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Old 28-12-2017, 14:48   #1
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Dehumidifier - will it make a difference?

Good day folks

Our first winter living aboard and the only real issue we're having is condensation! Warm, moist air hits the cold metal flanges of the portlights & hatches and we get rain!

I'm about to plunk down ~$200 on a Dehumidifier and wondering if it will actually make a difference. As I sit here writing this post it is 22 (degrees F) outside & 72 inside with 37% humidity.

If I'm understanding the relationship between Temperature, Relative Humidity & Dew Point correctly, I would have to get the humidity down to around 14% to stop the condensation at this moment.

Does anyone have personal experience with using a quality dehumidifier? Am I correct in my assumptions? If so, will one of the typical home units be able to do that?

Thanks for any and all help,
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Old 28-12-2017, 15:18   #2
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Re: Dehumidifier - will it make a difference?

Some of your problems may be helped by the type of heat you are using. We find electric heat to be the worst for humidity and diesel one of the best. A good dehumidifier also creates heat when it's operating. The warmer the temp the more humidity the air will hold. We use one when we store our boat in hot humid climates and it works wonders in not allowing mold and mildew to get going and keeps the boat smelling sweet. It's very common to have humidity levels in the 90's and we shoot to keep it around 50% and you want to go much lower. Make sure that the dehumidifier your wanting to buy has settings as low as you want and ensure you locate in in a central location with a drain that the hose can be attached to. Many dehumidifiers only have a pan that you can empty which is a pain, get one that has a hose connection so you can just set it and forget it. The more often you come and go the harder it will have to work to keep the boat dry. Good luck.
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Old 28-12-2017, 15:38   #3
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Re: Dehumidifier - will it make a difference?

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Originally Posted by SVRocinante View Post
Good day folks

Our first winter living aboard and the only real issue we're having is condensation! Warm, moist air hits the cold metal flanges of the portlights & hatches and we get rain!

I'm about to plunk down ~$200 on a Dehumidifier and wondering if it will actually make a difference. As I sit here writing this post it is 22 (degrees F) outside & 72 inside with 37% humidity.

If I'm understanding the relationship between Temperature, Relative Humidity & Dew Point correctly, I would have to get the humidity down to around 14% to stop the condensation at this moment.

Does anyone have personal experience with using a quality dehumidifier? Am I correct in my assumptions? If so, will one of the typical home units be able to do that?

Thanks for any and all help,
I can't tell you the exact dewpoint - but we are currently living aboard in Petersburg, Alaska - Southeast Peninsula. Very rainy and a lot of condensation to deal with. We had a small dehumidifier and it did almost nothing. We then got a larger one that we are very pleased with - removed a lot of water. Link on Amazon:

https://www.amazon.com/Eva-Dry-Edv-4.../dp/B00GOZ1XLK

It did make a significant difference and we highly recommend it, but there is still condensation in enclosed spaces that is very difficult to control.

Vent well, circulate air (with fans if possible) and use as much heat as practical. We also use a product called 'Golden Rods' for problematic places. Essentially just a small heated rod for small spaces.

Good luck
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Old 28-12-2017, 16:50   #4
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Re: Dehumidifier - will it make a difference?

Carlos and Maria,

The right dehumidifier will absolutely make a difference... [When used in conjunction with the right insulation, heat, and ventilation...]

We changed from the compressor type dehumidifier to the newer dessicant technology [no you don't change out any dessicant...] a couple of years ago and are very pleased with the efficiency, much lower level of ambient noise [you can hardly hear it running...], and low energy consumption.

The trade off for some is this type of dehumidifier emits a small amount of heat into the room- which is great for drying laundry and cool weather. [Conversely, compressor type dehumidifiers do not add heat to a room...] Therefore, this type of dehumidifier may not be as desirable for summer use in hot, humid climates- although they still work as expected.

If you are interested in more details- including links to related information- see the page we maintain on this topic.

In case this is helpful.

Cheers! Bill
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Old 28-12-2017, 17:00   #5
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Re: Dehumidifier - will it make a difference?

I believe that using propane for heating also produces water vapor.
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Old 28-12-2017, 18:35   #6
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Re: Dehumidifier - will it make a difference?

a REAL dehumidifier will make a tremendous difference, but stay away for the little toy Peltier plate ones etc.
I have no knowledge of the desiccant ones, ours is a larger compressor model. It is nothing more than a small air conditioner of course just the evaporator and condenser coils are together, so there is a heat gain from one, but in winter that isnít a bad thing.
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Old 28-12-2017, 19:41   #7
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Re: Dehumidifier - will it make a difference?

