View Full Version : AC advice?

Frantically Relaxing
10-26-2012, 09:13 PM
Thinking towards next year, want to change out the RV roof AC unit for a marine AC unit. I'd like the floor space up top the Coleman is eating up, and it's a bit noisy too. I've been searching online, and I could use some advice/recommendations..

The Coleman roof AC keeps the place quite nice, even on 100+ degree days, as long as we keep the bedroom and basement door shut. We have a small window AC unit in the bedroom that works great, no need to change it. Just guessing, but the dims of what I'll actually be cooling is 12' wide and about 20' long plus a couple of feet of hallway, 7' high, so roughly 1700 cubic feet.

Not sure the BTU of the Coleman, but around 12,000 I think. It's the "standard" unit that's been around since the 80's (and has been on top of every RV I've ever owned!). I'll be using 110v power.

Found a few brands-- Dometic, Webasto, Mermaid, Arctic, but so far I'm liking Marineaire... I'm thinking 12k BTU's is a bit lean, but I don't think I need 16k, and Marineaire has a 14k unit (with heat pump) and at $1500 the price seems reasonable (compared to Dometic, f'rinstance)...

BUT, I'd like some input from those with a little more experience than me! :)

Also, FWIW, install will be cake, I have oodles of room for the unit and air plumbing, power available, and 2 capped thru-hulls under the boat just itching to be used...

Any advice will be greatly appreciated! :cool:

10-27-2012, 05:43 AM
You will need the 16k unit.

Tony B
10-27-2012, 06:06 AM
I have owned Mermaids on 3 different boats. They are very reliable and have excellent customer service. They are located in Fl.
I have always had the the ones with reverse cycle heat and also the optional Condensator. This will keep your bilge dry.
I don't have the specs handy but you might want to check and see what size unit you need. I know you will need the 16K unit but not sure if you would need larger.
Mine have always been on sailboats on the very hot Gulf of Mexico and out in the open. Having a covered slip would make a big difference. I probably have about 1500 CuFt in direct sun all of the time and in the summers 98* F and higher, my unit runs continuously but does keep the boat comfy.
The reverse cycle heat is much faster at heating up the boat than the AC is in cooling it.
Hope that helps some.

10-27-2012, 08:48 AM
The reason your satisfied with the performance of your roof unit is that its output is at the highest point of the cabin. Cold flows down.

If you go to Marine Air YOU WILL require the strongest unit you can run on 120 volts. (16,000 BTU) It is EXTREEMLY important that you place the outlets as high in the cabin as possible. If heat is important to you arrange a top and bottom outlet on each duct with closeable vents.

If your generator and dock pedestal support 220 volts. You might consider a residential heat pump. (worked for us on our 55 Pluckebaum in North Alabama)

STRONGLY urge you not to remove roof unit until you verify performance of marine unit. You can get a table to put over the roof unit. We never did remove our roof units. We used them on cooler days when we weren't topside.

10-29-2012, 07:52 AM
Yep, As OHB stated. Get your new one installed first, run it awhile, and then removed the roof top. My brother never did remove his roof top. Then when he loaded the boat down with people, he could run the roof and the marine, and freeze meat.

Frantically Relaxing
10-30-2012, 04:55 PM
Good stuff to know-- I have 220 available at the boat but the genny is only a 6.5 Westerbeke, and on hot days on the water I want the AC on. Good advice on leaving the roof air up, and I'd planned on doing that. As for mounting vents high, I can only mount 'em as high as the floor, although it may be possible to run some ductwork behind the fridge and run duct above it...

10-31-2012, 06:43 AM
If your outlets are at floor level you might as well abandon the project. Cold flows down. Even if you push the air flow up you will not cool the boat.

Put a table over the roof air and save your money.

I had to build ducts from the floor to the ceiling on our Pluckebaum. I put closeable grills top and bottom so I could switch from cool to heat.

10-31-2012, 07:40 AM
If your grills are near the floor, use a ceiling or portable fan to mix the air in the room. A ceiling fan moves hot air down and mixes it with the cooler air, or moves air up and vice versa. A portable fan can be aimed to move cool air around. I have a small marine air conditioner in a closet in my bedroom, and the ceiling fan mixes the air just fine.

10-31-2012, 01:00 PM
My vents were at floor level, I used regular fans to move the air.

10-31-2012, 07:14 PM
The properly designed and installed system doesn't need extra devices. Plain and simple - cold flows down and heat rises. Therefore you need MORE installed BTUs when you have to lift cold air than letting it fall naturally. A significant reason to install a !6,000 BTU marine unit to replace a 12,000 roof unit.

Again: The roof air works great because it's on top and the defusers direct the air downward with NO duct losses.

Back to my experience with the Pluckebaum.

Initial installation utilized the factory installed heating ducts. (floor level) If you sat on the floor you were cool but not much higher than waste level. Totally unsatisfactory. I fabricated ducts that brought outlets to ceiling level and performance exceeded the 2 roof units. In all fairness the central unit was 2 1/2 tons Vs the pair of 12,000 BTU roof units.

01-18-2013, 01:04 PM
I know this is an old thread but I will tell you what I added to our new to us boat this last summer. Let me start by say hi and been its great reading, couldn't post for awhile Thanks Katie for clearing that up. We are the 3rd owners of our 1988 Liberty Bell she is 52 x 15 single level. Got her the 1st of July, moved up from a 1972 Stardust that I had more money than brains in. See was made in Wi for a rental boat and made like a tank and with simple strait forward systems. But being built for a rental they didn't put air in her nor did the last owner. Also the wiring was not up to handling air. Only 2 breakers 15 and 20 amp with 12g wire from the shore power to the breakers. So we redid some of the wiring, added a main panel with a selector switch and breakers. We also added 2 roof top air units. After much reading and research and talking with the engineers at Coleman I went with their 13500btu Mach3 POWER SAVER model and here is way. It will run and start off a gen as small as the Honda 2000 and you can run 2 of them off a 30 amp shore power they only draw 10.2 amps each running. We ran our 2 in the last bit of the heatwave last summer with our gas elc frig on, two small battery Chargers on tv, lights at night with no problems. Just to see if I could pop the breaker, I ran our small microwave too, didn't pop. I look at putting marine air in but it was just not possible with the duct work and the amount of btu's that was recommended was eye popping to say the least.