How this calculator works
A passive house is designed so that almost no active heating is needed. Thick insulation and a continuous airtight layer hold heat in, triple-glazed windows keep it from escaping, and a mechanical ventilation system with heat recovery brings in fresh air while capturing most of the warmth from the outgoing air. The standard allows a space heating demand of 15 kilowatt-hours per square metre a year, about a tenth of a typical older Canadian house, or a peak heating load of 10 watts per square metre. The calculator multiplies the floor area by the current and target demand to get the annual energy, converts the difference to money at your energy price, and to carbon at 0.19 kg CO2e per kilowatt-hour for natural gas. The extra construction cost is the premium over a conventional build, not the whole cost, and the payback ignores energy price changes, maintenance and the health and comfort benefits, which are real but not money in the table.
Formula
heating energy (kWh/year) = floor area x demand in kWh per m2 per year. energy saved = (current demand - passive demand) x area. cost saved = energy saved x price per kWh. carbon saved = energy saved x 0.19 kg CO2e per kWh. extra cost = area x extra cost per m2. simple payback = extra cost / annual cost saved.
Worked example
A 150 m2 house using 120 kWh/m2 a year consumes 18,000 kWh for heating. A passive house at 15 kWh/m2 uses 2,250 kWh, saving 15,750 kWh. At $0.05 per kWh the saving is $787.50 a year, and at 0.19 kg CO2e per kWh it avoids 2,992.5 kg CO2e. An extra cost of $500 per square metre is $75,000, which repays in 75,000 / 787.50 = 95 years at that low gas price. Rooftop solar or a heat pump would change the economics, and the comfort and air quality benefits are not priced here.
Advertisement
Frequently asked questions
Why is the payback so long at my gas price?
Natural gas is cheap, so a deep retrofit that removes a small gas bill takes decades to repay on energy alone. The economics improve where heating is electric and expensive, in a colder climate, or when the passive measures are built in from the start rather than retrofitted.
Does the standard apply to any climate?
Yes, but the construction details change. The 15 kWh/m2 limit is the same, which means a house in Winnipeg needs more insulation and better windows than one in Victoria. Certified designers adjust the assembly to the local climate.
What is the peak load limit?
The standard also caps the heating load at 10 watts per square metre, which keeps the house from needing a large furnace even on the coldest day. A small heat pump or a heater in the ventilation air can cover it.
Is the extra cost really $500 per square metre?
It varies widely. Studies of passive house construction report premiums from a few percent to 10 percent of build cost, and a retrofit costs much more than new construction. The default is a middle figure for a new build; enter your own quote for a real comparison.
Sources
- Passive House Institute: the passive house standard and its 15 kWh per square metre heating demand limit
- Natural Resources Canada: passive house and net zero home programs
- Environment and Climate Change Canada: emission factors and reference values for greenhouse gas quantification (national inventory edition, updated annually)