How To Look At A House
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Is the energy efficiency of the furnace part of the SEER rating of a central air conditioning system?
Monday, June 11, 2018
How Heating Efficiency Is Rated
The efficiency of the heating part of an HVAC (Heating Ventilation and Air Conditioning) system is rated separately from the cooling system. How efficient a system is while in heating mode does not affect the SEER (Seasonal Energy Efficiency Rating). Each type of heating has a unique way of evaluating efficiency:
- Gas Furnace - An AFUE (Annual Furnace Utilization Efficiency) rating is the standard. It is a percentage and, for example, a furnace with an 82% AFUE converts 82% of the fuel used into heat, with the other 18% wasted--typically up the flue and into the atmosphere.
Mid-range efficiency furnaces have an AFUE of 78% to 82%, and high efficiency systems are AFUE-rated at 88% to 97%. A high-efficiency gas furnace is easy to spot, because so much heat is extracted and the exhaust gases have been cooled-down enough that a white-plastic PVC pipe is used as a flue.
- Electric Furnace - Although electric resistance heat from a heating coil in the air handler also uses the AFUE percentage system, it is always 100% because no heat is lost up a flue like at a gas furnace. While 100% seems to be ideal, it’s actually not. A air-source heat pump in heating mode would have a 200% AFUE and even higher, due to the fact that it uses energy to move heat rather than create it. When outdoor heat is readily available (not an extremely low temperature outside) a heat pump is quite efficient.
- Electric heat pump - Heat pump efficiency, however, is not measured in the AFUE system. HSPF (Heating Season Performance Factor) is the measure most often used, and it is the ratio of BTU heat output over a heating season to the watt-hours of electricity used. A higher HSPF number means better efficiency, and 8.2 is the minimum standard now required by the U.S. Department of Energy for new heat pump system .
Trying to figure out the SEER of your system? Visit our blog post How can I find out the SEER of my air conditioner?
Also, see our blog post What causes air leakage energy loss in a house?
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To learn more about heating and air conditioning systems, see these other blog posts:
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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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