Selecting a new furnace is all about efficiency, value, and comfort. – 4/19/13
Efficiency is easy – sort of. Every furnace has a rating – AFUE, which stands for annual fuel utilization efficiency. It is a measure of what percentage of energy is available for heating compared to how energy is put in. If a 95% AFUE furnace is supplied with 100 btus of energy, 95 btus of energy will be output as heat. AFUE does not account for electricity used to run blower fan (moves air in home) or inducer fan (draws air for combustion).
Furnaces are offered with three types of blower and inducer motors: PSC (permanent split capacitor), DC ECM (Electronically Commutated Motor) and X13 ECM. X13 is single speed ECM motor made by Regal Beloit. DC motors are inherently more efficient than AC motors. If you run, or intend to run your blower fan continuously, DC is a good choice. Downside is DC is more expensive to purchase and replace if it fails. ECM is only option if variable speed is your choice (until someone offers a variable frequency AC motor for furnace use). Variable speed allows for different blower speeds. Many two stage furnaces with ECM motors run two speeds. Fully modulating furnaces change blower speed depending on load. If you are offered a variable speed furnace, learn how many speeds blower will run or if it changes to many different speeds depending on load.
In a nutshell, overall efficiency is dependent on how furnace is used. An AFUE at or above 95% coupled with ECM motors will maximize you efficiency. Next time, I will discuss value and how efficiency interact to affect your overall best value.
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