When a make-up air unit stops heating, restaurant staff usually feel it before anyone knows which piece of equipment is responsible. The kitchen gets drafty, the front door starts pulling harder than usual, the hood feels off, and everyone starts saying the building is uncomfortable.
A make-up air unit is not just another heater. It is part of the pressure balance of the whole restaurant. If it is running cold, the issue may involve the burner section, the control sequence, airflow safety devices, or the relationship between the MAU and the exhaust side of the kitchen.
1. Start with the control sequence, not the burner
Many MAU heat complaints begin with a control problem. The unit may be receiving a fan call but not a heat call. A thermostat, discharge air sensor, control board, or interlock can keep the unit moving air while never actually telling the heating section to fire.
This is why the fan working does not mean the make-up air unit is fine. On service calls, those are often two separate findings.
2. Burner lockout is a common restaurant problem
If the unit uses gas heat, ignition and safety faults are high on the list. Ignitors wear out, flame sensors get dirty, safeties trip, and burners lock out. When that happens, the fan may still run and bring untempered outside air into the kitchen, which is exactly why the room suddenly feels much colder.
3. Airflow problems can keep the heat from coming on
Make-up air equipment depends on correct airflow. Dirty filters, slipping belts, bad fan motors, or blocked intake sections can trip safeties or make the unit operate outside the conditions it expects. In some setups, poor airflow prevents the burner section from running properly at all.
If the unit is noisy, vibrating, or obviously moving less air than it used to, that matters. The heat problem may be downstream of an airflow problem.
4. Exhaust and make-up air have to work together
Restaurant kitchens are not simple comfort spaces. The hood exhaust, the make-up air unit, and the building pressure all interact. If the exhaust side is pulling harder than the replacement-air side can keep up with, the kitchen may feel like the MAU is not heating when the bigger issue is that the system is badly out of balance.
That is also why doors start slamming, cold air shows up at entrances, and staff complain about drafts at the same time.
5. Gas supply and safety components still matter
Some calls do come down to the basics: manual gas valve issues, bad gas valves, pressure switch faults, or other safety components in the gas train. Those are not items to guess at. They need proper diagnosis because the point of those safeties is to prevent unsafe operation.
What restaurant staff can check safely
- Confirm whether the fan is running. Cold airflow is a different clue than no airflow at all.
- Check whether the issue happens only during hood operation. That helps identify interlock and pressure-balance problems.
- Look for dirty filters or obvious belt issues.
- Notice building symptoms. Door pull, drafts, smoke behavior, and hood performance all matter.
When to stop troubleshooting and call
If the unit is running cold, locking out repeatedly, or affecting pressure in the building, it is time for service. Make-up air problems tend to show up as comfort issues, but the operational consequences are bigger than that. They affect hood capture, staff comfort, and how the kitchen behaves during service.
YYC Mechanical handles make-up air unit service and broader commercial HVAC support for Calgary restaurants. If the kitchen is pulling cold air and the MAU is not tempering properly, we can help you work through the heat side and the pressure-balance side together.