Furnace Myths: What’s True and What’s Not

NisAir Air Conditioning • October 24, 2025

Furnace Myths: What’s True and What’s Not

Furnaces have come a long way from those behemoths full of roaring fires that needed to be fed shovelfuls of coal. Now, they are almost sleek, quiet and amazingly energy efficient. Still, some myths about furnaces persist. Which ones are true, and which ones are not?

Some Things That Are Not True

There’s a surprising number of beliefs about home furnaces that just aren’t true. Here are some.

The Furnace Doesn’t Need Regular Checkups

Every appliance in your home needs a regular checkup by a professional, and that certainly includes your furnace. Ideally, your furnace should be checked at the start of every heating season. In between those checkups, it’s up to you to change its filter every month or every quarter and keep your senses alert for funny sounds, smells and diminished performance. Neglecting a furnace results in either expensive repair costs or an appliance that simply dies when you need it most.

You Should Hold on to Your Old Furnace

Holding on to your old furnace until the bitter end is tempting. However, a furnace that’s very much past its prime becomes less efficient. This will cost you money in the long run because you’ll be constantly calling your HVAC professional for repairs. It’s simply better to get a new furnace.

Closing the Vents Makes the Furnace More Efficient

Closing the vents in your rooms doesn’t make the furnace more efficient. It only makes it work that much harder and unbalances the air pressure in the ducts. This can cause your ducts to leak, which makes your HVAC system even more inefficient.

Things That Are True

As there are myths about your furnace that need to be debunked, there are other beliefs that are actually true. Here are a couple of them.

Modern Furnaces Don’t Explode

You’ve probably heard horror stories about furnaces that get so hot that they explode. The good news is that modern furnaces have all kinds of safety protocols to keep this from happening. Indeed, if it gets too hot, your furnace will just switch itself off.

A Furnace Can Have a 99% AFUE

Modern furnaces are so efficient that they can attain a 99% annual fuel utilization efficiency, or AFUE. However, your house has to be very energy-efficient. This means keeping registers and vents clean and sealing up leaks in your ductwork and drafts in your windows and doors.



Your furnace keeps your home comfortable during the winter months, and it can make up a good percentage of your energy bill. Because of this, it’s important to maintain it or replace it if it’s on its last legs. If you need heating replacement services, give our HVAC professionals of NisAir of Fort Pierce, FL a call.

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