Dehumidifier - will it make a difference?

[derfy]

Originally Posted by Sailmonkey

I don’t have that exact model, one VERY similar. Complete with electronic push buttons. Mine does resume operation after power failure. I think most manufacturers now have gotten wise to the fact that not resuming after a power failure isn’t acceptable.

Ok. Thanks again.

[CaptTom]

Originally Posted by mikedefieslife

...By venting the hot air out of the boat, you are also venting out the moisture with it...

Most will realise how daft this is, as it costs good money to heat the air.

I once read about an air-to-air heat exchanger, that, if the air travels far enough along it, is almost 100% efficient at using the outgoing air to warm up the incoming air. I didn't believe it at first, but when I read up on it, it started to make sense.

I always wondered why someone doesn't market one for a boat.

[stormalong]

Originally Posted by CaptTom

I once read about an air-to-air heat exchanger, that, if the air travels far enough along it, is almost 100% efficient at using the outgoing air to warm up the incoming air. I didn't believe it at first, but when I read up on it, it started to make sense.

I always wondered why someone doesn't market one for a boat.

Because they are quite bulky and there is no room for one on a small boat.

[a64pilot]

Originally Posted by CaptTom

I once read about an air-to-air heat exchanger, that, if the air travels far enough along it, is almost 100% efficient at using the outgoing air to warm up the incoming air. I didn't believe it at first, but when I read up on it, it started to make sense.



I always wondered why someone doesn't market one for a boat.

Your absolutely correct
IF It travels far enough along it. Air to air can require quite large exchangers, for example the turbo intercooler on my Duramax powered truck was in front of and larger than the radiator, it was HUGE, but the Dmax lived on boost, and heat of course negates boost.
A very big reason why water cooled air conditioners have lost favor in residential heat pumps is because they are now fitted with huge air to air heat exchangers, and they are as efficient as water cooled. I think my house heat pump had a 24 Sg ft heat exchanger and it was when running on the big compressor 2.5 tons, normally 1.5 tons.
A ton is about 12,000 BTU, so based on that decide how big a heat ex a standard Marine AC would need.
Now mine was the most efficient there was at the time I bought it so you don’t need that big unless you want efficiency.

[Symphony]

If you want to avoid condensation you need a barrier bewtween the cold winter and the surface of your boat, especially ports. Get a boat cover; shrink wrap is bright but humid, canvas like Fairclough, will make your cabin cozy and dry while protecting the topsides.

[sailorcherry]

Do it now before you have a mold outbreak! Been there, done that. Had to tear out hull blanket/liner.

Spent $200 on a big one. R2 hasn't allowed any mold in since. Your boat will smell better too. When I spill water on my pillow, I seem to have a drinking problem in bed, I don't put it outside to dry, I flop it over the dehumidifier and it's dry in a few hours. They work as excellent primary or secondary heaters as well, even when on the hook, thanks to the genny.

[SVRocinante]

Originally Posted by senormechanico

...
Who cares what it looks like if it's keeping you warm and DRY ?

My lovely wife!

[MarkusK]

Originally Posted by CaptTom

I once read about an air-to-air heat exchanger, that, if the air travels far enough along it, is almost 100% efficient at using the outgoing air to warm up the incoming air. I didn't believe it at first, but when I read up on it, it started to make sense.

I always wondered why someone doesn't market one for a boat.

Heat Recovery Ventilators (HRV) are an excellent way to get pre-heated fresh air while exhausting stale air. In fact, here in Quebec, they are part of our building code and all new homes MUST have one. However, they cannot be considered instead of a dehumidifier. If it is 60°F outside and raining (90%RH), then this is ~57° Dew Point air you are intruding into your ~45°F DP space…you are adding moisture. Remember, heating this air does not change the DP.
The main job of an HRV is to improve air quality.
A scaled down version for boat use would be interesting but likely only applicable to larger boats with a ducted heating/cooling system.

[Luckyknot]

Originally Posted by thinwater

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.

