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Heat Loss Calculator

Construction
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Estimates the heater power (in Watts) needed to heat a room, based on room dimensions, insulation, and desired temperature.

How To Use

How to use this calculator

Start with your values, or try a preset.

Step 1

Enter Room Length, Room Width, Room Height, Temperature Difference (Outside - Inside), U-value of Walls, U-value of Windows, Window Area, U-value of Roof, Roof Area, U-value of Floor, and Floor Area in the units shown.

Step 2

Read Heat Loss through Floor, Heat Loss through Roof, Heat Loss through Windows, Wall Area, Heat Loss through Walls, and Total Heat Loss in the results panel. Results update as you change the inputs.

Step 3

Choose a preset to load an example, then adjust the values for your situation.

Worked Examples

Example calculations

See the inputs and their calculated results.

Small Room, Poor Insulation

Room Length: 4 meters; Room Width: 3 meters; Room Height: 2.4 meters; Temperature Difference (Outside - Inside): 20 °C; U-value of Walls: 1 W/m²K; U-value of Windows: 2.8 W/m²K; Window Area: 2 square meters; U-value of Roof: 0.7 W/m²K; Roof Area: 12 square meters; U-value of Floor: 1.2 W/m²K; Floor Area: 12 square meters

Heat Loss through Floor: 288 Watts; Heat Loss through Roof: 168 Watts; Heat Loss through Windows: 112 Watts; Wall Area: 33.6 square meters; Heat Loss through Walls: 672 Watts; Total Heat Loss: 1,240 Watts

Medium Room, Average Insulation

Room Length: 6 meters; Room Width: 5 meters; Room Height: 2.5 meters; Temperature Difference (Outside - Inside): 18 °C; U-value of Walls: 0.6 W/m²K; U-value of Windows: 2 W/m²K; Window Area: 4 square meters; U-value of Roof: 0.4 W/m²K; Roof Area: 30 square meters; U-value of Floor: 0.9 W/m²K; Floor Area: 30 square meters

Heat Loss through Floor: 486 Watts; Heat Loss through Roof: 216 Watts; Heat Loss through Windows: 144 Watts; Wall Area: 55 square meters; Heat Loss through Walls: 594 Watts; Total Heat Loss: 1,440 Watts

Large Room, Good Insulation

Room Length: 8 meters; Room Width: 6 meters; Room Height: 2.7 meters; Temperature Difference (Outside - Inside): 22 °C; U-value of Walls: 0.2 W/m²K; U-value of Windows: 1.5 W/m²K; Window Area: 6 square meters; U-value of Roof: 0.2 W/m²K; Roof Area: 48 square meters; U-value of Floor: 0.6 W/m²K; Floor Area: 48 square meters

Heat Loss through Floor: 633.6 Watts; Heat Loss through Roof: 211.2 Watts; Heat Loss through Windows: 198 Watts; Wall Area: 75.6 square meters; Heat Loss through Walls: 332.64 Watts; Total Heat Loss: 1,375.44 Watts

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