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Heat Loss Calculator

Estimate room or building heat loss using U-values (or R-values), surface areas, temperature difference, and air changes. Includes a full surface breakdown table and heating load sizing.

U/R Values Walls, Windows, Roof ACH Infiltration BTU/hr & Watts

Room Heat Loss & Heating Load Estimator

Calculate conductive and air-change heat loss, total heating load, and a surface-by-surface breakdown with export.

Units

Indoor Temperature

Outdoor Temperature

Sizing Margin (%)

Room Length

Room Width

Ceiling Height

Air Changes per Hour (ACH)

External Walls Area

Wall U-Value

Windows Area

Window U-Value

Doors Area

Door U-Value

Roof/Ceiling Area

Roof/Ceiling U-Value

Floor Area (to outside/unheated)

Floor U-Value

Export

Air Loss Method

Airflow Value

Volume

Temperature Difference (ΔT)

Units Context

Temperature Difference (ΔT)

Surface

Area

U-Value Before

U-Value After

Upgrade Cost

Heating Cost (per kWh or per therm)

Cost Basis

Heating Hours per Season

Heat Loss Calculator

Room Heat Loss & Heating Load Estimator

Total Heat Loss

Conductive Loss

Air Change Loss

Suggested Heating Size

Air Heat Loss

Equivalent Airflow

Notes

Heat Loss Before

Heat Loss After

Season Energy Saved

Simple Payback