Soldato
- Joined
- 18 Oct 2002
- Posts
- 6,669
I'm a data nerd and love measuring / tweaking things.
Given the rise in energy prices, along with optimising my combi boiler, I thought it would be interesting to try and estimate how thermally efficient my home is.
According to the EPC, which was done in 2017, our small 1985 3 bed detached is C71.
With a total floor area of 96 sq. m (it's actually a little larger than that in terms of floor area because the loft was converted, adding perhaps another 40 sq. m), the EPC estimates consumption of 211 kWh/sq m per year.
Our actual energy usage (combined gas and electric) is 7800 kWh, which equates to 82 kWh/sq m per year (using the same 96 sq m figure from the EPC). Not sure why the EPC more than doubles the consumption...
To try and estimate thermal losses, I put together the total surface area of the house (it's roughly a cube of 8m D x 6m W x 5m H with a typical roof adding another 2m) and ended up with the following
Assuming U-values as follows:
Assuming Delta-T of 18 (0 outside in winter, 18 inside), I estimate thermal losses of 3200 W.
At current gas prices, that would cost £0.46 per hour to maintain constant temperature. (This is not a million miles away from what it seems to cost, although it's tricky to estimate because we don't have the heating on all the time, and it takes an initial surge of gas to get the central heating up to temperature).
If I replaced the old double glazing with new stuff, I reckon that would drop the U value of the windows to 1.2, saving £179 a year on thermal losses / heating. (That's a pretty poor return, so I think I'll leave it until they really need replaced!)
Given the rise in energy prices, along with optimising my combi boiler, I thought it would be interesting to try and estimate how thermally efficient my home is.
According to the EPC, which was done in 2017, our small 1985 3 bed detached is C71.
With a total floor area of 96 sq. m (it's actually a little larger than that in terms of floor area because the loft was converted, adding perhaps another 40 sq. m), the EPC estimates consumption of 211 kWh/sq m per year.
Our actual energy usage (combined gas and electric) is 7800 kWh, which equates to 82 kWh/sq m per year (using the same 96 sq m figure from the EPC). Not sure why the EPC more than doubles the consumption...
To try and estimate thermal losses, I put together the total surface area of the house (it's roughly a cube of 8m D x 6m W x 5m H with a typical roof adding another 2m) and ended up with the following
- Total window area = 18 sq m
- Total wall area = 145 sq m (subtracting the window area from the total wall area)
- Roof = 65 sq m (approx. treating roof as right-angle triangle!)
- Ground floor = 46 sq m
Assuming U-values as follows:
- Windows (mostly old double-glazing) = 3.3
- Walls (cavity wall insulation) = 0.25
- Roof (loft conversion, cold loft storage) = 0.5
- Floor (assume no insulation) = 1
Assuming Delta-T of 18 (0 outside in winter, 18 inside), I estimate thermal losses of 3200 W.
At current gas prices, that would cost £0.46 per hour to maintain constant temperature. (This is not a million miles away from what it seems to cost, although it's tricky to estimate because we don't have the heating on all the time, and it takes an initial surge of gas to get the central heating up to temperature).
If I replaced the old double glazing with new stuff, I reckon that would drop the U value of the windows to 1.2, saving £179 a year on thermal losses / heating. (That's a pretty poor return, so I think I'll leave it until they really need replaced!)
- Can anyone who knows about U values and EPCs comment on how far out my U value / thermal loss estimates are?
- How closely does this equate to a C72 EPC?
If I measure the rate of temperature drop overnight, how can I convert degrees C per hour into BTU / kWh? (I'm stumped with this one)EDIT - Gave up. Too hard to estimate as I need to know the mass of the house!EDIT - rough estimates in post below.
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