Skin burns on a curve of temperature and time, not on a single number. Water at 49 degrees Celsius needs about 5 minutes to raise a blister; the same skin at 60 degrees gives up in 5 seconds. Most domestic heaters sit in the 60-90 degree band somewhere on their surface, which is why the clearance you leave matters more than the setting you choose.
What each temperature does to skin
The thresholds below are standard first aid figures for intact adult skin. A child's skin is thinner, and a cat's thinner again, with fur that hides damage until it is deep.
| Surface temperature | Time to a full-thickness burn | What reaches that temperature | Margin for a cat |
|---|---|---|---|
| 49 degrees C | About 5 minutes | Warm radiator on low, heating pad on high | Uncomfortable at 2 minutes, will move off |
| 54 degrees C | About 30 seconds | Radiator flow pipe, older oil-filled panel | No margin, cat will not stay |
| 60 degrees C | About 5 seconds | Most electric heater grilles at full output | Blister in one contact |
| 66 degrees C | About 2 seconds | Convector fins, hot water pipe surface | Deep burn before the reflex lands |
| 68 degrees C and up | About 1 second | Stove ring, fan heater element housing | Immediate, often full thickness |
Three burn types, three different mistakes
Contact burns are the obvious one: skin against a hot surface, and the fix is distance and a guard, not behavior. Anything above 60 degrees needs a physical barrier if a child or a cat can reach it, and a barrier means a fixed guard with gaps under 5 cm, not a towel draped over the top.
Steam scalds come from the humidifier on the same shelf, the kettle beside the heater, and the pot of water some people put on a radiator to add moisture. Steam at 100 degrees carries far more heat than dry air at 22 and condenses on skin at once. A 200 ml spill of near-boiling water across a forearm burns in under 1 second, and the bowl on the radiator is the one a cat knocks over at 3 in the morning.
Low-temperature burns are the ones people miss. A heating pad at 42-45 degrees held against the same patch of skin for 2 hours will burn through, because the skin cannot dissipate heat that arrives slowly. The classic pattern: older adults, and cats asleep against a heat source, with damage and no yelp, found hours later as a red patch.
Clearance numbers that matter more than the setting
One meter is the working distance for anything that produces heat and anything that can burn: curtains, bedding, drying laundry, the sofa arm, the cardboard box the cat sleeps in. Half a meter is the distance at which fabric starts to discolor near a 2 kW convector. Thirty centimeters is the minimum gap to a wall for a panel radiator, and 15-20 cm above a skirting-level vent.
Put the unit where the cable cannot be pulled, which in practice means not on a low table with a cat underneath and not at the end of a walkway. A 2 kW fan heater on a carpet with a 1 cm pile has its intake half blocked and its casing 10-15 degrees hotter than on a hard floor. Feet or a plinth fix that better than any thermostat.
Cats choose the worst spot available
A cat's normal body temperature is about 38-39 degrees, and its preferred surface is roughly 32-35 degrees. A radiator top at 60-70 degrees is not a warm spot, it is a hot plate, and the cat will lie on it for 20 minutes before the skin damage becomes obvious under the fur. Radiator tops, the shelf above a convector and the top of a fan heater are the three places to block with a 45 degree board.
Watch the tail and the ear tips. Cats tuck their limbs, so the first burns usually appear on the flank they were lying on, the tail that hung against the pipe, and the ear that touched the casing. A burn that is hairless but not blistered can still be full thickness by the time it is found.
Watts, amps and the cord
A 2 kW heater draws about 8.7 amps at 230 volts, which is most of a 10 amp circuit and close to the limit of a 16 amp one shared with a kettle. Run it on its own socket, not a multi-way adapter with 4 other plugs, and never on an extension lead thinner than 1.5 square millimeters. A coiled lead under a rug is how cable fires start: 2 kW through a partly uncoiled drum can reach 70 degrees on the sheath.
Check plug and socket after 30 minutes. Warm is normal; hot to the touch, hot plastic smell, or a brown mark at the pin means stop using that socket. A damaged cord is a retirement, not a tape job: the conductor breaks at the gland.
Fuel heaters add a second hazard
Fuel heaters produce carbon monoxide, which has no smell and no color. A paraffin or gas heater in a closed room can raise indoor CO from a normal 1-2 ppm to dangerous levels within an hour, and headache, nausea and drowsiness look like a cold. Keep a CO alarm within 3 m of the appliance, never sleep in a room with an unflued combustion heater, and ventilate at least one window by 5 cm while it runs.
Refuel only when off and cooled for 20 minutes, never in the room where it runs, and store fuel outside in a child-resistant container.
Set up in this order
- Choose the position first: 1 m from fabric, 30 cm from the wall, cable out of the walkway.
- Test the surface after 15 minutes at full output with an infrared thermometer; anything above 60 degrees gets a guard.
- Block the three cat spots (radiator top, convector shelf, heater top) with a 45 degree board.
- Move the humidifier and any water bowl off the same surface as the heater.
- Check the plug and cord after 30 minutes, and again at the start of each season.
- If the unit burns fuel, fit a CO alarm within 3 m and open a window 5 cm.
A thermometer that settles arguments costs less than a takeaway meal and turns a vague worry into a number. If you are also weighing air quality appliances, the ozone question is worth reading before you buy; for what a season of heating adds to the household budget, the cost calculator does the arithmetic. Plants near a radiator have their own failure mode, covered in the plant safety checklist.
Frequently asked
How far should a space heater be from furniture and curtains?
One meter is the working distance for curtains, bedding, drying laundry and upholstery, and half a meter is where fabric starts to discolor beside a 2 kW convector. Keep 30 cm from the wall for a panel radiator and 15-20 cm above a skirting vent so air can move. Distance beats a higher thermostat setting every time.
Why does my cat sleep against a radiator and then get burned?
Because fur hides the damage and cats seek surfaces near 32-35 degrees, which is well below a radiator top at 60-70. A cat will lie there for 20 minutes without moving, and low-temperature burns build slowly with no yelp. Check the flank, the tail and the ear tips after any session by the heat, and block the top with a 45 degree board.
Is a heating pad safe to leave on all night?
Not against bare skin, and not for hours on the same patch. At 42-45 degrees a pad burns through in about 2 hours because skin cannot shed heat that arrives slowly. Use it for 20 minutes at a time, keep a cloth layer between pad and skin, and never let an older adult or a sleeping cat lie on one unattended.