Calculations‎ > ‎

Fabric Heat Loss

This section covers the heat lost through the walls, floor and roof.

Heat Loss through Walls

 Surface Wall Area (m2) U Value Current Heat Loss (W/K) U Value Without insulation Heat Loss (W/K) Front, Main 19.41 1.64 31.83 1.64 31.83 Front, Extension 6.48 0.32 2.07 1.47 9.53 Side, Right, Extension 16.50 0.32 5.28 1.47 24.26 Side, Right, Main 17.36 1.47 10.82 1.47 25.52 Rear, Extension 5.02 0.32 1.61 1.47 7.38 Rear, Pillar 3.41 0.32 1.09 1.47 5.01 Rear, Main 13.95 0.36 5.02 1.39 19.39 Side, Left 36.48 0.32 11.67 1.47 53.63 Total 118.61 69.39 176.66

Heat Loss through Floor

Heat lost through the floor is dependent on a proportion being conducted vertically down plus that which flows horizontally via the walls and foundations. As a result, a precise calculation takes into account the floor shape as defined by a ratio of the floor perimeter to area. However, the calculation below is for indicative purposes and so uses a generic values.

Current Insulation

 Surface Area(m2) U Value(W/m2K) Heat Loss(W/K) Main Building 42.56 0.8 34.05 Extension 22.68 0.25 5.67 Total 39.72

No Insulation

 Surface Aream2 U ValueW/m2K Heat LossW/K Main Building 42.56 0.8 34.05 Extension 22.68 0.8 18.14 Total 52.19

Heat Loss through Ceiling

With insulation

 Component Aream2 U ValueW/m2K Heat LossW/K Main Building 42.56 0.16 6.81 Extension 22.68 0.16 3.63 Total 10.44

Without Insulation

 Component Conductivity (W/mK) Thickness(m) Conductance(W/m2K) Resistance (m2K/W) Resistance (m2K/W) Inside Air Layer (In Room) 0.1 0.1 Plasterboard 0.16 0.0095 16.67 0.06 0.06 Ceiling Joist 0.13 0.1 1.3 - 0.77 Outside Air Layer (In Loft) 0.04 0.04 Totals 0.2 0.97 Net Resistance 0.22 Overall U-Value (W/m2K) 4.55

Ceiling joists are are 4cm x 10cm at 46cm centres
Percentage of ceiling area occupied by joists = (4/46)x100 = 9%
Net resistance = 1/(0.09/0.97)+(0.91/0.2) = 1/0.093+4.55 = 0.22

 Component Aream2 U ValueW/m2K Heat LossW/K Main Building 42.56 4.55 193.65 Extension 22.68 4.55 103.19 Total 296.84

Through Uninsulated Loft Hatch

Loft hatch dimensions = 63cm x 78cm
Loft hatch area = 0.49m2
U Value = 5W/m2K
Heat Loss = 5 x 0.49 = 2.46W/K

Heat Loss Through Doors and Windows

 Total Area of Windows and Doors 27.81m2 Approximate U Value 2.8 W/m2K Overall Heat Loss per deg K 77.87 W/K