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.
Yes, you should turn your heater off if it's blowing cold air to prevent potential damage to the system. Running a malfunctioning heater can strain the components, leading to more significant issues and increased energy usage.
Issues with the pilot light, high limit switch, blocked burners, leaky ductwork, electrical problems, and blower motor failures are common reasons for HVAC systems blowing cold air. These problems often require professional maintenance and repairs.
Check the thermostat
Maybe your heater is not blowing hot air even though the fan is running. As a result, any air that blows out of the vents while your heater is off will usually feel cold. In such a case, there could be an easy solution, particularly if your thermostat setting is the problem.
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.
Ensure that all the ductwork connections are sealed properly on the interior and exterior points of the ductwork. You can seal gaps using metal tape, foaming insulation spray, or mastic sealant. You do not need to remove any existing sealant and may build up the sealant over top of any current filler.
A furnace blowing cold air could be the result of a leak in your ducting. Over time, the changing temperatures wear on all sorts of things, including your ductwork. In fact, it's rather normal for ductwork to develop leaks over time. When ductwork has a leak, cold air will enter a duct and blow into your home.
A clogged filter is one of the most common causes of a heater blowing cold air. However, even if you replace the air filter with a new one, dirt, and other particles can still be inside the system. This could lead to overheating in the long run.
In most newer systems, the button is often directly next to the blower motor, while in older systems, it may be harder to spot as it is sometimes underneath or behind the motor. The reset button is often made of yellow or red plastic and marked with a large “R ” to make it easier to spot.
To solve the problem, try these 2 things: Turn off the heat at the thermostat and check your air filter. If it's dirty, change it! Make sure the thermostat is set to “AUTO”, not “ON”.
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.
While furnaces can stop operating for complicated reasons, home owners should check a few usual suspects first behind a lack of hot blowing air: Electrical problems causing a loss of power. Blocked air vents and ducts restricting airflow. Improperly configured thermostat settings.
It's possible your furnace could be overheating due to a dirty air filter. Because air flow is interfered with, your furnace overheats and turns off the burner, causing the heater fan to emit cold air. Replacing the dirty air filter and restarting the furnace may do the trick.
Blocked registers or vents can also cause a heater breakdown in the same way that clogged air filters do. If your HVAC system can't take in enough air, it will be unable to distribute warm air. It is also worth noting that occasionally a vent will get closed by accident.
First, check to make sure the thermostat is set correctly. You will want to make sure that the fan control is set to auto, and not 'on'. If the thermostat appears set correctly, turn off your heater at the thermostat and check the filter. If the filter is dirty, replace it.
A bad thermostat can be detected when your AC or furnace is not turning on, your HVAC systems are not turning off, the thermostat not responding, your HVAC system is short-cycling, the room temperature not matching the temperature displayed on the thermostat, and the programmed setting resetting themselves.
Emergency Heat, also known as Auxiliary Heat, refers to electric resistance heating. This involves little coils of wire with an electric current running through them in your air handler, similar to what you see in a hair dryer.
Typically, there's a 10 to 15 minutes allowance for this. However, if after this time it's still producing cold air, then there's an underlying problem that needs to be addressed. It would be wise to turn the furnace off and get in touch with a pro immediately for help dealing with the issue.
Check Furnace Air Filter
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.
Carrier furnaces typically have a small reset button inside the burner compartment. It may be red or yellow and is usually labeled “Reset.” If you're unsure where to find it, consult your furnace's user manual. Hold the button down for about 10 seconds before releasing it.
Accidentally leaving your thermostat set to "cool" or setting the fan to "on" can cause cold air to come out instead of hot air. It also could have run out of batteries. Either way, the solution here is simple. Head over to your thermostat, make sure it has plenty of battery, and verify that the heating function is on.
Dirty filters, leaky ducts, and poor insulation can cause cold return vents. Leaky ducts often cause cold air to blow even after cranking the heat up. 20-30% of air, especially hot air, is lost because of leaky ducts. Cracked, holey ductwork needs sealing or replacement.
The short answer is no; closing your vents does not save energy. When you close vents in unused rooms, your central air conditioning and heating system will push the excess air to other places in your home and build pressure within your ducts.