Yes, because the installer will convert  near the end point if to thick.

You ask the installer, not every installer know what can or cannot be done.

Most important pull 5wires instead of 3.

Ah sorry, read too fast haha.
RM600 each then. But i think u can get cheaper than this.

what is the conceal length?

my aircond installer charged me RM200 each aircond for the conceal work (including cementing back the hacked wall).

the conceal length for each aircond is about 10 ft.

Ya true.
My main contractor also charge me RM600 for 1.0 HP inverter conceal copper pipe and outlet pipe.
But I planned to install only 2 of them because it needs some coordination with the living room extension.

Ya,
he quoted me 1.0 HP x 3 (RM600) and 2.0HP x 2 (RM650) all inverter.
both concealed copper pipe and outlet pipe.
and he assume worst case scenario like putting the aircon in the middle wall instead of back-to-back.

actually he just quoted me, but if back-to-back installation he said just ask the aircon shop to do it for free.

Because my living room hasn't extended now that i plan to put the aircon compressor at top of the car porch instead of in front of the main door (too hot later all the wind blow in all the hot air), and the ground floor living room is in the middle of the houseplan (probably more than 15 feet) with affected plaster ceiling and etc.
So better ask him to do it, it need lot of coordination and correct timing.
the rest master bedroom, bedroom 2 and 3 just need back to back.

Ya, I just can put back-to-back enough already.
Top of the aluminium windows if you view from outside backyard can already.

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Added on November 29, 2012, 3:45 pm

if 1.5HP i think 15 feet is still OK.
Your room is the small room at ground floor? or big big one? 

For Daikin, inverter, R410A gas.
My aircond contractor quoted me the following.

To lay copper pipe and water drain pipe, WITHOUT conceal into wall:

1hp @ RM 500 x 3 = RM 1500
2hp @ RM 570 x 3 = RM 1710

Installation only,
RM 200 x 6 = RM 1200

TOTAL: RM 4410

Is the price reasonable? It's a double-storey house.