Use dehumidify mode or reverse cycle heat

I have been trying to find the best way to hold the humidity down in our very changing temperatures up in the Florida panhandle. We have multiple cruise air systems with reverse cycle heat. I have the dehumidify mode to run every six hours but I have always wondered when it is cold like today, 42 degrees, if I would be better off running the heat. We do not live aboard so the temperature is not a comfort factor, just humidity. What has your experience been. Thanks

When we run the heat overnight without the humidifier, we wake up with dry throats and sinuses. Those units, whether heating or cool, dry the air out pretty well. I would say running the heat will be fine.

Roger

I know of several people who place a purpose built dehumidifier or two in or near a sink for drainage. The amount of water they pull out of the air is astounding. In the cooler months where the heat they generate is not an issue it is a plus. Mechanically a lot simpler than running the AC units.

Generally the cooler the temperature, the less humidity you have. By heating the space you will drive the moisture out of the environment,and into the air. A portable dehumidifier would work at a set point and work only when needed. Would set a/c heat at 50* and humidity at 65%.

sunchaser said:

Roger



I know of several people who place a purpose built dehumidifier or two in or near a sink for drainage. The amount of water they pull out of the air is astounding. In the cooler months where the heat they generate is not an issue it is a plus. Mechanically a lot simpler than running the AC units.

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This is what I do. I have a smallish room dehumidifier that I keep running in my boats full time. It sits on the galley counter and drains into the sink. It runs almost full time as I set the humidity level at 35%. That is very low but since it only sits in the galley the rest of the boat won't hit that same level.

The only downside is that even though it is "portable" it still is a bit of a pain to take off the boat and put in a dock box or stash in an empty cabin when getting under way. The boat stays very dry however.

For years my prefered method of controlling humidity was ventilation.
It worked to a point, but pulling in near 100% humidity air to replace the same humidity air doesnt really help much.

The symptoms were what we all have experienced. Boat feels damp, towles dont dry, etc....

Then last fall I bit the bullet and bought a real dehumidifier. What a huge difference!

Mine, like the one Dave describes above has a hose attachment. Right now it sits on the counter when we are not on the boat, draining into the galley sink.

When we are on the boat, my intention is to secure it on the floor, and use the built in water collection "bucket", so the boat will stay dry all the time. You have to empty the bucket daily, or before getting underway for the daybut it's a two minute job.

I cannot believe that I went all those years with a damp boat!

ksanders said:

For years my prefered method of controlling humidity was ventilation.
It worked to a point, but pulling in near 100% humidity air to replace the same humidity air doesnt really help much.

the symptoms were what we all have experienced. Boat feels damp, towles dont dry, etc....

Then last fall I bit the bullet and bought a real dehumidifier. What a huge difference!

Mine, like the one Dave describes above has a hose attachment. Right now it sits on the counter when we are not on the boat, draining into the galley sink.

When we are on the boat, my intention is to secure it on the floor, and use the built in water collection "bucket", so the boat will stay dry all the time.

Click to expand...

This last weekend we had 4 adults on board the boat in very cold weather which meant that the boat was buttoned up tight. Add propane cooking, making hot drinks etc, we were putting out a lot of moisture into the boat. Since it was below freezing outside any moisture in the boat would condense on the windows and hatches. This was the first time we ran the dehumidifier away from the dock. It helped a lot. The only downside is that the fan is pretty noisy. I am considering getting a small Peltier dehumidifier to use out on the boat. Quiet and uses less electricity, just not as effective as the regular one.

Kevin

What brand, daily liter/gallons listed output and rated amperage draw is your unit?

Second that about a purpose built dehumidifier.

For years I battled high moisture in SE USA conditions. Here we get significant temperature and humidity swings and using the installed reverse cycle units gave poor results.

So I finally bought a dehum. Problems solved. Completely.

Boat stays dry and fresh and smells better. Minimal power use. Only runs when actual dewpoint rises over 45F. Less wear and tear on rev cyc units.

dhays said:

This last weekend we had 4 adults on board the boat in very cold weather which meant that the boat was buttoned up tight. Add propane cooking, making hot drinks etc, we were putting out a lot of moisture into the boat. Since it was below freezing outside any moisture in the boat would condense on the windows and hatches. This was the first time we ran the dehumidifier away from the dock. It helped a lot. The only downside is that the fan is pretty noisy. I am considering getting a small Peltier dehumidifier to use out on the boat. Quiet and uses less electricity, just not as effective as the regular one.

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What I didn't share in my first post was that the unit I purchased was physically large, and yes noisy. It was what the big box store had left in stock.

