Sparky's Journal

📅 July 7th, 2026

Why Electricians Use Duct Seal Around Liquidtight Conduit on Walk-In Coolers and Freezers

By JoshTheSparky.com (@JoshTheSparky4) (@JoshTheSparky on X)

If you've ever worked in a commercial kitchen, you've probably noticed electricians packing duct seal around the liquid-tight conduit where it enters the top of a walk-in cooler or freezer.

At first glance, it may seem unnecessary. After all, the conduit is already installed—so why add a duct seal?

The answer comes down to protecting the walk-in and maintaining its performance.

The Purpose of Duct Seal

1. Stops Warm, Moist Air from Entering

Commercial kitchens are warm and humid. Even a small opening around a conduit can allow moisture-laden air to migrate into the insulated wall or ceiling panel.

Inside a freezer, that moisture can freeze. Inside a cooler, it can condense into water.

Neither is good for the building or the refrigeration system.

2. Protects the Vapor Barrier

Walk-in coolers and freezers rely on a continuous vapor barrier to keep moisture out of the insulation.

An unsealed conduit penetration creates a pathway for moisture intrusion, reducing the effectiveness of the insulation over time.

3. Helps Prevent Ice Buildup

When warm air reaches freezing temperatures inside the panel, it turns into frost and ice.

Over time, this can create ice around conduit penetrations and contribute to insulation damage or panel deterioration.

4. Keeps Out Grease, Dust, and Pests

Commercial kitchens produce grease, dust, and debris. Small openings also provide an entry point for insects and other pests.

Duct seal closes those gaps while remaining flexible.

5. Makes Future Maintenance Easier

Unlike silicone or epoxy, duct seal stays pliable.

If the wiring ever needs to be serviced or replaced, the seal can be removed and reapplied without damaging the conduit or enclosure.

Is Duct Seal Required by the NEC?

The National Electrical Code does not generally contain a rule stating that every liquid-tight conduit entering a walk-in cooler or freezer must be sealed with a duct seal.

Instead, a duct seal is commonly used because of:

• Manufacturer installation instructions

• Building and energy code requirements related to air and vapor barriers

• Good workmanship and industry best practices

Always follow the equipment manufacturer's installation instructions, as they are enforceable under the NEC when equipment is listed and labeled.

The Bottom Line

Duct seal is inexpensive, quick to install, and helps protect expensive refrigeration equipment from moisture intrusion.

While many electricians think of it as just another finishing step, it actually plays an important role in maintaining the integrity of the cooler or freezer, preventing condensation and ice buildup, and ensuring a professional installation.

Sometimes the smallest details are the ones that keep an installation performing reliably for years.

Have you seen inspectors require a duct seal on walk-in coolers and freezers? Share your experience in the comments at JoshTheSparky.com and help other electricians learn from the field.

Learn why duct seal is commonly installed around liquid-tight conduit entering commercial walk-in coolers and freezers, and whether the NEC requires it.