You can tell how energy-efficient a furnace is by its official efficiency rating, the Annual Fuel Utilization Efficiency (AFUE). It’s a measure of how much of the heat originally in the fuel that’s being burned is available for delivery to the home. The more heat that gets lost up the flue or through the cabinet, the lower the AFUE.
But that rating doesn’t capture all the ways a furnace can lose efficiency. Some, like how well the heat gets distributed to the house, aren’t related to the furnace itself. But there’s one big one that is related to the furnace.
Unlike air conditioners and heat pumps, furnaces use two sources of energy. The fuel that it burns is the obvious one. (It’s usually natural gas or propane.) The other is the electricity that runs the blower. And that’s the key to finding a high-efficiency furnace that truly operates at high efficiency.
A peek at manufacturer’s specs
I was working on a mechanical design for one of our clients recently and was going through the equipment selection process. The software we use (RightSuite Universal) has a lot of equipment data built in, so I can just find a manufacturer, set the limits for sizing and efficiency, and look at the options.
Once I get my list of options reduced to a reasonable number, I can choose a model that meets my requirements. But I have to go in and make sure to look at the blower power rating for each one or I could end up saddling the client with a furnace that looks like it should be efficient but really isn’t.
I took a look at the RightSuite listed blower power ratings for five different manufacturers. They were all in…