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Kilowatt Heating, Air Conditioning and Electrical Blog

Efficiency With Gas and Electric Furnaces—It Can Be Tricky


The hunt for your next high-quality heating system will probably involve looking for the best efficiency you can find. Efficiency is an important word with most home appliances today—the more efficient the appliance rating, the less power it will consume when it runs. At least, ideally. (Poor installation or poor unit selection can negate those benefits, making information about efficiency essential for any consumer.) If the type of heating system you’re looking at is a furnace, either gas or electric, you may run into a dilemma about their efficiency ratings, one that might lead you to the wrong unit.

We’re going to analyze the big trick with gas and electric furnace efficiencies to help you out. But to ensure you have the best unit that does what you need with the ideal efficiency, always call on our professionals. We’ll ensure you don’t end up with the wrong type of heating system.

Furnace Efficiency Is Measured as AFUE

When you look at a new furnace model, one of the first things you’ll notice is whether it has an ENERGY STAR label on it or not. The ENERGY STAR label means the heating system has passed the minimum requirements for energy efficiency set by the US Department of Energy. It’s a good starting place—but it’s not the whole story.

The actual furnace efficiency rating is AFUE, and it is also prominently displayed on furnaces. AFUE is a percentage. The simple explanation is that it’s the percentage of the furnace’s energy source the system converts into heat power. Whatever is left over goes to waste. For example, an older mid-efficiency gas furnace might have 80% AFUE. This means for every 100 units of natural gas the furnace burns, 80 units become heat and 20 units leave the furnace as exhaust gas.

How AFUE Works for Gas and Electric Furnaces

The current high-efficiency furnaces with special features like a second heat exchanger (a condensing furnace), variable-speed fans, multi-stage burners, and sealed combustion can score AFUE ratings in the high 90s. That’s an immense change from the older 70% to 80% AFUE ratings.

But then you’ll see an electric furnace with an astonishing 100% AFUE. That means no energy waste. And it’s less costly to install than the top-of-the-line gas furnaces. Obviously, this is the best deal, right?

No, it doesn’t quite work that way. All electric furnaces have 100% AFUE because all the electricity channeled through the heating elements becomes heat energy. That’s simply how electrical resistance heating works. There’s no exhaust.

The difference is the cost of the energy source. An electric furnace may not waste electricity, but electricity is more expensive to use than natural gas. A 100% AFUE furnace will run up higher utility bills over a season compared to a 90% AFUE gas furnace. This is why we often warn consumers not to take AFUE as the only criterion for furnace buying. If your home has a natural gas connection, we recommend staying with a gas furnace rather than paying more to run an electric furnace.

To find out your best options, or to schedule furnace repair in Studio City, CA, give our team a call.

Kilowatt Heating, Air Conditioning and Electrical serves Los Angeles and the San Fernando Valley. Call our certified service technicians 24/7 for exceptional customer service!

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