What I am thinking of doing is replacing the large unit I bought, with two much smaller models, one in the salon and one downstairs where the cabins are. I am hoping for a quieter situation, and also hoping to more evenly dry out the air, since there is no forced air exchange between the two areas.

If noise is still a factor the only other choice will be to turn them off at night. Time will tell how it all works out since we havent been at anchor with one running all the time.

sunchaser said:

Kevin

What brand, daily liter/gallons listed output and rated amperage draw is your unit?

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I don't remember, sorry it's on the boat. It was the only size left in stock last fall, and is if memory serves correctly the largest unt they sell.

I'll probably move that one to the house, and buy two smaller ones this spring.

This is the one we use. Ecoseb DD122EA-SIMPLE desiccant dehumidifier. It's about $200 from Amazon. We drain it into the galley sink. Sorry, don't have the current draw handy, but I know it's not much.

sunchaser said:

Kevin

What brand, daily liter/gallons listed output and rated amperage draw is your unit?

Click to expand...

I have used two dehumidifiers since I have too often had two boats (anyone want to buy a 40' sailboat?). I have used the smaller 30 pint units and they work great for my boats from 36 - 43 feet. I have found that using a couple fans in the boat to help circulate the air between cabins and the saloon helps. The next size larger Re typically rated at 70 pints (i.e. Remove 70 pints per 24 hour period). The two that I have are very old. If I was to buy. New one I would likely get this one.
https://www.amazon.com/30-Pint-Dehu...eywords=Frigidaire+FAD301NWD+Dehumidifier#Ask

I believe it uses about 320 watts at under 4 amps.

We use two Eva-Dry units, one std size in the v-berth and a petite size in the aft stateroom. Quiet and efficient. We are pleased with their performance.
Purchased at Fisheries in Seattle.

Bill

sunchaser said:

Roger

I know of several people who place a purpose built dehumidifier or two in or near a sink for drainage. The amount of water they pull out of the air is astounding. In the cooler months where the heat they generate is not an issue it is a plus. Mechanically a lot simpler than running the AC units.

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+1 to that.

Tuttouomo said:

We use two Eva-Dry units, one std size in the v-berth and a petite size in the aft stateroom. Quiet and efficient. We are pleased with their performance.
Purchased at Fisheries in Seattle.

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Good to know Bill, thanks.

I too use dehumiifiers. Two Eve Dry petites. One in the galley sink and one in the head sink. Both modified to use a drain tube to self drain into the sinks.

My boat is much smaller so they are enough to help a lot along with the plethora of fans to force circulation constantly. I no longer winter boat so getting away quickly is not a consideration any longer.

Before I got the fans and the dehumidifiers mildew and high humidity was a problem.
Several winters, although no boat use, we were home and I was frequently aboard and the difference was huge-no odour and no whitish spots.

So so know the boat is fully winterized.

Rogerh said:

I have been trying to find the best way to hold the humidity down in our very changing temperatures up in the Florida panhandle. We have multiple cruise air systems with reverse cycle heat. I have the dehumidify mode to run every six hours but I have always wondered when it is cold like today, 42 degrees, if I would be better off running the heat. We do not live aboard so the temperature is not a comfort factor, just humidity. What has your experience been. Thanks

Click to expand...

Between your dehumidify mode and your heat you should be in good shape. Heat simply depends on how many degrees you raise the temperature as to how much it will dry the air. I would get some thermometers with humidity readout and simply check to see how well what I was doing was working.

Normally as long as humidity is below 50% you're ok. However, that doesn't hold true for winter and 42 degrees as typically you'll have to lower the humidity further to avoid condensation on the windows, lowering to below 40% and perhaps as low as 30%.

I honestly do not think the dehumidify mode on these reverse cycles work that well. WHen selling my last boat, I had a mildew issue and did not know why. I had the boat 6 years at that point and in 3 different marinas. THis particular year I was fighting it. My boat was a very clean boat...as far as showing it by the broker. So he was always confident when showing my boat. I get a phone call....WHAT THE HELL????.....is going on with your boat. I go down there and it is BLACK on the inside....overcome with mildew....headliner...walls...everywhere!!! Well I get the cleaner lady to clean it all up and then buy a small dehumidifier. Never had the issue again. The boat sold to the people who saw it all mildewed out. It really was a clean boat.

My dehumidifier actually fits INSIDE the sink so I just plug it in and drop it inside the sink. It works WAY better than the mode on your AC. I would highly recommend!

