Activair fan heater size calculator

Building length:   metres
Building width:   metres
Building height:   metres
Temperature required:   C

Notes on use

Temperature required - The HSE recommends a minimum figure of 16C for workplaces. Depending on the type of work undertaken, the actual temperature required for comfort is likely to be much higher (16 - 28C).

Insulation type - select the type that most closely matches your building:

Hardly any - Structure clad in corrugated iron or asbestos sheet.
Poor / high leakage - Little insulation, single brick walls, single glazed windows, no roof insulation.
Average - Cavity or insulated walls, insulated roof, single glazed windows.
Good / low leakage - Well insulated walls, roof and floor, double glazing etc.

This calculator must not be used for buildings with open loading bays, doors or windows. Fan heaters are generally not suitable for these applications, consider using radiant heaters instead.

For more detailed guidance see doing a heatloss calculation.


This calculator is provided as a quick check of heatloss. It is not a replacement for a detailed heatloss calculation. W. Tombling Ltd has taken every precaution to ensure it is accurate, however we accept no responsibility or liability resulting from its use.