Furnaces – Part 1 – Efficiency

Posted by on Apr 17, 2012

For our first conversation about furnaces, let’s focus on efficiency. Most people immediately go to this issue because they want to know – “How much money will I save owning this new unit?”

Efficiency for furnaces is rated in AFUE. This is the Annual Fuel Utilization Efficiency. It is stated in terms of a percentage. Here is a simple way to look at it. If a furnace is 80% efficient, for every dollar of gas you buy, you get $0.80 of heat into the house and $0.20 goes up the flue. So, the higher the AFUE or efficiency, the lower your gas costs will be.

Many of the older furnaces that I see are in the 60% efficiency range. The minimum efficiency by law in 2012 is 78%. Most manufacturers’ standard units are rated at 80% efficiency. So, even a standard unit made today is a big increase in efficiency over older units.

The next step up in efficiency is to go to a 90% furnace. Manufacturers efficiency vary by model between 92% all the way up to 98% with Lennox’s top of the line furnace. So with this furnace, $1.00 of gas will buy $0.98 of heat. As a side note, if you are interested in Energy Star efficiency (which is set by the US Department of Energy), they require 95% efficiency for gas furnaces to meet their criteria.

The benefit of a higher efficiency furnace is strictly what it will cost you to heat your home. There is basically no difference in the way a furnace will heat if it is 80% of 98%. It won’t feel any different in the house and you won’t even know what you have installed from an operation standpoint – it is strictly a matter of how much you will be spending on your gas bill.

So for a homeowner, it comes down to a basic decision on this issue – do I want to spend more up front (95% furnaces are more expensive than 80% furnaces) in order to save each month. It’s completely your call on this one. All of the other features and benefits available in furnaces are available in each efficiency level.

Next time, we will look at the blower motor in the furnace. In the mean time, as always, please call or email us with any questions as you work through the decision process on which type of furnace you want.

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