homeassistant

I might be able to help you get an approximation.
Though quite honestly, you'd probably save time and effort by just using a thermostat in each room, and setting HA not to power the heat on when pricing is >75% day average, since you know ahead of time, and it'll probably save you about as much.

Overall, you'll need to calculate the heat loss per delta T per room.
You'll likely have to do this by best estimate, then perhaps a bit of real-life experimentation with a 1KW heater, or similar.

For each room, make a list of the external walls, their composition, and the depth of each layer of material depth.*
Look up the rough WMK (watts of heat lost per square meter (at 1m thick), per degree difference from the outside to the inside) for each material.
Take those values, and use them to make an estimate of the room loss.
So for example, a room with 1 external wall of 10m2, made of 215mm brick (0.7WMK), and 50mm of fibreglass insulation ( 0.038WMK).
1÷(((1÷0.7)×0.215)+(1÷0.038)×0.05) = 0.61 WMK.
Multiplied by 10m2, 6.1Watts per degree difference.
So if it's 0 outside, and 20 inside, 120W lost by that wall.

There are a lot of other factors that you can bring in (air tightness, rsi, thermal gain). But this will give you a low ballpark number you can start working off for each room.
So long as you're supplying more than the room is losing, it will gradually heat.
If you want to work out how much it will take to warm all the objects/walls, that's a whole other calculation. But if you're maintaining temps, it doesn't matter so much.

Oh, and a thin sheet of glass will lose about 5W/m2/k. Scary!

* I'm ignoring internal walls, as I'm assuming you'd plan to keep the house roughly the same temperature. And it would get complicated.