You need to ask contractor #4 why he thinks this can't be done. If it's just a matter of increasing the lineset length, there are ways around this, but he may not be knowledgeable enough to know how.

Actually, I asked contractor #4 a quote just because he is local and he was the first of the four to call me back. He is known in the area for botched installations, like a friend of mine who had a furnace that would not shut off, even after removing the thermostat from the wall, if the furnace ran for a long time.

My concern is more about 18,000 BTU's being oversized for the house. Of the other three, who would you choose? Thank you!

The reason contractor #4 gave me is that the indoor unit would have to be installed above the roof line, code prohibits running the lineset through the indoor closet and it's also against code to go down through the roof and through the attic. I think the real reason is because it looks more complicated than usual and he lacks the skills to do it properly.

Hi, wOlley32,

You're right to be concerned about sizing of any HVAC system--even a simple single zone mini split. An improperly sized unit may perform poorly and fail to provide the appropriate level of comfort across the range of expected outdoor conditions. In the U.S., residential HVAC equipment is sized according to ACCA manual S which is driven by ACCA manual J heating and cooling calculations. Given the proposed systems are single-zone with a single wall mounted indoor unit, I think the 12,000 Btu/hr. air conditioner performance is a good proxy for the calculations. You noted that the 12,000 Btu/hr air conditioner provided only a marginal comfort level on the hottest of days, so selecting a system with a capacity greater than 12,000 Btu/hr. would be appropriate.

Mini splits are variable-speed systems which gives them the ability to adapt to a range of outdoor conditions. Some can produce cooling rates above their nominal rates. I like extended run times versus a lot of on/off operation, so I tend to look at turndown ratios. The 18,000 Btu/hr Mitsubishi operates from 5,800 to 22,000 Btu/hr; (turndown ratio of 3.8) the 18,000 Btu/hr Carrier operates from 8,870 to 19,400 Btu/hr (turndown ratio of 2.2) and the Fujitsu operates between 9,000 and 12,000 Btu/hr. (turndown ratio of 1.3) While the 18,000 Btu/hr. Mitsubishi may be oversized much of the time, it's greater turndown ratio will provide better performance and comfort over the range of outdoor conditions than the other two. Plus, it is capable of producing more heat in heating mode. It would be my pick.

I'll second the Charles Ross suggestion on the Mitsubishi and add they are more durable, reliable and have a longer life span than Fujitsu and Carrier on average. I believe Mitsubishi has a better warranty also.