Just a thought and a question. The cooling cycle on these reverse cycle systems compresses and condenses and takes the water out of the air. If you reverse that cycle, are you not adding water back into the air??? I am asking based on theory AND reality...the reality being when I run reverse cycle heat the air coming out of the vent is noticeably moist/humid!!!

Baker said:

Just a thought and a question. The cooling cycle on these reverse cycle systems compresses and condenses and takes the water out of the air. If you reverse that cycle, are you not adding water back into the air??? I am asking based on theory AND reality...the reality being when I run reverse cycle heat the air coming out of the vent is noticeably moist/humid!!!

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The issue is that we're dealing with relative humidity vs. absolute. As you warm the air it is capable of holding more moisture. So, if the amount of moisture in the air remains the same, the relative humidity drops. Therefore, heat 30 degree air to 60 degrees and the relatively humidity drops significantly. The numerator doesn't change, the denominator does.

As to running the dehumidifying cycles, I also question how well many of them work. i run the air conditioning itself to keep things dry when not aboard.

I've found over the years, whether house or boat, regardless of location, maintaining as near a normal temperature as possible minimizes issues of humidity, mildew, mold and freezing. I've seen homes on the market that the owner didn't want to pay for heating or cooling suffer a lot of damage in fairly short periods of time. I just checked our electric bills on Pickwick for November and December and they were about $50 per month although January will be much higher. Even at $100 per month when compared to all the other costs such as the slip itself, just seems a good investment to me plus maintains the equipment in good working order.

BandB said:

The issue is that we're dealing with relative humidity vs. absolute. As you warm the air it is capable of holding more moisture. So, if the amount of moisture in the air remains the same, the relative humidity drops. Therefore, heat 30 degree air to 60 degrees and the relatively humidity drops significantly. The numerator doesn't change, the denominator does.

As to running the dehumidifying cycles, I also question how well many of them work. i run the air conditioning itself to keep things dry when not aboard.

I've found over the years, whether house or boat, regardless of location, maintaining as near a normal temperature as possible minimizes issues of humidity, mildew, mold and freezing. I've seen homes on the market that the owner didn't want to pay for heating or cooling suffer a lot of damage in fairly short periods of time. I just checked our electric bills on Pickwick for November and December and they were about $50 per month although January will be much higher. Even at $100 per month when compared to all the other costs such as the slip itself, just seems a good investment to me plus maintains the equipment in good working order.

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I am well aware of the ability of air to hold water relative to temp. I are a pilot...remember... I was just referring to the cycle of a reverse cycle AC. On the cold cycle, (relative)moisture is taken out of the air not only by the physical effect of cooling the air, but also by the system itself that is designed to take moisture out of the air on that cycle(hence the condensate that drains out). Now if you reverse that cycle, I don't see the ability to dry the air since the drying portion is optimized on the normal "forward" cycle.

In our homes, we simply take ambient air and heat it. That will dry the air.

In an airplane, we take ambient air(usually -40 of colder which is extremely dry)and then it is heat thru the engine's compressor section(that heats it to about 700C) and then run it through about 3 compress and condense cycles with dryers after each cycle. You end up with VERY DRY air(less than 5% humidity).

But we aren't heating the air by any other means than reversing the cycle on a boat. I realize we are extracting heat out of the water. But I am just thinking out loud here....and somewhat ignorantly I will admit.

In cool mode water condenses out of the air and is drained away as a liquid. Result is lower RH and lower moisture content in the air.

In heat mode, the water content in the air is not changed like it is in cool. But the temp is raised which means RH goes down.

In cool mode the evaporator is damp. If you switch to heat, it drives out that moisture so you get the muggy smell for say the first ten minutes. Maybe that is what you are detecting. Once dried out, the damp muggy sensation out the vents should vanish.

My biggest problem with humidity was not in the winter or summer, but spring and fall when there was no real need for any hvac. Boat turned into a swamp and rev cycle in dehum mode was simply not effective. Dedicated dehum was effective.

If I am away from the boat, I use my reverse cycle A/C dehumidifiers to run for 2 hours in the morning and two hours in the evening. I have 4 but only run two, one downstairs and one up. I realize a lot of boats don't have this luxury, but this keeps it totally dry and prevents that damp odor.

I have a question concerning Eva-dry
If I have an Eva-dry in my aft cabin head, so it can drain into the sink will it be effective in drying out my aft cabin? I would like to put one in my aft cabin head and one in my galley sink.
During the winter I cover my boat with a full Lohman winter cover and I also tighten my stuffing box and towel dry my bilge, so I have a dry boat. But my humidity level is stlll over 80%. This is with 3 camframo dehumidifier air dryers.
I saw a video blog of a guy living on a sail boat in Prince Rupert, with two Eva-drys and a diesel heater and his humidity level was 36% in the winter time.

