Heat Loss Through Roof
The table below shows a breakdown of the heat lost through the various surfaces of a 1970's Wimpey house. It shows
- Heat loss without insulation. (As it was when the house was first built).
- Heat loss with insulation installed.
- The heat loss expressed as a percentage of the total.
- The annual cost of the heat loss.
With respect to the roof the addition of loft insulation was calculated to - Reduce the heat loss by 97%
- Reduce costs by an estimated £381 per annum
| Heat Loss without insulation. (W/K) | Approximate Annual Cost. (£) | Heat Loss with Insulation. (W/K) | Approximate annual cost. (£) | Annual Saving. (£) | | Roof | 297 (45%) | 395 | 10 (5%) | 14 | 381 | | Walls | 177 (27%) | 237 | 69 (34%) | 93 | 144 | | Doors and Windows | 133 (20%) | 176 | 86 (42%) | 115 | 61 | | Floor | 52 (8%) | 70 | 40 (20%) | 55 | 15 | | 659 | 878 | 205 | 273 | 601
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The calculations for heat loss per degree difference between inside and outside temperature gave a figure of 10.44W. Using this figure the calculated heat loss for a cold winters day would be as follows
Heat loss through ceiling with insulation = 10.44W/K
Outside temperature = -1C
Indoor temperature = 18C
Temperature difference = 19C
Heat loss = 10.44x19 = 198W
This is 1% of the boilers output.
For comparison, if there were no insulation, the heat loss would be
Heat loss through ceiling without insulation = 296.84W/K
Heat loss = 296.84 x 19 = 5640W
This is 35% of the boilers output.
And finally, the heat lost through an uninsulated loft hatch will be
Heat loss = 2.46 x 19 = 47W | 