Passive House Calculator

Because ACH50 is a pressurized test result, not the building's natural air-change rate. This calculator divides your Airtightness (ACH50) input by 20 -- the standard LBL (Lawrence Berkeley Lab) conversion factor -- before using it in the infiltration heat-loss formula, since air moves through leaks far faster under the blower door's 50 Pascal test pressure than it does under everyday wind and stack-effect pressures. A building at the Passivhaus 0.6 ACH50 limit has a natural infiltration rate of just 0.03 air changes per hour, which is why its contribution to total heat loss is smaller than the raw 0.6 figure might suggest.

Not necessarily -- Floor Area affects the calculation on both sides at once. It sets the internal-gains credit (about 20 kWh per square meter per year) that gets subtracted from total heat loss, AND it's the denominator Heating Demand (kWh/m²/yr) is divided by. A larger floor area gets a proportionally larger internal-gains credit, but it's also spreading (and dividing) the same transmission and infiltration losses across more area -- which direction wins depends on how Thermal Envelope Area and Average U-Value compare to the floor area you entered.

Because this calculator floors Net Heating Demand at zero rather than letting solar and internal gains overshoot total heat loss into negative territory. Passive Solar Gain (%) is applied as a straight percentage offset against total heat loss (before internal gains), so raising it keeps lowering Heating Demand (kWh/m²/yr) right up until the combined gains equal or exceed the loss -- at that point the calculator reports 0, not a negative heating demand, which wouldn't represent anything physically meaningful.

No -- it's strictly all-or-nothing. Heating Demand, Cooling Demand, Primary Energy, and Airtightness are each checked against their own Passivhaus limit (≤15, ≤15, ≤60 kWh/m²/yr, and ≤0.6 ACH50 respectively) independently, and Passivhaus Certifiable only reads 1 when every one of the four passes. Missing just one criterion -- even by a small margin -- reports the same 0 as missing all four; the individual output fields are where you'd look to see which specific criterion is the problem. These four limits come directly from the Passive House Institute's published Building Criteria for Passivhaus Classic certification, not from this calculator.