Ventilation Calculator

Area, m²

Ceiling height, m

Room type

People

Duct speed, m/s

Homes use 3–5 m/s; faster gets noisy.

Result

Required, m³/h60
Duct diameter, mm84
By area, m³/h54
By occupancy, m³/h60
By air changes, m³/h49
Air changes an hour1.23
Roomliving room

Three norms, the strictest wins

Works out the required air flow against three separate norms — by floor area, by occupants and by air changes — and sizes the duct for the flow speed you choose.

Ventilation requirements are written three different ways, and the most demanding of them is the one to satisfy. For living rooms that means three cubic metres an hour per square metre, thirty per person, and one full air change of the room volume per hour.

Kitchens and bathrooms work differently: their air is changed three to five times an hour regardless of how many people are in there. That is not about breathing, it is about moisture and smells that have to leave quickly.

What this calculator shows

The required flow, plus the result of each of the three norms separately
The air-change rate you end up with
The round duct diameter for the flow speed you choose

What to keep in mind

Duct speed in homes is taken at 3 to 5 m/s: above that the noise becomes noticeable.
The result is a round duct diameter; a rectangular duct is chosen by equivalent cross-section.

FAQs

How much air does one person need?

Thirty cubic metres an hour in a living room, forty in a study, sixty where there is physical work going on.

What is an air-change rate?

How many times an hour the whole volume of air in a room is replaced. One for a living room, three for a kitchen, five for a bathroom.

What duct diameter should I use?

One that keeps the speed between 3 and 5 m/s at the required flow. Narrower ducts are noisy; wider ones take space and cost more.

Is natural ventilation enough?

In a building with old wooden windows, usually yes — air leaks in through the gaps. Once airtight double glazing goes in, that supply disappears and trickle vents or a supply unit are needed.

Worked example

A bedroom for two

Input: 18 m², 2.7 m ceiling, living room, 2 people

Output: 60 m³/h, an 84 mm duct

Note: The occupancy norm wins here: 60 against 54 by area and 48.6 by air changes. That works out to 1.23 changes an hour, comfortably above the minimum.

Useful links

All tools in Home & Utilities

Ventilation Calculator

Result

Related tools

Dew Point Calculator

Air Conditioner Sizing Calculator

Heating Power Calculator

Useful links