Passive House Savings Calculator (heating cost now vs Passive House / EnerPHit)

Understanding the Passive House savings calculator — concept and principle

This calculator estimates how much heating energy and money a home would save by meeting the Passive House, EnerPHit or PHI Low Energy Building heating standard, compared with its current heating demand. Homeowners and designers use it to weigh a deep-retrofit or new-build decision.

From 120 to 15 kWh/m²: with the default inputs the result is $1,680 a year (saved · demand cut 87.5%).

How it is calculated

Heat needed = heating demand (kWh/m² per year) × heated floor area.
Energy bought = heat ÷ system efficiency.
Yearly saving = (energy bought now − energy bought at the target) × price per kWh.
Targets: Passive House 15, EnerPHit (cool-temperate, demand method) 25, PHI Low Energy Building 30 kWh/m²·yr.
Simple payback = upgrade cost ÷ yearly saving; 1 kBTU/ft² = 3.15459 kWh/m².

The principle

The Passive House Institute sets a limit on how much space-heating energy a certified building may need per square metre of treated floor area each year. Very good insulation, airtightness, high-performance windows and heat-recovery ventilation bring the demand down to that level. Heat demand is what the building needs; the energy you buy is that divided by the heating system's efficiency (above 100% for a heat pump). The difference between the current and target demand, times area and price, gives the saving.

Worked example

Default inputs: 120 m², current demand 120 kWh/m²·yr, Passive House target, $0.12/kWh, efficiency 90%, no upgrade cost.

Heat now = 120 × 120 = 14,400 kWh/yr; at target = 15 × 120 = 1,800 kWh/yr.
Energy bought now = 14,400 ÷ 0.9 = 16,000; at target = 2,000 kWh/yr.
Cost now = 16,000 × 0.12 = $1,920.00; at target $240.00.
Yearly saving = $1,680.00; demand cut = 1 − 15 ÷ 120 = 87.5%.
Payback not shown (—) because no cost was entered; target = 15 ÷ 3.155 = 4.75 kBTU/ft²·yr.

Each point is the calculator re-run with only “Heating system efficiency (%)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Heating system efficiency (%)	Yearly saving
22.5	$6,720.00
45	$3,360.00
67.5	$2,240.00
90	$1,680.00
112	$1,344.00
135	$1,120.00
180	$840.00

How to read the result

Enter the real upgrade cost to see the simple payback. It ignores interest, rising energy prices and maintenance, and the comfort and health benefits that many owners value. The current demand is best taken from an energy certificate or from your bills divided by floor area and efficiency.

Common mistakes

Using total energy (including hot water and appliances) as heating demand.
Using gross floor area instead of treated floor area.
Assuming the target will be met exactly in use.
Forgetting that a heat pump's efficiency is a COP above 100%.

Keep in mind: The targets are design values for certification; actual use depends on weather and occupants. This is an estimate, not financial advice. Real projects need a qualified designer and modelling.

Frequently asked questions

What is the Passive House heating limit?

15 kWh per m² of treated floor area per year.

How much can a Passive House save?

In the example, about 87.5% of heating demand, or $1,680 a year.

What is EnerPHit?

The Passive House Institute's standard for retrofits, with a higher heating limit depending on climate.

Sources: Passive House Institute, "Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard", version 10b (2022)

Checked 9 Nov 2026. Passive House Institute, “Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard”, version 10b (IP edition, 2022): Table 1 (Passive House heating demand 4.75 kBTU/ft²·yr), Table 3 (EnerPHit cool-temperate 7.92 kBTU/ft²·yr) and Table 5 (PHI Low Energy Building 9.51 kBTU/ft²·yr); 1 kBTU/ft² = 3.15459 kWh/m².

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