---
title: "Functional requirements of ventilation"
subject: "Building Technology"
chapter: 1
key: "semester_6/building_technology:vent-requirements"
source: https://www.bctengineer.com/q/semester_6/building_technology/vent-requirements
site: BCT Engineering
---

# Functional requirements of ventilation

Building Technology · Chapter 1: Functional Requirements of Buildings

- Asked in: 2078 Poush, 4 marks; 2075 Bhadra; 2069 Bhadra, 4 marks (asked 3 times)
- Video: [Ventilation and functional requirements of ventilation system](https://www.youtube.com/watch?v=D6wjjzhJX3g) — WIT Solapur - Professional Learning Community
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/vent-requirements
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-1

## Question

Describe briefly the functional requirements of ventilation.

## Short answer

Ventilation supplies fresh air and removes stale air. It must provide oxygen, remove CO2, odour, smoke, humidity and excess heat, give 0.1 to 0.5 m/s air movement without draught, dilute airborne infection, and provide adequate air changes (6–8 ACH living room, 15–20 kitchen).

## Answer

**Ventilation** is the supply of fresh outdoor air to a space and the removal of stale air, without causing discomfort. Its functional requirements are:

1. **Supply of oxygen**: Each occupant uses only about 0.02 to 0.03 m³/h of oxygen at rest; fresh air keeps the oxygen level near 21 %.
2. **Removal of carbon dioxide**: CO₂ from breathing (about 0.02 m³/h per person) must be kept below about 0.1 %.
3. **Control of odour, smoke and gases**: Kitchen, toilet and body smells, fumes and dust are carried out.
4. **Control of humidity**: Removes vapour from cooking, bathing and breathing, and so prevents condensation, dampness and mould.
5. **Heat removal**: Removes excess heat from bodies, appliances and the sun, and air movement gives a cooling effect on the body.
6. **Thermal comfort**: Gives air movement of 0.1 to 0.5 m/s without draught.
7. **Prevention of airborne infection**: Dilutes the load of bacteria and viruses.
8. **Adequate air change**: The rate is fixed by use, such as 6 to 8 air changes per hour (ACH) for a living room and 15 to 20 ACH for a kitchen. Standards are given in the National Building Code.

Ventilation openings should be placed to give cross flow, with inlets low on the windward side and outlets high on the leeward side.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. CO2 from breathing should be kept below about
   A. 1 %
   B. 0.1 %
   C. 5 %
   D. 21 %
   Answer: B. The answer says CO2 must be kept below about 0.1 %, while oxygen is kept near 21 %. (Key point: CO2 limit)

2. Why does ventilation help control humidity?
   A. It removes vapour, which stops condensation and mould
   B. It adds vapour to dry the air
   C. It lowers the oxygen
   D. It increases the dew point
   Answer: A. Removing vapour from cooking, bathing and breathing prevents condensation, dampness and mould. (Key point: Humidity control)

3. Which pair of ACH values matches the answer?
   A. Living room 15 to 20, kitchen 6 to 8
   B. Both 1 to 2
   C. Living room 6 to 8, kitchen 15 to 20
   D. Living room 30, kitchen 3
   Answer: C. A kitchen needs far more air changes than a living room because of fumes and vapour. (Key point: Air change rate)

4. For good cross flow the inlets should be
   A. High and on the leeward side
   B. High and on the windward side
   C. On the same wall as outlets
   D. Low and on the windward side
   Answer: D. Inlets low on the windward side and outlets high on the leeward side give cross flow. (Key point: Opening placement)

## Related in Building Technology

- [Roof types, functional requirements, timber roofs](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aroof-types-requirements-timber) — Building Technology, chapter 4, asked 5×
- [Mechanical ventilation and building code](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Avent-mech-conditions-nbc) — Building Technology, chapter 1

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