Calculations‎ > ‎

Ventilation Heat Loss

Draughts - Windows


Outside Temperature 1deg C
Outside Conditions Rain/sleet/windy
Outside Relative humidity 100%
Air Velocity  1m/s
Inside Temperature 18deg C
Total window perimeter 31m
Average gap size 0.001m
Aperture area for draught, 50% 0.015m2
Air volume flow rate 0.015x1 = 0.015m3/s
Specific enthalpy of outside air 12kJ/kg
Specific enthalpy of heated, inside air 29kJ/kg
Specific volume of outside air 0.772m3/kg
Air mass flow rate (0.015x1)/0.772 = 0.02kg/s
Heating requirement (29-12)x0.02 = 0.34kW
Energy Consumption at 80% Boiler Efficiency 0.34kW/0.8 = 0.425kW

Draughts - Door


Outside Temperature 1deg C
Outside Conditions Rain/sleet/windy
Outside Relative humidity 100%
Air Velocity 1m/s
Inside Temperature 18deg C
Total window perimeter 5.6m
Average gap size 0.001m
Aperture area for draught 0.0056m2
Air volume flow rate 0.0056x1 = 0.0056m3/s
Specific enthalpy of outside air 12kJ/kg
Specific enthalpy of heated, inside air 29kJ/kg
Specific volume of outside air 0.772m3/kg
Air mass flow rate (0.0056x1)/0.772 = 0.00725kg/s
Heating requirement (29-12)x0.00725 = 0.123kW
Energy Consumption at 80% Boiler Efficiency 0.123kW/0.8 = 0.154kW

Draughts - Gas Boiler


Outside Temperature1deg C
Outside ConditionsRain/sleet/windy
Outside Relative humidity100%
Boiler Input Power13.2kW
Inside Temperature18deg C
Air:Natural Gas Combustion Ratio (By Volume, 10% excess air)10.472:1
Natural Gas Energy Content40100kJ/m3
Gas flow rate13.2/40100 = 3.29x10-4 m3/s
 Air flow rate 10.472x3.29x10-4 = 3.44x10-3  m3/s


Specific enthalpy of outside air12kJ/kg
Specific enthalpy of heated, inside air29kJ/kg
Specific volume of outside air0.772m3/kg
Air mass flow rate (3.44x10-3)/0.772 = 4.46x10-3kg/s
Heating requirement(29-12)x4.46x10-3 = 0.076kW