Oversizing and heat loss rule of thumb

[JonathanM]

I can't find them now, but I know I've read a couple of articles about oversizing boilers, which had a rule of thumb for heat loss vs outside temperature. The articles said something along the lines of, "the average home requires 8KW at -3C, but only needs 2KW at 10C". I think it might have been used on here a couple of times as well.

Anyway, I was just hoping that somebody could point me in the direction of this approximation for how heat loss changes with temperature?

 

[oldbuffer]

1. For a given surface area and level of thermal conductivity, heat loss is proportional to temperature difference.
2. Thermal conductivity depends on materials used and their construction.
3. In consequence, every property will have it unique "heat loss signature".
4. Talk of average home differences is just that, an average. So unless you know that your property is average, it is largely meaningless. The sort of figure that journalists like to quote but which means very little.
5. You could try an online calculator, but you would need one that requires you to enter the outside temperature. Do one calculation at -3 and another at +10 and use the difference.

 

[ScottishGasMan]

Heat loss = the energy it takes to keep your house at x°C inside when its z°C outside.

So if your heat loss was 10kW when rooms are 20°C and its -2°C outside, it has a 10kW heat loss when the difference between outside and inside is 22°C.

Half that difference, Half the heat loss. Double the difference Double the heat loss.

If you want the maths. Then in this case the heat loss is 10kW when there is a 22°C difference between inside and outside. 10kW divided by 22°C = 0.4545, so you need 0.4545kW for ever degree warmer that you want the house than outside.

 

[muggles]

It's entirely linear. Heat loss is a function of the difference between internal and external temperatures. If it's 21°C outside and 21°C inside, the heat loss will be zero. A building with a target internal temperature of 21°C losing 8kW when it's -3°C outside will lose 4kW when it's 9°C outside

 

[JonathanM]

Thank you, all, that's so much simpler than I imagined. I was expecting some sort of complex relationship. It will help me with my sums this winter.