Dehumidifier...

The Admiral is convinced we need a dehumidifier on-board. I can understand one running whilst away, but when we are onboard either the windows are open, the A/C is on or we have the heat going so its either in-effective or redundant.

Thoughts?

I leave one running in the galley sink when the boat is tied up in the winter but put it away in the summer. They draw quite a bit of power.

Running a dehumidifier with the windows open would about as effective as running either A/C or heat with the windows open. That makes no sense.

An A/C IS a dehumidifier.

Forced hot air does a pretty darn good job of drying the air as well.

We only ever used a dehumidifier when the boat was closed and no A/C or heat running, which is typically when we were away for several days.

Osprey69 said:

The Admiral is convinced we need a dehumidifier on-board. I can understand one running whilst away, but when we are onboard either the windows are open, the A/C is on or we have the heat going so its either in-effective or redundant.

Thoughts?

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Our dehumidifier is on while boat is in slip and we are not aboard. When we are on board the a/c is running and don't have the need to run the dehumidifier as well.

I have a built in ducted dehumidifier and we run in a lot while on board. However that is in the PNW where it is cool and moist. The dehumidifier adds a small amount of heat and removes the moisture. In Florida, where either the AC will be running or the windows open, a dehumidifier will do nothing except consume power. Still good when you are away from the boat as it uses less energy to dehumidify than the AC.

I just hope this doesn’t turn into another salty air thread.

SeaDogAK said:

I just hope this doesn’t turn into another salty air thread.

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lol, i remember that one.

Yup. Your conclusions are my conclusions. Thanks Now I must (hopefully) transfer those thermo-dynamic conclusions effectively.

And about that salty air...

Dehumidifier is one of the first things we got for new to us GB 42 in Puget Sound.
Eva dry desiccant, drains to sink. Works in lower temps than compressor types, they say. Runs on “auto” all the time. Interior Humidity has been consistently low to mid fifties. No condensation. Seems to work as designed.
Way down the road I would consider installing a built in one, also desiccant, like they did on MV freedom.
We don’t run this one underway.

SeaDogAK said:

I leave one running in the galley sink when the boat is tied up in the winter but put it away in the summer. They draw quite a bit of power.

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Sorry, but that sounds completely backward. Unless you live in some weird location, around here, humidity is not a problem during the winter, often, it is very low. Summertime, it usually runs very high. Now, if you keep your AC on for a good amount of time, I can see putting it away.

I guess Juneau, Alaska is a weird location. Things get damp and mildewy in the winter. It’s not so much of an an issue in the summer.

Chuck34 said:

Sorry, but that sounds completely backward. Unless you live in some weird location, around here, humidity is not a problem during the winter, often, it is very low. Summertime, it usually runs very high. Now, if you keep your AC on for a good amount of time, I can see putting it away.

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Where's "around here"? My boat is sitting in Anacortes, humidity is measured in 3 locations and uploaded every 15 minutes all winter long. It has been running about 70 - 75% with no dehumidifier running. I have the compressor type, it shuts down at around 45 deg to keep from freezing, and it's been colder than that for the last month.

Is 75% humidity a problem? Probably not as long as temps are in the 40s or below. Mold and mildew don't grow much then.

NWboater2 said:

Dehumidifier is one of the first things we got for new to us GB 42 in Puget Sound.
Eva dry desiccant, drains to sink. Works in lower temps than compressor types, they say. Runs on “auto” all the time. Interior Humidity has been consistently low to mid fifties. No condensation. Seems to work as designed.
Way down the road I would consider installing a built in one, also desiccant, like they did on MV freedom.
We don’t run this one underway.

Click to expand...

Questions on your experience with the Eva Dry, I assume it is a rotary desiccant type. Do you know what the lifetime of the wheel is?

I was looking into the Ecor Por, which are a ducted unit seemingly idea for a boat (ss cabinet), but they state that the desiccant wheel has about a 4-5 year life, and a new one costs around $500 or $600 - half the price of the unit. This seems like a big drawback to the technology.

Experience so far so good - same weather as your boat, and about 20-25% less RH in the boat this winter, only had it about 4 months. I bought the Eva-Dry Edv-4000H Rotary Desiccant Dehumidifier on amazon - $300 ish.

