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Serving Northern California Since 1946

Serving Northern California Since 1946


DeHart Plumbing, Heating, and Air Inc. Blog

“Why Is My Furnace Blowing Cold Air?”


With cooler temperatures lingering a bit longer this year, the last thing you need in your home is a malfunctioning furnace. So if yours is all of the sudden blowing out cold air, this is of course a big problem.

There are a number of reasons that this might be happening. We’ll dive into that below, so keep reading! But please do not try to diagnose or fix your furnace yourself. You could wind up with more problems rather than less and a pretty big headache. Instead, call our professionals if you suspect any of the following issues, or if nothing you do will resolve the cold air coming out of your room vents.

Thermostat Trouble

Sometimes your furnace problem is not a problem with the heating system itself, but instead with the thermostat. If your thermostat is malfunctioning, it can be misreading indoor temperatures, or it might not be properly regulating the temperature in the furnace.

First, check your thermostat and make sure it’s not set to “ON” instead of set to “AUTO.” Otherwise, the fan will keep blowing, even if your furnace isn’t heating the air. So when the temperature of the room has reached the desired setting on your thermostat, the air coming through won’t be heated. As a result, it may feel lukewarm or even cold to you in comparison.

Don’t worry if this was the mistake—many times family members can accidentally change the setting! If this is the problem, it’s an easy one to fix!

A Clogged Air Filter

This is another problem that’s easy to fix. The air filter that comes standard with your furnace is in place to protect the interior components of the heater, and when it gets too clogged up in can create resistance against airflow. As a result, hot air can get trapped inside your furnace and the air you feel coming through won’t be as powerful, which you can mistake for cool or lukewarm air.

Be sure to change out this air filter every 1-3 months. If you do this, and your thermostat isn’t to blame for the cold air coming from your furnace, then it might be one of the next couple problems to blame.

Broken Heating Element in an Electric Furnace

Do you have an electric furnace? There are heating elements (called heat exchangers within a gas-powered furnace) that allow the air going into your home to actually pick up heat. If any of these become damaged, due to wear and tear or whatnot, then you’re furnace cannot adequately do its job.

Damaged Ductwork

Whether you have a gas or electric furnace, it utilizes ductwork. Over the years that ductwork can accumulate damage from extreme temperatures, rodents in the attic or crawlspace where the ductwork is installed, or even poor installation to begin with.

Damaged ductwork can allow heated air from your furnace to escape into unoccupied spaces in your home, and therefore one or more of the vents won’t distribute fully warmed air. You may feel a drop in heating power or a drop in the temperature. Be sure to give us a call if this is what you suspect!

For quality furnace services, look no further than DeHart Plumbing, Heating, and Air Inc. Contact us today!

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