This calculator was built by Serge (MSc) using government standards (AHAM, ASHRAE, EPA, ISO). My academic background covers Plant Biochemistry, Environmental Biology, Biogeochemistry, and Ecotoxicology. This is an estimation tool for educational purposes, not professional advice, medical diagnosis, or assessment.

Home Ventilation ACH Calculator

Home Ventilation (ACH) Calculator

How many times per hour does fresh outside air replace the stale air inside your home? That number is ACH: Air Changes Per Hour.

I studied how air and moisture move between outdoor and indoor spaces. What I learned is that ACH matters. It tells you whether your home is exchanging air fast enough to remove moisture, odours, and pollutants.

This calculator estimates your home’s ACH based on its size and ventilation type. Not a precise measurement, but a real picture of how often your air is being refreshed.

Calculate Your ACH

Home Volume (cubic metres) Calculate: length (m) × width (m) × ceiling height (m). If multi-storey, calculate each floor and add them. Ventilation Type Choose the option that matches your situation. Home Age and Condition This affects how much air leaks naturally through gaps.

How This Works

ACH measures how many times per hour the volume of air in your home is completely replaced with fresh outside air.

An ACH of 1 means the entire volume of your home’s air is replaced once per hour. An ACH of 5 means it is replaced five times per hour.

The calculation depends on your home’s volume and your ventilation rate. Natural ventilation comes from air leaking through cracks and gaps. Mechanical ventilation (fans, MVHR systems) delivers air on purpose, raising ACH.

Understanding Your Result

Below 0.5 ACH: Very little air exchange. Moisture and odours can accumulate.

0.5 to 1 ACH: Minimal air exchange. You rely on opening windows to improve this.

1 to 2 ACH: Moderate air exchange. Reasonable for comfort and moisture control.

Above 2 ACH: Good air exchange. Moisture is removed regularly. Condensation risk drops significantly.

Important Limitations

This is an estimation, not a measurement. Real ACH depends on weather, occupancy, window opening, and fan operation.

✗ Does not account for wind or weather
✗ Does not measure actual ACH (only professionals with equipment can)
✗ Does not account for room-by-room variation
✗ Does not replace professional blower door testing

Scientific Basis

Based on:

ASHRAE 62.1 Ventilation Standard. ASHRAE recommends at least 0.35 ACH for residential buildings, but higher rates are better for moisture control.
Learn about ASHRAE →

EPA Ventilation Guidelines. The US Environmental Protection Agency provides guidance on home ventilation for moisture and pollutant removal.
Read EPA guidance →