Portable Air Conditioner

By Carolyn Shearlock © 2015 • all rights reserved

What we've learned about using a portable air conditioner on a boat. Turns out, there are a few tricks!

A few weeks ago, I wrote about why we felt the need to (temporarily) put an air conditioner on Barefoot Gal while we were in the boatyard this summer. Read that post here.

Newer Gemini catamarans have built-in air conditioning; ours doesn’t. So I’ve gotten a few questions about what we bought, how we set it up and how it’s working out.

First off – we have shore power. At our boatyard, running an AC costs an extra $1.50 per day. The unit we have uses about 13 amps at 115/120 volts or a tad over 1500 watts. We have no intention of ever using it without shore power.

We decided to get what’s called a “portable” air conditioner. Designed for a house, portables sit on the floor and have a duct (very similar to a dryer vent) that goes to a nearby window. Unlike a window unit, the entire AC is inside, and the duct allows the hot air to vent outside. Instead of the condensate going to a drain, it is used to cool the motor, which heats it and the moisture also goes out via the duct.

Some people use a traditional window air conditioner in their boat and it works well (and is quite a bit cheaper) if you have a window or hatch that will work with it. Some boats put them on deck, partially over a deck hatch, and then build a hood to direct the cool air into the boat and hook up a hose to direct the condensate off the boat. The problem usually comes in sealing the hood both for rain and bugs. With the tropical rainstorms, mosquitoes and no-see-ums in southern Florida, that’s why we opted for the portable unit.

NOTE: A portable air conditioner is NOT the same thing as an “evaporative cooler” (also known as a swamp cooler). Evaporative coolers just don’t do much in places with high humidity and thus are unsuitable for most boats.

I’ll be the first to admit that we did very little research on what size and brand portable AC to get aside from talking to a couple of other people in our boatyard. Basically, when we got to the boat yard to drop some items off a few days before the boat was to be moved from storage to the work yard, we realized that we wouldn’t last a day without AC. We talked to two friends in the yard for a couple minutes about what they had, then headed off to Ft. Myers to buy an AC so we could set it up the minute the boat was in the work area.

Both Home Depot and Lowe’s had only one brand of portable AC, and both carried the same sizes: 10,000 BTU, 12,000 BTU and 14,000 BTU (the 14,000 was a combination AC and heater at both stores). The prices were almost identical. We decided that we’d get a 12,000 BTU unit both for size/weight reasons (we had to be able to lift it onto the boat) and because the 14,000 combo unit cost nearly 50% more and we certainly didn’t need a heater. We went with the Idylis from Lowe’s because it had slightly better online reviews.

Most portable units use the air inside the “house” (boat) both as what they are cooling and what is being exhausted. In other words, not all the air they suck in is being returned to the boat. This means that, over time, some outside air is going to get sucked into the boat and you’re going to have to cool it too. Since very few boat are totally sealed against air leaks (think companionway doors, lazarette lids, refrigerator and engine vents, plus if you’re on the hard there are probably sink thru hulls that are open), this isn’t a problem – particularly as you go in and out of the boat a few times a day. Fresh air will definitely find its way in!

The other option is a two-hose system which brings in outside air. As I understand it, these are designed for airtight homes. None of the units we looked at had this option.

Okay, on to how we set the AC unit up . . .

Let’s start with a photo of our whole unit, then I’ll talk about specific details and give close ups of various items.

AC complete

Number one is that you want the air conditioner where the cool air will blow onto you. Ours is in the saloon and we use a fan at night to push the cooler air into our cabin. Areas of the boat that are out of the direct path of the air flow will be hotter, so it’s not good to put the unit in an “out of the way” spot such as an unused cabin or second head. If your boat is in the water, make sure that the unit is secure where it won’t tip over if the wake from another boat rocks you (not a problem with us being on the hard).

Second, you have to find place where you can run the vent hose outside through a VERTICAL window or hatch – or if horizontal, one protected from the rain (you don’t want rain pouring down the open vent into the AC). Most units come with 6’ or 8’ of hose, so that limits your options. Units also come with some sort of window adapter that the hose will fit into. In a normal house arrangement, you partially open a sliding window, put the adapter in the opening and then close the window on it.

Most boats will have to modify this. We got lucky and only had to cut the adapter to make it narrower, then use duct tape and Gorilla tape judiciously (okay, liberally . . . ) to seal up the gaps. Since the top of our window is on an angle different from the the adapter, we simply used Reflectix (the silver stuff that’s covering our windows) to cover the gap. I’ve seen several boats here in the boat yard that have cut a piece of wood to the size of one of their port holes and put the hose through that – again, with lots of duct tape. Channel your inner MacGyver!

