Start with the room, not the fan
Ventilation sizing is not about fitting the biggest extractor you can find. It starts with the room size, the number of people inside, the type of heat or fumes being made, and whether the space is sealed by brick, roller doors or roofing that traps heat. In New Park, Roodepan and Galeshewe, we often see rooms where a single unit was fitted for a space that should have had three or four air changes already.
A simple first check is the room volume. Measure length, width and ceiling height in metres, then multiply them to get cubic metres. A 12 m by 8 m workshop with a 3.2 m ceiling is 307.2 cubic metres. Once you know that number, you can start working out how many air changes per hour are needed. A light storage room may only need basic movement, while a welding bay, kitchen or chemical area needs much more.
Also look at doors and openings. A room with shutters left open half the day behaves differently from a sealed plant room. In hot months, Kimberley afternoons can push indoor temperatures up fast, so heat build up is often the real problem, not only stale air.
Use the activity level to set the airflow target
The type of work decides how much air the room needs. A small office annex, motor workshop, takeaway kitchen and battery charging room all need different ventilation rates. If the air carries grease, dust, fumes or humidity, the system must remove that load at the source where possible.
As a rule of thumb, start with air changes per hour and then adjust for the task. A low load room may work with 4 to 6 air changes per hour. General workshops often need 6 to 10. Kitchens, wash areas and enclosed processing rooms can need 10 or more depending on the equipment and cooking method. For local sites in Upington or Kuruman, where rooms can heat up quickly and stay warm after sunset, you may need to add extra capacity for comfort and safe working conditions.
If you are unsure, write down what happens in the room during a normal shift. How many people are inside, what machines run, whether doors stay shut and if fumes collect near the ceiling. That gives a better sizing result than guessing from floor area alone.
A practical sizing checklist for workshops
Workshops usually need a mix of extraction and fresh air make-up. If you only pull air out, the room can become hard to work in and dust may enter through every gap. If you only push air in, the hot air and fumes stay trapped. A balanced approach works best in most Northern Cape sites.
- Measure the room in metres and calculate cubic metres.
- Count the people normally inside during peak use.
- List the machines that give off heat, dust or fumes.
- Check whether roller doors, louvres or windows stay open.
- Note any ceiling pockets, mezzanines or partitioned bays.
- Allow for summer heat and dust from nearby yards.
For fabrication bays, spray areas and mechanical rooms, place extraction close to the source. Hot air rises, so high wall or roof extract points are often better than low level units alone. If the workshop is in an older building in New Park or an exposed site near the edge of town, also check for roof leaks and gaps that may affect airflow paths.
Kitchen and food area ventilation needs
Kitchens are different because the air carries grease vapour, steam and odour as well as heat. The system must clear the cooking zone without spreading smoke through the room. For smaller food prep areas, a well-sized canopy over the cooking line can do most of the work, but it still needs enough make-up air to stop doors slamming and smoke backflow.
When sizing a kitchen system, look at the heat from hobs, ovens and fryers, plus how long they run each day. A canteen serving lunch to staff in Galeshewe has very different demand from a school kitchen in a cooler part of town. If there is dishwashing or steaming, add capacity for moisture too, because damp air can lead to condensation on ceilings and walls.
Keep filters easy to reach. In practice, if a filter is awkward to clean, it often gets ignored and airflow drops fast. That is when smells linger and grease builds up in places it should not be. Good access matters as much as motor size.
Enclosed rooms, plant spaces and problem zones
Some rooms need ventilation even when nobody thinks of them as work areas. Generator rooms, inverter rooms, pump rooms, battery spaces and small storerooms can become hot, stale or unsafe if air is not moving. These spaces often sit behind locked doors, so they trap heat from equipment and can overheat during load shedding or summer power interruptions.
For enclosed rooms, check both heat rejection and fresh air. A small room with pumps or power equipment may need continuous low level ventilation rather than short bursts. If the space contains chemicals, solvents or strong odours, use separate extraction and avoid mixing it with general building air.
Dust is another issue in the Northern Cape. Fine dust can block fans, filters and louvres quickly, especially on sites near gravel yards or busy roads. Where possible, fit access panels and plan for regular cleaning. A good system that is never serviced becomes a weak system very quickly, often with no warning.
How to size in steps without overbuying
You do not need to overspend to get the sizing right. A step by step approach helps you avoid buying a fan that is too small or one that is far larger than the space needs.
- Calculate the room volume in cubic metres.
- Choose the target air changes per hour for the activity.
- Multiply volume by air changes to get cubic metres per hour.
- Check if extraction, supply or balanced ventilation is needed.
- Allow for duct bends, grills and filters, because they reduce flow.
- Confirm power supply, mounting space and service access.
For example, a 300 cubic metre room needing 8 air changes per hour requires about 2,400 cubic metres per hour before losses are considered. If the duct run is long or full of bends, the real fan selection may need to be higher. This is where many installations fall short. The unit may be rated correctly on paper, but the final air movement at the room is too low.
Before installation, check these final points
Once the size is worked out, a final site check saves trouble later. Look at mounting height, roof structure, noise levels, access for cleaning and where the discharged air will go. You do not want hot exhaust blowing back into the same room or into a neighbour’s boundary where it may cause complaints.
It is also worth checking local building rules, fire separation and any municipal requirements for commercial kitchens, workshops or altered rooms. In some cases the ventilation layout must support other safety systems, not fight them. If the room is near sensitive equipment or has staff working long hours, ask whether extra cooling or air movement is needed during peak summer.
When in doubt, have the room measured and the duty explained properly before equipment is ordered. That is the cleanest way to avoid repeat call outs, poor comfort and wasted power.
