Older space conditioning systems (more than 10 years old) are often unreliable and much less efficient than a modern system. When it’s time for a new replacement, choosing one of the correct size (heating and/or cooling output) is critical to getting the best efficiency, comfort, and lowest maintenance and operating costs over the life of the new system. Some national surveys have determined that well over half of all HVAC contractors do not size heating and cooling systems correctly.

The most common sizing mistake is in oversizing. This not only makes the new system more expensive to install, but also forces it to operate inefficiently, break down more often, and cost more to operate. Oversized heating equipment also often creates uncomfortable and large temperature swings in the house. Oversized air conditioners (and heat pumps) do not run long enough to dehumidify the air, which results in the “clammy” feeling and unhealthy mold growth in many air-conditioned houses.

In this post, I’ll discuss

Incorrect Sizing Methods
Why Most Older Systems Are Oversized
Manual J and D: The Correct Way to Size a System
A Special Case: Sizing Steam Heating Systems
Steps a Good Contractor Should Take to Size a System

Read below for the full post, if you have any in-depth technical questions, feel free to leave a comment or ask them in our geothermal technical help community. 

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