Freezer Floor Systems Frost heave prevention for freezer and cold storage floors
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Subfloor heating for refrigerated buildings

Frost heave prevention for freezer floors

A freezer draws heat out of the ground beneath it for as long as it runs. If that ground freezes, ice lenses can lift and crack the slab. An electric heat cable system placed below the floor insulation replaces the lost heat and keeps the soil above 32 °F.

These pages explain how the system is built, laid out, sized, controlled and checked out, with working details for engineers, contractors and facility owners.

How frost heave develops See the system design
Cutaway of a freezer building showing heat cable conduits in the aggregate base below the floor insulation, with the control panel mounted outside the freezer wall
Fig. 1Heat cable conduits sit in the aggregate base under the insulation. The control panel is mounted outside the freezer. Illustration, not to scale.
36–48″Conduit leg spacing, center to center
12–25″Outside legs from each side wall
¾″ / 1″Rigid conduit for loops under / over 100 ft
30 mAGround-fault equipment protection, each circuit

Typical values used in our layouts. Every project is laid out from its own dimensions, temperatures and electrical service.

01Why a freezer floor needs heat underneath

Insulation slows the flow of heat from the ground into the freezer. It does not stop it. The ground under a floor held at −10 °F keeps giving up heat, and very little heat comes back from deeper soil to replace it. Over months and years the 32 °F line moves out of the insulation and down into the soil.

Where the soil holds water and is fine-grained, freezing does more than expand the pore water. Water is drawn toward the freezing front and builds into layers of ice called ice lenses. The lenses push the slab up, usually most in the middle of the room where the ground is coldest.

Floors have been measured to rise 12 in., 24 in. or more. Cracked slabs, doors that bind, racks out of plumb and damaged walls follow. Repair means removing the floor and thawing or replacing the frozen ground.

Read the full explanation of frost heave →

Section comparison of an unheated and a heated freezer floor Without subfloor heat the 32 degree line moves down into the soil, ice lenses form and the slab heaves. With heat cable in the base below the insulation, the 32 degree line stays inside the insulation and the soil stays above freezing. Freezer −10 °FSlabInsulationBase / aggregateSubgrade soil32 °F line moves downIce lensesHeaveA · No subfloor heat (after years)Freezer −10 °FSlabInsulationBase / aggregateSubgrade soil32 °F lineGround held above freezingB · Heated base
Fig. 2A: after years without subfloor heat, the 32 °F line is in the soil and ice lenses lift the slab. B: heat in the base keeps the temperature drop inside the insulation.

02How an electric system works

  1. Conduit in the baseRigid conduit hairpin loops are laid on the subgrade and covered with aggregate or a mud slab, below the vapor barrier and insulation.
  2. Self-regulating cableHeat cable is pulled through each loop after the floor is built. Its output rises as it gets colder, so the coldest ground gets the most heat.
  3. Ground temperature sensingThermocouples in separate capped conduits measure the base temperature between heating legs toward the center of the floor.
  4. Supervisory controlsA PLC switches each circuit, confirms each cable is energized to its far end, watches ground-fault breakers and alarms on any fault.

Because every cable is in conduit with both ends in an accessible junction box, a cable can be tested, pulled out and replaced without disturbing the slab.

03Technical sheets

Exploded view of freezer floor layers
SHEET 01

Frost heave

Heat flow through an insulated slab, soil and water conditions, and why the damage appears years later.
Stepped cutaway drawing of freezer floor construction
SHEET 02

System design

Floor build-up, conduit loops, spacing rules, sensor placement, cable selection and heat load tables.
Typical conduit layout drawing for a 52 by 58 foot freezer
SHEET 03 · REPRESENTATIVES

Layout calculator

Loop layout, circuit zoning by breaker size, sensor locations and heat load. For representatives.
Interior of a freezer floor control panel with PLC, breakers and solid-state relays
SHEET 04

Controls & monitoring

What is measured, how faults are found, alarm behavior, electrical protection and enclosures.
Diagram of a hydronic glycol floor heating system
SHEET 05

Electric vs. glycol

Component-by-component comparison of electric, hydronic and ventilated-air methods.
Junction boxes and conduit risers along a freezer wall
SHEET 06

Project support

What to send us, what you get back, installation sequence and startup checkout.
Touchscreen showing freezer floor zone temperatures
SHEET 07

Guide specification

Three-part specification text you can copy into project documents and edit.
Electric heating mat for ramps and door thresholds
SHEET 08

Door & ramp ice

Why ice forms at freezer doors and how surface heating is applied at thresholds and ramps.
Illustration of conduit and junction box routing on a freezer wall
SHEET 09

Resources

Drawings and data sheets to download, a glossary and answers to common questions.

04About Freezer Floor Systems

Freezer Floor Systems is a division of Thermal Equipment Sales Co., Inc. of Memphis, Tennessee. The company designed and built the controls for its first frost heave prevention system in the mid-1970s and has refined the design since, from single-loop controllers to the PLC-based monitoring panels in use today.

For each project we provide the conduit layout, electrical and control wiring details, the control panel, installation and startup instructions, and phone support during checkout. More about us →

Application help(901) 452-4516
EmailSales@thermalinc.com