Trace heating is an electric heating cable fixed along a pipe, under the pipe’s insulation, that keeps the pipe above freezing or holds it at a set temperature. In homes it is mainly used to stop condensate pipes, outside tap feeds and pipes in unheated lofts, garages and outbuildings from freezing, and it only works safely with proper insulation over it and a correctly protected electrical supply.

How trace heating works

A trace heating cable is laid along the outside of a pipe, taped in place, and then covered with pipe insulation. When the cable is powered, it gives off a small, steady amount of heat, enough to replace the heat the pipe loses to the cold air. The insulation keeps that heat around the pipe instead of letting it escape.

A thermostat decides when it runs. On a frost protection system the thermostat senses the air or pipe temperature and switches the cable on when it falls towards freezing, then off again once it has warmed up a little. In a mild winter it may barely run at all.

Most domestic cable is self-regulating. It has two parallel copper wires with a special conductive polymer between them. As the polymer warms, it lets less current through, so the cable automatically puts out less heat where the pipe is already warm and more where it is cold. That makes it safer and more economical than older types, and it can be cut to length on site.

Types of trace heating cable

Type	How it works	Typical use	Things to know
Self-regulating	Conductive polymer core that reduces output as it warms	Frost protection on domestic pipes, condensate pipes, outside taps	Can be cut to length. Usual choice for homes
Constant wattage	Heating zones along the cable give a fixed output per metre	Longer commercial runs, temperature maintenance	Needs a thermostat to control it. Must not overheat plastic pipe
Series resistance	A single resistance wire heats along its whole length	Long pipelines and industrial use	Cannot be shortened, and overheats if crossed over itself
Mineral insulated	Metal-sheathed cable for very high temperatures	Industrial processes	Not a domestic product
Pre-made frost protection kit	A fixed length of cable with a plug and built-in thermostat	A single outside pipe or condensate pipe	Cannot be cut. Must suit the pipe length and be plugged into a suitable socket

Where trace heating is used in homes

Trace heating earns its place on pipes that are exposed to the cold and cannot easily be insulated, moved or drained. Common examples:

• Boiler condensate pipes that run outside and cannot be rerouted indoors. A frozen condensate pipe is one of the most common winter breakdowns, and our guide to a frozen condensate pipe explains why.
• Outside tap feeds in exposed spots, especially on a building used through the winter.
• Pipes in unheated spaces, such as lofts, garages, outbuildings, garden offices and holiday lets left empty over winter.
• Pipes in exposed voids, for example under suspended floors or in external boxing.
• Gutters and roof valleys on some properties, where cable is used to keep a drainage path open through ice.

In larger buildings it is also used to keep hot water pipes hot, so water arrives at the tap quickly and stays at temperatures that help control Legionella. That is a design job for commercial systems rather than something most homes need.

When you do not need it

Trace heating is not usually the first answer. Before fitting a cable, consider the simpler fixes our plumbers use every winter on general plumbing repairs:

Problem	First thing to try	When trace heating makes sense
Condensate pipe freezing outside	Reroute it inside, or replace the external section with larger pipe and insulate it	The pipe has to run outside and cannot be upsized or rerouted
Outside tap freezing	Fit an isolating valve inside, turn it off and drain the tap for winter	The tap is needed all winter
Loft pipes freezing	Insulate the pipes and cold water tank properly, and do not insulate under them so heat rises from the house	The loft space is exceptionally exposed or the pipe runs close to the eaves
Garage or outbuilding pipes	Insulate, and drain down if the building is not used in winter	The building is used and heated only occasionally, or not at all
Empty property in winter	Keep the heating on a low frost setting, or drain down	The heating cannot be left on, and the water must stay on

How trace heating is installed

A proper installation follows the cable manufacturer’s instructions, which vary between products. The general steps are:

1. Survey the pipe. Measure the length, note the pipe size and material, and identify valves and fittings, which need extra cable because they lose more heat.
2. Prepare plastic pipe. On plastic pipe, manufacturers usually specify aluminium tape along the pipe so the heat spreads evenly. Only use cable that is rated for plastic.
3. Fix the cable. Run the cable along the pipe and secure it with the tape the manufacturer specifies, without kinking it or bending it tighter than its minimum bend radius.
4. Fit the thermostat or sensor so the system switches on as temperatures fall.
5. Insulate over it. Cover the pipe and cable with insulation of the right thickness, and weatherproof it outside.
6. Label it. Warning labels on the insulation show that the pipe is electrically trace heated, so nobody cuts into it later.
7. Connect a safe supply. A fused spur or suitable outdoor socket with RCD protection, installed to the wiring regulations (BS 7671).
8. Test it. Check the cable’s insulation and that the thermostat switches it on and off.

A plug-in frost protection kit on a single pipe is something a competent homeowner can fit. Anything involving a new circuit, a fused spur or a connection outdoors is electrical installation work and should be done by a qualified electrician, and a new circuit in a home is notifiable under Part P of the Building Regulations. Our electrical installations team can provide the supply.

What it costs to run

Trace heating uses electricity only while it is on, and the thermostat means it only switches on in cold weather. Self-regulating cable cuts its own output as the pipe warms, and good insulation reduces how much heat the cable has to replace. The running cost depends on the length of cable, its rating and how many cold days you get, so a short run on a condensate pipe uses far less than a long run in an outbuilding.

What it costs with Vantage

In normal working hours there is no call-out fee. After the first hour, time is charged in half-hour steps, and parts are quoted before we fit them. Evening, weekend and overnight visits are charged at the out-of-hours rates. Every rate is published on our prices page, so you know what you will pay before we arrive.

In many homes, rerouting or upsizing a condensate pipe is a quicker and more lasting fix than trace heating, and we will tell you if that is the case. If the pipe has already frozen and burst, our emergency plumbing service can help, and the phone is answered 24 hours a day, 7 days a week.

Frequently asked questions

Does trace heating need RCD protection?

Yes, it should have it. Manufacturers of frost protection cable generally specify a 30mA RCD on the supply, and the wiring regulations require RCD protection for most socket circuits and outdoor equipment in homes.

Can trace heating be used on plastic pipes?

Yes, if the cable is rated for plastic pipe. Self-regulating cable is normally used, with aluminium tape on the pipe to spread the heat, following the manufacturer’s instructions.

Is trace heating expensive to run?

It is usually modest for a short domestic run, because the thermostat only switches it on in cold weather and self-regulating cable reduces its own output. Longer runs, poor insulation and a thermostat set too high all increase the cost.

Does trace heating need insulation?

Yes. The cable only puts out a small amount of heat, and without insulation that heat is lost to the air and the pipe can still freeze. Insulation also protects the cable.

Can I fit trace heating to my boiler’s condensate pipe?

It can be done where the pipe has to run outside, but rerouting the pipe indoors or replacing the outside section with a larger insulated pipe is usually the better fix. Any work on the boiler itself must be done by a Gas Safe registered engineer.

Help in Hertfordshire, Bedfordshire and Cambridgeshire

If you have pipes that freeze every winter, our plumbers and electricians can look at the whole picture and recommend insulation, rerouting or trace heating, whichever will actually solve it. See our general plumbing repairs service or call 01462 506374.