What Btu Rating For A New Air-Con?

[apex2000]

I have just moved to a new four-storey building here and would like to know the correct method for calculating the BTU rating for an air-conditioner. The room is north-facing and so receives very little sunshine (only early morning). The room is approximately 5 metres long x 4 metres wide. I have heard that the way to calculate is to multiply the floor area by 700 for a room that is not affected by direct sunlight, which gives me a rating of 14,000 BTU. Having checked online (e.g.BTU Calculator), the size required appears to be only 7,800 BTU.

Can someone please give me correct advice on this matter please?

[Crossy]

I'll move this to DIY, however HomePro use a quick-and-dirty calculator, look here

According to this calculator your 20m2 room is at the top of the 12000 BTU/H range, 14000 would seem a good fit.

Unfortunately the calculator you link too does not indicate the ambient temperature used in it's calculations, it could be based upon Alaska.

[bankruatsteve]

From my experience/opinion - the less (in terms of BTU rating) is better than more for A/C and the mfg don't always have EXACTLY what you want. Tell you what - I would go with a 9+ BTU or 12 at the most. I like the Mitsubishi "slim" line which has a Thai model at 9+ BTU for about 17.5K installed.

Cheers

[trogers]

My experience with air-con units is that they cool a volume of air, not a sq. metre of air.

A 20 sqm room with 2,5m high ceiling has a different load to a 3m high ceiling.

[basjke]

^ heat and cool units are calculated in cubic meters since heat rises,cooling units are calculated in square meters because cold stays down.

[powderpuff]

A 12,000 BTU MIGHT cool it but why take a risk? Get an 18,000 BTU & let it run on low speed.

I hate wall mounted units. Yes they look nice & are designed to be quiet but they always plug up with junk & you have to have them pressure washed out..

I like old fashoined split units.

[mdechgan]

^ heat and cool units are calculated in cubic meters since heat rises,cooling units are calculated in square meters because cold stays down.

I agree, height is not part of the calculation for BTU cooling it is the area and insulation of the room that matters most.

BTU cooling ranges from 400-1,200 BTU per sqm. 400 is minimal and usually only for countries with ambient tempratures under 32 degrees outside ambient temperature, low humidity and very good insulated rooms.

I would go for 18,000 btu for a 20 sqm room in Thailand because once the outside ambient temperature gets near or past 35 degrees ambient (units are designed for 35) like it does during April or May your cooling capacity will be diminished greatly.

It is alway better to slightly have excess cooling capacity than to have a unit that is under capacity. If it is slightly over capacity once the room gets cool the thermostat and the compressor cuts and stops runiing. If it is under capacity the unit will be unable to cool the room efficiently and the compressor will be running all day and possibly all night long wasting electricity.

[lopburi3]

I have a 9,000 btu which provides full cooling for ground level 26 sq meters here in Bangkok if clean (dirty is another story). The temperature in Thailand seldom gets very high as the air is moist and that is what needs attention here and lower BTU units operating longer will do that better. I am quite sure a 12,000 btu unit would take care of OP if ceiling not cement board non vented attic type space. Also suspect inverter models may be well worth the price difference here as suspect they would work better as dehumidifier (although have not checked or seen any reports on that).

[trogers]

^ heat and cool units are calculated in cubic meters since heat rises,cooling units are calculated in square meters because cold stays down.

I agree, height is not part of the calculation for BTU cooling it is the area and insulation of the room that matters most.

BTU cooling ranges from 400-1,200 BTU per sqm. 400 is minimal and usually only for countries with ambient tempratures under 32 degrees outside ambient temperature, low humidity and very good insulated rooms.

I would go for 18,000 btu for a 20 sqm room in Thailand because once the outside ambient temperature gets near or past 35 degrees ambient (units are designed for 35) like it does during April or May your cooling capacity will be diminished greatly.

It is alway better to slightly have excess cooling capacity than to have a unit that is under capacity. If it is slightly over capacity once the room gets cool the thermostat and the compressor cuts and stops runiing. If it is under capacity the unit will be unable to cool the room efficiently and the compressor will be running all day and possibly all night long wasting electricity.

Not in cases where air return into the fan coil unit is near ceiling level.

[mdechgan]

^ heat and cool units are calculated in cubic meters since heat rises,cooling units are calculated in square meters because cold stays down.

I agree, height is not part of the calculation for BTU cooling it is the area and insulation of the room that matters most.

BTU cooling ranges from 400-1,200 BTU per sqm. 400 is minimal and usually only for countries with ambient tempratures under 32 degrees outside ambient temperature, low humidity and very good insulated rooms.

I would go for 18,000 btu for a 20 sqm room in Thailand because once the outside ambient temperature gets near or past 35 degrees ambient (units are designed for 35) like it does during April or May your cooling capacity will be diminished greatly.

It is alway better to slightly have excess cooling capacity than to have a unit that is under capacity. If it is slightly over capacity once the room gets cool the thermostat and the compressor cuts and stops runiing. If it is under capacity the unit will be unable to cool the room efficiently and the compressor will be running all day and possibly all night long wasting electricity.

Not in cases where air return into the fan coil unit is near ceiling level.

The height calculations are minimal unless your celings are like 6-8 meters high.

The a/c is actually designed to have hot air enter the return and have the cool air away or blown far away from the return grill.

That is you see cassette type and central units have their return grilles high up and the cool air far away.

Don't worry about the height of the celiing and concentrate more on the insulation of the room.