A thermostat on the wall reads 21 degrees and the cat still curls into a 12 cm ball on the tile. The number that matters in winter is the floor temperature, and the working threshold is 15 degrees. Below 15 degrees at 5 cm above the floor, a cat loses heat through its belly faster than a 4 kg body can replace it, and the cat stops using that part of the room.
Measure the floor, not the air
Take 5 readings with an infrared thermometer, holding it 5 cm above the surface: the middle of the room, both exterior walls, the bathroom tile, and the spot where the cat sleeps. Write them down at 07:00 and 21:00, because a floor that reads 18 degrees at noon can read 12 degrees at 2 in the morning when the heating drops.
The vertical gradient is the part most owners miss. In a room with an outside wall and a single radiator, the air at 1.5 m is often 3 to 5 degrees warmer than the air at ankle height, and the first 20 cm above the floor is the coldest layer in the house. So a bed on the floor is a cold bed even in a warm room.
Drafts are measurable too. A 5 to 10 mm gap under a door moves air at 0.3 to 0.8 m per second, which is enough to strip the warm boundary layer off a cat's coat at 2 m away. Hold a tissue at the gap; if it lifts past 30 degrees from vertical, seal it.
Seal 4 gaps, in this order
1. Door bottoms: a brush or rubber seal sized to the gap, 5 to 10 mm, cut 2 mm long so it compresses. 2. Window frames: self-adhesive foam 3 to 6 mm on the frame rebate, not on the sash face, or the window will not close. 3. Pipe and cable holes: silicone or a 2 part filler around the pipe, leaving a 3 mm gap for movement. 4. Extractor fans and letterboxes: a backdraught shutter; a flapless bathroom fan pulls cold air 24 hours a day.
Seal the cat's room first: 4 gaps shifts the floor by 2 to 4 degrees within 48 hours, the cheapest win here. Never seal a boiler or wood stove room, and keep 1 air brick open per room.
Lift the bed 20 cm
Twenty centimetres is the number that clears the cold layer and still lets a cat step up. Put the bed on a 20 cm wooden box, a low shelf, a chair seat at 45 cm for a jumper, or a windowsill at 60 cm for a confident climber. The bed surface should sit at 20 to 25 cm for a cat that has stopped jumping, and never above 40 cm for a cat over 12 years old without a ramp at 30 degrees.
Check what the bed sits on. A 20 cm lift over a stone or concrete floor still conducts cold, so put a 10 mm foam or cork pad between the box and the floor. Bedding is 3 to 5 cm of lofted fleece or wool, washed every 7 to 10 days; a damp bed at 40 percent humidity loses most of its loft.
3 draft-free spots, tested for 24 hours
Every cat needs 3 options; a cat that is too warm will move rather than complain. Spot 1: an interior corner, at least 60 cm from an exterior wall, bed at 20 to 25 cm. Spot 2: 1 m from a radiator, never touching it, bed at 45 cm, radiant heat being gentle at 1 m and a burn at 10 cm. Spot 3: a covered box with 1 entrance and a 60 cm sightline, on the side of the room away from the door the household uses most.
Test each spot for 24 hours with a thermometer on the bedding: 18 to 24 degrees overnight is a keeper, under 15 degrees by 03:00 is a shelf.
Humidity at 40 to 50 percent
Air at 22 degrees and 25 percent humidity dries the nasal lining within 2 hours, and that is why herpesvirus flares in winter. A 20 square metre room needs about 2 to 3 litres of water per day added to the air to move from 30 to 45 percent at 22 degrees.
Use a hygrometer, not the humidifier dial, and place it 1 m from the floor in the cat's room. Below 40 percent, add moisture; above 60 percent, you get condensation on the window glass at 12 degrees and mould in the 3 coldest corners within 2 weeks. Keep the range at 40 to 50 percent and clean the humidifier tank every 3 days, because a dirty tank mists bacteria straight into the cat's face.
Heat sources ranked by risk
| Heat source | Surface temp | Min distance | Verdict |
|---|---|---|---|
| Radiator, hot water | 60 to 75 C | 100 cm | safe at 1 m, burns at 10 cm |
| Heated pad, thermostat | 38 C | 0 cm | best option, 15 to 20 min sessions |
| Electric blanket | 40 to 60 C | 0 cm | chewed cables, burns, no thermostat |
| Fan heater | 80 to 120 C | 150 cm | dry air, tip risk, avoid overnight |
| Open fire or stove | 200 C plus | 200 cm | only with a fixed fireguard |
A heated pad set to 38 degrees, capped at 40, with an uncovered exit and 15 to 20 minute sessions, does more for an old cat than raising the whole room by 4 degrees. An electric blanket does not belong in a cat bed: the thermostat sits under the fabric at the cat's weight point, and the cable is at chewing height.
Signs the cat is actually cold
Check 3 things: the ear pinna should feel warm, the pads pink not pale, and a cat sleeping with its nose under its tail, all 4 feet gathered, is conserving heat. A rectal temperature under 37.5 degrees is a same-day vet call, and under 37 degrees is an emergency, because a cat at 36 degrees cannot shiver its way back up.
A cold cat also eats 10 to 20 percent more and drinks less, which is a quiet route to dehydration in a 4 kg animal. Weigh the cat every 14 days in winter; a 200 g loss in a month is a reason to look at the room, not just the food. Coat condition follows: the winter coat routine works better at 45 percent humidity, and the wider question of how much heat a cat needs is covered in heating and cold. Any space heater, antifreeze or rodent bait in the same room deserves a check against the toxicity list.
Work through it in this order:
- Read the floor at 5 points, 5 cm up, morning and night; fix anything under 15 degrees.
- Seal 4 gaps in the cat's room before touching the thermostat.
- Lift every bed to 20 to 25 cm, with foam under the box and a ramp for old cats.
- Set 3 spots and test each for 24 hours, keeping only 18 to 24 degrees.
- Hold humidity at 40 to 50 percent with a hygrometer, and clean the tank every 3 days.
Terms mentioned in this article
Frequently asked
My thermostat says 21°C, so why is the cat cold?
Because thermostats sit at 1.2 to 1.5 m and floors run 3 to 5 degrees cooler, with the first 20 cm of air the coldest layer in the room. Measure 5 cm above the floor at 07:00 and 21:00; anything under 15 degrees needs a sealed gap, a lifted bed or both.
How high should a cat bed be off a cold floor?
Twenty to 25 cm clears the cold layer and is still easy to step into, and 45 cm suits a cat that still jumps. Put a 10 mm foam or cork pad under the box, use 3 to 5 cm of fleece bedding, and add a 30 degree ramp for any cat over 12 years old.
Does indoor humidity really matter in winter?
Yes. Air at 22 degrees and 25 percent humidity dries the nasal lining within about 2 hours, which is why herpesvirus flares in winter. Hold 40 to 50 percent with a hygrometer, add 2 to 3 litres of moisture per day for 20 square metres, and clean the humidifier tank every 3 days.