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 insulationHeat Loss (W/K)
Front, Main19.411.6431.831.6431.83
Front, Extension6.480.322.071.479.53
Side, Right, Extension16.500.325.281.4724.26
Side, Right, Main17.361.4710.821.4725.52
Rear, Extension5.020.321.611.477.38
Rear, Pillar3.410.321.091.475.01
Rear, Main13.950.365.021.3919.39
Side, Left36.480.3211.671.4753.63
Total118.6169.39176.66

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

Area

m2

U Value

W/m2K

Heat Loss

W/K

Main Building

42.56

0.8

34.05

Extension

22.68

0.8

18.14

Total52.19


Heat Loss through Ceiling

With insulation

Component

Area

m2

U Value

W/m2K

Heat Loss

W/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

Area

m2

U Value

W/m2K

Heat Loss

W/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