I'm renovating a space where there will be a partition of 2 rooms (3m height, dimensions are approximates, high humidity location, 23-34degC avg outside temp)

Room 1: 5x7m Room 2: 2x7m

Room 1 will be most frequently used while Room 2 is planned to be some sort of a baby room (maybe nursery, tbc). I plan to install AC system in Room 1 (wall mounted inverter - though I actually wanted a floor type).

To cut cost, I don't intend to install another AC in Room 2, instead I'm thinking of installing 2 exhaust fans on the wall between Room 1 and 2. These fans will only operate when Room 2 is used.

The setup would be:-

Exh.fan 1: from Room 1 to Room 2 (adjacent to AC)

Exh.fan 2: from Room 2 to Room 1 (on the other side of the room)


Q1.Is it advisable to do so (will it affect my AC? Will Room 2 benefit from the AC thru the exhaust fans?)

Q2.How much power does the AC require with the area given?

Q3.What if I went for the floor type AC?

Q4.Any suggestions for alternative setup?

  • @ C_9141 Did you execute your plan of fixing exhaust fan? Can you please share the outcome of this? Was it useful?
    – Nobleking
    Apr 28, 2019 at 14:44

1 Answer 1


First, "recommended"? Coming from a contractor and engineer, it sounds like a good solution, and it will work.

You don't need two fans. One with a transfer grille will do.

Power-wise, I have to this in IP so bear with me. Room 1 is 5 x 7 x 3.28 x 3.28 = 376 ft^2. Rule of thumb- and this is only an estimate - is 400 sq ft \ 3.5 kW. (1 ton refrigeration = 12000 btuh = 3.5 kW). It could be 600, but you would need to know construction type, insulation, fenestration, exposure, latitude, etc. and consult ACCA manual J. With high humidity, you want to make sure it runs long enough to dehumidify. Now add the second room which is 14 sq m = 150 sq ft. Total area is 527 sq ft. Using our rule of thumb, that would be 527 sq ft x 3.5 kW\400 sq ft = 4.6 kW of cooling. If we assume 6 air changes per hour (another rule of thumb), the volume of both spaces is 147 cu m or 5187 cu ft. X 6 air changes = 31,123 cu ft per hour which is 518 CFM. Again, rule of thumb is 400 CFM per ton, so 518 \ 400 x 3.5 is 4.5 kW.

So your exhaust fan should provide a minimum of 14 x 3 x 3.28^3 x 6 \ 60 = 148 CFM or 4.2 m^3\min.

Size the transfer grille for a maximum 500 ft\min, so about 42 sq in. A6 x 8 will be quiet. Probably quieter than the fan.

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