Therefore, your furnace blowing cold air could result from a clogged or dirty air filter. If you have a dirty or clogged furnace filter, the cool air from inside your home will struggle to travel through it and into the furnace. This means you have insufficient air to heat and redistribute.
A dirty air filter hinders air movement through the furnace. This raises temperatures inside the furnace, and the limit switch shuts heating cycles down if the unit becomes too hot. If you have a dirty filter, replacing the filter typically stops cold air from blowing.
If the coil becomes clogged with dirt, dust, or debris, it hampers the heat absorption process. A clogged coil reduces the furnace's ability to absorb heat efficiently, leading to your furnace blowing cold air instead of warm air.
If your furnace is blowing cold air in your home, this is a sign of an issue with the flame detector, gas supply, air filter, pilot light, or condensate lines. Many of these issues are able to be easily solved on your own by sanitizing or replacing components in the gas furnace.
You shouldn't turn off your furnace just set the thermostat so the furnace will only come on if the temperature drops around 50F 10Celsius. On thermostats that run both the heater and AC, make sure the system is switched over to ``cool'' and the furnace won't turn on.
A propane furnace or oil furnace blowing cold air might indicate a low or empty fuel supply. And, a clogged oil filter can also cause an oil furnace to turn on and blow cold air. If you suspect a fuel supply issue with your natural gas furnace, it's best to contact a qualified professional.
The heat exchanger uses coils to transfer heat from the ignited gas to the air. When cold air blows from a furnace the heat exchanger, furnace burner, or exhaust are likely the cause. This may be due to dirty components, broken parts, or the many safety mechanisms within the gas system.
The cause of your furnace not blowing hot air could be the thermostat configuration, a dirty air filter, the high limit switch, a clogged condensate line, insufficient fuel, leaky ducts, ignition problems, a blocked burner, flame sensor issues, gas valve malfunctions, a cracked heat exchanger, or a clogged coil.
Simply reset the thermostat to AUTO. What causes the heater fan to emit cold air is the ON switch allows the fan to operate even when heat isn't required to maintain temperature control. Checking the pilot light and seeing if it is out could be a quick fix also. If the pilot is out you can try relighting it.
The air in our surrounding is always cooler than the air from our lungs. When we blow air from our mouth, if it reaches to an object fast, then a lot of ambient air gets mixed with it. The result is that the air falling on the object gets cold.
Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.
Under normal circumstances, once your furnace comes on it should take approximately one hour to increase the temperature by one degree. After that, it typically takes 45 minutes for each additional degree.
If you have a dirty or clogged furnace filter, the cool air from inside your home will struggle to travel through it and into the furnace. This means you have insufficient air to heat and redistribute. The result is your heater blowing cold air.
If your heater doesn't start, chances are the problem stems from having a dirty furnace. Having dirt on your blower motor or flamer sensor could render your furnace unable to perform. When the blower motor is too dirty, it won't pass enough cool air to the heat exchanger, leading to equipment failure.
Get your ductwork checked. If your furnace is blowing hot but your home is still cold, it may be a problem with your ductwork. You may have leaky or damaged ducts that are letting hot air escape and cold air in.
Check your thermostat's batteries and replace any that are exhausted or defective. Clean all of the parts of your furnace, especially the ones that are susceptible to dust and dirt. You could also hire HVAC technicians to clean the system thoroughly. Ensure that the gas valve is open and not obstructed by any debris.
Check Furnace Thermostat Settings
Incorrect thermostat settings can be the cause behind no heat coming out of the vents, even with the furnace blower turned on. Check the thermostat to ensure the setting is in HEAT instead of COOL. It is a common mistake that happens. The fan runs continuously when it is switched on.
It's Defrosting
To protect the outdoor coils from freezing up in the winter, heat pumps go through a defrosting period every hour or so in which they are truly blowing out cold air. This defrosting period only lasts a few minutes and should not affect the overall temperature of your home.
It's most likely an incorrect thermostat setting if you find your furnace blowing warm air, not hot. The fan is set to “on” instead of “auto.” Furnaces only pump hot air until the thermostat setting is reached, so if your fan is always on, it will blow both hot air when the furnace is heating and cold when it's not.
With a furnace blowing cold air, the first question you should ask is if the furnace has been turned ON. Two thermostat issues that could cause your furnace to blow cold air include (1) your thermostat is still set to COOL, not HEAT and (2) your thermostat fan is set to ON, not AUTO.
Clean your Air Filters, Vents, and Ducts – A clogged air filter will struggle to meet the thermostat's set temperature since the dirt and debris buildup prevents air from circulating through the vents. And as airflow into living spaces drops, so do comfort levels.
Gas furnaces produce air that is 130-140°F range. So 85-92°F feels cold to new heat pump owners. Your body temperature is around 98.6°F (everyone's body temperature is slightly different, but that's the average). Since heat pumps produce air that's below that, it can feel cold to you.
Butterfly Flat Dish Dampers (BFD) – HVAC Dampers
The butterfly flat dish damper is shaped like a circle with two semicircles attached to it. The semicircles are called flaps, and they open and close to direct airflow through a system.
A dirty filter can cause repeated overheating, and repeated overheating can cause the high-limit switch to fail altogether. So your furnace does not burn fuel and instead continually blows cool air. The fix: Get professional HVAC help. Call an HVAC technician to troubleshoot and replace the switch.