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Wjpetersen 11-11-2012 09:32

AC/heat question
I am considering on putting central air and heating on my boat in December. A couple of questions :

1. Where is generally the best place to put the main unit?

2. Is it possible to have multiple thermostats?


Cavalier 11-11-2012 10:24

I see that you have a 46' so i'll answer the question by explaining our setup.

We have two reversible units - each with condenser/evaporator and heatex (to water) together with blower.

The unit which covers the forward stateroom and salon is located in the forward-most under-seat void in the saloon C-berth (sofa) the return for that unit is connected to a grille under that seat, the other is located in the port side of the lazerette and the return is at the back of the port quarter-berth on the bulkhead between the stateroom and the lazerette. Each unit has its own controller/thermostat.

Both units are 'water cooled' (of course), two sea-cocks are mounted on through-hulls located just after of the keel and the associated inboard strainers and pumps are next to them under the boards (with a dedicated highwater alarm, bilge pump and float) - the outbound flow is out of seacocks located above the waterline.

You lose some under-seat storage, of course, but the main thru-hulls remain easily accessible.

Hope this helps...

Sailmonkey 11-11-2012 10:41

Re: AC/heat question
for a boat like yours I would be inclined to install split systems. Evaporators in the areas to be cooled and the condensors in the engine compartment.

Two to three units. One large unit for the salon, one medium unit for the aft cabin and one medium unit for the foreward cabin/galley.

Another option is a chilled water system. then you can have seperate thermostats for every zone.

There are a lot of ways to do this, it really depends on how much you want to spend and how "zoneable" you want to make it.

Wjpetersen 11-11-2012 11:04

Re: AC/heat question
Thanks guys for your help. Looks like I cannot get away with just one unit if I want seperate zones. I need to have basically four zones: 1) aft cabin, 2) salon/galley, 3) forward cabin, 4) sun deck. The fouth area I am hesitant on because right now it has canvas. But I plan on completely enclosing the sun deck with walls and windows.

The reason for the different zones is because each area currently has a temp difference of sometimes 15 degrees.

The follow up question about the unit(s). Isn't it better to have air coming from outside? Is that possible?

My budget will be about $5k.

But I also want to start researching invertors and batteries which can handle the extra electrical load....

Sailmonkey 11-11-2012 11:18

Re: AC/heat question
Outside air is a grand idea, until you want the inside to be comfortable.

Lookup the cruisair systems from dometic. Their website has information about multiple zones using either a direct expansion system(s) or tempered water.

If you want one unit to do all, I would think your best bet would be a tempered water system. These work by circulating cold or hot water through the system, and a valve controlled y a thermostat allows the temperature to be regulated in each zone, but I think you may be a bit low on your budget to have it work correctly and be installed (you might be OK if you plan on doing the install).

Sailorman375 11-11-2012 11:27

Re: AC/heat question
Your budget is low and you won't be able to have enough batteries to reasonably handle this large of a system. With four areas to control you're looking a a heap more than 5K even doing the install yourself.

Sailmonkey 11-11-2012 11:29

Re: AC/heat question

Originally Posted by Sailorman375 (Post 1081918)
Your budget is low and you won't be able to have enough batteries to reasonably handle this large of a system. With four areas to control you're looking a a heap more than 5K even doing the install yourself.

I forgot to address the batteries.......

forget about it

edit......I was just doing some rough pricing on defender of only the units, no plubming....etc... You're roughly 1/4 of where your budget needs to be.

Wjpetersen 11-11-2012 11:45

Re: AC/heat question
My original budget came with the assumption I could get away with one unit with seperate controls. I install myself along with vents, etc. However, since I cannot, I will need to cut it down to one to two zones or increase my budget to accommodate a tempered water type of system. I already have two extra through holes that I can use for water. Thanks to your inputs - I now know what to research. Thank you.

