Article — Passive House
Passive House calculator: heating demand and compliance
A passive house is a building that uses 15 kWh per square metre of floor area per year or less for space heating, with a peak heating load at or below 10 W/m². That is roughly 80 percent less heating energy than a typical new home. This calculator estimates both figures from your envelope U-values, window performance, climate and heat-recovery efficiency, then tells you whether the design clears the standard.
The Passivhaus standard was developed in Germany in the late 1980s by physicist Wolfgang Feist. It is not a brand of house or a list of products. It is a performance target backed by physics: build an envelope good enough, and the building stays comfortable with almost no active heating. More than 25,000 certified passive house buildings now operate across Europe.
What is a passive house?
A passive house keeps a stable, comfortable indoor climate using mostly the heat that is already inside it: sunlight through windows, body heat from occupants, and waste heat from appliances. Active heating handles only the small shortfall on the coldest days.
Five design principles make this possible. Continuous thick insulation wraps the whole building. Triple-glazed windows with insulated frames cut conductive loss while still letting solar heat in. Mechanical ventilation with heat recovery supplies fresh air without throwing warmth away. Thermal-bridge-free detailing keeps the insulation layer unbroken at every junction. And an airtight envelope, verified by a blower-door test, stops uncontrolled drafts.
A certified passive house in central Europe can be kept warm through winter by the equivalent of a single hair dryer running per room. The 10 W/m² peak load limit means a 150 m² home needs only about 1.5 kW of heating power.
The passive house criteria
The Passive House Institute (PHI) sets three hard limits that a building must meet to be certified. Annual heating demand must not exceed 15 kWh/(m²·yr). Peak heating load must stay at or below 10 W/m². Airtightness must reach 0.6 air changes per hour or better at 50 pascals of pressure, measured by a blower-door test.
Alongside these, the design must hit component-level targets. Window U-values should be 0.80 W/(m²·K) or lower, wall U-values around 0.15, and roof U-values around 0.12. For comparison, a code-minimum wall in many regions sits near 0.30 to 0.50, meaning a passive house wall loses two to three times less heat per square metre.
- Heating demand ≤ 15 kWh/(m²·yr)
- Peak load ≤ 10 W/m²
- Airtightness ≤ 0.6 ACH at 50 Pa
- HRV recovery ≥ 75 percent
- Windows ≤ 0.80 W/(m²·K)
- Walls ≈ 0.15 W/(m²·K)
- Roof ≈ 0.12 W/(m²·K)
- Thermal bridges Ψ ≤ 0.01 W/(m·K)
How the passive house calculator works
The passive house calculator builds a steady-state heat balance for the heating season. It adds up the energy lost, subtracts the energy gained for free, and divides by floor area to get a demand figure in kWh/(m²·yr).
Transmission loss is the heat conducted through walls, roof, floor and windows. It is the sum of each element's U-value times its area, multiplied by the indoor-outdoor temperature difference and the number of heating hours. Ventilation loss is the heat carried out by stale air; the calculator applies your heat-recovery efficiency so only the unrecovered share counts. Solar gains through windows and internal gains from people and equipment are then subtracted.
losses = transmission + ventilation demand = (losses − gains) / areapeak load = UA × ΔT / area target: demand ≤ 15, peak ≤ 10The result is a planning-grade estimate. It captures the terms that dominate a real heat balance, but certification still requires the full Passive House Planning Package (PHPP), which models monthly weather, shading geometry and every thermal bridge.
If your result fails on heating demand, improving window U-value usually moves the number fastest, because windows combine a high U-value with a large temperature swing. If it fails on peak load, focus on airtightness and reducing the worst thermal bridges.
Heat recovery in a passive house
Mechanical ventilation with heat recovery is the component that makes the passive house maths work. Once an envelope is heavily insulated and airtight, ventilation becomes one of the largest remaining losses. A heat-recovery ventilator (HRV) passes outgoing warm air and incoming cold air through a counterflow exchanger, transferring 75 to 85 percent of the heat without mixing the two streams.
An HRV moves heat only. An ERV, or energy recovery ventilator, also transfers moisture, which matters in hot humid climates where you want to keep incoming air dry, and in very cold dry climates where you want to retain indoor humidity. PHI-certified units must recover at least 75 percent of the heat to count toward the standard.
Passive house by climate zone
The passive house concept adapts to local climate, though the way the targets apply changes. In cold and temperate climates the 15 kWh/(m²·yr) limit applies to space heating, and an HRV is essentially mandatory. Cities like Berlin, Warsaw, Toronto and Chicago fall here, with insulation often 20 to 30 cm thick.
In hot climates the limit applies to combined heating and cooling, and an ERV handles moisture. In hot humid regions like Miami or Houston the North American Phius CORE standard is generally used instead of the fixed PHI limit, because it sets climate-adjusted targets rather than one global number.
A passive house that is excellent at keeping heat in can also trap unwanted summer heat. Designs that pass the heating check can still overheat without external shading, careful window orientation and a free-cooling or night-purge ventilation mode. Always check the cooling and overheating frequency, not just the heating demand.
Passive house costs and payback
Building to the passive house standard typically adds 5 to 10 percent to construction cost, occasionally up to 20 percent where local trades lack experience. The extra spend goes into thicker insulation, better windows and the ventilation system.
That premium is recovered through lower energy bills. Payback periods of 3 to 7 years are common in regions with high energy prices, stretching to 5 to 10 years in mild climates with cheap energy. Because the insulation and windows last the life of the building, the savings continue for decades after the payback point.
Over a 50-year life cycle, a passive house can cut total carbon emissions by around 40 percent compared with a conventional home of the same size, even after accounting for the extra embodied carbon in insulation and glazing.
Common passive house mistakes
The most frequent design error is treating the passive house standard as an insulation problem alone. Thick walls help, but uncontrolled air leakage and thermal bridges can quietly destroy the heat balance. A single poorly detailed balcony slab or window reveal can add measurable load.
A second mistake is ignoring the blower-door test until late. Airtightness has to be designed in and verified during construction, ideally once when the airtight membrane is complete and again at handover. Retrofitting airtightness into a finished building is slow and expensive. Finally, oversizing windows on the wrong orientations boosts winter loss and summer overheating at the same time, so glazing should be planned alongside shading from the start.