Q [kW] = [Σ(U×A) + 0.33×V×n×(1−η)]×ΔT / 1000. Roof and floor areas are assumed equal to heated floor area. This is a comparison estimate, not heating sizing: bridges, infiltration and ground modelling are excluded. Verify the temperature for the site.
ZeroHouse
Preliminary heat-loss estimate
Transparent assumptions and a preliminary result.
Understand the assumed geometry
The tool takes wall and window areas separately, so opaque wall area should not count glazing again. One area input is used for both roof and floor, and volume V is that area multiplied by height. This assumes simple geometry. It may not represent a complex multi-storey building, unequal floor and roof areas or partially heated spaces, even when every entered number is individually correct.
Follow the units in the formula
The envelope sum UA is expressed in W/K. The tool adds 0.33Vn(1−η), where V is in m³, n is air changes per hour and η is the heat-recovery fraction. This gives H in W/K. Multiply it by the indoor–outdoor temperature difference ΔT in K to obtain watts, then divide by 1000: Q [kW] = H × ΔT / 1000. The factor 0.33 is a simplified air heat-capacity conversion for these units, not a separate equipment rating.
Keep the result within its scope
The calculation is steady-state and excludes thermal bridges, infiltration and heat gains. A single recovery fraction cannot reproduce every ventilation-unit operating mode. The output is not an annual bill, room-by-room capacity or hot-water requirement. Change one parameter at a time to understand its influence and save the assumptions with the number. Heating selection needs complete loads and a coordinated emitter system; this tool is useful for exploring relationships before that detailed assessment.