I'm not sure this one would be worth a new wheel. Didn't realize mine or even the more industrial ones like ECOR had to get a new wheel in 4-5 years.

good luck!

Shrew said:

An A/C IS a dehumidifier.

Forced hot air does a pretty darn good job of drying the air as well.

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Air Conditioning does dehumidify, in that every 20 degree drop lowers the absolute humidity by 50%. Sending warm moist air past chilled coils will cause the humidity in that air to condense out. However, to gain that effect, one must actually be conditioning that air. In cooler temps, cooling the air results in cold, unhappy people.


AC-style dehumidifiers work by sending warm moist air past a set of chilled coils to cause the humidity to condense out, then sending that cooled dryer air past a set of heated coils where the waste heat of the prior cooling function is waiting to rewarm the air. Efficiency losses aside, the air comes out at the same temperature it went in, but with less humidity as that H20 has gone out the condensate drain. Using a dehumidifier in cooler temps doesn't result in cold, unhappy people unless further heating is needed.

NWboater2 said:

Experience so far so good - same weather as your boat, and about 20-25% less RH in the boat this winter, only had it about 4 months. I bought the Eva-Dry Edv-4000H Rotary Desiccant Dehumidifier on amazon - $300 ish.

I'm not sure this one would be worth a new wheel. Didn't realize mine or even the more industrial ones like ECOR had to get a new wheel in 4-5 years.

good luck!

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Yeah, at $300 if you had to replace the whole unit every 5 years, not so bad. The only desiccant wheel ducted unit I've seen is the Ecor, it is considerable more expensive at about $1300, and replacing the wheel is expensive. Assuming they are around when you need to replace it. I want the ducted unit because I'd like to install it as I have the compressor unit, in the air conditioning ducting, so that it blows air throughout the boat.

I realize there are a lot of folks here that are older and saltier than the MV Freedom crew on youtube but i think they do a good job and they have that early N43 pretty buffed out. Take a look at the episode where he installs one of those Ecor or similar dessicant dehumidifiers. didnt look too hard and they were very happy with it.

In the shed and when at the dock We use a 110v home dehumidifier during the winter Just leave it on and draining out to deck .Different we usually have 4 to 6 people on board and it does pump up he moisture and running dishwasher and cooking . Come summer we might run it overnight so that the upper bridge windows are clear .
It helps keeping everything dry and fresh. I feel a few extra bucks on running it for the cost of your boat worth is worth it.

Osprey69 said:

The Admiral is convinced we need a dehumidifier on-board. I can understand one running whilst away, but when we are onboard either the windows are open, the A/C is on or we have the heat going so its either in-effective or redundant.

Thoughts?

Click to expand...

You answered your own question. Your Admiral thinks you need a dehumidifier so OF COURSE you need a dehumidifier!

Tak

Takoradi said:

You answered your own question. Your Admiral thinks you need a dehumidifier so OF COURSE you need a dehumidifier!

Tak

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Yup…

I have a tip and trust me, I have proven this a few times. For the driest air with A/C, keep the room temp UP! 70 - 75, higher better, as long as the compressor is cycling regularly. The air that comes out of the vent is saturated, 99% RH, it becomes relatively dry air once it's re-warmed by the air and objects in the space. For effective dehumidifying there has to be a good difference between the outlet temp and room temp.

And, incidentally, you will see 'Dehumidify' on some controls - it doesn't do anything unless the dehumidifier option is installed in the air handler, and that consists of a heater that re-warms the outlet air.

Dehumidifier

Part of the answer may be in where you boat.

IF you are going to be a boater who gravitates towards a FL/Bahamas environment then a dehumidifier may be in your future.

IF on the other hand you will branch out to further ports of call then maybe not.

A few clarifications on our cruising while on the Loop for the last 7 yrs.

We are not big A/C people. When we run the A/C while at a dock (we don't have a soft-start necessary to run our A/C on battery) we have all of our windows open. At night we use a Dyson hot/cold fan set to cool and point it into the MSR.

We store our boat for the winter wherever we stop for the season while on our Loop or the Chesapeake before we started. We have never run a dehumidifier.

One of the 1st things I did was to add solar fans to our 2 hatches. One is on the fwd deck house the other on the sundeck over our MSR. When the boat is buttoned up for the winter the solar fans provide the right amount of air flow to keep the boat neutral as to humidity. Even under shrink-wrap in the Chesapeake we've never had a mold or mildew problem.

