If you need a furnace replacement in the near future, you’ll want to learn about the factors involved with furnace sizing and your home’s heating load. Smaller furnaces cost less to purchase and don’t use as much fuel. Considering the length and intensity of Minnesota winters, anything you can do to reduce your heating expenses is an effort well spent.
When HVAC contractors size furnaces, they use a tool called Manual J. It was developed decades ago by the Air Co
nditioning Contractors of America and takes the many systems in your home into account to find the right size furnace, including:
- Cubic footage to heat
- Number of windows, their energy efficiency and exposure to the sun
- Exterior doors
- Air infiltration rates
- Insulation levels
- Layout of your home
- Preferred indoor temperatures
- Number of home occupants and their ages
- Heat-producing appliances
- Landscaping factors
Once they’ve determined the size of the furnace you need, they complete the analysis by using Manual D for the ductwork system. Manual D requires the input from Manual J, and properly sized ductwork is important for efficient heating.
While the HVAC contractor goes through Manual J with you, you can see if the furnace sizing changes if you increase insulation levels, seal air leaks, increase window energy efficiency or take other home-weatherization steps.
Proper sizing is crucial for your comfort and the system’s longevity. Systems that are too large will short cycle, which means that they turn on and off frequently. Your air won’t be as thoroughly heated and the objects in your home won’t have as much time to warm, making you feel cool shortly after the furnace turns off.
Mechanically, short cycling creates more wear and tear on the furnace and increases energy bills. Heating equipment uses more energy at start-up than any other point in the heating cycle. Meanwhile, the problem with too-small systems shouldn’t be surprising – they simply lack the capacity to heat your home.
If you would like to learn more about furnace sizing, please contact us at Marsh Heating & Air Conditioning. We’ve provided quality HVAC services for the Twin Cities area since 1974.
Our goal is to help educate our customers in Minneapolis-St. Paul, Minnesota about energy and home comfort issues (specific to HVAC systems). For more information about furnace sizing and other HVAC topics, download our free Home Comfort Resource guide.
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