AC vent from inside

AC vent outside

The vent hose near where it exits the portable will get quite hot. I worried about it being a fire hazard as it was pushed right up against wood and gelcoat, and so wrapped it in a double layer of Reflectix. Yeah, more duct tape.

AC vent bottom

The rest of the hose gets warm but not nearly as hot. Several people have recommended insulating the entire thing to keep from heating up the inside of the boat, and that’s a great idea. However, with ours we discovered that it interfered with removing the air filter to clean it and after a few times of having to take it all off and then put it back on, we simply left the extra insulation off.

The other “interesting” part is that despite what all the manufacturers say about the condensate mostly going out the vent, some does collect in the AC. Supposedly all of these have a reservoir that it will go into and when it’s full, a light will come on and the machine will shut off. You have to drain the water (various units have the drain in different places).  All of us here in the boat yard – with three different brands of portable ACs – have exactly the same problem: water overflows from the reservoir with no light coming on and no, the AC doesn’t shut itself off then. And almost nothing comes out of the overflow drain.

We tried Googling to find the problem and after several fruitless hours, settled on the solution that the other two had adopted (and what we would have bought when we bought the air conditioner had we known about the problem and had we known these existed). A hot water heater pan.

Just put the hot water heater pan under the AC and every few days, mop up the water that collects there. We get less than a cup a week, but without the pan it runs everywhere, including into the locker beneath it.

AC water

NOTE: We wondered if we could avoid the problem totally by using the continuous drain connection meant for the dehumidify function. We called Idylis and learned that this would cause the AC compressor to have insufficient cooling and burn up the motor. So it’s the water heater pan.

Where we are and the projects we’re working on put a fair amount of dust in the air. We’ve learned to clean the air filter every few days by running it under water (the shower works well) and then thoroughly drying it (hand dryer) before reinstalling it. If you don’t get it good and dry, fresh dust will be pulled into the water and the resulting mud will dry rock hard and totally block the air flow. If the air flow is sufficiently blocked, our unit will shudder and then blow the circuit breaker.

Any time our unit is turned off (including a power outage in the yard or the breaker blowing), it has to sit three minutes before it can be turned on again. The first time that we had a power blip we didn’t know this and thought that a surge had fried the AC. Thankfully it was just the time out.

The final question is how well does it work?

My answer is that it keeps things tolerable during the day and nice at night. If your boat is like ours and has virtually zero insulation and numerous ways for hot air to come into the boat, nothing is going to keep the boat truly cool when the cockpit thermometer is reading 105 in the shade, with 80% humidity.

We give the AC what help we can:

  • Outland Hatch Covers over the deck hatches and Reflectix over all other windows and doors. We’ve left two small windows that open into the cockpit and are shaded by tarps uncovered so that we have at least a bit of outside light.
  • Tarps over the cockpit and partially over the deck (we could have more tarp coverage but we’re also doing some deck projects . . . )
  • Wherever we feel hot drafts of air coming in, we’ve fitted foam insulation (generally pipe insulation) to stop as much as practicable. (NOTE: Be sure not to block any refrigeration vents.)

When it’s 105 in the cockpit in the middle of the afternoon, it’s in the low 90’s inside the boat. If it’s 100 in the cockpit, it’s 86 to 88 inside. When it drops to 90 in the cockpit, it’s in the high seventies. And the few days that we had that were in the high 80’s outside were 75 or less in the boat. After dark the temperature inside the boat drops into the 70’s pretty quickly and is usually 75 or below when we go to bed.

A final but very important note: don’t count on the AC working all the time, and when it doesn’t, it gets very hot very fast inside the boat (not quite as bad as a closed car but along the same lines). Don’t leave a pet inside the boat with the AC on when you leave the boat, figuring that they’ll be okay. Between thunderstorms, power outages in the boatyard, someone accidentally flipping the breaker at your power pole, the breaker on the boat flipping off due to the air filter being clogged and for other unknown reasons, and the unit turning itself off (again, no apparent reason) a couple of times, you simply cannot rely on 100% up time. Either one of us stays at the boat with Paz while the other one runs errands, or she goes with us. Dinner out happens only after sunset on cool days.

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Comments

  1. Lots of great information (as usual)! Thank you!

  2. Great article. Thanks for the practical info.

  3. We used a 12k BTU unit on our Catalina 30 and it worked well. I hooked a hose to it and ran it into the bilge to deal with condensate and exhausted it out a fixture I made for the companionway. I never got around to insulating the exhaust hose but it would help with excess heat (you can feel the heat radiating off it).

