conventional HVAC. A big part of that effort can go into selling your system when going up against the competition.

    There will always be someone out there willing to do the job cheaper. It’s up to you to educate the client about the value you bring to the table. At that point, the argument becomes one of quality over price. It’s not always the easiest argument to make, but the customers you retain by sticking with your principles will be much more loyal and much more satisfied in the long run.

  • http://www/ Judith Karpova

    We at Altren don’t even proceed without the homeowner having a home energy audit done by a BPI-certified home energy auditor with Envelope certification. And even among those, we had to winnow out to find the most professional person. The blower-door test gives a pretty accurate idea of the leakiness of the home. In NY State, the NYSERDA program we’re in lets us share the data collected and make projections on how many btus will be saved by tightening and insulating the envelope. We can usually translate this into one or more tons of diminished heat load, which directly translates into short and long-term savings for the homeownr. We make a case to the homeowner that the dollar they spend in insulation is not only a dollar less in geothermal system sizing, but has a multiplier effect on running costs. Yes, we install smaller systems, and yes, we have a regionally recognized reputation for integrity and professionalism. Our clients are always happy, because their systems perform at, or exceed expectations, in a tight home.

  • Ryan Carda


    That’s a great strategy! It definitely takes some of the uncertainty out of system design and helps to maximize the overall efficiency of the home. Win-win.

  • Dana

    I like Judith’s comment. It is always great to have as much information as possible as the homeowner. Research is a good thing. I have heard so many horror stories about homeowners who get ripped from different companies because they weren’t educated on what it was they were getting. It’s a shame that a few bad apples destroy the chances for those that do the right thing.
    Geothermal units are efficient and sustainable. It’s a great investment as long as you understand what it is you are getting and you get the right unit to run your home. A helpful website is:

  • Pingback: "How Can I Design Geothermal Systems?" A 4 Step Guide to Designing Geothermal | HeatSpring Magazine

  • Pingback: Manual J Software and Training and Calculation | HeatSpring Magazine