Air Changes Per Hour (ACH) Calculator
Find the ventilation airflow a room needs. Set the room area and height, pick the type (which sets a target air-changes-per-hour), and get the airflow in CFM and m³/hr — to size an exhaust fan or fresh-air system.
Higher for wet/smoky/crowded rooms (kitchen, bathroom); lower for living spaces.
= 340 m³/hr · room volume 800 cu ft at 15 air changes/hr.
Pick an exhaust fan or fresh-air unit rated at or above this airflow (in CFM or m³/hr) — an under-rated fan barely ventilates. For a whole building, an MEP engineer designs the system.
A planning estimate. The target ACH values are indicative good-practice figures; the exact rate depends on occupancy, use and the applicable code (NBC / ASHRAE / ISHRAE). Fresh-air needs can also be driven by people (a per-person rate), not just volume. Use this to size simple exhaust; a professional designs engineered ventilation.
Related Guides — Deep-dive reading
Cross Ventilation in Indian Homes
Science, Physics, and Planning — A Professional Guide for Architects
Room PlanningHome & Building Ventilation: Why Fresh Air Matters and How to Get It
The most under-rated half of HVAC — how ventilation brings in fresh air and removes stale air, moisture and pollutants, the difference between natural and mechanical ventilation, what 'air changes per hour' and fresh-air rates mean, and why sealed, air-conditioned homes especially need it.
HVAC & CoolingThe Complete Guide to Residential HVAC in India
Everything a homeowner needs to plan and choose home cooling, ventilation and comfort — how to select the right system for your home, size it correctly, get clean air and low bills, and where smart HVAC genuinely helps, all grounded in India's climate and market.
HVAC & CoolingRelated Tools — You may also find these useful
AC Capacity Calculator
Find the right air-conditioner tonnage for a room — from area, sun, floor, occupancy and climate. Right-sized, not oversized.
HVACAC Installation Cost Calculator
An indicative equipment + installation budget for your home's air conditioning — by AC type, tonnage and number of units, with a realistic range.
HVACAC Running Cost Calculator
What your AC costs to run each year — from tonnage, BEE star rating, hours and tariff — plus how much a higher star rating saves.
HVAC