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Calcimator

Passive House Calculator

Evaluate whether your building meets Passivhaus (PHI) certification criteria for heating demand, cooling demand, primary energy, and airtightness.

Inputs

%

Results

Heating Demand (kWh/m²/yr)

2.6

Cooling Demand (kWh/m²/yr)2.4
Primary Energy (kWh/m²/yr)34.9
Airtightness (ACH50)0.5
Peak Heating Load (W/m²)7.5
Passivhaus Certifiable1
Internal Gains3,344.4
How to Use This Calculator
  1. Enter Floor Area and Thermal Envelope Area in sq ft.
  2. Enter Average U-Value of the entire envelope in Btu/hr·ft²·°F and Airtightness in ACH50.
  3. Enter Heating and Cooling Degree Days for your climate and Passive Solar Gain percentage.
  4. Review Specific Heating Demand in kWh/m²/yr — Passivhaus limit is ≤ 15 kWh/m²/yr.
  5. Check Peak Heating Load in W/m² and Passivhaus Certifiable status against all criteria.

How the result changes with Heating Degree Days (HDD65)

Heating Degree Days (HDD65)Heating Demand (kWh/m²/yr)
1,5000
5,2500
9,75016.6
13,50030.7

What each input means

Floor Area (sq ft)
Treated floor area (TFA) of the building in square feet.
Thermal Envelope Area (sq ft)
Total area of the thermal envelope (walls + roof + floor + windows).
Average U-Value (Btu/hr·ft²·°F)
Area-weighted average U-value of the entire thermal envelope. R-35 ≈ 0.028, R-50 ≈ 0.020.
Airtightness (ACH50)
Air changes per hour at 50 Pascals pressure. Passivhaus requires ≤ 0.6.
Heating Degree Days (HDD65)
Annual heating degree days (base 65°F) for your climate. Denver ~6000, Minneapolis ~8000.
Cooling Degree Days (CDD65)
Annual cooling degree days (base 65°F). Phoenix ~4000, Seattle ~200.
Passive Solar Gain (%)
Percentage of heating load offset by passive solar gains through south-facing glazing.

What each result means

Heating Demand (kWh/m²/yr)
Specific annual heating demand. Passivhaus limit: ≤ 15 kWh/m²/yr.
Cooling Demand (kWh/m²/yr)
Specific annual cooling demand. Passivhaus limit: ≤ 15 kWh/m²/yr.
Primary Energy (kWh/m²/yr)
Total specific primary energy including DHW, lighting, appliances. Passivhaus limit: ≤ 60 kWh/m²/yr.
Airtightness (ACH50)
Blower door test result. Passivhaus limit: ≤ 0.6 ACH50.
Peak Heating Load (W/m²)
Peak heating power demand. Passivhaus limit: 10 W/m².
Passivhaus Certifiable
1 = meets all criteria, 0 = does not meet one or more criteria.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Floor Area (sq ft) = 1800, Thermal Envelope Area (sq ft) = 4000, Average U-Value (Btu/hr·ft²·°F) = 0.028, Airtightness (ACH50) = 0.5 = 7 input(s) provided
  2. Calculate Heating Demand
    2.6 = 2.6
  3. Calculate Cooling Demand
    2.4 = 2.4
  4. Calculate Primary Energy
    Primary Energy = totalPrimaryEnergy / floorAreaM2
    34.9 = 34.9

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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