The main difference other than seawater condensers rather than forced air is
that the domestic unit's sheet metal (drip pans, covers etc) is mild steel
rather than stainless.

Medium size commercial boats like ferries do use domestic type A/C units but
that is because when you get into the 10 to 20 ton range it is cheaper to
replace them every couple of years than invest in a true marine system that
a similar size megayacht would use. Also noise is not normally a factor.
In the 3/4 to 1.5 ton sizes typical of most under 60' boats it is far
cheaper to get a marine unit that will last 7 to 8 years rather than a
domestic unit that only last two seasons and water cooled marine A/Cs are
much quieter.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"MarshallE" wrote in message
...
I hear that some of the commercial boats use a residential unit and mount
on
top of cabin with better success than marine grade heat pumps.

What brands are best for marine grade? Is this a project that the average
boat owner can handle?

The cost to go with a residential is much less but I am concerned that the
marine products would be better.

thanks for help,
marshall