Cold air coming from the vents on a winter night feels urgent, but the cause is usually one of a handful of ordinary faults. Some you can sort out yourself in a few minutes. Others need a gas technician. This guide walks through them in the order worth checking, and explains how the answer can differ between an older house in the Binbrook village core and a newer house off Fall Fair Way.
Cold air for the first minute is normal
When a gas furnace starts, it runs through a sequence. The inducer fan clears the burners, the igniter heats up, the burners light, and only then does the main blower start pushing air through the ducts. On many furnaces the blower comes on slightly before the heat exchanger is fully warm, so the first puff of air can feel cool. If the air turns warm after a minute or two, the furnace is working as designed.
The same happens at the end of a cycle. The blower keeps running for a short while after the burners shut off to pull the last heat out of the heat exchanger. That air cools as it goes.
The thermostat is the first thing to look at
A surprising number of cold-air calls come down to a thermostat setting. These are safe to check:
- Make sure the thermostat is set to heat, not cool or off.
- Check the fan setting. If it says on rather than auto, the blower runs all the time, including between heating cycles, and you will feel cool air whenever the burners are resting. Set it to auto.
- Set the temperature a few degrees above the room temperature so the furnace has a reason to call for heat.
- Replace the batteries if the screen is blank or faint.
If the furnace lights and the air turns warm after these changes, nothing else needs doing.
A clogged filter can shut the burners off
A furnace needs steady airflow across the heat exchanger. When the filter is packed with dust, the heat exchanger runs too hot and a safety switch called the high limit turns the burners off. The blower often keeps running to cool things down, which is when you feel cold air. The furnace may then relight, overheat and shut down again in a loop.
Pull the filter out and hold it up to a light. If you cannot see through it, replace it. Make sure supply and return vents in the house are open and not covered by furniture or rugs. If a fresh filter does not fix it, the blower motor or the limit switch itself may need attention, and that is a job for a technician.
Newer houses: condensate drains and side-wall vents
The newer subdivisions and townhouses around Fall Fair Way, Fletcher Road, Royal Winter Blvd, Binhaven Blvd and Reid Ave N usually have high-efficiency condensing furnaces. These furnaces produce water as they run, and they vent through two plastic pipes in the side wall of the house. Both features lead to common cold-air calls.
The condensate drain carries water from the furnace to a floor drain or a small pump. If the drain line or trap clogs, or the pump fails, water backs up and a pressure switch stops the burners. The blower may still run. Signs include water around the base of the furnace, a gurgling sound, or a condensate pump that hums but does not empty. You can check that the pump is plugged in and that the tubing is not kinked. Cleaning the trap and the internal drain is best left to a technician, since it involves opening the furnace.
The side-wall pipes need clear air. After a heavy snowfall or drifting, the intake or exhaust can be covered, and in a long cold stretch the exhaust can frost over. The furnace senses this and shuts itself off. Go outside, find the two pipes, and gently clear snow and ice by hand. Do not use a shovel blade or anything sharp on the plastic. Then turn the furnace switch off, wait a moment, and turn it back on. If the pipes keep icing up, the venting may need to be changed, which a technician should look at.
Binbrook sits up on the Mountain, and the Environment and Climate Change Canada climate normals for the Hamilton airport station nearby are the local reference for the kind of winter these furnaces work through. Wind and drifting snow on open lots make vent checks worth adding to your routine after any storm.
Older houses: ignition, venting and age
The older houses along Highway 56 and Binbrook Road often have mid-efficiency furnaces vented through a chimney. Some were heated with oil or coal long ago and later converted to gas. In these homes, cold air often points to an ignition or venting problem.
- A flame sensor coated with residue can fail to confirm the flame, so the burners light and then shut off within seconds.
- A worn igniter may stop glowing, so the burners never light at all.
- A chimney that was never relined, or venting that is the wrong size for the furnace, can trip a draft safety switch that stops the burners.
Many furnaces have a small window on the front panel with a status light that blinks a code. Write down the pattern before you call. It helps the technician arrive with the right parts in mind. Removing panels, cleaning sensors or adjusting gas components should be left to a technician.
A note on carbon monoxide and cracked heat exchangers
A furnace that keeps shutting down on its high limit for a long time, or an older furnace near the end of its life, can develop a cracked heat exchanger. This is the one cause of poor heat that should not be left running. A crack can let combustion gases, including carbon monoxide, into the air the furnace blows through the house.
The Ontario Fire Code requires a working carbon monoxide alarm next to each sleeping area in a home with a fuel-burning appliance, a fireplace or an attached garage. Check that yours are in place and working. If a carbon monoxide alarm sounds, or anyone in the house has headaches, dizziness or nausea that ease when they go outside, leave the house and call the gas utility's emergency line or 911 from outside. Do not go back in to check the furnace. Our guide on carbon monoxide covers this in more detail.
What is safe to do, and what to leave alone
Safe for a homeowner:
- Check thermostat mode, fan setting, temperature and batteries.
- Replace the filter and open blocked vents.
- Clear snow and ice from side-wall pipes by hand.
- Make sure the furnace power switch is on and the breaker has not tripped. A tripped breaker can be reset once. If it trips again, leave it off.
- Confirm other gas appliances, such as the stove or water heater, are working, which tells you gas is reaching the house.
- Note any blinking codes, sounds or smells.
Leave to a technician:
- Opening the burner compartment or touching gas valves and lines.
- Cleaning flame sensors, igniters or internal drains.
- Any smell of gas. If you smell gas, leave the house and call the gas utility's emergency line from outside.
- Repeated shutdowns after you have cleared the vents and changed the filter.
In Ontario, gas appliances are installed and serviced to the CSA B149.1 Natural Gas and Propane Installation Code. Work is performed by TSSA-certified gas technicians.
What repairs usually involve
Most cold-air faults are fixed with a small part or a cleaning: a flame sensor, an igniter, a pressure switch, a cleared drain or a new condensate pump. These are modest repairs. A failed blower motor or control board costs more. A cracked heat exchanger on an older furnace often makes replacement the more sensible choice, and our guide on how long a furnace lasts can help you weigh that. Either way, ask for the price in writing before any part is fitted.
If the air is still cold after these checks, our furnace repair page explains how a repair visit works.