01What this calculator checks
The Passive House (Passivhaus) standard is a performance-based way to design ultra-low-energy buildings. Rather than prescribing specific materials, it sets a small number of hard limits on how the finished building performs. This calculator takes the three headline figures a designer already has — annual space heating demand, primary energy renewable (PER) demand and airtightness (n50) — and checks each one against the Passive House Institute (PHI) limits, then gives you a pass/fail per criterion and an overall verdict.
It is a fast sanity check, not a certification tool. Formal Passivhaus verification is done with a full energy-balance model (PHPP) and a measured blower-door test. But knowing early whether your design is inside the limits — and by how much — tells you where to focus. The same efficiency-first, fabric-first thinking underpins the U.S. Department of Energy building-technologies programme and the ENERGY STAR certified homes programme. For related tools, see our embodied carbon calculator and energy efficiency upgrade calculator.
02The Passivhaus criteria
These are the core criteria for the Classic Passive House class. Meeting all three (verified in PHPP) is what earns certification. The heating-demand limit can alternatively be met on a peak-load basis (heating load ≤ 10 W/m²), which suits buildings that cannot economically reach 15 kWh/m²/yr on the annual demand route.
03How to close the gap
If a criterion fails, the fix depends on which one. Passivhaus is a fabric-first standard, so most of the work is in the envelope:
- Space heating demand too high. Add continuous insulation to walls, roof and floor, upgrade to triple glazing, improve solar orientation and shading, and eliminate thermal bridges with careful junction detailing.
- PER demand too high. Switch to an efficient heat source (typically an air-source heat pump), add mechanical ventilation with heat recovery (MVHR), reduce hot-water losses and add on-site renewables such as solar PV.
- Airtightness worse than 0.6. Design a single continuous air barrier, tape and seal all junctions and penetrations, and run an early blower-door test to find and fix leaks before finishes go on — see the ENERGY STAR guidance on sealing and insulating.
- Everything marginal. Compact form (a lower surface-area-to-volume ratio) reduces heat loss for free, so revisit massing before adding more insulation.
- Enter the treated floor area (TFA) in square metres — the conditioned living space across all storeys.
- Enter the annual space heating demand in kWh/m²/yr (from PHPP or your energy model).
- Enter the primary energy renewable (PER) demand in kWh/m²/yr.
- Enter the airtightness result as n50 in air changes per hour at 50 Pa.
- Press Check to see a PASS/FAIL on each criterion, the headroom against each limit and the overall verdict.
Working on the wider build? Our conduit fill calculator helps size electrical containment during first fix.
This is a pre-check for design guidance and learning, not an official certification. It compares three figures you supply against the Classic limits; it does not:
- Model the building — you must obtain the heating and PER figures from PHPP or an equivalent energy balance.
- Cover the Plus and Premium classes (which have lower PER limits and renewable-generation requirements) or the alternative heating-load route.
- Verify airtightness — that requires a measured blower-door (pressurisation) test on site.
- Assess comfort, overheating, moisture or non-energy criteria that full certification also considers.
01The pass/fail logic
Passivhaus certification is a set of threshold tests: each performance figure must be at or below its limit. The design passes overall only when every criterion passes. The headroom shows how far inside (or outside) each limit you are.
Where:
- space heating demand= annual heat energy per m² of treated floor area (kWh/m²/yr).
- PER demand= renewable primary energy for all uses, per m² per year (kWh/m²/yr).
- n50= air changes per hour at 50 Pa pressure difference (ACH50).
- treated floor area= the conditioned living space used to normalise the demands (m²).
02Worked example
A 150 m² dwelling is modelled in PHPP at 12 kWh/m²/yr space heating demand, 48 kWh/m²/yr PER and an airtightness of 0.4 ACH50. Does it pass?
All three criteria pass, so the design earns a provisional Passivhaus ✓ — subject to a full PHPP model and a measured blower-door test. The 1,800 kWh annual heating figure makes the 12 kWh/m²/yr intensity tangible: that is a fraction of a conventional home. Had the airtightness come back at 0.8 ACH50, that single criterion would fail and the verdict would drop to “Not yet certified” until the envelope was sealed and re-tested. For the carbon side of the same project, try our embodied carbon calculator.