What’s the Difference Between an 80% and 90% Efficient Furnace?

If you’re in the market for a new furnace, you might be seeing a lot of advertising about efficiency. Today, there are generally two basic levels of efficiency—80% efficiency and 90%+ efficiency. But what do those numbers mean in lay terms?

This efficiency reference directly correlates to the amount of money you spend on gas to heat your home as a percentage of the total gas used. In other words, an 80% furnace uses 80% of the gas to heat your home—the other 20% is wasted and exhausted through the flue on your roof. Another way to think of this is that for every dollar spent on gas, 80 cents is used to heat your home and 20 cents goes up in smoke (in the form of waste).

Aside from their performance, another major difference between an 80% and 90%+ efficient furnace is the installation. An 80% efficient furnace exhausts from a metal flue through your rooftop. This flue is often shared with your water heater.

In contrast, a 90%+ efficient furnace is exhausted through a plastic pipe commonly known as PVC. A noncorrosive material, like PVC, is needed in this application because so little gas is exhausted that condensation can build in the exhaust pipe. As this condensation builds, it rolls back down the exhaust pipe and is emptied in a drain installed in the floor of your utility room. Alternatively, the collected condensation can be pumped outside or to a drain located elsewhere. And, unlike an 80% furnace, the exhaust for a 90%+ furnace can exit your home through the roof (vertical ventilation) or through a nearby wall (horizontal ventilation). This does provide some additional flexibility when installing one of these new systems.

When it comes to cost, a 90%+ furnace is typically $600 to $800 more expensive than its less efficient counterpart. (Obviously this ranges some based on who actually sells and installs your unit.) However, there have traditionally been a number of rebates available from local utility companies, tax rebates, or even manufacturer rebates on 90%+ efficiency units that can reduce (and in some cases, eliminate) the difference in price.

Contact one of the specialists at Blue Best Plumbing, Heating, Air, Generators today to learn more about the type of furnace that is right for your home. As a resident of the Wasatch Front, we can also tell you about the rebates that are available to you.