Passive House Calculator — Annual Heating Demand

Formula

How this is calculated

The simplified steady-state energy balance used here follows the structure of the Passive House Planning Package (PHPP) at a high level. Heat losses are split into two streams: transmission losses (conducted through the opaque and transparent envelope at rate U × A_env per degree Kelvin, accumulated over all heating hours via heating degree days) and ventilation losses (the energy needed to warm cold incoming air, reduced by the HRV's heat-recovery efficiency η). Heat gains offset these losses: direct solar gains through south-facing glazing (glazing area × SHGC × annual irradiation) and internal gains from occupants and appliances (roughly 3–4 W/m² in dwellings). If gains exceed losses, no mechanical heating is required (SHD = 0).

The Passive House Institute (PHI) standard, established in Darmstadt in 1990, requires a specific heating demand ≤ 15 kWh/(m²·year), a specific cooling demand ≤ 15 kWh/(m²·year), airtightness n₅₀ ≤ 0.6 h⁻¹, and primary energy demand ≤ 120 kWh/(m²·year). The 15 kWh threshold was chosen because it matches what a well-insulated building can supply with its ventilation air stream alone, eliminating the need for a separate heating system. Typical U-values in passive house construction are ≤ 0.15 W/m²K for opaque elements and triple-glazed windows with U_w ≤ 0.80 W/m²K.

This calculator is a simplified first-order estimate — it uses annual heating degree days (HDD) with a 20 °C base, treats the building as a single thermal zone, ignores thermal bridges, infiltration losses beyond the ACH input, and summer cooling loads. For a compliant certification assessment, use the official PHPP software or an accredited Passive House Designer.