Why Is My Heat Pump Blowing Cold Air?
A heat pump that feels like it is blowing cool air is usually working fine. Here is how to tell the normal reasons from the ones worth a service call.
By Derek Mills, Co-owner, service lead ·
This is the call I get most in January, and about half the time nothing is wrong.
Heat pumps do not heat the way a furnace does. A furnace burns fuel and pushes out air somewhere around 120 to 140 degrees. That is hotter than your skin, so it feels warm when it hits you. A heat pump moves heat instead of making it, and it delivers a much bigger volume of air at a much lower temperature, usually somewhere in the 90s.
Your body runs at about 98.6. So 95 degree air is genuinely warming your house, but on your hand it reads as cool. That surprises people the first winter they own one.
Before you call anybody, here is how to sort out which situation you are in.
Check the easy stuff first
Is the air actually cold, or just not hot? Hold your hand at the register for a full minute. Not-hot is normal. Cold, like the air conditioning kicked on, is not.
Is it in defrost? When it is near freezing and damp, frost builds on the outdoor coil. The system reverses itself for a few minutes to melt it off, and during that window your indoor air really does go cool. You will usually see steam coming off the outdoor unit. It should end within about ten or fifteen minutes and go back to heating on its own. If you catch it mid cycle and panic, you are seeing normal operation.
Did somebody bump the thermostat? I have driven out for this more than once. Make sure it is calling for heat and not stuck in cool or on a schedule somebody set and forgot.
When was the filter changed? A loaded filter starves airflow. Less air across the coil means the air that does get through can feel weak and the system runs longer to do the same work. This is the single most common thing I find.
Is the outdoor unit buried? Snow drifted against it, a plow bank in front of it, ice built up on the base. It needs to breathe. Clear a couple feet around it and do not chip at ice with anything metal, you will put a hole in the coil and turn a free fix into an expensive one.
Now the ones that need us
It runs constantly and never satisfies. Could be low refrigerant, could be a sizing problem, could be the reversing valve. All of those need gauges on the system.
The outdoor unit is a solid block of ice, repeatedly. Occasional frost is normal. A unit that ices up, gets cleared, and ices right back up has a defrost problem. Usually a sensor or the control board.
Auxiliary or emergency heat is on all the time. Most systems have backup electric heat for the coldest stretches. Running once in a while in single digits is expected. Running in 35 degree weather means the heat pump is not carrying the load it should be, and you are going to feel that on your electric bill.
It is blowing genuinely cold air with the thermostat set to heat. That is a reversing valve stuck in cooling, or a control problem. Shut it off and call.
The thing nobody tells you
A lot of the complaints I get in the first year are not equipment failures, they are expectation mismatches. Somebody switched from an oil furnace that blasted 130 degree air in short bursts to a heat pump that runs long and low. The house is the same temperature. The delivery just feels different.
The way to actually be comfortable with one is to stop treating the thermostat like a throttle. Set it and leave it. Deep setbacks work against a heat pump, because recovering from a big drop is exactly when it has to lean on expensive backup heat. Pick a temperature you like and let it hold there.
If you have gone through the list above and something on the second half applies, give us a call. If it was the filter, you are welcome, and change it every couple months during the heating season.