80 or 90 Percent - What Furnace Should You Buy?

Are you in the market for a new furnace? Efficiency is probably your main concern.

If you’re going to install a new furnace, you should make sure it’s as efficient as possible. And if it’s going to last for years - the average furnace has a lifespan of up to 20 years - higher efficiency is better … right?

First, let’s define AFUE - short for annual fuel utilization efficiency. The AFUE rating of a furnace is designed to help you compare efficiencies of the different makes and models. AFUE represents the percentage of fuel used and converted to a heat source, versus the amount of heat lost during the combustion process.

An 80 percent rating is considered a standard model on the market. A 90 percent AFUE rating is pushed into the high efficiency models. In the different makes and models, this means different things.80 or 90 Percent - What Furnace Should You Buy?

Condensing Furnace

For a standard furnace with an 80 percent AFUE, 20 percent of the heat energy is exhausted up and out of the system. In a condensing furnace with a 90 percent AFUE, it uses a condensing process to further eliminate 10 percent of that heat loss. Combustion gases are diverted into a condenser, where heat is released as the gases are condensed to water and extracted in the exchanger. This can help you save money over time both in heating bills and in operating expenses, including repair and replacement costs.

Sealed Combustion Furnace

With a standard 80 percent AFUE, the furnace draws air in for the burner flame directly from the home’s interior air supply. Over time, this dries out the air. If you’ve ever had itchy skin, dry eyes, or experienced static electricity shocks, this is why. When you move to a 90 percent AFUE furnace, it incorporates a combustion chamber into the process that is sealed off from the house. Instead of drawing from the interior, air is filtered in via an inlet pipe from the outdoors, with all gases exhausted through a separate pipe. Humidity can remain at a more comfortable range.

Multistage Burner Furnace

For a 80 percent AFUE furnace, the gas burner is designed to run at optimal speed throughout the heating process. While this doesn’t matter on the coldest days, it isn’t the most efficient process on milder days. For a 90 percent AFUE furnace, it operates using multistage burners that sense the heating needs of a home and operate accordingly. It lowers the burner level on the milder days, increasing energy efficiency and lowering operating costs.

Variable Speed Furnaces

A standard 80 percent AFUE furnace uses a conventional single speed, on/off blower to heat your home. This abrupt on/off process often creates noticeable temperature fluctuations throughout the home. When you move to a more efficient model with variable speeds, this process no longer occurs. Instead, when the house reaches certain temperatures, it adjusts the speed of the blower to maintain the heat, rather than an all or nothing approach to heating. The blowers instead run at variable speeds to keep the house a more consistent temperature. And because this technology doesn’t use the high wattage of electricity to turn on and off again, it saves on your utility bills over time.

Which furnace is right for you?

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