Furnace Blowing Cold Air

Blowing unheated air through the ducts actively pulls the house down, so it's worth calling before the temperature inside gets away from you.

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When this becomes an emergency

Air from the registers feels cooler than the room it's blowing into.
The system runs long stretches without the house gaining a degree.
You hear ignition attempts followed by silence, over and over.
The furnace ran fine yesterday and turned cold after the first deep freeze of the season.

What a pro does

This is a fuel-and-flame problem, not an air problem. The tech watches an entire attempt and notes exactly where it stops: the inducer spinning but the pressure switch never proving, an ignitor that glows without the burner catching, or a flame that establishes and then drops out a few seconds later on a weak sensor signal. Weather-triggered failures deserve their own attention here, because an exhaust termination that frosts shut in a hard freeze locks a furnace out cold and behaves perfectly again by afternoon. Anything intermittent in the coldest week of the year is worth describing carefully, since it may not misbehave while somebody's standing there.

Frequently asked questions

Why would a furnace only fail during the coldest nights?

Cold-specific failures are real. A frosted-over vent termination, a condensate line freezing, or marginal gas pressure under peak demand all show up in a deep freeze and hide the rest of the year.

Can the exhaust pipe outside really ice over?

Yes, especially on a high-efficiency furnace that vents moist exhaust through a sidewall. Ice forming at the termination stops the burner from proving airflow.

What does it mean if warm air comes for a minute and then goes cold?

The burner is lighting and then getting shut down, most often because the flame isn't being proven or a safety limit opened once the unit warmed up.

Should the system be left running while waiting for service?

If it's only moving cold air, switching the thermostat to off keeps the fan from stripping what warmth is left out of the house.

Furnace Blowing Cold Air?

Get connected with a local pro now.

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