Why Is Furnace Sizing So Important?

Every home has different heating requirements, and therefore needs a furnace that’s the appropriate size to meet them. In this blog, residential and commercial HVAC repair contractor Schmitt shares insight on the importance of furnace sizing.

Size Does Matter

Your home needs a furnace that will supply heat efficiently, consistently and in the appropriate amount, which is why choosing the right furnace size is important. An undersized furnace will redline all the time—and consume a lot of fuel in the process—just to meet minimum heating requirements. To illustrate using an extreme example, it’s like trying to heat an entire house using a portable space heater.

Oversized furnaces can also be problematic, as they provide too much heat too fast, leading to “short cycling”. In other words, the furnace turns off and on too fast, which places additional strain on it, consumes more energy and can potentially lead to premature breakdown. The right sizing applies to both heating and cooling systems, so your air conditioner needs to be properly sized as well.

How Furnace Size Is Calculated

Your HVAC technician will take several factors into consideration before estimating the furnace size that will fulfill your home’s heating requirements:

Your Home’s Square Footage — This includes all the rooms that require heating, including finished basements and attics. Rooms vary in size and shape, of course, all of which will be taken into account.

Heating Factor — Heating as well as cooling is relative to outdoor temperatures. There are five standard zones in the United States, all with different BTU (British thermal unit) requirements. The farther from the equator, the higher the required BTUs will be. California is located in Zone 2, with a heating factor of 30 to 35 BTUs. By contrast, some of the northernmost areas in the country, such as Minneapolis, require 50 to 60 BTUs.

Insulation — A well-insulated home won’t require as much heating. In addition to wall and attic insulation, ceilings and floors in certain rooms should be insulated, and don’t forget to caulk and seal your windows and doors as well.

To calculate your home heating requirements, multiply the square footage of your house by the heating factor. The better insulated the house is, the lower the required BTUs within the resulting range. For example, if your home’s total floor area is 2,000 square feet and is well-insulated, then it will take around 60,000 BTUs to heat your home. A furnace with a corresponding output will then be selected and installed.

Call Schmitt for All Your Heating Needs

Are you looking for HVAC contractors? If so, call Schmitt Heating at (415) 689-7849 or fill out our contact form. We serve customers in San Francisco.