I think that the problem arises due to lack of air circulation, so people add a dehumidifier.

That is our experience, hope it helps.

Nepidae said:

When we run the A/C while at a dock (we don't have a soft-start necessary to run our A/C on battery) we have all of our windows open.

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Not sure what the point of that is. Are you hoping to solve Global Warming?

Dehumidifier

Some need a direct line to follow the flow, others might be able to think between the lines.

A fresh air environment is much better for an individual as to a closed AC environment. Windows open and fresh air flowing in, to us, is a much nicer way to live.

Since most AC units have a thermostat that can be set to a temperature that would allow for the AC to come on ONLY if the indoor temps were to reach a certain high temperature would seem to offer the fresh air living and yet if the temperature were to get too hot, allow for AC to come on and offer cooling.

OR, I'm fighting the global warming lie in my own way.

Thanks for your interest.

I'm having a hard time wrapping my head around the topic of dehumidification on a boat. It's a given that the interior of a boat is far, far from air tight. Even if all the hatches and windows have good watertight seals, there are multiple vents to the outside atmosphere that cannot be conveniently sealed. For instance, engine room ventilation provides a huge opening into the boat from which outside air can enter the boat 24/7.

So, if one runs a dehumidifier inside the boat, and IF the interior temperature is held high enough to ensure the dehumidifier actually works, then yes, moisture is removed from the interior air, with the condensate returned to the sea. Only to be immediately replaced with moist outside air that must be heated for the dehumidifier to work effectively. Rinse and repeat.

So what is the end result? Lots of energy expended to dehumidify the outside atmosphere! And yes, I get it that responses to this topic is very very location-dependant. Those blessed with warm ambient air temps year-round probably can benefit from some form of moisture removal. However, for those of us that routinely heat our boats in the winter, either to prevent freezing or simply for comfort, seem to have limited options to keep the interior dry.

Both in SoCal, and here in the PNW, it has been my experience that maintaining the inside air temperature above the dew point, combined with continual air exchange via vents and fans, and leaving the boat with the interior opened up (i.e.-cabinet and interior doors propped open) as much as possible minimizes issues associated with moisture. Dehumidification seems like a fruitless undertaking to me.

Regards,

Pete

If it's cold enough that you're heating the boat, then yes, you're often better off lowering humidity via air exchange rather than dehumidifying. But in warm weather, dehumidifying the air (either with a standalone dehumidifier or via air conditioning) is the only way to dry things out.

EngNate said:

And, incidentally, you will see 'Dehumidify' on some controls - it doesn't do anything unless the dehumidifier option is installed in the air handler, and that consists of a heater that re-warms the outlet air.

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The “Dehumidify” function on some HVAC units will cause it to run the AC on a programmed schedule, such as 15 minutes every 12 hours, an is intended for an unoccupied boat. That will effectively reduce the humidity in a boat that is reasonably well sealed up. No RE-warming required.

jungpeter said:

I'm having a hard time wrapping my head around the topic of dehumidification on a boat. It's a given that the interior of a boat is far, far from air tight.
.....

Dehumidification seems like a fruitless undertaking to me.

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Your boat may be leaky, or may not be. If there is much air exchange, then dehumidification either doesn't work, or takes a lot of energy. But not all boats are leaky. Once the humidity has been brought down (and this takes a day or so, because the woodwork and upholstery store quite a lot of moisture), ours runs at around 20 - 30% duty cycle in the wet PNW. It uses 300W when running. So averaging about 100W or less.

The difference is substantial. The windows don't fog. There is no condensation at the bottom of the aluminum frames. Fabric feels dry, not slightly damp. Bath towels dry in a few hours, not a few days. And you don't feel sweaty. Air circulation helps, if the humidity isn't terribly high, but when it is 65 deg and foggy, a hurricane of wind doesn't change anything.

Here in SE Alaska, the ambient humidity in winter is quite high. Even with some heat on the boat - needed to keep things from freezing - it’s humid enough in the winter to grow mold. So a dehumidifier is needed. Yes, there’s a little air exchange (not much) with the outside, which is why the dehumidifier cycles all winter.