Heat Load Calculator

How It Works

A heat load calculation determines how much heating and cooling your home actually needs. The Manual J method, used by HVAC professionals, accounts for every path heat can take into or out of your home: walls, windows, ceiling, floors, infiltration (air leaks), and internal heat sources. This calculator provides a simplified version. Walls and attic are the biggest heat loss paths in most homes. Windows are a close second, especially older single-pane windows. Air infiltration through cracks and gaps can account for 25 to 40 percent of total heat loss. Improving insulation and sealing air leaks can dramatically reduce the size (and cost) of the HVAC system you need.