Why Is My Furnace Blowing Cold Air?

Nov 10

Written By Jennifer Nelson

Nothing’s worse than turning on the heat and getting a blast of chilly air. The good news: many causes are simple and fixable. Below are the most common reasons your furnace (or heat pump) might blow cold air, what you can safely check, and when to call a pro.

Quick Checks You Can Do Now

Thermostat settings

Make sure HEAT is selected.
Set Fan to AUTO (not ON). ON runs the blower constantly, even between heat cycles, which can feel like cold air.
Replace thermostat batteries if the screen is dim or blank.

Air filter

A clogged filter restricts airflow, can overheat the furnace, and trigger a safety limit that shuts off the burners—leaving only cool air from the fan. Replace 1″ filters every 30–90 days (or check your media filter cabinet schedule).

Warm-up window

After startup, furnaces need a couple minutes to heat the air. If the cold air happens only for a minute or two at the beginning, this can be normal.

Gas supply / switch

Confirm the furnace power switch is ON.
If you use natural gas/propane, verify the gas valve is open and your propane tank isn’t low.

Condensate drain (high-efficiency furnaces)

If the drain is clogged, a safety switch can stop the burner. Look for standing water around the furnace and call if you see it.

Heat pump specific

During defrost mode, heat pumps can temporarily send cooler air inside. This lasts a few minutes and then returns to heat.
If the outdoor unit is iced over or the fan isn’t spinning, call for service.

Smell gas or suspect carbon monoxide? Leave the home and call your utility or 911 immediately, then contact us. Safety first.

Common Causes (and Whether You Can DIY)

Dirty flame sensor (gas furnaces):
The burner lights, then shuts off—air feels cool. Pro fix.
Extinguished pilot (older furnaces):
If the pilot won’t stay lit, you may have a faulty thermocouple. Pro fix.
Tripped high-limit switch:
Often from poor airflow (dirty filter, blocked vents). Replace the filter and open supply/return vents. If it keeps happening, call us.
Faulty ignitor or gas valve:
Blower runs but burners don’t light. Pro fix.
Electric furnaces / air handlers:
If heat strips fail or a breaker trips, you’ll get cool air. Check the breaker panel; repeated trips need a pro.

Special Case: It Heats, Then Turns Cold Mid-Cycle

Overheating due to restricted airflow (filter, closed vents, blocked returns) trips a safety limit.
ECM/variable-speed blower may keep moving air while the burner is off, which feels cold.
Fix airflow issues; if it continues, schedule service.

When to Call a Professional

Burning or electrical smell, repeated limit trips, or short cycling
No heat after basic checks
Water around the furnace (condensate issue)
Outdoor unit iced over or loud grinding/metallic noises
You haven’t had annual maintenance this season

Our experienced technicians will complete a comprehensive system diagnostic to pinpoint what’s causing the problem and get your home comfortable again—fast.

Prevent It Next Time: Maintenance Matters

A fall heating tune-up catches small problems before they become no-heat emergencies and helps:

Improve safety (CO checks, venting)
Boost efficiency and comfort
Reduce breakdowns and extend equipment life

Serving Central Ohio—We Can Help Today

Still getting cold air? We’ll diagnose the issue and get your home comfortable again.

Call Service First Heating & Cooling to schedule your repair or tune-up, or ask about our Service First Advantage Plan (2 seasonal tune-ups, priority service, and member discounts).

Stay warm out there! ❄️🔥