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Serving Northern California Since 1946

Serving Northern California Since 1946


DeHart Plumbing, Heating, and Air Inc. Blog

“Help! My Furnace Is Blowing Out Cold Air”


This is obviously a very concerning problem—getting cold air from your vents when you turn on your furnace. After all, that’s the absolute last thing you need when you turn on your furnace, whether it’s the first time this season or you’ve already been utilizing it on a regular basis. If your furnace has indeed started blowing cold air, the best thing you can do is give our pros a call!

We cannot definitively tell you in a blog post what’s wrong with your specific system, but we can speculate. There are a number of reasons that it may experience this issue. Please don’t try to fix it on your own, as you can do more harm than good, without ever resolving the actual issue. Read on as we uncover what might be going on with your heater while you wait for a pro to come for repairs.

First, Check the Thermostat!

Sometimes the problem with your furnace isn’t actually a problem with the heating system itself. Rather, the problem is with the thermostat. If you have a malfunctioning thermostat, it may be misreading indoor temperatures, or it might not be accurately regulating the temperature of the furnace.

The first thing you’ll want to do is take a look at the thermostat to make sure it’s not set to “on” rather than “auto.” When it’s set to “on,” the fan is going to keep blowing, even if the furnace isn’t actually heating the air. The air you will notice coming from the vents will actually be room temperature, which can of course feel pretty cold depending on the temps outside!

Next, Check Your Air Filter

What if the air coming through your vents isn’t actually cold, but doesn’t feel as comforting because it’s not coming through as powerfully? This is the result of low airflow and a clogged air filter can be to blame. A dirty or clogged air filter restricts the airflow coming into the furnace, causing the system itself to potentially overheat.

When this occurs, the system will shut down as a safety measure. The fan, however, may still continue to blow air. Like the problem we mentioned above, that air may be room temperature. Be sure to check your air filter! Homeowners should change or clean their HVAC air filters every 1-3 months.

You May Have Broken Heating Elements

This is one of those repair needs you can’t, or at least shouldn’t, check for on your own. And this one applies if you have an electric-powered furnace. When any of the electrical elements that are responsible for actually heating up the air leak, you will get cooler air from the furnace.

Our professionals will inspect each element of your system and pinpoint the exact cause of the problem so we can repair it accordingly. You want broken heating elements repaired as fast as possible since this can lead to a number of other problems.

Your Ductwork Might Be Damaged

Again, sometimes the problem with your furnace isn’t actually with your furnace. In some cases, it may be due to a ductwork breach. When this happens, warm air can leak from the ventilation system. Depending on where the breach is, this will prevent heated air from reaching a room or two, and you may feel cold spots or uneven heating throughout your home.

For professional Modesto furnace services, contact DeHart Plumbing, Heating, and Air Inc. today!

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