Sizing coverage for a whole 5-room HDB flat

Key takeaways

• A 5-room flat rarely needs five separate units; sizing room by room usually points to two or three.
• The living room, each bedroom and the kitchen area should each be measured and calculated on their own.
• Adjoining rooms with a shared open doorway can sometimes share one unit's coverage if the combined area still fits.
• Required CADR equals floor area multiplied by ceiling height multiplied by a target ACH of roughly 3 to 4 for a home.
• Confirm the final plan with the calculator rather than assuming a whole-flat figure without checking individual rooms.

Why Buying One Unit Per Room Isn't Always Necessary

A 5-room HDB flat typically has a living and dining area, three bedrooms and a kitchen, and it is easy to assume each of those five spaces needs its own purifier. In practice, some rooms in a typical layout see far less occupied time than others, a store room or a rarely used bedroom for instance, and do not need the same priority as a main bedroom or the living area.

Working through the flat room by room, rather than assuming a flat figure per room, usually points to fewer units than five, placed in the rooms that are actually used the most, with coverage extended later if the household finds it necessary once the first units have been running for a while and everyone has a feel for whether more coverage is actually worth adding.

Sizing the Living Room, Bedrooms and Kitchen Area Separately

Each room type in a 5-room flat has a different footprint and usage pattern, so each deserves its own pass through the sizing formula. The living and dining area is usually the largest continuous space and often benefits from a higher-coverage unit such as the Classic 400S. Bedrooms are generally smaller and suit a compact unit like the Reno 500S, particularly where quiet overnight operation matters.

The kitchen area is worth treating separately too, since cooking smoke and odours add a different kind of airborne load than a bedroom or living room sees, even though HDB kitchens are often smaller and may already have exhaust ventilation doing some of that work.

When Adjoining Rooms Can Share One Unit's Coverage

Some 5-room layouts have a living and dining area that opens directly onto a household shelter or a small study nook without a full dividing wall. In these cases, the adjoining space can often be included in the living area's combined footprint rather than sized and equipped separately, provided the total area still falls within one unit's coverage.

Bedrooms with closed doors, on the other hand, should almost always be sized and covered on their own, since a closed door limits air exchange between rooms in the same way it does in any home. Do not assume two bedrooms can share one unit simply because they sit next to each other, even if the household members using them are happy to leave both doors ajar during the day.

Applying the CADR Formula Across the Whole Flat

The formula stays the same for every room in the flat: required clean-air delivery rate in cubic metres per hour equals floor area in square metres multiplied by ceiling height in metres multiplied by a target air changes per hour, generally 3 to 4 for a home space. HDB ceiling heights are fairly consistent across most flats, which makes this calculation more predictable than it would be in a landed home or a condo with varied ceiling heights.

Work through the living area, each bedroom you plan to prioritise, and the kitchen using this same formula, then compare the results against AIRE's coverage ranges: Fillo Plus up to 30 square metres, Classic 400S for 31 to 54 square metres, and Pro 800S for larger 56 to 96 square metre spaces uncommon in most flats but occasionally relevant for a combined living, dining and kitchen footprint in a larger executive flat.

Confirming the Plan With the Calculator

Once you have rough figures for each room, run them through the size calculator to confirm the exact fit against AIRE's product range rather than eyeballing which model looks about right. This is a quick step that avoids the two most common mistakes: buying a unit too small for an open living and dining area, or buying an oversized, noisier unit for a compact bedroom.

If the flat has an unusual layout, such as a converted household shelter used as a study, a free room-by-room Air Report can settle any remaining doubt about how many units the whole flat actually needs.

Next step

Work through your flat room by room with the air purifier size calculator, or request a free room-by-room Air Report if your layout is more unusual.

Frequently asked

Does every room in a 5-room flat need its own unit?

Not necessarily. Sizing each room separately usually shows that some spaces, such as a rarely used bedroom or store room, do not need the same priority as the living area or a main bedroom, so most flats end up with two or three units rather than five.

Can adjoining rooms share one unit's coverage?

Open adjoining spaces without a full dividing wall, such as a living area opening onto a small nook, can sometimes share coverage if the combined area still fits one unit. Bedrooms with closed doors should generally be sized and covered separately.

How is the whole flat's requirement calculated?

Each room is measured for floor area and ceiling height, then run through the same formula: floor area multiplied by ceiling height multiplied by a target air changes per hour of roughly 3 to 4 for a home, giving a required clean-air delivery rate for that specific room.

Related reading

• The Best Air Purifier in Singapore: An Honest Market Guide