Heat Loss Calculator

Heat loss is the transfer of thermal energy from inside your building to the outside environment. It matters because it determines how much heating power you need to maintain comfortable indoor temperatures and directly affects your energy costs.

The main factors are: surface area (walls, windows, doors), material properties (U-values), temperature difference between inside and outside, insulation quality, air infiltration rate, and building orientation.

Heat loss is calculated using the formula: Q = A × U × ΔT, where Q is heat loss (BTU/hr), A is surface area (ft²), U is the U-value (thermal transmittance), and ΔT is temperature difference (°F).

Typical U-values: uninsulated walls (0.5-1.0), well-insulated walls (0.15-0.3), single-pane windows (1.0-1.3), double-pane windows (0.3-0.6), solid doors (0.5), and insulated doors (0.2-0.3). Lower U-values indicate better insulation.

Air infiltration causes heat loss when warm indoor air escapes and cold outdoor air enters. This is calculated based on air changes per hour (ACH) and can account for 20-40% of total heat loss in poorly sealed buildings.

Your heater capacity should be 15-25% higher than calculated heat loss to account for system inefficiencies and safety margin. For example, if heat loss is 40,000 BTU/hr, choose a 46,000-50,000 BTU/hr heater.

Improve insulation in walls, ceiling, and floors; upgrade to energy-efficient windows and doors; seal air leaks around windows, doors, and penetrations; and consider thermal curtains or storm windows for additional protection.

Yes, corner rooms with more external walls lose more heat than interior rooms. Ground floors lose heat to soil, while top floors lose heat through the roof. Rooms with more windows or facing prevailing winds also have higher heat loss.