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Old 07-04-2020, 11:26   #1
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Venting portable AC into engine compartment

Good day folks

Well, it looks like were going to be spending some time a lot further south than we normally do, so Im looking to use one of the self-contained portable AC units that have the 6 diameter exhaust hose you normally place out a window.

Im thinking of running said hose such that it exhausts into our engine compartment... Its well insulated, the engine wont be running (so temp will be lower than usual), etc.

Does anyone have any thoughts on why this might NOT be a good idea?

Thanks again for any insight!
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Old 07-04-2020, 12:10   #2
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Re: Venting portable AC into engine compartment

One risk, unless the engine ventilation fan is on and/or the engine compartment is completely sealed from the rest of the boat, is that engine room odors will be driven into the cabin. Venting into engine spaces and bilge spaces is considered bad practice.


I would not do it. Rig it out a window.
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Old 07-04-2020, 12:25   #3
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Re: Venting portable AC into engine compartment

Not necessarily a risk but an inefficiency issue. What is the resistance to airflow out of your engine compartment? If it is only vented through a long, smallish hose then you may have air being pushed out of the engine compartment back into the cabin, with accompanying engine smell as noted in the previous post. Even if you don't have that issue your air conditioner will struggle as the airflow will be low. This may cause the coils to freeze up in which case your cooling will be severely impaired.
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Old 07-04-2020, 12:29   #4
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Re: Venting portable AC into engine compartment

I bought some portable stand up AC units last year as we stayed in hot weather. In my experience they performed very poorly. I made up board that fit into the hatch but had a hole to vent the AC directly out of the boat, so the AC unit was in no way constrained.

What ended up happening is that the unit is pushing air out of the boat and that was creating a vacuum into the boat. When running, we'd have air coming in through the above water thru hulls (like the sink drain) or if we closed the thru hulls, it would suck air in through any space in the boat that wasn't 100% air tight, like the companionway.

This resulted in some cooling, but it sucked so much hot outside air into the boat it couldn't cool down very effectively. If I did it over again, I would by a window AC unit and build some sort of box to adapt it to blow through a hatch.
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Old 07-04-2020, 12:58   #5
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Re: Venting portable AC into engine compartment

You ideally should use a "Dual Hose" unit. This way they intake hot air from the outside to run over the condenser and then back out. It leaves the cold air inside and doesn't suck air out of the boat. Even in a home they are WAY more efficient. As for venting into the engine room I would avoid it as mentioned above unless you leave the engine open, and then whats the point.

This unit on Amazon is an example;

https://www.amazon.com/Whynter-ARC-1...obvila-20&th=1

Although I am not necessarily recommending this exact on as I have no experience with it.
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Old 07-04-2020, 13:01   #6
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Re: Venting portable AC into engine compartment

You might find this article useful. https://theboatgalley.com/portable-air-conditioner/

We decided to go with a window unit instead for two reasons. First, at Lowes a window unit with the same capacity as a portable unit was cheaper. Second, the one hose type portable unit they had must exhaust all the heat it removes from the boat plus the heat it generates in its exhaust air. As that exhaust air goes out of the boat hot outside air from outside the boat must come into the boat to take its place. This can't be avoided. We looked at the places where those hot air drafts would be and did not like the idea.

When we bought the window unit, we bought a 4'x8' sheet of 1" polyurethane foam. I left half of it at Lowes, and it was gone before we left the parking lot. Back at the boat I opened the main cabin overhead hatch and placed the window unit to one side of the hatch with its inside face facing the open hatch. I took the slide-out-seal-the-window things off the air conditioner. With a serrated bread knife I cut up the foam sheet and made a nearly cubical box; one side was the face of the window unit, the bottom was the open hatch, and the other four sides were foam board. I glued the foam together with epoxy. The window unit was leveled with blocks of the foam. The box was held tight to the hatch rim by two ratchet straps hooked on the handrails and passing over the box. From inside the boat I could reach up and adjust the air conditioner. I added an extra piece of foam board diagonally inside the box to separate the air going to the air conditioner from the air coming from the air conditioner. I painted the box white with latex house paint. A bit of rubber foam seals both the air conditioner to the box and the box to the top of the rim of the overhead hatch.

