Why Is My Heater Not Blowing Hot Air In House? Know How to Fix!

Is your heater not blowing hot air in house? The last thing you’d want is a malfunctioning furnace. So, you need to troubleshoot it to find out what is wrong and make the repair process smoother.

If your heater is not blowing hot air, there may be issues with the thermostat. You may have incorrectly set the mode. In this case, set your furnace to AUTO to make sure the fan only runs when the air passing through the coils is warm.

Focus your initial troubleshooting on the thermostat as you can fix the problem yourself.

Once you have crossed out issues with the thermostat, check for other circumstances that may cause your heater not blowing hot air and perform the necessary solutions. 

Why Is My Heater Not Blowing Hot Air In House?

Heaters have highly conductive coils called heat exchangers, which are heated by oil, natural gas, or electricity.

They also have fans that blow air towards the heated coil, pushing hot air into the ductware of your house. But, if your heater blows out cold air, check for the following:

1. Thermostat Issues

Is your electric heater not blowing hot air in house? Check your thermostat. The fan may be set to ON, which makes the furnace blow cold air during downtime.

Also, make sure no one else is adjusting the thermostat. More importantly, check the batteries. Sometimes, a low battery can cause your device to malfunction.

2. Filter Issues

If your furnace is still blowing hot air after you checked for thermostat issues, check the filter.

A clogged filter can restrict the airflow to your HVAC system, limiting the ability of your heater to produce and distribute warm air throughout your house.

When the color of the filter resembles mud, it’s time to replace it.

3. High Limit Switch Issue

If the high limit switch fails, your furnace interprets it as your heater overheating. It will turn on the fan to cool everything down, causing your heater to blow cold air.

You may need the help of an HVAC technician as the switch can be difficult to find.

4. Damaged or Dirty Ducting

Inspect for leaks, holes, and loose joints as they allow cold air to get into the ventilation.

Accumulated dirt or debris can also block the airflow and slow down the movement of warm air. A completely blocked airflow can cause the furnace to overheat and shut down.

5. Condensate Line Issue

Without Regular Maintenance, the condensate line of your heater can get plugged with grime and dirt.

Once clogged, the float switch will get tripped and cause the heater to kick off, blowing cold air throughout your house.

6. Problems at the Source

Sometimes, the problem may be the heating system itself. If you have a gas furnace, check if the gas supply line valve is open.

For older models, see if the pilot light is lit. If you have an electric heater, check for tripped circuit breakers and reset them.

Note: If the heat pump is not blowing hot air, call for an HVAC technician. The level of refrigerant may be low, or the auxiliary steps may be malfunctioning.    

Now that you know why your heater is not blowing hot air in your house, here are some furnace troubleshooting tips to get your device running effectively. 

How to Fix Heater Not Blowing Hot Air In House

Heaters are simple in concept, but it can be very frustrating when they’re not blowing hot air.

But, don’t panic! This post will help you understand the cause of the issue. We also set up a few possible solutions to correct the problem.

Solution #1: Check Your Thermostat

First, make sure the thermostat is set correctly. The fan control should be in AUTO and not in ON mode. In AUTO mode, the device will function according to your specified settings.

Generally, it will start the fan about 30 seconds before the burner is lit and shut it down about a minute after it reaches your desired temperature, resulting in more energy efficient usage.

If the heater is still blowing cold air, check the batteries. Almost empty batteries can interfere with temperature inputs. Replace them to solve the issue.

If replacing the batteries does not work, hire a professional to recalibrate your thermostat or replace it with a new one.

Solution #2: Check If Your Heater Is Just Turned On

Always check to make sure if your heater is just turned on. The device may still be warming up.

It takes between 15 to minutes for the engine to reach operating temperature. Cold air trapped inside needs to be expelled first.

If the heater has been turned on for a while but is still blowing cold air, go to the electrical box and check for a tripped fuse.  

Solution #3: Clogged or Dirty Furnace Filter

If you still get cold air blown by your heater after checking the batteries and surveying household members for sneaky thermostat adjusting activities, change the furnace filter.

A dirty old filter is clogged, restricting airflow to your heating system.

Filters are cheap and easy to change. Here’s how:

1. Turn off your furnace.
2. Locate the filter housing.
3. Open the compartment door.
4. Slide the filter out.

Note: Make sure the size of the replacement filter matches the old one.  

Slide the new filter in with arrows pointing towards the heater in the direction of the airflow. Secure the compartment cover, then turn on the furnace.

Solution #4: Damaged or Leaking Ducts

Inspect the ducts for leaks, tears, and loose joints. Cold air can enter the ventilation if the ducts are damaged.

Contact a professional to service your ductwork and restore the efficiency of your heating system.

How to check your furnace ducts for leaks and damages:

1. Take a look at the visible vents.
2. Examine each section and connection for obvious tears, gaps, and disconnections.
3. Look for areas with duct tapes.
4. Turn your heating system on and place your hand over the ducts. If you feel the air, there is a leak, or a connection is loose. 
5. Using a pencil or incense stick, watch for movement in the ducts.

If you find areas with leaks, mark them and seal them.

Solution #5: Check Your Condensate Lines

Keep the condensate lines clean and open to prevent your heater from blowing cold air. If there is standing water, they may be clogged. Generally, clogged condensate lines can be cleaned with suction.

1. Turn off your heater at the thermostat and the breaker and find the drip pan.
2. Use a vacuum to remove water and clean the pan with soap and water.
3. Find the drain outlet outside your house and remove the clog with a vacuum or plumber’s snake.
4. Find the access point on the condensate lines and inspect for debris.
5. Use distilled vinegar or hot water with mild soap to flush out the drain.
6. Leave the solution for 30 minutes, then rinse it clean. water

Note: Ask someone to watch the exterior condensate line to make sure water moves through freely.

Read Next: Why is Heating Still On When Thermostat is Off?

Last Thoughts

If your furnace is not blowing hot air, there’s a good chance the thermostat is the culprit. Make sure it is set on Auto mode to coordinate it with the furnace. Auto allows the thermostat to switch temperature based on specified settings.

If you have a problem with the heater not blowing hot air in house, this post will help you understand why this is happening and learn how you can fix the issue.

If you have tried all possible solutions but still cannot fix the issue, the problem may be on the installation and requires the service of a professional.

If you find this post helpful but have another difficulty with your heating setup, our blog can help.