18,000 btu would appear to be way too much...unless there's some unusal factors such as 115 degree heat with no insulation whatsoever,room is on top floor with almost all windows which face south and west,etc. 18,000 btu mini split even in a very warm climate would typically cool a larger area. Even with lousy insulation 12,000 btu would probably be on the high side in my opinion.

Also in my opinion the typical calcultors used to determine AC/btu sizing are off when it comes to mini splits. Those calucaltors assume a typical split system with normal duct runs not the direct from air handler to room that is most often seen with mini splits...therefore, no duct loses to account for.

A too powerful setup combined with higher humidity in the tropics or elsewhere results in short operating intervals which in turn makes the room feel cold and clammy (caused by excess humidity not being dealt with). If a room with an 18k BTU unit feels comfortable and it runs quietly all the time or a good percentage of the time when needed, it should be suitable.

An inverter model mini split will "throttle back" when it's full output is not needed so an 18,000 btu model might throttle back to 8,000 btus or maybe less...so oversizing is much less of an issue with this technology. However, you wouldn't get the benefit of even lower btu outputs/fan speeds that a smaller unit would throttle down to...maybe 5000 btu's with lower fan speeds and resultant lower power bills when full capacity isn't needed.

Thank you for your responses.

I know what you mean about 'cold but clammy'... dealt with it before in small hotel rooms with too-strong ACs.

Heat here is usually in the high 80s or low 90s.

The apartment is on the second floor of a 3 floor building.

One thing should be mentioned, I guess: The landlord pre-installed the tubing for mini-splits in the rooms that don't have access to the outside. The compressor(s) would actually be on the roof, with the tubing reaching all the way down to the second floor. Is this what you're talking about regarding potential duct losses?

No not talking about the tubing going from the outside unit to the room unit. Woudn't worry about that based on the distance you noted.That should have little or no effect on your unit.

Traditonal split systems have duct work usually in the ceiling of the rooms served (sometimes the flooring)...so there's bunch of ductwork that the cooled air has to travel through before it enters the room, some of which might be in an unconditoned space such as an attic or crawl space. Based on the literature that some manufactrures have put out those duct loses could be up to 30%. A mini split with a wall hanging unit has no duct loses at all.

Oh, I see. Thanks...

BTW, what would be the best option for sealing up the space that used to hold an in-wall window unit? It can't be permanent because this is a rented apartment. I'm thinking some insulation and drywall, then just cover it with a picture?

These are the ACs available in this country (in general).

http://www.extrastores.com/site/ProductList.aspx?Page=Air%20Conditioners&SubFamilyID=451

3750 SR = 1000 US dollars

I have a suspicion that some of the higher-priced models *might* use inverter technology but even the company's sites (LG, Samsung, Panasonic) don't have any useful info in that regard.

Any advice?

Store clerks were utterly useless.

We have an LG, and ours is an inverter. Mitsubishi is also available (if not all) inverter technology.

Who will install this if you are buying from useless store clerks?

They offer delivery + installation with the price. I'm sure they have a guy or two who can actually put it together, seeing as every single building in this country has tens of ACs due to the extreme heat.

When I said 'utterly useless' I meant with regards to any technical info. But I'm sure the installer guys know what to attach where and so on.

Update: Found one confirmed inverter model that was about $150 more than the non-inverter.

This is it: http://www.samsung.com/ae/consumer/home-appliances/air-conditioner/wall-mounted-split-ac/AS18ESPXSG-features

Catch: It was their last piece... the display model. It had some marks on it from being on display, heh.

So I just gotta find it in a different store, then.