The cozy heat you’re expecting isn’t there. There are a few common reasons why your furnace might be blowing cold air
Fan is set to “ON”: This runs the blower constantly, even when the furnace isn’t heating. Try switching it to “AUTO” so it only runs during a heating cycle. Else, could be a wrong temperature setting: Double-check that the thermostat is set to “HEAT” and that the target temperature is higher than the current room temp.
When the furnace first kicks on, it may blow cold air for a minute or two while the system warms up—this is totally normal. If it doesn’t turn warm shortly after, something else may be going on.
Older furnaces use a pilot light, and if it’s out, the furnace won’t produce heat. Newer models use electronic ignition, and if that fails, you’ll get cold air. You might need to relight the pilot or call a tech for the ignition system.
A clogged filter can restrict airflow and overheat the furnace. Many systems will shut off the burner as a safety measure, causing it to blow unheated air.
Furnaces have safety switches that shut off the heat if it gets too hot or a part fails. The blower may keep running to cool the system down—resulting in cold air.
Leaky or poorly insulated ducts can let in cold air. Else, a malfunctioning flame sensor might shut off the burners shortly after ignition.
Check thermostat settings. Make sure it's set to "HEAT" and the temperature is higher than the room temperature.
Change the air filter. A dirty or clogged air filter can block airflow and cause your furnace to shut down.
The pilot light is on (if applicable). If the pilot light is out, your furnace won’t produce any heat.
Error codes or flashing lights on your furnace panel. These can point to specific problems—check your furnace’s panel or manual.
Make sure all vents are open and unblocked. Closed or blocked vents can cause poor airflow and cold air blowing.
If your furnace keeps blowing cold air and none of the basics help, it’s best to call a Fast Heating and Air. They can safely diagnose and fix the issue before it becomes a bigger problem.
We are authorized dealers and installers of the most common and trusted furnace manufacturers.
A faint gas smell when first starting your furnace can be normal, especially at the beginning of the heating season. However, a strong, persistent gas odor could mean there’s a serious gas leak. Leave your home immediately and call 9-1-1 from a safe location. Once you’re in a safe place, contact an HVAC professional to inspect your system.
Furnaces burn fuel, which produces carbon monoxide—a deadly, odorless, and colorless gas. A well-maintained furnace safely vents this gas, but a malfunctioning unit can allow it to accumulate to dangerous levels. If your carbon monoxide detector sounds an alarm, evacuate your home immediately and call 9-1-1.
Loud hissing, banging, or other unusual sounds could point to an electrical issue or another serious internal problem. If your furnace is making strange noises, stop using it and call a licensed HVAC technician to investigate and make necessary repairs.
If you’ve tried basic troubleshooting or don’t feel comfortable doing it yourself—and your home is still cold—it’s time to call in the experts. Your furnace may need professional repairs or replacement beyond DIY fixes.
If your furnace is running but blowing cold air, the issue might be a clogged air filter, incorrect thermostat settings, or an ignition failure. This can also happen if your furnace does not turn on properly during the heating cycle due to a malfunctioning sensor or overheating.
If your furnace won’t turn on, check the thermostat, circuit breaker, and air filter. A dirty or clogged air filter can trigger a safety shutoff. If basic troubleshooting doesn’t work, your system may require professional repair.
Yes, a clogged air filter restricts airflow, leading to overheating. Many furnaces will shut down the burner as a safety feature, causing cold air to blow. Regular furnace filter replacement helps prevent this issue.
If your HVAC is not cooling, the problem could be a dirty air filter, low refrigerant, or thermostat issues. Like with heating problems, airflow restrictions or malfunctioning components are common culprits.
If my furnace does not turn on even after adjusting the thermostat, inspect your air filter, circuit breaker, and ignition system. An issue with the pilot light or electronic ignition may prevent startup.
No, if your air conditioner is not cooling, it may have a refrigerant leak, frozen evaporator coil, or airflow issue caused by a clogged air filter. Regular maintenance can catch these problems early.
Furnace filter replacement is recommended every 1 to 3 months, depending on usage, filter type, and indoor air quality. Skipping this can lead to a clogged air filter and system performance issues.
If the system is on but you’re not getting warm air, the furnace might not turn on the burners due to safety shutoff, ignition issues, or thermostat problems. This is a common cause of cold air blowing from vents.
Let’s bring your vision to life with expert craftsmanship and thoughtful design.
16120 Woodinville Redmond Rd NE STE. 15
Woodinville, WA 98072
(206) 558 5112
hello@fastwaterheater.com
Monday – Friday 7:30am-5pm
24/7 Emergency Service Available
HVAC License
NORDSHA772L2
Electrical License
NORDSHA774MR
©2025 Fast Heating & Air