Why Is My Heater Blowing Cold Air?
A heater blowing cold air means one thing on a furnace and something quite different on a heat pump. On a furnace it usually means ignition failed or a safety limit shut the burners down. On a heat pump, mildly cool air can be completely normal — heat pumps deliver warm air at a lower temperature than a furnace does, and they periodically run a defrost cycle that blows cool on purpose.
First, which one do you have?
If your outdoor unit runs in winter, you have a heat pump. If the outdoor unit only runs in summer and you have a gas appliance indoors with a flue, you have a furnace. This distinction changes what the symptom means, and it is worth knowing before you call anyone.
On a furnace
- The fan is set to ON rather than AUTO, so it blows room-temperature air between burns
- Ignition failure — the blower runs but the burners never light
- A flame sensor dirty enough that the furnace lights and then shuts down within seconds
- A tripped high-limit switch, usually caused by restricted airflow from a clogged filter
On a heat pump
Heat pump supply air typically runs cooler than furnace air. That is how the technology works and it is not a fault. What is a fault: air that is genuinely cold rather than merely less warm, a system stuck in defrost, or a reversing valve that has not switched over into heating.
The safety one
If you have a gas furnace and smell gas, leave the house and call your gas utility from outside before calling us. That is a utility emergency, not an HVAC service call.
Common questions
Why is my furnace blowing cold air?
Commonly the fan is set to ON instead of AUTO, ignition has failed, the flame sensor is dirty, or a high-limit switch has tripped because a clogged filter restricted airflow.
Is it normal for a heat pump to blow cool air?
Somewhat, yes. Heat pumps deliver warm air at a lower supply temperature than a furnace, and they run periodic defrost cycles that blow cool briefly. Genuinely cold air is not normal.
What if I smell gas?
Leave the house and call your gas utility from outside. That is a utility emergency and takes priority over any HVAC service call.
Reviewed by Briton Davis, owner, and the Cool Guys Home Services service team · Licensed, bonded & insured (CSLB #1156890)
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