Tengah BTO sizing: rooms in use, not bedroom count

A Tengah BTO handover came with an installer quote written straight off the floor plan. Four rooms meant four indoor units. Room count and cooling need are not the same thing, and the gap between them is paid for at the outdoor unit.

By Team Snowflake | Reviewed 25 Jul 2026

Case summary

Mitsubishi Electric Multi-split2 years oldHDBTengah, Singapore

Concern: The original quote assumed one indoor unit per bedroom, which fixed the outdoor unit capacity, the pipe run and the price before anyone had looked at how the rooms are used.
Found: The flat needed a three-outlet system rather than four, because two bedrooms are used for storage and a study desk and are never cooled
Key check: Walked each room and asked how it is used through the day before counting outlets on the plan
Result: Install finished inside the handover window on a smaller outdoor unit than the one first ordered. The capped fourth point stays available for whenever that room changes use. Both bedrooms in daily use hold the same cooling a four-outlet layout would have given them.

What we were told

The flat was a new BTO nearing handover, and the appointed installer had quoted a four-outlet layout covering every bedroom. Two of those rooms were already earmarked for storage boxes and a study desk. The quote had been issued before anyone set foot inside the flat, and the outdoor unit had already been ordered against it.

What we checked

Capacity gets locked at the outdoor unit, so the room walk had to happen before that number was agreed. We asked how each space is used in the morning, the afternoon and late evening. Cooling demand follows where people actually sit and sleep, not how many doors a plan shows.

Two bedrooms held storage and a desk, with nobody sleeping in either of them.
The living and dining area carried almost all of the daytime and evening occupancy.
A four-outlet outdoor unit would have driven two branches that stay switched off all year.
Ceiling trunking for a fourth run could still be laid now and left capped for later.

What we found

The quote came off the floor plan, where a bedroom is simply a bedroom. On the ground only two rooms are lived in and cooled. Sizing an outdoor unit for four indoor heads sets a larger compressor, a longer total pipe run and two extra wall penetrations than this household will ever draw on. That is not a pricing error. It is a planning step that nobody had carried out before the numbers were fixed.

What fixed it

We specified a three-outlet system covering the master bedroom, the second bedroom in daily use and the living area. The storage room kept a capped point inside the trunking, so a fourth head can be added later without reopening the false ceiling. The outdoor unit sits on the service ledge with clearance kept on the coil side. Gas quantity was calculated from the run we walked and measured on site, plus a proper vacuum before charging.

Outcome

Install finished inside the handover window on a smaller outdoor unit than the one first ordered. The capped fourth point stays available for whenever that room changes use. Both bedrooms in daily use hold the same cooling a four-outlet layout would have given them.

What this case teaches us

Size a new system by the rooms you cool, not the rooms you own

A quote drawn off a floor plan counts doors. It cannot tell which rooms get lived in and which stay shut.
Every extra indoor unit adds outdoor capacity, pipe length and a wall opening, used or not.
Ask the installer to walk the flat with you before the outdoor unit size is committed to paper.

Questions this case answers

Is a System 3 enough for a 4-room HDB flat?

Often yes. On this Tengah BTO the quote listed four outlets because the plan showed four rooms, but two of them hold storage boxes and a study desk and never get cooled. Three outlets covered the master bedroom, the second bedroom in daily use and the living area. Count the rooms you cool, not the doors you own.

Can I add another aircon point later after the false ceiling is up?

Much easier if the trunking is run before the ceiling closes. We left a capped point inside the trunking for the storage room here, so a fourth head can go in later without reopening anything. Deciding this at handover is a trunking detail. Deciding it two years on means opening the ceiling again.

Why did my BTO installer quote one aircon per bedroom?

Because the quote was written off the floor plan, where a bedroom is just a bedroom. A drawing shows doors. It cannot show which rooms get slept in and which stay shut all year. Nobody had walked the Tengah flat before the outdoor unit was ordered, and that unit was already sized for four heads.

Is there any harm in fitting an extra aircon point I never use?

You pay for capacity that never switches on. Each extra indoor head pushes the outdoor unit up a size, adds pipe length and puts another opening through a wall. Two of the four branches on this quote would have sat idle all year. The outdoor unit is where that decision gets locked in.

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