Heating Calculator

Work out the heat output your space needs, then request a quote for a suitable heater. Enter the room or enclosure size in metres.

1 What kind of space is it?

Brick or block with cavity wall Better insulated solid buildings — offices, workshops, site cabins with cavity construction. Brick or block without cavity Older or solid-wall buildings with less insulation. Timber frame or heavy plastic Marquees, tents, temporary covers and lightly insulated enclosures.

2 Enter the size

Length (m)

Width (m)

Height (m)

Desired temperature rise (°C)

Default 20°C — raise the space by about 20°C above outside air. Adjust if you need a smaller or larger lift.

Estimated heat output required

Kilowatts

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Watts

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BTU / hour

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BTU/hr

This is a guide for sizing portable or temporary heaters on site. It does not replace a full heating design. Factors such as open doors, high air change, very cold weather or poor seals can increase the output you need. Always allow a little spare capacity.

How we calculate it

Heat (W) = length × width × height × building factor × (temperature rise ÷ 20)

Building factors (watts per cubic metre at a 20°C rise):

Brick/block with cavity wall — 35 W/m³
Brick/block without cavity — 50 W/m³
Timber / heavy plastic (marquee, tent) — 85 W/m³

1 kW = 1,000 W. BTU/hr ≈ watts × 3.412. Figures are a practical rule of thumb for UK site and temporary heating.