Furnace Motor: AC or DC?

Furnace Motor: AC or DC?

AC vs DC Furnace Blower Motors

When considering purchasing a new furnace the topic of whether to go for a DC or AC motor comes up a lot and it is a very valid point of consideration because depending which way you choose to go, it will affect your home comfort and also could amount to energy savings.

AFUE and Energy Efficiency

When shopping around for furnaces, the term AFUE comes up a lot but that only tells part of the story when it comes to energy efficiency. AFUE only measures how much of the gas is actually turned into heat but one must consider that inside every furnace, there is an electric motor that is responsible for circulating the air and is therefore another matter to consider when measuring energy efficiencies. This is why looking at the Energuide tags tells a more  complete story.

AC Motors

Most mid-efficiency and low-end furnaces have these kinds of motors. They do their job just fine and are usually cheaper than DC motors but that’s about their only advantage; If the blower motor ever breaks outside of warranty, replacing an AC one is cheaper.

ECM motors, DC motors or variable speed motors

All of the above terms are used to refer to the same thing: DC Motors. These motors do the same job as AC motors but they operate at least 50% more efficiently than AC motors. DC motors come in either constant torque or variable speed modes. Most high-end furnace models have a variable speed motor because it allows them to control the amount of output air more smoothly than any other model, thus resulting in increased overall comfort. In general, a modulating furnace with a variable speed dc motor produces a steadier, more comfortable temperature.

What about cost savings?

If you ask an expert, they will most likely tell you that in general DC motors will move air around your home while consuming less watts – but in terms of real energy savings, it does depend a lot on your usage. Buying an energy efficient furnace is a bit of a long term investment and sometimes the price difference is not made back in savings until a couple of years down the road but if you think of it in the sense that, yes, you might be putting more money down up front but your yearly energy bills will be lower.