So now the question is: should I even consider adding an invertor along with a bank of batteries to handle this extra load? Or just enough to carry me with fridge, lights, etc while traveling?

Sailmonkey 11-11-2012 12:18

Re: AC/heat question
If you don't have a generator, or you don't want to run the generator while underway you need to research things like this

MEPS // Products

or this

Generators : VANAIR - truck-mounted air compressors, generators and welders

But for a boat your size, with heat loads from a lot of vertical glass there is no way you'll come out ahead doing anything other than a generator.

hellosailor 11-11-2012 13:14

Re: AC/heat question
"The reason for the different zones is because each area currently has a temp difference of sometimes 15 degrees."
While boat systems are usually hobbled by the need to be much smaller than home systems, they can be "the same" if you work on them. The problems can be the same as well. Many home systems suffer from poor designs and are "out of balance" from one room to the next. The problem is finding a designer/installer who gets the numbers right, in terms of btu's the system supplies in each place, and CIRCULATION. If you have ever seen a home heating or ac system without return ducts, that means someone has saved half the price on ductwork--and the system will never be in balance unless every door is open, if it is in balance at all.

Same same on a boat, you even out differences by placing different rooms on different loops, which is going to cost money, or by adjusting the airflow or the supply, and that must be a black art because if it was a science, it might be practiced more often.

It is all a matter of balance, and then, having the budget and space to install equipment that will keep the balance.

Cavalier 11-11-2012 13:46


Originally Posted by hellosailor
It is all a matter of balance, and then, having the budget and space to install equipment that will keep the balance.

Even if you try to get away with one unit, then zone it with an actuated manifold you'll always fall foul of the placement of the returns which on vessels <100ft LOA are usually located at or next to the unit itself. A highly unbalanced system is an inefficient system: it'll have to stay on longer to get to the indoor environment required temperature and consequently use more power.
The advantage (except budget) with multiple independent units is that you can have the benefit of a zonal balance without the additional headache of where to run all of the duct-work.

I know it's not 'insurance friendly' but the OP may want to consider something like a gasoline powered Honda 2000i generator to drive the system (plugged into the shore-power coupling) while at anchor: there's many of them on eBay and it may come within budget - certainly cheaper than a fitted marine diesel generator!

Sailmonkey 11-11-2012 13:52

Re: AC/heat question
but I don't see a honda generator being able to supply the juice needed to run a system to cool a boat the size were talking about here.

On the subject of balanced systems.....the chilled water system needs no duct work other than from the air handler to outlet. That's the beauty of the type, you can have a completly balance cooling effect in the entire boat by zoning individual air handlers. That way, when the main cabin reaches the set point the chilled water is throttled back to the main cabin air handler, but the full flow is still moving through the sundeck circuit.

But it's not cheap.

DeepFrz 11-11-2012 16:07

Re: AC/heat question
Many reverse cycle systems also require an electric heat element at the condenser/air handler in order to be able to keep the boat warm when in cold water.

swisscraft 11-11-2012 17:48

Re: AC/heat question
I have on 16k BTU Unit for a 40ft boat - it works OK even in the Caribbean. It sometimes starts with a Honda 2000 but mostly not. I was thinking about a slow start Unit. But if it runs its a pain as the gennie is on his limit and therefore loud. Never used again on Anchor this way. And I could not always use it on shore du the power limit in Marinas in some remote areas.

If I would do it again, I would buy one or max two small units. 8 - 10k BTU. Then I do what I do mostly anyway - I distribute the the cooler air with 12V fans within the boat. Yes you may not get the boat down to 20C but you will bring the humidity out and get it reasonable cool. It will be able to run with a Honda 2000 without too much noise.

I think 5K budget is short for several units - so maybe think about the distribution with 12V fans. Try the most important area first and then check. 12V fans are a must anyway.

motion30 11-11-2012 18:18

Re: AC/heat question
I have a 16000btu unit for the main cabin split system The 12000btu unit services two condensers for the front and rear cabin

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