Heat pump supply air can feel cooler than furnace air during normal heating, and defrost cycles can temporarily change operation. Understanding the difference between normal behaviour and a real problem is the first step before calling for service.
The most important thing to understand about a heat pump "blowing cold air" is that some of what homeowners describe as cold air is completely normal behaviour — specifically, the lower supply temperature compared to a gas furnace, and brief periods of cooler air during defrost cycles.
A heat pump in heating mode delivers supply air at lower temperatures than a gas furnace. This air should still be warm — above the current room temperature — but it will not feel as intensely hot as furnace air. If you are switching from a furnace to a heat pump for the first time, this difference can be surprising.
Persistent cold air during a heating cycle — meaning the system is in heating mode, has been running for more than 10 minutes, and air at the supply register still feels cool or the same as room temperature — is different and warrants investigation. Possible causes include a wrong thermostat mode, refrigerant issue, reversing valve fault, or compressor problem.
The difference in supply air temperature between a heat pump and a gas furnace is a matter of equipment design — not a malfunction.
| System Type | Typical Supply Air Temp (Heating) | Cycle Duration |
|---|---|---|
| Gas Furnace | 50°C – 65°C (120°F – 150°F) | Short, intense cycles |
| Heat Pump (heating mode) | 30°C – 45°C (86°F – 113°F) | Longer, gentler cycles |
| Heat Pump (defrost) | Cool air or ambient, temporarily | A few minutes, then resumes heating |
A heat pump moves heat rather than generating it by burning fuel. This process is highly efficient, but the resulting supply air temperature is lower than what a furnace produces. The space still reaches the setpoint — the heat pump runs longer cycles to achieve this — but the air from the registers will not feel as intensely warm as furnace air. This is expected and correct operation for a heat pump.
Before concluding there is a problem, check whether the "cold air" is actually one of these three normal operating conditions.
During cold and damp weather, frost accumulates on the outdoor coil. To clear this ice, the heat pump periodically reverses the refrigerant cycle — effectively running in cooling mode briefly to melt the frost. During defrost, the system stops delivering warm air and may briefly deliver cool or ambient air. Some systems also activate the auxiliary heat strip during defrost to compensate. Defrost typically lasts 2–10 minutes and then the system returns to normal heating. You may also hear gurgling or a hiss at the start and end of defrost — this too is normal.
If the thermostat's fan setting is set to "On" rather than "Auto," the fan runs continuously — including during periods between heating cycles when the compressor is off and no heat is being produced. During these continuous-fan intervals, the air delivered to the registers will be at or near room temperature, which can feel cool. Check your thermostat's fan setting: if it is set to "On," switching it to "Auto" will stop the fan from running outside of active heating cycles.
At the very start of a heating cycle, the refrigerant circuit takes a moment to reach operating pressure and temperature. During this brief ramp-up period, the supply air may feel cool or neutral. This is normal and typically resolves within 1–3 minutes as the system reaches full heating output. If the air never warms up during the cycle, that is a different situation.
If the air is still cool or room-temperature after 10+ minutes of a heating cycle, one of these causes may be responsible.
The thermostat is set to Cool, Fan Only, or a temporary hold that overrides the heating schedule. This is the first thing to verify. Confirm the mode selector shows Heat, and that the setpoint is above the current room temperature. If the thermostat has a schedule active, check that the current time slot calls for heating.
If the outdoor unit is heavily iced over and the defrost cycle is not clearing it, the system may be stuck in an extended defrost or a protective lockout. Visible heavy ice buildup — covering the coil, building up over the top of the unit — that has not cleared after an hour is unusual. Do not chip or pry ice off the unit; call for diagnosis.
The heat pump refrigerant circuit requires the correct charge to transfer heat effectively. A leak or undercharge reduces the system's ability to extract heat from outside air. A refrigerant issue will often cause the system to run continuously while delivering inadequate heating. This requires licensed diagnosis and repair — refrigerant work is regulated and cannot be DIY.
A failed reversing valve (the component that switches the system between heating and cooling mode) can cause the heat pump to operate in cooling mode even when the thermostat calls for heat — genuinely blowing cold air. A compressor fault or a control board failure can also prevent the system from producing its rated heat output. These require a technician to diagnose.
Work through this list before scheduling a service call. If any of these resolve the issue, no call is needed.
Diagnosis and repair for heat pumps that are not heating correctly across Metro Vancouver.
System runs but produces no heat at all — different from reduced or cool air output.
Systems designed to maintain heating output at low outdoor temperatures.
Annual tune-ups to maintain heating performance and catch issues before they worsen.
Persistent cold-air problems that don't resolve with basic checks may require professional heat pump diagnosis.
Answers to the questions we hear most often about heat pumps delivering cool or cold air.