The whole thing stays inside the boat when we are at home and stays in the car when we go sailing.

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Old 07-04-2020, 13:02   #7
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Re: Venting portable AC into engine compartment

ditto on 2 hose units. I have one of each, learned the hard way. Both rated the same, but the 2 hose unit seems to have twice the cooling.
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Old 07-04-2020, 13:17   #8
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Re: Venting portable AC into engine compartment

Thanks folks; appreciate all the great feedback!
No engine room or bilge smells (sail drive so dry as dust bilges), and well insulated, but did not consider the “back pressure” that might be caused by a potentially small exhaust from said compartment. Unfortunately, hose is a bit short so won’t reach the hatch overhead; that’s why I’m considering venting into engine compartment.

That said, might look to see if I can extend the hose with some sort of jury rigged adapter to clothes dryer hose and go out the hatch as suggested.

Will keep everyone posted.
Thanks again!
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Old 07-04-2020, 13:34   #9
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Re: Venting portable AC into engine compartment

I notice in the marina I frequent a couple of boats with split unit with just hoses running down through the hatches. Daikin brand I think.
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Old 07-04-2020, 13:42   #10
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Re: Venting portable AC into engine compartment

You absolutely should get a dual hose unit, and you do not want to vent it to the engine room, as even though most do have a drain, most of the water that drips from the evaporator goes out that hose so you will be pumping lots of warm very moist air into the engine room, and I’d suspect that would help mold to grow and corrosion.
But you want a dual hose unless the power isn’t meters as the single hose ones are very inefficient.
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Old 07-04-2020, 13:42   #11
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Re: Venting portable AC into engine compartment

Maybe this might be a good time to consider adding an engine room ventilation blower. All the new diesel boats have them these days now just like they do for gas inboards. Rig the exhaust up with a good hull fitting, and also add an intake port for make-up air and Bob's your Uncle.

Personally, building a box out of insulation board around and over a hatch to house a cheap household window unit AC is probably the way to go, for a down and dirty extended marina stay in a hot climate like many cruisers are facing aboard right now because of The Lockdown.

Suspend a small tarp over it to keep water intrusion at bay and plug it in to a good heavy #12AWG extension cord. Run a condensate hose over the side or to a deck scupper to keep staining off of your deck and avoid a slip hazard.
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Old 07-04-2020, 13:53   #12
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Re: Venting portable AC into engine compartment

Quote:
Originally Posted by thinwater View Post
One risk, unless the engine ventilation fan is on and/or the engine compartment is completely sealed from the rest of the boat, is that engine room odors will be driven into the cabin. Venting into engine spaces and bilge spaces is considered bad practice.

right. in essence you would be pressurizing the engine compartment and creating a partial vacuum in the salon. so you would probably get a return flow thru the bilge to the salon
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Old 07-04-2020, 13:58   #13
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Re: Venting portable AC into engine compartment

A dual hose unit would not pressurize anything as it sucks air in through one hose, then blows that air out the second hose.
But I do not think venting it into the engine room is a good idea.
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Old 07-04-2020, 15:22   #14
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Re: Venting portable AC into engine compartment

Those single hose units are useless. They pump out the hot air, but create low pressure in the room they are cooling which means they have to replace it with warm air drawn from outside. So what you will end up with is a high pressure engine room and a low pressure cooled area. Guess where the replacement air will likely originate from?
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Old 08-04-2020, 09:44   #15
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Re: Venting portable AC into engine compartment

Bad idea. Engine compartment is not sealed and unless you constantly run exhaust fans the outflows can enter the cabin. Safety hazard, especially when sleeping at night.
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