    • Shane
      I have a C 30 and looking to buy a portable. I have been racking my brain to see how I can rig this in my boat.
      Do you have any pics you could send me on how you did this?
      Best Regards
      Alan
      acarleton9@gmail.com

  4. Doug Crawford

  5. This is our set up now with 8000 btu and one duct venting out.

  6. Jim Combs says:

    We went through the same ordeal several months ago…also in Ft Myers. After a week of sub-par performance we returned the 12K BTU Idylis to Lowes. It would only drop the temp to 78 degrees after a full nights running…..85 degrees during the day. We decided to exchange it for the 12K BTU Frigidaire window unit. Just to see what was possible, I set the thermostat to 65 degrees and left the boat for 8 hours. Upon my return (during the day…90 degrees) the boat was a frigid 65 degrees. Go Figure….. I adjusted the thermostat to 70 degrees and the boat has been dead-on 70 degrees all summer. AMAZING!!! One would think that 12K BTU’s would be 12K BTU’s across all AC’s…..NOT SO! After discussing with other folks at the Yacht Basin, all have had a similar experience. Just my 2 cents! Cheers!

    • WOW. Wish we’d known that before we bought ours. Might have inspired us to figure out how to make it work with our hatches.

    • Richard Mulvey says:

      I too am experiencing the same issue with a stand alone airconditioning unit. Not much variance between outside and inside temperatures, and it makes little impact for the coolness of my boat compared to my much older “Swamp Unit” (of which the compressor went).
      My problem is the amount of condensation that the machine puts out from its drain. I must dump a 5 gallon pail at least three times a day with this stand alone portable unit! Way too much if you ask me.
      I lived aboard my sailboat and found that a window unit, aside from its awkward placement on my fwd hatch, had much better coolling abilities. Not to mention, the condensation was always OUTside of the boat where it belongs!
      Therefore, I am considering on the idea of returning my portable unit as well to swap it out for a window unit. Not many places to install a window unit on my 1966 Egg Harbor, with the exception of the main and V-Berth roof hatches.

      • Yeah, the portables that aren’t ducted to the outside do put out a lot of water! After reading the comments from those here, I think that the window units are a better deal, except for figuring out how to place them.

  7. We plan to upgrade to this one for two reasons. 1400 btu and 2 ducts. The intake and venting outside makes it so we are not creating a vacume inside the boat. If you only vent out then you are sucking hot air in from other places taking away a lot of your cooling power. http://amzn.to/1JKyh0h

    • But you’re still sucking in hot air . . .

    • Yes, but we are sucking in hot air into the compressor that then cools in and only cool air is going into the boat. If you only vent then you are sucking hot air into the far reaches of the boat so the Master cabin for example will be hard to cool. I am actually posting this with interest in other opinions, I am not an engineer.

    • Interesting as we were told that cooling the hot outside air was harder work for the compressor and thus the interior temp would be higher. But like you, I’m not an engineer. There was just an interesting comment left on the post from someone who tried the portable and switched to a window unit with much better results. Maybe because it’s just recirculating the cooler inside air and all the hot air is staying outside?

      • John Turner says:

        I had the very same experience. I tried the portable unit standing unit and it would only make it a bit more comfortable. Switched to the window unit and it makes it quite cool in the boat to a point I don’t have to run it full blast either. I live in Tampa, Florida and its running 95 to a hundred here every day too.

      • I think it would be worth a try on using a second vent for the intake if it is possible to rig something. Replacing every bit of the exhaust air with hot air sucked from outside doesn’t make sense, although clearly it’s the design.
        Using hot outside air for the heat exchange would not be as efficient for a temperature drop, but you wouldn’t be having to cool a constant influx of hot air. This is why the same Btu window units are performing better, and why the cooled air has to be directed toward you. Before giving up on it, I would try to add some kind of intake duct.
        Worst that can happen? Tripping off as when the filter is clogged? A test might be just to check the temperature at the output as it is installed. Then set it outside in the shade so it it bringing in hot air. Check the temperate at the output and see if it fails.
        (I’m an engineer, but have not done any math on this, and no warranties, and this is not professional advice. I’ve just lived in the south with none or various types of AC. 🙂 )

    • I don’t believe advertisements at face value but most of the dual vent websites say that they cool 40% faster because of that feature. For boats, I was more interested in eliminating the vacuum effect that pulls hot air in all the cracks around the boat. We all know boats are not air tight LOL. Hard enough to try and make them water tight.

    • PS. Love your blog. We have a 1997 Gemini 105M

  8. the are very inefficeint, and must be drained daily.

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