Heat tape for pipes, and the rules nobody reads

What it is, in one paragraph

“Heat tape” is a resistance cable you run along a water pipe. It converts electricity to a small, steady amount of heat — the standard domestic product is 120 volts at 7 watts per foot — and a thermostat clamped to the pipe switches it on when the pipe gets cold. Frost King publishes the set points: the cable turns on below 38 F and off above 45 F, and the kits are stated to keep water flowing down to -40 F.

The name is a small lie that causes real problems. It is not tape. You do not wrap it around and around like tape, and on most kits you must not let it cross over itself at all. It is a cable that runs along the pipe, secured at intervals, and then gets covered with insulation.

Why this belongs on a garage site

Because the pipe that freezes is almost never the one in the heated part of the house. It is the hose bib on the garage wall, the run feeding a utility sink, the line crossing an unheated garage ceiling to the far side of the building. Those runs sit in a space that follows the outside temperature, and they are the ones with no warm air moving past them.

A frozen pipe is not primarily a water-supply inconvenience. Water expands as it freezes, the pressure has nowhere to go, and the pipe splits — often at a point away from the ice itself. You then have a split pipe that is plugged with ice and therefore not leaking. It leaks when it thaws, usually while nobody is standing there, into a garage with a sealed slab and things stored on it.

The prohibitions, because this is the part that matters

Heat cable has a poor reputation in some quarters, and the reason is that it is installed wrongly a lot. Frost King publishes the restrictions plainly. On the automatic kits, the cable is not for:

Two more that are not on the prohibited list but should be on yours. Use the clips or tape supplied with the kit, not something improvised — ordinary electrical tape and duct tape both fail in that environment. And plug it into a GFCI-protected outlet: this is a resistance heater lying against a wet pipe in a cold room, and a ground-fault device is the cheap part of that circuit.

Insulation over the top is not optional

This is the step people skip, and it halves the value of the whole job. A bare cable on a bare pipe heats the pipe and then heats the garage. Insulation over the cable keeps that heat against the pipe, which means the thermostat satisfies sooner, the cable runs less, and the pipe stays warmer on the coldest night when it matters most.

Pre-slit tubular polyethylene foam is the standard answer: closed cell foam, published in 3/8, 1/2, 5/8 and 1 inch wall thicknesses, sized to fit half-inch through two-inch copper. It is pre-slit so it goes onto an installed pipe without disconnecting anything, and it cuts with scissors. Frost King does not publish an R-value for it, so wall thickness is the only figure you can compare on — buy the thickest that will still close around the pipe with the cable underneath it.

One sequencing note: cable first, against the pipe, then insulation over both. Insulation under the cable would be exactly backwards.

What to do instead, where you can

Heat cable is the answer for a pipe that must stay in a cold space. It is not the answer for every cold pipe, and a site that only sold you cable would be leaving out the cheaper fixes.

Drain the outside line. A hose bib fed from an isolating valve inside can be shut off and drained in November. No water, no freeze, no electricity. This is free and it is better than any cable.

Close the gap the cold is coming through. A garage that leaks air around the door is a garage that tracks the outside temperature closely. Sealing the door raises the floor temperature of the whole space, and it is the change that makes every other item in this hub work better.

Insulate even without a cable. Foam sleeve on its own buys you hours, not immunity — but hours are often the whole difference on a single cold night, and it costs a few dollars a length.

Buying it: the two decisions

Length. Measure the run and buy the kit that covers it. Frost King publishes seven lengths, from 3 to 30 feet, all at the same 7 watts per foot. Buying long and coiling the excess is precisely the overwrapping the maker forbids, so buy the length you need rather than the length that was on the shelf.

Thermostat or not. The automatic kits have one built in. Bulk cable sold by the foot often does not, and running unswitched cable from October to April is how a cheap purchase becomes an expensive one. A separate thermostat with the same published set points — on below 38 F, off above 45 F — solves that, and is redundant on any kit that already includes one.