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Old 10-06-2019, 07:41 AM   #1
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Dehumidifier that doesn't get hot

Shopping for a dehumidifier that will keep the boat dry when at my slip. 110v is fine... perhaps in the 100w range. But want one that doesn't get hot.



Is there a good one out there?


400 Mainship, about 2000 cu feet.
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Old 10-06-2019, 08:17 AM   #2
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Here are some thoughts and recommendations:

Don't get a Peltier effect dehumidifier. They can only remove limited water and are very inefficient. Get one that can remove about 30 pints per day. That will cover a good sized boat. If possible get one with a built in drain hose and run it to your galley sink drain.

Here is one that meets those criteria. There are lots of others.
https://www.amazon.com/Inofia-Dehumi...s%2C200&sr=8-8

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Old 10-06-2019, 09:04 AM   #3
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We followed the advice of many here and bought a common 30-pint unit.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

It has performed very well and we would seriously miss not having it aboard. The amperage draw is low enough to run underway from the inverter (think PNW wet season). The doormats get dry and condensation on the windows is almost eliminated. We cook, shower, etc. inside with no moisture issues. The mold battle around the window frames has been over for some time. It is left on while we are away from the boat during the week, and it’s often full when we return. I don’t understand why they are not permanently installed on boats in our region. It is one of the most utilized (and inexpensive) items contributing to comfort on the boat.

The thing is running right now, as we are on the hook at Friday Harbor.

Good Luck
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Old 10-06-2019, 11:15 AM   #4
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I don't think you will find an efficient dehumidifier that does not produce heat. They all use heat as they remove the water. I do not totally understand the process but I think they have coils like an air conditioner that freeze and water condenses on the coils. Then the coils are heated to thaw the water and have it drain away. Basically air conditioning with out the cold.

But then what do I know, I just can say everyone I have had produces heat as a by product.
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Old 10-06-2019, 11:35 AM   #5
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Any dehum that uses refrigerant cycle will make heat. It is not that it is inefficient, it is just the nature of the thermodynamics.

I leave one in my pilothouse and set it to like 50 (can't remember if that is dewpoint or rh, I think it is rh). I leave it on and pilot house gets HOT in full sunshine. This heat depresses the rh, so thing probably does not run at all in daytime heat. When boat cools off at night, rh goes up and it cycles on. So I don't think it contributes to the worst of the mid day heat. And the heat has not killed it, it has been doing this for three years and still works like a charm. I leave the AC units off.

Win win win. Worry not about the salon getting hot.
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Old 10-06-2019, 12:01 PM   #6
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A 30 pint dehumidifier is very efficient, doesnít put out too much heat (just like a refrigerator), and when use in conjunction with some small fan to move the air around inside the boat, will keep your entire boat dry. Most any of them will work well as they are almost all the same.
- Set it on a galley counter and have it drain into the sink.
- I leave it running continuously rather than setting a humidity level.
- I leave it on the low fan setting.

I know Dave mentioned not to use the peltier type of dehumidifier. They are less efficient, wonít remove nearly as much water as a compressor type, and will tend to freeze up when temps get down to the low 40s. However, they are a lot quieter and smaller than a 30 pint compressor dehumidifier. A couple years ago I swapped my 30 pint dehumidifier that Iíd been using for a decade with a few of the small peltier type dehumidifiers. The reason was that our boat doesnít sit during the winter, it gets used (not as often as I might like) and it is a bit of a pain to store the 30 pint dehumidifier before getting underway. With the peltier type dehumidifiers I just leave them in place. I have an Eco-Dry 2000 in the galley, draining into the sink and an Eco-dry 1000 in the forward cabin that will fill up after a couple of weeks. That combination has worked really well. In the winter when we are on board and plugged into shore power, we leave them running as they are extremely quiet.
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Old 10-06-2019, 12:47 PM   #7
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I have an Eco-Dry 2000 in the galley, draining into the sink and an Eco-dry 1000 in the forward cabin that will fill up after a couple of weeks.
Hey Dave,
Do you mean the EVA-DRY like this?
https://www.amazon.com/Eva-Dry-Edv-2.../dp/B001QTW6KQ

