Walk-In Cooler Glass Door Problems: Fogging, Sticking and Seals

Glass merchandising doors are where customers meet your walk-in. In a convenience store or beer cave, a fogged, sweating or dark door costs sales directly, and a door that doesn't close costs energy all day. Most problems trace back to a handful of parts.

How glass display doors work

A walk-in glass door is a framed, sealed glass unit mounted in a door frame that is built into the walk-in's front wall. A typical assembly includes:

• The insulated glass pack. Two or three panes separated by spacers and sealed at the edges. The space between panes may be filled with an insulating gas, and panes may carry a heat-reflective coating.
• Anti-sweat heat. Heat in the frame, mullions and sometimes the glass itself (through a conductive coating) keeps outside surfaces above the dew point so they don't fog or sweat.
• Self-closing hardware. Usually a torque rod or spring in the hinge that pulls the door shut, often with a hold-open feature at a certain angle for stocking.
• Gaskets around the door that seal against the frame, often magnetic.
• Lighting, typically LED strips in the mullions between doors, powered by drivers (power supplies).

The federal rules for glass doors

Federal design standards (10 CFR 431.306) set these requirements for glass doors on walk-ins:

• Freezer glass doors and windows: triple-pane glass with heat-reflective treated glass or gas fill.
• Cooler glass doors: double-pane with heat-reflective treated glass and gas fill, or triple-pane.
• Anti-sweat heaters without controls are capped at 7.1 watts per square foot of door opening for freezers and 3.0 for coolers. Above that, the heaters must have controls that reduce power based on the room's humidity or on condensation on the door.
• Display doors have also had to meet daily energy-use (kWh/day) standards since 5 Jun 2017.

This matters for repairs: replacement doors and glass packs should meet these requirements, and replacing anti-sweat controls with a plain on/off switch may not. See DOE walk-in regulations and repairs.

Common problems and causes

Fogging, in more detail

Fog on the customer side. Glass fogs when its surface is colder than the dew point of the room air. The anti-sweat heat keeps the glass and frame just warm enough to stay clear. If fog appears in humid weather, after a remodel, or right after the heater circuit was worked on, suspect:

• a heater switch that has been turned off or a controller set too low;
• a failed heater circuit on one door or one mullion;
• a humidity sensor or heater control that has failed;
• unusually high humidity in the store, for example from an HVAC problem.

Heater controls are there to save energy in dry conditions, not to be switched off. Turning anti-sweat heat off entirely usually shows up as fog on the first humid day.

Fog between the panes is different. The glass pack is sealed at the factory. When its edge seal fails, moist air gets into the space between the panes and fogs, streaks or leaves a white film that can't be wiped off from either side. The only fix is a new glass pack or door.

Fog on the inside (product side) usually means warm, moist air is getting in: a door that doesn't close fully, a torn gasket or a door left open during restocking.

Checks staff can do safely

1. Note which doors fog, sweat or are dark, and when. Fog only in the afternoon on humid days points to heat or humidity; one door always fogged points to that door.
2. Check the heater and light switches, if the walk-in has labeled switches outside the box. Don't open electrical panels or remove door frames.
3. Test the close. Open each door to about 90 degrees and let go. It should close and seal (see door closers and hinges for how self-closing hardware works). Doors that stay open at a set angle have a hold-open feature; check that it releases with a light push.
4. Look at gaskets on each door for tears, flat spots or gaps, and wipe them clean. See door gaskets.
5. Clear obstructions. Price channels, display racks, boxes on the floor and product sticking out of shelves can stop a glass door from sealing.
6. Clean the glass with a cleaner that is safe for coated glass. Some doors have coatings that harsh or abrasive cleaners damage.

Safety: Door frames and mullions contain heater wiring and lighting circuits. Leave frame trim, mullion covers and driver housings closed. Report any door with cracked glass right away and keep customers away from it.

What a technician or door service company will do

• Check heater circuits for power and continuity, and check the anti-sweat controller and humidity sensor.
• Adjust or replace torque rods and hinge parts so doors close and hold open correctly.
• Replace LED drivers, light strips or connectors.
• Replace gaskets and realign doors that sag or rub.
• Replace failed glass packs or complete doors, matched to the door model and the rules above.

Repair or replace doors

Individual repairs make sense for most door problems. A full door replacement starts to make sense when several doors have failed glass seals, the doors are an obsolete model with scarce parts, or the store is remodeling anyway. Newer doors can also lower heater and lighting energy; see walk-in cooler high electric bill.

JayComp supplies and installs Anthony, Styleline and DisplayRite glass doors for walk-in coolers and beer caves. For the broader question of whether the whole walk-in is due, see repair or replace your walk-in. Related pages: door frame heaters, walk-in cooler sweating outside and walk-in cooler lights not working.