Estimate annual space-heating demand from your building's envelope, ventilation, and climate, and compare it to the Passive House target of 15 kWh/(m²·yr).
m²
m²
W/m²K
m³
ACH
K·days/yr
Quick Facts
Heating demand
≤ 15 kWh/(m²·yr)
PHI Classic target, or a peak load of ≤ 10 W/m².
Airtightness
n50 ≤ 0.6 ACH
Measured at 50 Pa by a blower-door test; not the same as the effective rate used below.
Results
Calculated
Specific Heating Demand
—
kWh per m² per year (before gains)
Annual Heating Demand
—
Whole-building space heat, kWh/yr
Heat Loss Coefficient
—
Transmission + ventilation, W/K
Peak Heating Load
—
At a 30 K design ΔT, W/m²
Ready
Enter your building's envelope, ventilation, and climate data, then press Calculate.
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How this calculator works
Enter your building's treated floor area, envelope area, average U-value, volume, effective ventilation rate, and local heating degree days, then click Calculate. The tool adds transmission heat loss (through walls, roof, and floor) to ventilation heat loss (from fresh air and infiltration), then multiplies by your climate's degree days to estimate annual space-heating energy — the standard degree-day heat-loss method used in building physics.
The formula
Transmission heat loss coefficient: H_T = U-value × envelope area (W/K). Ventilation heat loss coefficient: H_V = 0.34 × air change rate × volume (W/K), using 0.34 Wh/(m³·K) as the volumetric heat capacity of air. Combined, H = H_T + H_V is the whole-building heat loss coefficient. Annual heating demand is H × degree days × 24 ÷ 1000 kWh, and dividing by treated floor area gives the specific heating demand in kWh/(m²·yr) — the figure the Passive House standard caps at 15.
What this estimate leaves out
This is a gross heat-loss calculation: it does not subtract solar gains through windows or internal gains from occupants and appliances, the way a full Passive House Planning Package (PHPP) balance does. Because those gains only ever reduce demand, a design that already scores at or below 15 kWh/(m²·yr) here is virtually certain to meet the target once gains are added. A design scoring higher may still meet it after gains, but this tool cannot confirm that without modeling window area, orientation, and shading.
Interpreting the results
The highlighted card shows specific heating demand — compare it to the 15 kWh/(m²·yr) Passive House target. The other cards show total annual energy, the combined heat loss coefficient, and an estimated peak heating load (using a fixed 30 K design temperature difference) compared against the 10 W/m² Passive House load target.
Frequently Asked Questions
What is the Passive House heating-demand target?
The Passive House Institute's Classic standard sets a space-heating demand limit of 15 kWh per square meter of treated floor area per year, or alternatively a peak heating load of 10 W per square meter. Either threshold, if met, qualifies a building on the heating-demand criterion.
What formula does this calculator use?
It sums a transmission heat loss coefficient (average U-value times envelope area) and a ventilation heat loss coefficient (0.34 Wh/m³K times the air change rate times building volume), then multiplies the total by annual heating degree days and 24 hours per day to get annual heating energy in kWh — the standard degree-day heat-loss method.
Does this include solar and internal heat gains?
No. This calculator estimates gross envelope and ventilation heat loss only, so it excludes free heat from sunlight, occupants, and appliances that a full PHPP balance would subtract. Because gains only reduce demand further, a result already at or below 15 kWh/(m²·yr) will still meet the target after gains; a higher result may still meet it once gains are counted.
What is n50 and why isn't it a direct input?
n50 is the air change rate measured by a blower-door test at 50 Pascals of pressure; Passive House requires n50 of 0.6 or less. That test value is much higher than the real, continuous infiltration rate, so this calculator instead asks for an effective (post heat-recovery-ventilation) air change rate, which is what actually drives ongoing ventilation heat loss.