Do you just detach the container and let it drip down into the sink drain on its own or does it have a hose attachment?
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Old 10-06-2019, 01:01 PM   #8
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If you happen to have a typical Taiwan Trawler with all wood window casings and doors. If you run a large dehumidifier 24/7 it is possible to remove enough moisture that the wood will shrink. The issues is with wood window casings this can cause leaks... To avoid this prblem we put the dehumidifier on a timer and only ran it about 8 hr's a day.
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Old 10-06-2019, 01:38 PM   #9
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...Do you just detach the container and let it drip down into the sink drain on its own or does it have a hose attachment?
The reservoir has to be installed for the Eva-dry to run. I guess it’s a safety feature. We drilled and threaded in a brass nipple into the reservoir then added some 1/4“ Tygon that drains into the sink.

We put the 120 vac to 13 vdc adapter on a cookie sheet. It can get hot and I’ve read of 1 or 2 meltdowns although after four summers we’ve never had any issues.
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Old 10-06-2019, 01:56 PM   #10
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We drilled and threaded in a brass nipple into the reservoir then added some 1/4ď Tygon that drains into the sink.

We put the 120 vac to 13 vdc adapter on a cookie sheet. It can get hot and Iíve read of 1 or 2 meltdowns although after four summers weíve never had any issues.
Genius.
Working well in FL humidity if the boat is closed up for a few weeks at a time?
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Old 10-06-2019, 02:13 PM   #11
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Genius.
Working well in FL humidity if the boat is closed up for a few weeks at a time?
We've been happy with the performance plus the electric bills. We left in May and got back 3 weeks ago. The boat was dry with no mold or mildew. We do leave a Hella Turbo fan on low in the master to keep air moving.
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Old 10-06-2019, 02:21 PM   #12
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Genius.
Working well in FL humidity if the boat is closed up for a few weeks at a time?
They work best in a closed up boat. If you live aboard more moist air enters every time the door is opened. We run two 70 pint units 24/7/365 down below and once you get everything dried out we empty the 70 pints about every three days. When you start from scratch with a humid boat we pull the 70 pints every day for several days. Make sure to open the hanging lockers and drawers too. BTW, the 30 and 70 pint units are the same footprint and internals except the height to accommodate the bigger reservoir. That means the power draw is the same too.
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Old 10-06-2019, 05:30 PM   #13
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Originally Posted by bobbyp View Post
Hey Dave,
Do you mean the EVA-DRY like this?
https://www.amazon.com/Eva-Dry-Edv-2.../dp/B001QTW6KQ

Do you just detach the container and let it drip down into the sink drain on its own or does it have a hose attachment?


Yes, sorry. Eva-dry. I drilled a hole in the container and uses some 1/4Ē hose to drain into the sink.
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Old 10-06-2019, 05:31 PM   #14
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Originally Posted by Ka_sea_ta View Post
If you happen to have a typical Taiwan Trawler with all wood window casings and doors. If you run a large dehumidifier 24/7 it is possible to remove enough moisture that the wood will shrink. The issues is with wood window casings this can cause leaks... To avoid this prblem we put the dehumidifier on a timer and only ran it about 8 hr's a day.

True. Even worse if you have a wood boat. Mine have all been designed such that I donít have that issue.
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Old 10-06-2019, 05:33 PM   #15
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BTW, the 30 and 70 pint units are the same footprint and internals except the height to accommodate the bigger reservoir. That means the power draw is the same too.

Not quite. 30 vs 70 pint doesn't indicate the reservoir size. The 70 pint has bigger (more power consumption) refrigeration bits. The 30 vs 70 is the number of pints of water it'll pull out of the air in 24 hours under the given test conditions (which are standardized across brands).
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Old 10-06-2019, 07:36 PM   #16
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Our AC has a humidity circuit that runs the ac on a schedule every day for a short period of time. Have never noticed mildew nowhere but my vision is not very good.
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Old 10-06-2019, 08:48 PM   #17
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Here are some thoughts and recommendations:

Don't get a Peltier effect dehumidifier. They can only remove limited water and are very inefficient. Get one that can remove about 30 pints per day. That will cover a good sized boat. If possible get one with a built in drain hose and run it to your galley sink drain.