If an Eva Dry is your common dehumidifier, then YES, it should help a LOT.

grahamdouglass said:

I have a question concerning Eva-dry
If I have an Eva-dry in my aft cabin head, so it can drain into the sink will it be effective in drying out my aft cabin? I would like to put one in my aft cabin head and one in my galley sink.
During the winter I cover my boat with a full Lohman winter cover and I also tighten my stuffing box and towel dry my bilge, so I have a dry boat. But my humidity level is stlll over 80%. This is with 3 camframo dehumidifier air dryers.
I saw a video blog of a guy living on a sail boat in Prince Rupert, with two Eva-drys and a diesel heater and his humidity level was 36% in the winter time.

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Look at Ski's explanation but also
If you are referring to the Caframo Stor-dri it is not a dehumidifier. It is a heater which by heating the air will drop the relative humidity but it will NOT remove moisture from the air. If that air is cooled again the moisture is still present and the relative humidity will rise, maybe to a problem level.
A real dehumidifier will condense moisture out of the air and , if it has a place for the condensate to go such as down a drain, it will remove moisture from a cabin.

You need a real dehumidifier. Those Caframo units are usefull as part of the package but will not do what a dehumidifier can.

Diesel stoves, heaters will dry a boat out, at least the area they are in. I have one, a Dickinson stove. The combustion air is often taken from the cabin which takes moisture out. The heat will drop the relative humidity, the dehumidifiers will actually remove moisture so he had a good system. However, where there is no heat from the stove there can still be problems especially if there is inadequate air exchange.


Whether or not the Eva dry will be enough in your case is a matter of trial and error. I would suggest the larger of the two Evas or try a small one and then another if needed. They really do not draw much power and they can do a decent job.

As noted the refrig. unit types can be noisy and if you are not aboard who cares. They will remove much more than the Eva. But if you are aboard the Evas are very quiet.

grahamdouglass said:

I have a question concerning Eva-dry
If I have an Eva-dry in my aft cabin head, so it can drain into the sink will it be effective in drying out my aft cabin? I would like to put one in my aft cabin head and one in my galley sink.
During the winter I cover my boat with a full Lohman winter cover and I also tighten my stuffing box and towel dry my bilge, so I have a dry boat. But my humidity level is stlll over 80%. This is with 3 camframo dehumidifier air dryers.
I saw a video blog of a guy living on a sail boat in Prince Rupert, with two Eva-drys and a diesel heater and his humidity level was 36% in the winter time.

Click to expand...

It will help immensely but....

If you are primarily storing your boat in the winter (you mentioned the cover and drying the bilge) then I would recommend a 30 pint household dehumidifier rather than a Peltier type dehumidifier like the Eva Dry. Peltier will tend to ice up in cool weather where as a regular dehumidifier can still function down to 40 degrees. Once a Peltier ices up it really has a hard time getting hawing out while it is running.

Second issue is that the Eva Dry does not have a hose connection. Once the bucket fills it will turn off. You can create one with a drill and some fittings but even then it won't be as effective as drying the air as a standard 30 pint dehumidifier.

I would suggest get two 30 pint units and drain them into the galley and head sinks, or simply use one and a then a couple of fans to help get air exchange in the boat. That is what we do and it is keeping the humidity in our boat down around 35%.

I am interested in getting an Eva Dry to use while we are on the boat in the winter. The interior of the boat is warm when we are on board and we are there to empty the bucket as needed.

harvardrvr said:

If I am away from the boat, I use my reverse cycle A/C dehumidifiers to run for 2 hours in the morning and two hours in the evening. I have 4 but only run two, one downstairs and one up. I realize a lot of boats don't have this luxury, but this keeps it totally dry and prevents that damp odor.

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How do you get over the anxiety of having a running pump that is open to sea while you are away?? We have thought about having two of our four heaters run while we are gone too, but I can't force myself to get over this mental hurdle.

(BTW we made it to Manteo and are in the slip right next to the T-head where you were all those years ago )

If the guy living on the boat goes in and out a lot, just good old fashion air exchange could be the answer.

Especially if the diesel heater uses make up air from the outside.

His boat might be fine without the Eva dry things.

Your boat once all closed up and gets a dose of humid air could take a long time to dry out with tiny dehumidifiers...at that point you have to do the math to match minimum performance of the units with your situation.

I don't know anything about them...but they look like you would need a bunch of them....but that is not really knowing their specs, just typical skepticism of manufacturer claims.