Maintenance
Snowstorm Behind the Racks: Tracking Down an Air Leak in a Freezer Ceiling
At the end of September 2025 I walked into one of our freezer rooms and found it snowing.
Not a little frost on a coil. It looked like a snowstorm had gone through the back of the room, and there was ice piled up behind the racking. I run an underground freezer in the Valmeyer bluffs, and this is one of the stranger things I’ve walked in on.
How I found it
Honestly, I found it by being lazy. We had recently finished a newer freezer room, and I was headed in there to figure out where to hang a fan. Instead of walking around to the usual way in, I unlocked the back door and went in from that side.
That’s the only reason I saw it. From the front, the racking hid the whole thing. And I hadn’t really looked straight up back there, either.
What it looked like
Up at the top of the ceiling, two spots looked almost wet. There was ice built up around them, and more ice on the floor directly below. Between the two, everything behind the racks had a coat of snow.
A coworker and I cleaned it all up first. Then we stood there and worked out what we were looking at.
Why a freezer makes its own snow
When warm, moist air gets into a freezer, it cools fast. Cold air can’t hold much water, so the moisture has to go somewhere. It comes out as frost on the nearest cold surface, or as loose snow-like crystals that drift down and pile up.
So snow inside a freezer room isn’t a weather event. It’s a sign that air from outside the insulated box is getting in somewhere. The wet-looking spots at the ceiling told us where. That’s where the outside air was meeting the cold, and the ice on the floor below was everything that had fallen out of it.
Our rooms run anywhere from about -15 to 8 °F depending on the room, so any leak into that space is going to show up as ice sooner or later. The only question is whether you notice it before it builds up.
The fix
The fix was not complicated. We concluded the room still had to be leaking air at the top of the ceiling, so I had my coworker hit those spots with a lot of spray foam. Not a polite bead of it, either. The goal was to plug wherever we thought the air was getting in.
It didn’t clear up overnight. Over the next several days I checked the room each day, and each day it looked a little better. A few days in there were still a couple of spots that looked like they might be seeping air, so those got another round of foam once more came in.
The lesson there: one pass of foam is a first guess, not a guarantee. Go back and look for a week or so afterward.
What I check now
I wish I’d noticed it sooner. Here’s what I’d tell anyone running a freezer, underground or not:
- Walk the back side of the racks. Racking turns a room into a set of hallways, and some of them nobody walks. Go in from a door you don’t normally use.
- Look up. Ceiling penetrations, seams and corners are where air sneaks in. Wet-looking spots or ice at the ceiling are a leak until proven otherwise.
- Treat ice on the floor as a clue. Ice on the floor with nothing obvious above it usually means something is dripping or falling from higher up. Trace it upward.
- Clean it up before you diagnose it. Once the snow and ice were gone, the wet spots at the top were much easier to see.
- Re-check after you seal. Foam can miss a spot. A daily look for a few days tells you whether you actually got it.
It’s a small thing, but small air leaks are how a freezer slowly fills itself with ice where nobody is looking. Mine was hiding behind a wall of racks until I happened to take the back door.
Related: The Defrost Game, on keeping evaporators clear of ice, and The Day From Hell, another week of things going wrong in the freezer.
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