Financial Calculations

Heat Loss Through the Floor


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 floor the addition of insulation beneath the floor slab was calculated to

  • Reduce the heat loss by 23%
  • Reduce costs by an estimated £15 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

With respect to the calculations for heat loss the following assumptions were made.
  • The ground temperature is approximately the same as the average annual air temperature.
  • No account was made of edge effects from the walls.
Taking these points into account the heat loss has been calculated to be 397W (which is probably very conservative). In terms of the boilers output this is approximately 2%.