Can I plug a heater or a tumble dryer into an extension lead?

Which appliances genuinely should not go on an extension lead and why, the narrow cases where a heavy-duty lead is acceptable, and what to do instead.

Difficulty: beginner
Time: 8 min
Read: 4 min
Safety: warning

Short answer

Electrically, a single 13A appliance on a good quality 13A lead, fully unwound and with nothing else on it, is within the lead's rating. Practically, heaters, tumble dryers, washing machines and dishwashers should go into a wall socket, because they run near the limit for hours and any weakness in the connection turns into heat. Never on a coiled reel, never on an adaptor, never sharing the lead.

The question is not really about the appliance's rating but about margin. A kettle on a lead draws 13A for two minutes. A fan heater draws 10A for six hours, in a room where the lead may be moved, trodden on, or tucked behind furniture. It is the duration and the position, more than the arithmetic, that make this a bad habit.

Safety

High-current appliances run near 13A for long periods, which is exactly the condition that exposes a marginal plug, a thin flex or a worn socket. Never run one through a coiled reel, a cube adaptor, a daisy-chained lead, or a lead run under a carpet. If the lead or plug is warm at any point, disconnect it.

Step by step

Read the appliance's wattage.Fan heater 2000 to 3000W, oil-filled radiator 1500 to 2500W, tumble dryer 2500 to 3000W, washing machine up to 2200W while heating, dishwasher up to 2200W, portable air conditioner 1000 to 1500W. Every one of these is a substantial fraction of a 13A lead's total.
Rule out the coiled reel absolutely.A coiled reel is rated around 750W to 1000W. Every appliance in the list above exceeds that by a factor of two or three. This is not a marginal call.
Rule out sharing the lead.A 2400W heater on a four-way leaves 600W for everything else, which one more appliance will exhaust. If a high-current appliance must go on a lead, it goes on that lead alone.
Rule out adaptors and daisy chains.Cube adaptors, unfused two-ways, travel adaptors and one lead plugged into another all add contact resistance at each junction, and each junction is a place heat can develop. High current through several junctions is how adaptor fires start.
Check the flex thickness if you must use a lead.A heavy-duty lead uses 1.5mm flex; cheap ones use 0.75mm or 1.25mm and are intended for lighter loads even though the plug is 13A. The flex size is usually printed on the sheath.
Make the run visible and straight.Not under a rug, not under a door, not coiled behind furniture, not through a doorway where it is crushed. A lead carrying 10A wants air around it and no mechanical damage.
Check it by hand during the first hour.Feel the lead's plug, the appliance's plug and the flex. Anything more than mildly warm means stop, and treat it as the hot plug problem.
Solve it properly if it is a recurring need.If a room genuinely needs a heater every winter, or a utility space needs a dryer, the answer is a socket in the right place, installed by an electrician. It is not expensive relative to the risk of a permanent extension lead arrangement.

Tips

A tumble dryer or washing machine on a lead is also a flood risk waiting to happen: a lead on a utility floor near a machine is in exactly the wrong place.
Never plug a high-current appliance into a lead that is itself plugged into a lead. Each connection is a resistance and they add.
If you are heating a room every day through an extension lead, work out what it is costing to run before deciding it is temporary — it is usually the most expensive way to heat that room too.

Common mistakes

Running a heater from a coiled reel in a garage or workshop — The coiled rating is a fraction of the heater's load. This is a documented fire scenario, not a theoretical one.
Assuming the appliance's own plug fuse protects the lead — A 13A appliance fuse protects the appliance's flex. The extension lead's own capacity, its coiled state and any adaptor in the chain are outside what that fuse knows about.
Treating a permanent extension lead as a solution — Leads are for temporary use. A lead that has been in place for two years is a fixed installation made from equipment not designed to be one, and it never gets inspected.

If it doesn't work

Lead's plug is hot after running a heater

Cause: Load near the limit, plus a marginal contact at the wall socket — Fix: Disconnect. Check the wall socket for discolouration. Use a wall socket directly and get the socket checked if it showed heat.

Extension lead fuse blows when the dryer heats

Cause: Total load exceeding the lead's rating, or a low-rated lead — Fix: Use a wall socket. Do not fit a larger fuse into a lead rated below 13A.

Circuit trips when the heater and the kettle are both on

Cause: Circuit overload rather than a fault — Fix: Spread the load across circuits, or have a dedicated circuit installed if the room's use genuinely requires it.

Lead's flex is soft or discoloured

Cause: Heat damage from sustained overload — Fix: Bin it. Damaged flex insulation is not repairable and not worth keeping.

Questions people ask

What about a fridge or freezer?

The load is small — typically 100 to 300W — so electrically it is not the issue. The practical objection is that it is a permanent appliance and a lead is a temporary arrangement that can be knocked out. Use a wall socket.

Is it different for an oil-filled radiator?

Only slightly: they are usually 1500 to 2500W and run for hours on a thermostat. Same answer — wall socket, and never a coiled reel.

What about an EV charged from a domestic socket?

Charging a car from a 13A socket draws around 10A continuously for many hours and must never be done through an extension lead, an adaptor or a reel. It requires a dedicated circuit and a proper chargepoint, installed by a qualified installer.