November 18, 2025

Key Takeaways

• Make-up air must be tempered in cold-weather regions to prevent dangerous temperature shocks inside commercial kitchens.

• An unheated or malfunctioning MUA system can cause literal snowfall inside the kitchen when warm, humid air meets sub-zero supply air.

• Cold snaps increase the risk—kitchens with untempered air are especially vulnerable during deep freezes.

• Regular inspections, quarterly maintenance, and emergency readiness can prevent system failures during peak service hours.

• HRI has firsthand experience with these events and the operational chaos they can cause.

In commercial kitchens, everyone expects heat—grills, fryers, ovens, steam.
What no one expects is snow.

But that’s exactly what happened in a restaurant here in Erie, Pennsylvania.

It was a February dinner service, packed house, tickets rolling in nonstop. Outside, temperatures had dipped to –5°F, the kind of cold that makes steel shrink and even the best equipment work harder than it should. Inside, line cooks were searing steaks, steam was rolling off sauté pans, and the hood system was pulling thousands of cubic feet of air out of the kitchen every minute.

And then it happened.

The make-up air unit (MUA)—responsible for bringing in fresh outside air to balance what the hood exhausts—stopped heating. In other words, the restaurant was suddenly pulling –5°F air directly into a 95°F kitchen.

When that blast of freezing air collided with the hot, humid cooking atmosphere, the moisture instantly condensed and froze.

Within minutes, it started snowing in the kitchen.

Not figuratively.
Not poetically.

Real, visible snowflakes drifting down over the line during peak dinner service.

Why This Happens (and Why It’s Preventable)

Commercial kitchen hoods remove massive volumes of air—sometimes up to 7,000 CFM. That air has to be replaced, and that’s the MUA’s job.

But in cold climates like Erie, Buffalo, Cleveland, or Pittsburgh, pulling in outside air without heating it isn’t just uncomfortable.
It’s dangerous for equipment, staff, and food safety.

Here’s what goes wrong if air isn’t tempered:

1. Rapid Temperature Shock

Cold air slams into humid kitchen air → moisture immediately freezes → snow.

2. Negative Pressure Problems

If the air isn’t heated or the unit fails, the building becomes starved for air.
Doors whistle, drafts intensify, and exhaust hoods stop working efficiently.

3. Frozen Coils and System Shutdowns

Extreme cold can freeze coils, halt fans, and shut down MUA systems entirely.

4. Food Safety & Comfort Issues

Snow, ice crystals, and condensation around prep surfaces is not something any restaurant wants to explain to guests—or the health department.

Tempered Make-Up Air: The Only Safe Option in Northern States

A properly designed system will:

• Warm incoming air before it enters the kitchen

• Keep humidity balanced

• Prevent freezing and condensation

• Maintain building pressure

• Keep staff comfortable and equipment running correctly

Heat options vary—gas-fired, electric, indirect-fired, or heat pump systems—but the outcome is the same: never let outside winter air enter the kitchen untempered.

In regions like ours, this is not optional.

What Restaurants Should Do (Simple Checklist)

1. Verify your MUA produces tempered air

If you’re not sure, you probably don’t have it.

2. Install a low-temperature lockout or freeze stat

This prevents the unit from running in dangerous conditions.

3. Schedule seasonal maintenance before winter

Fall is the time to clean burners, check belts, inspect coils, and test sensors.

4. Confirm the plenum is properly insulated

Cold metal plus hot steam = ice.

5. Have emergency contacts ready

When the MUA stops working at 6 PM on a Saturday, you don’t want to start Googling.

HRI Has Seen This Firsthand—And Prevents It Every Day

In the Erie “kitchen snowstorm” incident, our team diagnosed the issue, repaired the heat section, and got the restaurant operational again. But the truth is:

This should never have happened.

With the right equipment, the right setup, and the right maintenance plan, kitchen snowfall becomes a story you hear about—not a crisis you experience.

And in the winter months, our service team sees these issues more than anything else. Cold snaps expose weaknesses in poorly designed or poorly maintained systems.

If you operate in a northern climate, a tempered make-up air unit isn’t just a luxury.
It’s essential to safe, stable operations.

FAQ: Tempered Make-Up Air in Cold Climates

1. What temperature should make-up air be in winter?

Typically between 55°F–70°F to maintain comfort and prevent condensation.

2. Can I run a kitchen hood without make-up air?

Not safely. You’ll create negative pressure, backdrafting, and system inefficiency.

3. Why do kitchens get foggy or humid when the MUA isn’t tempered?

Warm cooking air hits cold, dry outside air → instant condensation and sometimes ice.

4. Does a tempered MUA cost more?

Yes upfront, but the energy savings and operational stability outweigh the cost—especially compared to shutdowns during service.

5. How often should make-up air units be serviced?

Minimum quarterly in high-volume kitchens; bi-annually for lighter operations.

6. Can existing MUA units be upgraded to heated/tempered?

Often yes. HRI can retrofit many systems with gas or electric heat sections.