Your heat pump is blowing cool air. Is that a fault?

In mild weather a heat pump runs long, gentle cycles at a low supply temperature. That is the efficient way for it to work — it is not the same as a furnace, which blasts hot air in short bursts.

• Check the house is actually reaching the setpoint over an hour or two. That is the test, not the temperature at the vent.
• If it holds temperature, nothing is wrong. Leave the thermostat alone rather than nudging it up and down.
• If it never reaches the setpoint in mild weather, that is worth a visit.

The colder it gets, the less heat a heat pump can pull out of the outdoor air, and the cooler the supply air becomes. Below about freezing this is noticeable in most houses.

• Does the house hold its temperature? If yes, the system is doing its job.
• If it slowly loses ground on a cold night, the backup heat may not be staged correctly — that is a settings check rather than a repair.
• Check the filter. A loaded filter makes exactly this symptom worse.

If the air is warm to your hand and the outdoor unit is running steadily, the system is heating. Whatever brought you to this page is worth describing to us, but it is not the classic cool-air complaint.

• If a particular room is the problem rather than the whole house, that is usually duct work — the homes page covers it.
• If the bill is the problem, check whether the backup heat is coming on when it should not be.

In damp, cold weather frost forms on the outdoor coil. The unit periodically reverses to melt it, which is why it steams, why the outdoor fan stops, and why the indoor air goes cooler for a few minutes.

• A defrost typically lasts a few minutes and happens periodically in frosty weather. Steam rolling off the unit is normal and is not smoke.
• Many systems bring the backup heat on briefly during defrost so the house does not get a draught of cold air. Also normal.
• Worth a call if it defrosts very frequently, never seems to finish, or comes out of defrost still covered in ice.

Frost that comes and goes is normal. A coil encased in ice that survives several defrost cycles is not, and running it in that state can damage the compressor.

• Switch the system to emergency or auxiliary heat so the house stays warm, and leave the heat pump off until somebody looks at it.
• Do not chip or hammer at the ice. Warm water on a coil is the gentlest thing you can do and even that is a last resort.
• Clear snow and leaves away from the unit and make sure nothing is blocking the airflow through it.

If the unit is sitting in standing water, or ice has formed around the electrical connections, leave it off entirely and tell us when you call.

Starting and stopping every few minutes is hard on equipment and it is always a symptom of something — airflow, a control problem, a refrigerant issue, or a system that is simply too large for the house.

• Check and change the filter first. Restricted airflow is the commonest cause and the cheapest to rule out.
• Check no supply registers have been closed off. Closing vents to "save" a room is a frequent cause.
• If it still cycles after that, book a visit. This one does get worse.

Below about freezing, most systems in this area bring in electric backup heat to keep up. It costs more to run, which is why the bill climbs during a cold snap, but it is the system behaving as designed.

• It should switch off again once the weather lifts. If the auxiliary light never goes out in mild weather, that is a settings problem worth fixing.
• Avoid emergency heat unless the heat pump is actually broken — it bypasses the efficient part of the system entirely.
• Big thermostat jumps call in the backup heat unnecessarily. Small adjustments cost less.

The backup heat should be the exception in mild weather, not the rule. If it is running above 35–40°F, either the heat pump is not carrying the load or the controls are bringing it in too eagerly.

• Check whether somebody has left it on emergency heat. It is a common accident and an expensive one.
• Change the filter and make sure the registers are open, then watch whether it still calls for backup.
• If it does, book a visit. This is usually a staging or balance-point setting rather than a broken part, and it is worth putting right before the bill arrives.

Many systems stop running the heat pump below a set outdoor temperature and heat with the backup only. If your thermostat is showing auxiliary or emergency heat and the house is holding temperature, that is likely what is happening.

• If the thermostat is calling for heat and nothing at all is producing it, check the breaker for the outdoor unit and the switch beside it.
• If the house is losing temperature, treat it as a no-heat call rather than waiting.
• Either way it is worth knowing what your balance point is set to. We can tell you on a service visit.

If the thermostat is calling for heat, it is above freezing, and the outdoor unit is doing nothing while the indoor fan blows, the system is moving room-temperature air around the house.

• Check the breaker for the outdoor unit, and the disconnect switch on the wall beside it. Both get switched off and forgotten.
• Check the thermostat is set to Heat and not to Fan only — the second is a surprisingly common one.
• If both are right, book a visit. Something in the outdoor unit is not starting.