The Most Critical Factor for Furnaces and Boilers

January 29, 2016

The vast majority of our homes employ either a furnace or a boiler for central heating. The FTC (Federal Trade Commission) requires that manufacturers of these heaters document their equipment’s AFUE ratings so that consumers can compare the efficiencies of various models they may consider purchasing. As you might imagine, this is a very important piece of information. But what the heck is an AFUE?

The AFUE rating–or Annual Fuel Utilization Efficiency–is essentially a measurement of how well a furnace or boiler converts its energy source to heat. This rating takes into account the various demands that are placed on the equipment over a full season’s use, providing a number that reflects all those conditions combined. Bottom line: The higher the AFUE efficiency of a piece of equipment, the lower its fuel consumption will be compared to a lower rated unit–and the lower your heating bill! So the AFUE rating is one the most crucial numbers to consider when you are looking to purchase a new heating system.

Understanding the Rating

Because your furnace or boiler burns a fossil fuel in order to produce heat for your home (in our region we typically burn natural gas or propane), the byproducts of the combustion process must be exhausted to the outdoors. Commonly known as ‘flue gases,’ these combustion byproducts contain hot gases that are poisonous to breath, so proper exhaust venting is always crucial. As this relates to AFUE, the hotter the exhaust temperature, the more heat is being lost to the outdoors, and the less efficient the unit. Conversely, furnaces and boilers with cooler flue gas temperatures capture and make use of more of the combusted heat, and are therefore the more efficient systems.

In the case of today’s 90% AFUE and higher-rated equipment, exhaust temperatures are so low that PVC plastic pipe is used for the flue pipe. [For the sake of this discussion we will not address electric heaters, whose efficiency is actually 100% because they don’t need a vent…but whose high cost to operate generally make them undesirable central systems in our region.]

What AFUE Rating Should You Buy?

The new furnaces and boilers currently available range in efficiency from 80% to as high as 98% AFUE. Exactly which piece of equipment makes the most sense for your home depends on many factors, including current heating bills, how long you plan to reside in your home, cooling and airflow concerns, equipment location–and, of course, budget.

If you decide that now’s the time to consider upgrading your home comfort system, take the time to survey the field of manufacturers and residential HVAC contractors who have a track record in your area. Ask friends or neighbors for referrals. When you start receiving written estimates, don’t let yourself be pressured into making a rushed decision. Take the time to learn about features like sealed combustion venting, two-stage heating and cooling, variable-capacity output, and variable speed blowers.

These enhanced-performance options are not well reflected in AFUE ratings, but they represent significant considerations. A professional, customer-focused heating contractor will take the time to help you fully understand your options, and will help you make a decision that is in your best interests, now and in the future.

A Word About Enhanced Comfort and Heat Loss

So you’ve just made the big purchase and invested in a great new furnace. Congratulations! We know it will have a positive impact. But just because you now own one of the most efficient heaters made, that doesn’t always automatically translate to the ultimate in comfort and super-low heating bills.

For instance, if your windows or doors create a small breeze whenever the wind blows a little, and your attic insulation is only 6 to 8 inches deep, these ‘little things’ can hold you back in achieving your final goals. Please remember that applying the ‘total home energy approach’ to addressing these or similar issues can pay huge dividends working in concert with your new high efficiency heating system.