This is a very good point. Humans like RH to be at least 25%. Drying the air too much will help you get sick. It sounds like you need some sort of thermal break between the outside and inside metal pieces. This is common practice in air handler construction to stop heat transfer from the cold interior to the warmer exterior (you have the reverse issue). You may also have air infiltration if any part of the seals are bad.

[Supers0nic]

Luckyknot is right.

I'm living full time on my sailboat in Maine. It was minus 20F this morning. Forget the dehumidifier. The winter air is already dry. You need a thermal break on those Port lights. Clear bubble wrap works good. I also put foilfaced bubble wrap against the hull in problem areas. Try to avoid leaving anything leaning against the cold hull. It will get wet. Sometimes this can't be avoided especially with bedding. Flip your mattress every couple of days to allow it to air dry. All these things are pretty simple. You'll be fine.

[DreaminFred]

Originally Posted by Symphony

What they all said. Good advice on the difference between condensation and relative humidity.

Below 40% RH is unhealthy for your mucous membranes and skin. Below 30% and you are in the Sahara.

Officially calling bs on this. Phoenix is the sixth most populated city in the US and our average humidity is 37%. Months at a time below 20%. You may not like the way you nose and skin feels, but not "unhealthy"

In contrast, sweating doesn't work to cool your body at high humidity. Heat stroke can kill you, dry nose doesn't.

Grew up in Florida, Phoenix for 15 yrs. I prefer Phoenix humidity.

[Symphony]

Originally Posted by DreaminFred

Officially calling bs on this. Phoenix is the sixth most populated city in the US and our average humidity is 37%. Months at a time below 20%. You may not like the way you nose and skin feels, but not "unhealthy"

In contrast, sweating doesn't work to cool your body at high humidity. Heat stroke can kill you, dry nose doesn't.

Grew up in Florida, Phoenix for 15 yrs. I prefer Phoenix humidity.

I'm glad you like it there, Fred. Great area with low humidity some times and monsoon season too, high humidity then. I doubt you live in <30% humidity for very long at a time, but it doesn't mean your body is different from average.

I won't bore you with links, but you can quickly and easily search for facts and studies to read. if you like medical studies you can use pasipedia.org to get through all the noise of commercial sites.

most healthful range is 40-60% relative humidity.
below 40% is sub-optimal for the average person of average health. issues are for the eyes, sinuses, skin, and the fact that it is easier to contract colds and flu, and the sickness lasts longer.
below 30% is unhealthful and magnifies the above problems.
below 25% is dangerous for very long, affecting first the eyes, then the sinuses. skin and general likelihood to suffer respiratory infections for long periods.

but I bet there are some people who feel peachy at 25% RH. That's called anecdotal evidence. Like you, I prefer Arizona to Florida. Right now I am in Connecticut winter, and we must humidify our home (a lot) to avoid respiratory and eye problems. We work to keep the house above 40% given how often the furnace runs.

the Sahara desert is average 25% RH

Spring is supposedly starting and I am looking at snow....

[john61ct]

I've lived in all those conditions and never had a problem myself.

That's my reality and I'm sticking to it.

Plenty of people may have real problems with "too dry" air besides minor discomforts, but for me, those are the anecdotes I ignore, way too many precious snowflake hypochondriacs out there.

[Cadence]

Originally Posted by SVRocinante

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 doubt you want to get it down to 14 % humidity. You would probably wake up with a sore throat. Come up with some form of insolation.

[CarinaPDX]

When I first returned from cruising, fully adapted to very high humidities, I began visiting my brother in Bend, OR (High Desert). Humidities are frequently below 20%. I had cracking lips, dry sinuses and sore throats whenever i visited. Once acclimated it isn't so bad, other than needing to drink water through the night. But the other health hazard that gets missed is that of the humidifiers - they can be breeding grounds for bacteria, which they effectively disperse into the air in the atomized water. They have to be kept meticulously clean - or do as my brother and stop using them.

Greg