De-humidifier alone or with heater?

[Gazza]

Boat will be coming out of the water next week, and will be using, for the first time, a de-humidifier draining into the galley sink. I usually use an greenhouse electric heater and am wondering if it's better to continue with this with the de-humidifier or not?
Any thoughts gratefully received.

 

[bobgoode]

With a heater will be more effective, although to some ectent it depends upon the type of dehumidifier you are using as well as ambient temp. A dehumidifier with hot gas defrost will work at lower temperature than the normal household type.

 

[l'escargot]

Dehumidifiers can take more moisture out of warm air than cold. I used to leave a heater on frost setting when it got really cold.

 

[knewboater]

Have used a dehumidifier only (bought from B@Q about £75 220w) for 3 seasons now, it uses little electricity and is left on all winter, the boat is always dry when going onboard, fantastic result.
RGH

 

[AIDY]

I use both on timers but not on at the same time. both 5 hours a day.

leaving a heater and dehumid on constant will eventually dry your interior wood out.

 

[Piers]

I use both heater and de-humidifier. Take care not to keep the de-humidifier on too strong a setting since it can dry and crack wood....

 

[maelstrom99]

I use a combination of a dehumidifier(with gas defrost + drain into sink) and a greenhouse heater.

The dehumidifier is on a timer set with 2 x 2 hour segments and the heater is set on a frost settiing.

I have used this set up for several years and the boat is always dry and warm.

Do not run the dehum. for long periods as any wood could dry out and split.

Do make sure you close all hatches and extra vents otherwise you'll be trying to dry out the boat yard!

Hope this helps

 

[alan17]

My de-humid gives me a choice of how dry by percentage. What is the ideal to keep the interior dry but not too dry?

 

[maelstrom99]

Unfortunately my dehumidifier doesn't read in percentages, its on the boat now but from memory I set it on "comfort" and when I check usually every 10 days or so the sink drain is wet and all other areas: uphostelry, instruments, charts etc remain dry.

I would guess my setting would be around 50/60%

 

[BlueSkyNick]

I run the tube from the dehumidifier into a large mug which sits in the sink. Obviously any container will do. When it is full it simply overflows into the sink. This way I can tell if the dehum. has worked much from one weekend to the next.

eg is it full and overflowing, only partly full .... or completely dry, which suggests the setting was too low or the boat is drying out.

 

[Stellina]

Anybody suffered cracked woodwork?

There are always comments in de-humidifier threads about the risk of cracking the wooden interior but I wonder if anyone has first-hand experience of this?

Varnished wood would surely be more or less sealed. The boat is not airtight so you will always get some circulation of more humid air from outside. In Scandanavia the winters can be very cold and the air is very dry. Humidity often drops under 30%. Many boats are on the hard but I have never heard of any suffering damage.

 

[BAtoo]

Re: Anybody suffered cracked woodwork?

I have in the past run a domestic dehumidifier 25/7 on full whack; boat nice and dry & no cracked wood in evidence!! Now, as my bit to help the CO2 problem ( and to reduce my electricity bills) /forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif, I run it on half setting - still dry & no cracked wood!!

Don't forget a dehumidifier will put heat into the boat..

 

[Rivers & creeks]

Re: Anybody suffered cracked woodwork?

[ QUOTE ]
There are always comments in de-humidifier threads about the risk of cracking the wooden interior but I wonder if anyone has first-hand experience of this?

[/ QUOTE ] Left ours on 24/7 for a week draining into the sink in the heads. Came back and all the tongue and groove paneling had separated and cracked. A few days without the de-humidifier and it was all back OK. Since then we have used it on a low setting and only at night. We then bought a 250ml a day one and leave it on all the time.

 

[Vonasi]

I used to work in the humidification industry (note not de-humidification - but the science is the same) so hope I can help.

Humidity is generally measured in rH (relative humidity). It is very effected by temperature, hence if you take a lump of air at a certain temperature and a certain rH and in a controlled manner warm it up its rH will reduce, if you cool it its rH will increase. A certain quantity of air at a certain rH will have a certain dew-point - a temperature at which moisture will start to fall out.
The problem on a boat will be that warm moist air inside may come into contact with say a cold hull due to low outside air temperature. The air in contact with the hull will drop in temperature so far that it will go below it's dew point and moisture will form on the hull.
So if you think about this then what you really need is warm, dry air in the boat. A de-humidifier will have to work less and be more likely to achieve set-point (desired rH) if it is dealing with warm lower rH air - if the inside of the boat is kept at a comfortable temperature and rH (40-60%) then the chance of hitting dew point when in contact with cold surfaces is decreased.

Most mid-settings on de-humidifiers will be 50%rH. Do remember that if you are using a de-humidiifier ensure that the boat is sealed shut (no vents/hatches open) otherwise you are asking the de-humidifier to de-humidify the whole world - which it is not designed for!

Hope this helps - now you just have to be aware of the fire risk of unattended electrical equipment!

 

[tcm]

Re: Anybody suffered cracked woodwork?

i've run dehums a lot in some very woody boats and no cracking to report. If in uk-style cold weather then a fan (no heater) blowing through and oil heater will move air around, and a dehum will remove moisture. Interesting to remove paddlewheel initially so cold air drops out fast when on the hard.

 

[KevB]

I believe standard household dehumidifiers work better with warm air? I use dehumidifier and fan heater on a single timer, both come on at the same time for an hour each day.
The fan heater also helps circulate the air so the dehumidifier isn't just recycling the same air over again.