AFUE - Annual Fuel Utilization Efficiency

A new furnace or boiler is a great way to save money on your winter heating bills. Or so all the 'experts' say, but how do you know for sure? And how do you know how efficient, or not, a particular furnace or boiler will be? The key is in the AFUE.

AFUE = How Efficiently You Burn Money

Say what now?

From a certain point of view, you are burning money every time you turn on the heat. You're not getting that heat for free. With a furnace or a boiler, you're either paying for natural gas or propane service to keep the unit going. Without fuel, the best furnace in the world is about as useful as a solid-gold life jacket.

Which brings us back around to annual fuel utilization efficiency.

Annual fuel utilization efficiency, AFUE for short, is how we measure the approximate thermal efficiency of a furnace or boiler. I say approximate, because it is truly an estimate of how effectively the unit will operate over a typical heating season. Which is more useful than simply testing the furnace under ideal circumstances and calling it a day. After all, very few people need heat in ideal circumstances.

Optimum Operation

What kind of rating should you look for in a new furnace or boiler? As with most things, higher is better. 80% AFUE is solid performance, and is about the lowest rating you will find on new products. The very best units on the market exceed 90%.

Should you get the bare minimum or the higher performer?

Depending on where you live, how expensive fuel is locally, and how much energy you need for winter heating a 10%-15% difference in costs could be trivial or quite substantial. The only way to know for sure is to do the math yourself. How much do you spend on heating fuel? How much money would a higher rating save you? Will that pay itself back over the life of the unit?

Investing in the higher efficiency unit will definitely make sense for some folks. For others who live in milder climates and don't need as much heat, a more economy focused model will work just as well. In either case, understanding AFUE will help you make a better decision about your next space-heating system.

Want to know more about furnace or boiler efficiency?

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4 comments (view/add)
  • Donna Millheim
    Donna Millheim
    Posted on 11/23/2018

    I'm in the need of the furnace for a very large room guess is preferred hope it's not something that's going to be on all the time only when we're open for business I do yard sales in

  • Kyle
    Kyle from Ingrams
    Posted on 11/26/2018

    You could use a programmable thermostat to ensure the heat was available for customers, and then turned down during non-business hours.

  • Ray Abney
    Ray Abney
    Posted on 4/24/2019

    One half of our 750 square ft house has a mini split electric system, other half has electric baseboard. Water is propane. What’s the energy cost of the 3?

  • Kyle
    Kyle from Ingrams
    Posted on 4/24/2019

    Wow! That is a heck of a good question. First, it would be hard to give you specifics without more information, but there are a few things to bear in mind.

    Electric baseboard is definitely the most expensive. Raw electric heating (like a toaster) is really inefficient. The upside is that it works in all weather conditions.

    Presuming your mini-split is a heat pump, that would be the most efficient heating method. The downside is that heat pumps lose efficiency as the outside temperature drops. The rate of loss varies depending on the heat pump model.

    The propane water heater is likely more efficient than the electric baseboard and less efficient than the heat pump. However, it will maintain the same relative performance regardless of weather.

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