OK mate, won't lie - I can't find it. I could have
sworn I saw on a YouTube channel (along the lines of Heat Geek, so not just some anti-heat pump loon or anything) that they need their arses run off them to keep the flow up at 65ºC, but I can't find the video or mention, nor find much other supporting evidence, so I'll hold my hands up and say that what I said must be incorrect in this case
![Smile :) :)](/styles/default/xenforo/vbSmilies/Normal/smile.gif)
talking of Heat Geek...
I've just been watching a couple of their vids, and using their cheat sheet/rules of thumb, tried to get an idea of heat loss in our house. We're a 2017 build, and HG reckon that as a rough guide, a post-2006 house will lose anywhere between 20-40W per m^2 of floor space. Having just gone wild with a tape measure, and taking the upper bound of 40W loss, our house
loses just shy of 3kW with an outside temperature of -3ºC. I also measured our radiators, and using HG's radiator output guide, I end up with a total output of 2.9kW while running at 50ºC mean water temperature.
My EPC does also have the U-values for walls, roof, and floor. From what I can see online, if I take the sum of these and multiply it by the temperature differential of outside to inside, I get a rough fabric heat loss. So me this ends up as 15.41W/m2. I assume any ventilation and window losses would need to be added, but it kinda looks like I'd still be at the lower end of the 20-40W guide from HG, so our heat loss of just about 3kW at -3ºC could actually be lower.
So outside air temp of 10ºC now, means the house at 19ºC is losing a minimum of 6W/m2, so rough floor space of 80m2 (ignoring garage conversion right now due to it not being on central heating) means a heat loss of about 480W. The minimum my boiler can put into the heating system is 7kW
![Eek! :eek: :eek:](/styles/default/xenforo/vbSmilies/Normal/eek.gif)
meaning my boiler is around 14x too big for the current weather
![Eek! :eek: :eek:](/styles/default/xenforo/vbSmilies/Normal/eek.gif)
and around 2.5x too big even for an outside temperature of -3ºC.