October is the month the windows stay shut without anyone deciding it. Indoor carbon dioxide climbs past 1000 ppm by mid-afternoon, daylight drops from about 11 hours to 10 by the 31st, and a cat that jumps onto the counter in September starts using a chair instead. None of these announces itself; all three are measurable in under 10 minutes a day.
What a closed window does to the room
A 20 square meter living room with 2 people and 1 cat passes 1000 ppm carbon dioxide in 3 to 4 hours once the window is shut, and 2000 ppm by evening in a bedroom with the door closed. That is not dangerous, but it correlates with stale air, higher dust, and a cat that sleeps more and plays less. Cooking fumes, candle smoke and scented plug-ins add fine particles that settle into coat and airway; a cat with asthma may cough 2 to 3 times a day before anyone connects it to the closed window.
Dust mites also prefer the change. Indoor humidity in October often sits at 50 to 60 percent, warm and still, which is the range where mites multiply; keeping 40 to 50 percent and cleaning filters is more useful than any spray. Vacuum with a sealed filter twice a week, wash soft bedding at 60 C, and wipe the radiator fins before the heating season starts, not after the first smell of hot dust.
Ventilation without losing the heat
Cross-ventilation beats a cracked window. Open 2 windows on opposite walls for 5 to 10 minutes, 2 to 3 times a day — morning, after cooking, before bed — and close them. That exchanges the air in a 20 square meter room roughly 1 to 2 times without dropping wall temperature more than 2 to 3 C. A window held 2 to 3 cm open all day is the worse option: it cools surfaces continuously and does little for the CO2 reading in the corner where the cat sleeps.
Put the cat's bed out of the draft line. A 0.5 to 1 m/s airflow at 18 C on a sleeping cat is enough to make it move to a shelf or a cupboard, and cats that relocate to closed spaces are the ones that get shut in. If a CO2 monitor reads above 1200 ppm at 6 p.m., add one more purge before the evening; the number should fall below 800 ppm within 10 minutes of opening up.
Daylight: 11 hours down to 10
Day length in a temperate zone drops roughly 1 to 1.5 hours across October, and indoor light near a north window can sit at 100 to 300 lux on a grey afternoon — the level of a dim hallway. Cats get most of their vitamin D from food, so the loss matters less for vitamins than for rhythm: less bright light means more sleeping, less playing, and a slow slide in activity that owners read as aging.
Build a sun spot on purpose. A shelf or chair by a south or west window that catches 30 to 45 minutes of direct light between 11 a.m. and 2 p.m. gives the cat a warm, bright place to sit, and 2 short play sessions of 5 to 10 minutes at dusk replace some of the light-driven activity. Keep the spot off radiators: 22 C air and a 60 C radiator surface in the same square meter is how cats get dehydrated without anyone noticing.
Joints: the 5-minute test
Watch for 5 minutes at the times the cat moves after rest, not while it is asleep. Four findings matter: stiffness that lasts more than 10 minutes after getting up, a jump onto a surface 20 percent lower than 3 months ago, refusal of the stairs it used daily in August, and matted fur over the lower back from reduced grooming. Any 2 of the 4, seen on 3 separate days in 2 weeks, is enough to book an exam rather than a wait.
Many cats over 10 have radiographic signs of joint disease, and most of them are never treated for pain because the change is gradual. October is the honest month to check: cold, damp mornings expose stiffness that summer hid, and the 8 to 12 C day-night swing makes a sore joint obvious at 7 a.m. Write the jump height down — a counter is 90 cm, a chair seat 45 cm, a windowsill maybe 60 cm — because a 20 percent drop is easy to miss without a baseline.
October watch list
| Sign | Normal | Book a visit when |
|---|---|---|
| Morning stiffness | under 5 minutes | over 10 minutes for 3 days |
| Jump height | 90 cm counter | 20 percent lower than in July |
| Indoor CO2 | under 800 ppm | above 1200 ppm at 6 p.m. |
| Room humidity | 40-50 percent | above 60 percent for 5 days |
| Play sessions | 2 per day, 5-10 minutes | refuses 3 days in a row |
| Grooming | 1 full groom per week | matted patch over 2 cm |
Cost, and where the rest of it lives
A joint exam with radiographs typically costs 120 to 300 USD; monthly pain management runs 30 to 80 USD depending on class, and a set of 3 raised feeding platforms or 2 ramps costs 40 to 120 USD once. The arithmetic of delaying is in the /tools/cost/ calculator. The cold-morning flare pattern is covered in /seasonal/autumn-arthritis-flare/, and the 40 percent floor that keeps the room from getting worse belongs to /seasonal/seasonal-winter-humidity/.
What October should leave you with
- A ventilation slot: 2 purges of 5 to 10 minutes, morning and after cooking.
- A CO2 or humidity reading taken at the same hour for 7 days.
- One bright sun spot the cat actually uses, checked on 3 afternoons.
- A 90 cm jump baseline written down, plus the 4-sign joint check.
- Filters and radiator fins cleaned before the heating season, not after.
If the cat still jumps to the counter, plays twice a day, and the 6 p.m. CO2 reads under 800 ppm, October needs nothing more than repetition. If a limp lasts 48 hours, or the cat stops using the litter box because the entry is too high, that is a same-week appointment: a 12 cm box lip is enough to stop an arthritic cat, and a 6 cm cut-out fixes it.
Frequently asked
How long should I air out a room in cold weather?
Do 2 or 3 cross-drafts of 5 to 10 minutes each day: after waking, after cooking, and before bed. That exchanges the air in a 20 square meter room 1 to 2 times and drops wall temperature by only 2 to 3 C. A window held 2 to 3 cm open all day cools surfaces continuously and barely moves the CO2 reading.
Does less autumn sunlight affect a cat's health?
Cats get most vitamin D from food, so the vitamin effect is small. What changes is rhythm: indoor light near a north window can fall to 100 to 300 lux on a grey afternoon, and activity drops with it. A 30 to 45 minute sun spot plus 2 play sessions of 5 to 10 minutes keeps the day structured.
What are the first signs of arthritis in a cat?
Stiffness lasting more than 10 minutes after rest, a jump height 20 percent lower than 3 months ago, refusal of stairs the cat used in summer, and matted fur over the lower back from less grooming. Any 2 of the 4, seen on 3 days across 2 weeks, justifies an exam with radiographs.