Furnace Blowing Cold Air

Air moving without heat behind it means the burner side has quit while the blower carries on, so call before the house drops further overnight.

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When this becomes an emergency

Registers are moving plenty of air, and none of it is warm.
The fan runs steadily while the temperature in the room stays flat.
Ignition sounds start up and stop again without heat following.
The unit locks out after several tries and then stays quiet.

What a pro does

Cool air usually clears the blower of blame right away. The technician watches a full call for heat from the start, checking whether ignition actually occurs, whether the flame sensor is coated enough to miss a flame it's sitting directly in, and whether a limit or pressure switch has parked the board in lockout while still permitting the fan to circulate. On oil equipment the trail often runs elsewhere. A worn nozzle or a pump losing pressure produces the identical complaint from the living room. Bypassing a lockout to force heat isn't a repair.

Frequently asked questions

Does cool air mean the whole furnace has failed?

Rarely. A flame sensor dulled by residue is the most frequent cause on gas equipment, and the control board reads that as no flame even though ignition briefly succeeded.

Could the fan setting alone explain this?

Sometimes. A thermostat fan left switched to continuous keeps air moving between burner cycles, and that unheated air feels cold coming out of a register.

Why does the problem come and go?

Intermittent faults usually mean a component is marginal rather than dead, so it works when conditions are easy and fails once the unit is hot or the outdoor temperature drops.

Is there harm in letting it keep trying to fire?

Repeated failed ignition cycles wear the ignitor and stress the gas valve, so leaving it hammering away for days isn't a good plan.

Furnace Blowing Cold Air?

Get connected with a local pro now.

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