7 Things I Tell Every Homeowner About Furnace Maintenance as an HVAC Pro to Avoid a Breakdown on the Coldest Night of the Year

With the start of December now exactly a week away and the holidays just around the corner, attention in homes has well and truly turned to keeping cozy and comfortable.

And, with heating more important than ever at this time of year, it's imperative to avoid a furnace breakdown when you need it most. But how can homeowners ensure a warm winter?

As an HVAC expert, my best advice is to test your system before you need it, switching the heat on and letting it run for 15 to 20 minutes, without waiting for the forecast to drop to 30°F if you can avoid it. Here's why it's essential when keeping keep a home warm all day.

Why Homeowners Should Test Their Furnace Now

Most importantly, testing furnaces now gives homeowners time to notice things like strange startup noises, the smell of burning dust coming off the heat exchanger, or a blower motor that's slow to heat up.

As the founder of AirConditionerLab, I know that early-season problems often stem from dust buildup or parts that stick after months of inactivity, while keeping a home cool over summer, which a simple test run would reveal. Then, if there are any issues, you'll have time to call in a pro before the cold weather really sets in.

Once that's been tested, these are the next steps I suggest:

1. Inspect the Air Filter

Next, I visually inspect the air filter, rather than checking the date. Hold it up to a bright light; if you cannot see through it, please replace it. A clogged filter reduces airflow, causing the heat exchanger to overheat and shut off. That trips the high limit switch, and the furnace keeps turning on and off every few minutes, doing the opposite of making heating more efficient. You’ll feel warm air at first, then nothing.

I usually recommend the Filtrete Air Filter, available in a pack of two at Amazon. It traps dust and pet dander without blocking airflow, unlike some higher-MERV filters. It comes in several size options, and the one-inch version works for most systems unless yours was designed for a thicker filter.

2. Vacuum Vents

Additionally, homeowners often forget about return vents and supply registers. Use your best handheld vacuum [our top pick is the BLACK+DECKER dust buster Handheld Vacuum available at Amazon] to go over the vents, especially the cold-air returns. Dust buildup forces the blower to work harder, and, if you're in a home with pets or kids, that dust adds up fast. Even wiping the outside of the furnace helps.

Fine dust can clog pressure tubes, leading to a pressure switch failure. I've replaced more of those than I can count, and they're usually $150 to $300 parts with labor.

3. Check the Condensate Drain

With high-efficiency furnaces, I always check the condensate drain, which is crucial when winterizing a house inside and out. These models produce water when they run. If the drain trap is dry or blocked, the furnace won't run.

Pour a cup of warm water into the drain to keep the trap primed. Some people also use condensate tablets [such as the QwikTreat Condensate Pan Treatment Tablets available at Amazon] to keep the line clean, especially if there's any slime or buildup.

4. Change Thermostat Batteries

A small but common issue is the thermostat. If it runs on batteries, swap them out to avoid any thermostat mistakes this winter.

Low batteries don’t always show a warning. What you usually see instead is the furnace turning on and off, the screen going blank, or the system not calling for heat at all.

This problem causes dozens of service calls every year, and most are fixed in seconds with fresh AA batteries, available at Amazon, or AAA batteries, available at Walmart.

5. Check the Flame Sensor

I also check the flame sensor if the furnace is five years or older. If the furnace starts but shuts off after a few seconds, the sensor is likely dirty, which is likely to make your heating system work harder.

You can clean it with a Scotch-Brite pad, available at Amazon. Don't use sandpaper – that ruins the coating.

6. Keep a Spare Hot-Surface Igniter on Hand

If your furnace is over 10 years old, it’s a good idea to keep a spare hot-surface igniter on hand. It’s the little part that lights the burners. When it goes out, the furnace won’t fire up at all. If that happens on a weekend or holiday, you’re stuck heating your house with the furnace out until someone can get to you.

The Emerson Hot Surface Ignitor on Amazon works with many models, but always check the number on your existing part first. Swapping it out is usually quick if you’re comfortable with basic tools. Just make sure the power is completely off before you touch anything.

7. Keep the Area Around the Furnace Clear

Last, keep the area around the furnace clear. I need at least 30 inches of working space. Don't store cardboard, leftover paint cans, or laundry next to it.

I've seen filter doors blocked by storage baskets and bins, and even a Christmas tree jammed between the unit and the wall. That space isn't optional. It affects safety and service access.

What to Shop

All prices were correct at the time of publication.

Meet the Expert

Josh Mitchell

As an HVAC and tech enthusiast and expert, Josh founded AirConditionerLab in 2014, bringing readers quality tips and findings about all things heating, cooling and air quality.

Wondering how long a furnace lasts? Our experts say anywhere between 10 and twenty years, but there are a number of things you can do to make yours last longer.