A 1.2 m/s draught across a cat's back at 18°C is not a breeze; it is a heat-loss event the cat cannot dress for. Indoor draught complaints are almost never about how much air enters a room — they are about where it lands and how fast. Two measurements, both under 5 minutes, settle it: air speed at cat height, and the surface temperature of the spot the cat chooses.
Measurement 1: air speed at 20 cm, not at head height
Anemometers are sold for HVAC work, so they get pointed at 1.5 m. A cat's torso sits at 20–30 cm, in the layer where cold air pools and where a window gap accelerates flow. Hold the probe 20 cm above the floor, 30 cm in from the window, and read for 30 seconds. Take 3 readings: at the window reveal, 1 m into the room, and at the cat's bed. Anything above 0.3 m/s at bed level is worth fixing; above 0.5 m/s at 18°C or lower is a real problem. A 12–25 euro handheld unit reads 0.01–30 m/s and is accurate enough for this job.
| Reading at bed | Speed | What the cat feels | Fix from here |
|---|---|---|---|
| Still | 0–0.15 m/s | Neutral at 20–26°C | 0 changes, 0 cost |
| Light | 0.15–0.30 m/s | Fine above 20°C | Recheck in 3 days |
| Noticeable | 0.30–0.50 m/s | 1–2°C cooler at the bed | Rotate bed 90 degrees |
| Chilling | 0.50–0.80 m/s | 2–3°C loss below 20°C | Baffle plus 1.5 m move |
| Strong | 0.80–1.50 m/s | Hunched within 5 minutes | Close 1 of 2 windows |
| Gap jet | over 1.50 m/s | Leaves in 1–2 minutes | Seal the 2–5 mm gap |
Measurement 2: the surface the cat actually lies on
Air temperature is the wrong number. An infrared thermometer pointed at the bed, the windowsill, and the tile in front of the door gives the surface temperature, and that is what a cat's belly reads. Concrete and uninsulated tile commonly run 3–6°C below room air in winter; a sunny windowsill can hit 40–45°C at 14:00 and 12°C by 22:00. A cat that abandons a bed at 21:00 is usually responding to a surface that dropped 5–8°C in 2 hours. Aim for a sleeping surface of 26–30°C; a 2 cm wool pad over a 20°C floor typically reads 27–29°C after 10 minutes of body contact.
Where the air actually goes
Single-sided ventilation moves air in and out of the same opening, so flow reverses every few seconds and the effective speed at 1 m is roughly 30–50% of the reading at the gap. Cross-ventilation with 2 openings on opposite walls can multiply flow 3–5 times for the same window area. That is why one 60 cm window on a still day barely moves a curtain, while 2 windows 4 m apart produce a 0.6–0.9 m/s stream down the middle of the room. Put the cat's furniture out of that middle band: a 1.5 m offset from the direct line between openings removes most of the draught.
The 15-minute ventilation routine
Ventilate in bursts instead of holding windows ajar for 8 hours. Open 2 windows wide for 10–15 minutes, 2–3 times a day, with the cat in another room and the door shut; that exchanges the air without chilling surfaces. In winter, do the last burst before 18:00 so floors recover before the cat's evening active period. Between bursts, close and latch: a 2–5 mm gap along a sash is enough to produce a 0.4–0.7 m/s jet at 20 cm in a 3–4 m/s wind. Door snakes, brush strips and 3 mm foam tape cost under 15 euro and cut those jets by half or more.
Baffles, beds and the 40 cm rule
A baffle works if it is at least 40 cm tall and set 15–25 cm from the opening; shorter panels just redirect flow downward into the cat's layer. Baffle height should exceed the gap height by 30%. For radiators under windows, a 20–25 cm shelf above the radiator deflects the cold downdraught outward and gives the cat a warm perch at 30–34°C — many cats choose it over a floor bed within 2 days. Keep beds at least 1.5 m from any opening and 30 cm off the floor on a frame or legs; the 0–20 cm layer is 1–3°C colder than 60 cm in a ventilated room.
Reading the cat instead of the gauge
Hunched posture with paws tucked, ears angled back, fur lifted along the spine, and sleeping with the nose buried are heat-conservation signals, not mood. A cat that moves through 3–4 sleeping spots in an evening is searching for a stable surface. Shivering is late and rare; cats usually leave first. Watch for a cat that stops using a favourite window perch after a weather change — that is a 1-line data point worth acting on, and it is the same signal set we track in the indoor humidity guide.
When damp air is the real problem
Draughts and damp travel together. At 70–80% relative humidity, a 0.3 m/s draught removes heat roughly 20–30% faster than the same draught at 45–50%. If windows fog on the inside in the morning, or bedding feels cool-damp at 07:00, fix humidity before adding more ventilation; 40–55% is the target band. Dust storms bring the opposite problem — fine particles that settle into the same 0–20 cm layer — so the filter and cleaning steps in our dust storm plan belong in the same weekly routine.
Six checks, one evening
- Read air speed at 20 cm in 3 spots; log the numbers.
- Read surface temperature of bed, sill and floor.
- Move any bed within 1.5 m of an opening, or rotate it 90 degrees.
- Seal gaps under 5 mm with foam tape; add a 40 cm baffle where jets persist.
- Ventilate 10–15 minutes, 2–3 times a day, cat out of the room.
- Keep sleeping surfaces at 26–30°C and humidity at 40–55%.
Terms mentioned in this article
Frequently asked
What air speed is too draughty for a cat?
Above 0.3 m/s at the sleeping spot is worth fixing, and above 0.5 m/s below 20°C is a real heat-loss problem. Read it at 20–30 cm, not at human head height, because cold air pools in the layer the cat occupies.
Do I need an anemometer, or can I use a candle?
A 12–25 euro handheld anemometer reads 0.01–30 m/s and takes 30 seconds per spot, which is far more useful than a flame test. A tissue held at 20 cm tells you direction only, not the 0.3 m/s threshold that matters.
Should I stop ventilating altogether in winter?
No. Keep 2–3 bursts of 10–15 minutes a day with the cat out of the room, and close the rest of the time. Sealing gaps and adding a 40 cm baffle fixes the draught without cutting the air exchange the room needs.