Why we count hours, not months
Nobody loses a conservatory for all of July. They lose it from 1pm to 6pm on most sunny days, then get it back in the evening. So the Comfort Calendar counts every waking hour from 8am to 10pm across two years of real weather, and calls an hour usable if the room is at or below 25°C, with a heater allowed for the chilly ones.
Divide by 14 waking hours a day and you get the month figures in the lede. The panel roof adds 1,003 usable hours a year, the same as about ten weeks of full days.
- 3,793
- usable waking hours a year, polycarbonate roof
- 4,796
- usable waking hours a year, panel roof
- 1,003
- extra hours the panel roof gives back
Month by month, what to expect
This is the pattern our model shows for a south facing room, averaged across 104 towns. A sunny year shifts it towards heat, a dull one towards cold.
| Months | Polycarbonate roof | Panel roof |
|---|---|---|
| December to February | Cold all day, needs a heater whenever you sit in it | Cold too, but a smaller heater copes |
| March and April | Lovely on sunny afternoons, chilly mornings and evenings | Chilly unheated, comfortable with a little heat |
| May | Hot afternoons start on clear days | Mostly comfortable |
| June to August | Close to half of waking hours too hot | Comfortable most of the time, warm in a heatwave |
| September and October | The best months to sit in it unheated | September easy, October needs some heat |
| November | Needs heating | Needs heating |
Where the missing time goes
Under polycarbonate the room spends 1,320 waking hours a year above 25°C. Glass is worse at 1,467. Spread over May to September, that is most afternoons in the warmest part of the year, exactly when you would want to open the doors and sit out there.
Where you live shifts the number. Our league table of overheating towns runs from 1,501 hours in Hounslow down to 949 in Buxton. Even the bottom of the table adds up to more than nine weeks of full waking days lost.
Winning back the winter
Winter hours are the easy ones to rescue: a heater turns a chilly hour into a usable one. Under polycarbonate you need a 1.7 kW heater to hold 19°C when it is 0°C outside, under panels 1.1 kW. A plain electric heater of that size costs about 45p or 29p an hour at 26.32p a kWh. See the best ways to heat a conservatory for cheaper options than a fan heater.
Winning back the summer
Summer hours are harder, because you cannot heat your way out of a hot room. Vents, outside shading and reflective film each claw back a little. Air conditioning works but costs to run and fights the roof all afternoon. Stopping the sun at the roof removes most of the lost hours, and nothing else comes close: the panel roof cuts too-warm time by 76%. The blinds and film versus new roof comparison puts numbers on each.