Here is one that meets those criteria. There are lots of others.
https://www.amazon.com/Inofia-Dehumi...s%2C200&sr=8-8





David,


Good info......


Did a search on the Peltier vs the compressor dehumidifiers and the Peltier sucks. Thanks much
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Old 10-06-2019, 10:07 PM   #18
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I donít understand why they are not permanently installed on boats in our region. It is one of the most utilized (and inexpensive) items contributing to comfort on the boat.
I installed a "whole house" dehumidifier permanently in place of one of the AC units. It blows through the duct work already installed for AC - staterooms, head as well as saloon. It is rated 70 pints, draws about 400W when running, and runs at less than a 30% duty cycle (and as low as 10% or so) once it has pulled down the humidity. Easily run on the inverter when driving, and a few hours at anchor won't kill a well designed DC system either. I will run it at anchor on batteries after showers, or cooking pasta, etc., with noticeable effect.

Yes, it is one of the best things you can do for comfort. On warmer sunnier days up here (PNW), the inside humidity will run at 50 or 55% and we will have the windows open anyway, so it is shut off. Colder, rainier days and the inside humidity gets up in the high 60s or low 70s, windows fog, towels don't dry, hatch frames sweat. All gone by running the dehumidifier.

A/C units will also dehumidify, and dump the waste heat outside the boat. This is less efficient, since a true dehumidifier recovers much of the energy gained by the evaporator. In the SE, often you run the AC enough to keep dehumidified. In the PNW, it is rare to run the AC, common to need extra heat anyway so you want the heat from the dehumidifier in the boat (usually).
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Old 10-09-2019, 06:57 AM   #19
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I installed a "whole house" dehumidifier permanently in place of one of the AC units. It blows through the duct work already installed for AC - staterooms, head as well as saloon. It is rated 70 pints, draws about 400W when running, and runs at less than a 30% duty cycle (and as low as 10% or so) once it has pulled down the humidity. Easily run on the inverter when driving, and a few hours at anchor won't kill a well designed DC system either. I will run it at anchor on batteries after showers, or cooking pasta, etc., with noticeable effect.

Yes, it is one of the best things you can do for comfort. On warmer sunnier days up here (PNW), the inside humidity will run at 50 or 55% and we will have the windows open anyway, so it is shut off. Colder, rainier days and the inside humidity gets up in the high 60s or low 70s, windows fog, towels don't dry, hatch frames sweat. All gone by running the dehumidifier.

A/C units will also dehumidify, and dump the waste heat outside the boat. This is less efficient, since a true dehumidifier recovers much of the energy gained by the evaporator. In the SE, often you run the AC enough to keep dehumidified. In the PNW, it is rare to run the AC, common to need extra heat anyway so you want the heat from the dehumidifier in the boat (usually).

DDW,


Can you comment more on your dehumidifier? Kind and model no? And how hot does it get?


Sounds like a good idea.
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Old 10-10-2019, 07:32 PM   #20
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These real world reports are useful. Here's the geeky side:

A dehumidifier works by passing air over a cold surface, if you chill it below the dew point water will condense. There are absorbent dehumidifiers, but that's a different beast and not a great long term solution.

Best way to make cold is a heat pump; one part gets cold, another gets hot. Most commonly refrigerant cycle type, the same as refrigerators or air conditioners (which may dehumidify as a side effect). A Peltier or Thermoelectric device is a solid state heat pump, but they have limitations: efficiency goes down as the temperature difference between hot and cold goes up, and it's zero at about 45 degrees delta. You get a lot more heat than cold.

These humidifiers pass air over the cold fins then the hot fins, so in theory there shouldn't be any change in temperature. But nothing's free, and ultimately there is power coming from somewhere and ending in the cabin. Specs on some of those listed above say 200W, but it might be less when averaged over time. As much heat as a couple of lightbulbs.
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