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How to Compare AFUE Furnace HVAC Energy Efficiency Ratings in 3 Steps

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Last Updated on June 25, 2015


If you’re reading this, you’re probably in the market for a new furnace or boiler. It’s a lot of cash to lay out so close to the end of the heating season, but if your current unit is DOA you may have no choice. If you’re among the smartest NYC business owners, maybe you’re planning ahead to get the best deal BEFORE the old unit dies.

In either case, the good news is you have an opportunity to get a more energy-efficient unit, which can save you considerable cash on your utility bills. But you may be confused about the HVAC energy efficiency ratings and what they mean. Also, you have probably realized that more efficient models can cost considerably more. Is it worth it? How much HVAC energy efficiency will give you the right return on your investment?

1. Understand how fuel efficiency is measured

HVAC energy efficiency for a heating appliance is measured by its annual fuel utilization efficiency (AFUE) rating. In simple terms, AFUE measures how much of the fossil fuel consumed by the appliance is converted to heat for the home or commercial establishment.

Today’s high-efficiency furnaces can have AFUE ratings as high as 98%. That means 98% of the fuel burned by the furnace becomes heat for your space. The remaining 2% escapes through the chimney or vent pipes along with the toxic gases produced by the combustion process.

The Federal Trade Commission requires all furnaces, boilers and water heaters to display an AFUE rating so that you can compare different models.

2. Compare new units to older furnaces and boilers using the AFUE rating.

No matter what type of new heating system you buy, the AFUE rating will be no less than 80%, and many have ratings of 90% or higher. Your old gas or oil-fired furnace or boiler is probably rated between 50% and 70%.

In addition to the AFUE rating, you can compare features on your old model versus those on the newer ones to get an idea about how much HVAC energy efficiency you stand to gain.

If your current system has a continuously burning pilot light, that’s a sign that it’s one of the oldest and least efficient systems out there. You stand to save a great deal even by upgrading to a mid-efficiency system with an AFUE rating of 80 to 85%. These units have electronic ignitions, an exhaust fan to control air flow and combustion gases, and a smaller diameter flue pipe. The highest efficiency furnaces, rated 90% and above, feature a sealed combustion chamber and a secondary heat exchanger that collects condensed moisture from flue gases in order to extract and re-use the heat.

3. Determine how much you can expect to save. has a chart that can help you calculate your energy savings per $100 of fuel costs based on the AFUE ratings of your old and new equipment. But there’s more you need to consider when selecting a new heating unit.

The capacity of your heating system needs to be closely matched to your building’s requirements, and those needs have likely changed since you bought your last furnace or boiler. Building usage, occupancy, and even design and layout of the space have probably changed. Have you installed energy-efficient windows and doors? Added more insulation or used better-insulating building materials for walls and floors? Changed to more efficient lighting? All of those things mean that you’ll need a smaller unit this time around. If you haven’t made those efficiency upgrades to your building, this may be a good time to do so, since you’ll pay less for a smaller furnace if you do.

For more information about choosing a correctly-sized system refer to our article: 8 Reasons Bigger is Not Always Better

To get the most energy savings from your new heating equipment, it’s also important to update your ducts for gas furnaces and insulate hot water pipes for boilers. The AFUE rating does not take into account heat lost through inefficient distribution. Especially if your ducts are located in an unheated crawl space, you can lose as much as 35% of the heat generated by your furnace.

Purchasing new heating equipment is a big decision. The advice of an expert HVAC service provider can be essential in making sure you choose the right equipment to meet your needs. An experienced professional can help you do a cost-benefit analysis to determine how much energy efficiency will bring you the desired return on your investment. They will also ensure that your new unit is properly installed to get the highest possible energy efficiency, and help you plan for the regular maintenance that’s needed to keep it running efficiently.

If you are concerned that your current HVAC provider may not be up to this task, now is a great time to seek out someone who can. For advice about handling this transition, grab a copy of our helpful guide to Contract Confidence: Transitioning to a New HVAC Service Provider.
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