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I believe that using propane for heating also produces water vapor.
Yes for sure, propane does produce lots of moisture.
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Old 28-12-2017, 19:46   #8
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Re: Dehumidifier - will it make a difference?

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Yes for sure, propane does produce lots of moisture.


Propane only adds to the moisture in the cabin if itís not vented. A vented propane heater will produce dry heat just as diesel and electric will. The moisture comes from the combustion gasses vented into the living space.
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Old 28-12-2017, 20:03   #9
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Re: Dehumidifier - will it make a difference?

Yes, unvented only, 1.64 pounds of water per gallon of propane used
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Old 28-12-2017, 20:50   #10
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Re: Dehumidifier - will it make a difference?

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Propane only adds to the moisture in the cabin if itís not vented. A vented propane heater will produce dry heat just as diesel and electric will. The moisture comes from the combustion gasses vented into the living space.
Yes of course unvented.. people will often turn on the oven or stove to add extra heat in a boat and it really ups the moisture. I'm only aware of one propane heater for sailboats that is vented and that was a small bulkhead mounted heater by Force 10. Not even sure if they are still made.
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Old 28-12-2017, 21:32   #11
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Re: Dehumidifier - will it make a difference?

Put some bubble wrap over each port lite. It will help a lot while still allowing light in.
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Old 28-12-2017, 22:59   #12
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Re: Dehumidifier - will it make a difference?

Yes! Absolutely! We lived aboard a 46 foot motor sailer through many winters on the Canadian border in Western Washington. We bought the smallest Sears home dehumidifier (35 pints) and solved our indoor rain problem. We emptied a gallon or two of water from it every day. Currently I run a small dehumidifier on my catamaran in Florida all the time since I'm not on board. I'm able to run the hose into the galley sink. No mold!
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Old 29-12-2017, 00:57   #13
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Re: Dehumidifier - will it make a difference?

Quote:
Originally Posted by SVRocinante View Post
Good day folks

Our first winter living aboard and the only real issue we're having is condensation! Warm, moist air hits the cold metal flanges of the portlights & hatches and we get rain!

I'm about to plunk down ~$200 on a Dehumidifier and wondering if it will actually make a difference. As I sit here writing this post it is 22 (degrees F) outside & 72 inside with 37% humidity.

If I'm understanding the relationship between Temperature, Relative Humidity & Dew Point correctly, I would have to get the humidity down to around 14% to stop the condensation at this moment.

Does anyone have personal experience with using a quality dehumidifier? Am I correct in my assumptions? If so, will one of the typical home units be able to do that?

Thanks for any and all help,
If the relative humidity is 37%, all of this talk about dehumidifiers is off the point; you can't practically go much lower. The problem is insulation. You need to double glaze the windows and add boxes over the metal rims. This is the best solution. 15% RH will make your nose bleed and your woodwork crack... if you could get there, which I believe is impossible (most dehumidifiers cut out above 30%).

Search live aboard in cold climates.
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Old 29-12-2017, 02:52   #14
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Re: Dehumidifier - will it make a difference?

I run a Maeco DD8L junior desiccant dehumidifier. The good thing about these is they will keep working below 5 deg Celcius when compressor types won't, so can be left running on the boat without heating. I have mine set on the mid setting which keeps the RH at 50%.

I only use it in the main saloon and forward cabin areas, tending to leave the pilot house to its' own devices. I find that I am pouring away around 1 to 2 litres of water each day, most of this seems to be through the night-time when I am sleeping.

I couldn't be without it from mid September through to April. Outside humidity where I am from can often be 90% plus...
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Old 29-12-2017, 03:17   #15
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Re: Dehumidifier - will it make a difference?

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Originally Posted by robert sailor View Post
Yes of course unvented.. people will often turn on the oven or stove to add extra heat in a boat and it really ups the moisture. I'm only aware of one propane heater for sailboats that is vented and that was a small bulkhead mounted heater by Force 10. Not even sure if they are still made.
Force 10 is out of business. However, Dickerson/Sig marine makes two vented propane models, one is the Cozy Cabin model which is an exact copy of the Force 10 unit. Sells for about $500. US. Note: Per Dickerson, their vented units must have at least two feet of exhaust pipe in order to vent properly.
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