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As a rule of thumb I use 0.095 m3 per Kw/h.
So a 30 kw boiler will use approx 3 m3 per hour.
One problem I have found in houses is undersized radiators which basically means to get warm the heating is on for ages.
A sensible equation is 5 btu per cubic foot.
3412 btu is 1 kw (1000watts) so calculate your room volume in feet
( length x width x height) by 5 and that’s how many btu you need in a space you occupy, lounge , dining, hallway etc.
Bedrooms are 4 x and kitchens bathroom are 3 x per cubic foot.
These areas are less because in bed you are covered and a bathroom is less time.
All radiators have an output, some are more efficient but cheap to dear will have an output.
You can measure your radiator in a space and look for that size on line.
Double, single, with fins without fins etc. familiarise yourself with the type and most plumbers merchants will have a brochure of some sort to see a picture.
You will be surprised how many rads are installed to fit a space on a wall rather than the actual space volume. Mine are over by about 15% and my heating is on for 15 minutes and I’m toasty hot. Then off for about half hour then on for 5 mins ad infinitum till bed time or I’m too hot. I haven’t got a time clock as my room stat sits at
about 12* c at all times unless I turn it up. This stops my place cooling down too much so it’s just a trim up when needed.
I have posted this before a while ago but now it might help a few holers bearing in mind it’s totally relevant with the cost of energy. Anyhow sorry to bore you but check out my info and I can guarantee many of you have undersized radiators which will invariably cost you money. It may seem a false economy oversizing but it’s defiantly nice to actually here your heating turning off occasionally.

Edited by cryrst (12 Oct 2022 9.16pm)

That seems excessive.

My estimate is 23K and I have a similar size house.

Do you have nest or hive?