Heat Pumps

[88v8]

It used to be common practice with oil and gas boilers to apply a margin of oversizing for both the boiler and the radiators but this is much more tricky to do with heat pumps and underfloor.
That calculation was complicated for us as we were significantly extending the living space but doing the calculations retrospectively I discovered the original design would have struggled to heat the house before we moved into the bits that were sealed off!

When I installed our gfch + cast-iron rad system in our previous house, I made full calculations for each room... it took ages.. all done manually back then.
The volume of each room, the area of floor, walls, ceiling, windows, the coefficient of heat loss through each, the design temperature in each room and in each space adjacent to the one being calculated, and, the main element of guesswork, the number of air changes per hour. That gives the heat requirement for each room plus of course the same calcs for hall stairs and landing. Then add the load of the hot water coil, work out the heat loss through all the different sizes and runs of pipe in the system, total it all and add 20% to cater for serious cold snaps, and that gives the minimum boiler size.
Our house was 1921 and the construction methods all conventional, so one could have a reasonable stab at heat loss calcs. Infinitely more difficult with a much older house, and just poking in a larger boiler 'for luck' results in unacceptable inefficiency. I doubt I'd have the courage to try anything as esoteric as underfloor heating - I prefer to admire the efforts of the brave from a safe distance. :shock:

Ivor

 

[Flyfisher]

Given that the recommendations I've seen suggest a complete change of air 4x per hour (higher for 'wet' rooms such as kitchens and bathrooms), I'm wondering how important the heat loss through walls really is, given that all the expensively heated air is going to be thrown out every 15 minutes anyway!