The most common reason a heat pump is blowing cold air through your air vents is defrost mode. This is a safety feature to melt frost and ice within the system. During defrost mode your heat pump made switch modes to heat up the outdoor coils. Indoor temperatures will fall because the system is briefly in cooling mode.
It May Be Blowing Relatively Cooler Air
Given that the ideal thermostat setting is at 68 degrees, blown air at 90 degrees is actually warmer than what is needed for heating. However, it is cooler compared to the average body temperature of 98.6 degrees, which makes it feel cool, and is often mistaken for cold air.
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.
If it's blowing cold air right after it fires up, it's just the cold air that's already inside the ducts, kind of like cold water in your hot water pipes.
Common Reasons For Furnaces Blowing Cold Air:
Your Thermostat is Set Incorrectly. The Furnace Filter is Dirty. Your Furnace Has Overheated. The Condensate Line is Clogged.
The most common reason a heat pump is blowing cold air through your air vents is defrost mode. This is a safety feature to melt frost and ice within the system. During defrost mode your heat pump made switch modes to heat up the outdoor coils. Indoor temperatures will fall because the system is briefly in cooling mode.
Make sure all vents and radiators are open and not blocked by furniture or curtains. Blocked vents can prevent the warm air from circulating freely in your rooms. It's also a good idea to bleed your radiators to remove any trapped air that can cause cold spots and reduce their efficiency.
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.
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.
If the heat is running and your house has oddly cold rooms, they are unevenly heated, or vents or radiators aren't giving off much heat – there could be a problem with heat delivery. Insulating your home will surely help keep the heat inside, but it first needs to be properly delivered.
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.
When weatherpeople talk about wind chill on a cold winter day, what they are referring to is how the wind increases convective heat loss (see How Thermoses Work for details on convection). By blowing air around, the fan makes it easier for the air to evaporate sweat from your skin, which is how you eliminate body heat.
Ensure your thermostat has not been set to a lower setting by someone else. 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.
Check the thermostat
The air coming out of your vents might seem rather cool or your home is not staying as warm as the temperature you set. 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.
Wind can similarly snatch away our body's warmth, making the air feel several degrees cooler. The recent wind chill in Florida, for instance, made it feel like it was 10 degrees F (5.6 degrees C) colder than the actual temperature in some places.
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. Conversely, if the air from our mouth reaches the object slowly, it remains warm.
The heater might blow cold air rather than warm if the gas line supply has been turned off. This usually happens when something goes wrong with the heater, and it breaks. For example, maybe there was a problem with a gas valve, the gas supply pipe, or something else in your furnace broke down.
When the thermostat can't signal that the engine is warm, the coolant won't be sent over to provide heat to the heater core and the air will blow cold. Solution: You need to install a new thermostat to get your heater working again. It's a relatively quick and easy fix.
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.
This means that if the air entering the system is 75°F, the air coming out of the vent should be between 55°F and 61°F.
Closing the intake vent to remove draft is a short-term solution because cold air will nevertheless flow into the building. Both the house and the inhabitants will benefit if the air flows in through an intake vent.
This problem often points to inadequate circulation of warm air. It could be due to blocked vents, a failing HVAC fan, or issues with the furnace itself. Ensure that furniture or drapes are not blocking your vents.
The causes of cold intolerance are clustered around problems involving the circulatory system, nervous system, and endocrine (hormonal) system. Often, multiple causes are involved. Even certain medications or the lack of sleep can trigger intolerance to cold.
In many homes, inadequate insulation in basements, crawlspaces, and attics create a problematic scenario. Cold air comes in from below while heat from the home gets lost through the attic. A lack of insulation around ductwork and points where electricity is wired into the ceiling contribute to these issues also.