When high-powered kitchen exhaust hoods turn on, they pull massive amounts of grease, smoke, and heat out of your building. To keep indoor air pressure balanced, a makeup air unit turns on simultaneously to pull fresh outside air back in.
In Ontario winters, that incoming replacement air is far below freezing. Modern makeup air systems use electric heating coils or gas burners to heat that incoming air before discharging it into your kitchen.
If your makeup air system suddenly starts blowing freezing outdoor air directly into your space, it creates an unbearable draft, strains your central heating system, and drops your indoor temperature rapidly.
Here is a detailed guide to why kitchen makeup air units blow cold air in winter, the most common mechanical faults, and how to resolve the issue safely.
When an exhaust fan runs, it creates negative pressure. Negative pressure makes exterior doors hard to open, causes backdrafts in fuel-burning appliances, and pulls cold air through every crack in your walls.
A makeup air unit prevents negative pressure by pulling fresh air from outside and pumping it inside. During winter, a makeup air heater tempers that incoming air to match your indoor comfort setting.
If the blower fan runs but the heating assembly fails to ignite or energize, the system acts like a giant fan dumping untempered sub-zero air into your kitchen.
The vast majority of commercial and high-capacity makeup air units rely on direct-fired or indirect-fired natural gas burners to heat massive volumes of moving air.
If your unit uses gas heating, several issues can prevent the burners from igniting:
The pilot light or spark ignitor failed to light.
The safety flame sensor is dirty or defective.
The gas supply valve is closed or locked out due to a pressure fault.
The pilot light or spark ignitor failed to light.
The safety flame sensor is dirty or defective.
The gas supply valve is closed or locked out due to a pressure fault.
If your system requires gas supply line modifications, burner servicing, or piping safety checks, you can review our dedicated service page for Gas Pipe Installation.
Makeup air units feature built-in safety controls designed to protect the equipment from catastrophic damage.
A freezestat is a temperature-sensing safety switch installed across the heating coil. If incoming outdoor air is excessively cold and the heating coil does not reach a safe operating temperature quickly enough, the freezestat trips to prevent water pipes or internal components from freezing and bursting.
Similarly, high-limit switches trip if the unit overheats internally due to restricted airflow, cutting off the heat source while leaving the fan running.
Makeup air units pull raw air directly from outdoors, meaning intake hoods and filter banks gather leaves, snow, dust, and heavy ice buildup during winter storms.
When intake filters become choked with debris, airflow drops significantly. This lack of proper air movement trips internal safety switches, shutting down the heating element or burner assembly while the main fan continues to run.
Checking and replacing intake filters regularly ensures your system maintains smooth, unobstructed airflow.
Makeup air units use specialized discharge air sensors located inside the supply ductwork. These sensors tell the modulating gas valve or electric heating coils exactly how much heat to add based on the incoming outdoor temperature.
If the discharge sensor fails, gets coated in dirt, or loses calibration, the main control board will not signal the heater to turn on, resulting in unheated air entering your kitchen.
If your property uses an electric makeup air heater rather than a gas-fired unit, the system relies on high-kW electric resistance heating coils.
If an electrical surge occurs, or if individual heating element strips burn out over time, the system will lose its ability to heat the air stream. A blown fuse or tripped circuit breaker on the heating circuit will leave the fan running without any heat output.
Proper preventative care is essential for complex air-handling equipment. You can protect your ventilation infrastructure by following these basic maintenance practices:
Inspect Outdoor Intake Hoods: Clear snow, ice, and fallen debris away from outdoor intake louvers after every major winter storm.
Replace Intake Filters Monthly: Clean filter media keeps air moving freely across heating elements and prevents nuisance safety tripping.
Schedule Annual Pre-Winter Diagnostics: Have a licensed HVAC technician test burner ignition, safety interlocks, gas pressure, and electrical heating elements before freezing weather arrives.
Inspect Outdoor Intake Hoods: Clear snow, ice, and fallen debris away from outdoor intake louvers after every major winter storm.
Replace Intake Filters Monthly: Clean filter media keeps air moving freely across heating elements and prevents nuisance safety tripping.
Schedule Annual Pre-Winter Diagnostics: Have a licensed HVAC technician test burner ignition, safety interlocks, gas pressure, and electrical heating elements before freezing weather arrives.
Balancing fresh air intake with heat retention is critical for energy efficiency. If you want to explore advanced ventilation technology that recovers energy from outgoing exhaust air to pre-heat incoming fresh air, explore our comprehensive guide on Heat Recovery and Energy Recovery Ventilators (HRV/ERV).
For general system upgrades, duct adjustments, or fresh air balancing, you can browse our full range of professional Ventilation Services.
A makeup air unit blowing cold air in winter demands fast, experienced service. At Atrium Air, our licensed technicians specialize in commercial and residential air handling systems, gas burners, and custom ventilation controls.
If your property is located in York Region, you can book local service through our regional HVAC Services in Vaughan, ON team.
Do not let a failing makeup air heater freeze your kitchen. Call Atrium Air today at 647-294-5454 or reach out through our official Contact Page to book your service appointment!
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