Dehumidifier & heating over winter?

[Matt341]

Hi All,

We have been staying on the boat over the last couple of weekends and have found that she is condensing badly. We have only owned her for 4 weeks so still unsure of certain things, our previous boat never condensed a lot and was always very warm but we are finding that the Konsort is condensing a lot and is also quite chilly at night. We used a small halogen heater on the previous boat but find that this really isnt enough on this boat. In the bow cabin there are 2 square windows that condense so badly that they end up dripping, that annoying drip always goes straight in my eye, LOL!

So I am wondering whether we should consider putting on a dehumidifier through the winter, say 2 hours a day. Also maybe some sort of heating.

As we have only just bought the boat im not that familiar with the electrics etc. but I believe it was installed professionaly in 2004 by a marine electrician, I have had a quick look and the only earth wires going to the anode is from the shaft and engine. The power is RCD protected.

She has been left plugged in for periods through the winter with the previous owner and a dehumidifier has been kept on, she doesnt look like she has suffered any galvanic problems and both anodes have plenty left.

The next question is what sort of heating should be used? Im thinking that oil filled is probably the safest option, I dont like leaving halogen on even when on the boat so leaving a halogen on timer is a definite NO NO I think.

Thoughts would be great,

Many Thanks
Ian

 

[FrancisRutter]

Francis Rutter

You will be told that one way is to make sure of very good ventilation, preferably a through draft.
The way I go with a Fisher 25 is to have a dehumidifiier over the sink and turned on by timer for one hour each morning and evening. I find that that keeps the boat reasonably clear of damp. If heating is also needed [and I don't find it neccessary] then oil filled bar in the engine compartment seems to be the safest way to go. If you do this, then ventilation is not so desirable, or you will be dehumidifying the whole neighbourhood.

Francis Rutter

 

[johnpye]

Dehumidifer and heating

If the interior is damp it makes it feel much colder. If it hasn't been in regular use, there may be quite a bit of residual moisture that can be dispersed just by regular warming through and ventilation. As far as heaters go, I wouldn't entertain any kind that has a glowing element.

For a boat in storage and unheated over the winter, mould growth, musty smells etc. are reduced by keeping it dehumidified - this is generally much cheaper to operate than heating and ventilation.

Make sure that any dehumidifier can work at low temperature. The refrigerant types don't do much below about 10 to 15 Celsius, but desiccant types remain effective in the lower temperature range.

Other points to check out on a dehumidifier -
Can it drain out or only drain to an internal reservoir?
Does it have an effective humidistat?
Can it work on a timer? (Some won't restart from power off without pushing a button)

 

[Matt341]

Thank you both for your comments,

I have seen a dehumidifier on Force 4 website for £119, it can work below 12 degrees and can drain down the sink as well as having its own container.

As the boat is nearly 2 hours away from home it is difficult to bring all the cushions & upholstery home so I would prefer to leave them onboard through the winter and hope the dehumidifier would keep them damp free.

When we stay onboard I try to keep as much ventilation as possible with the hatch on vent, windows open etc. I think the main problem is that we use the shower onboard so that causes a lot of moisture in the air as well.

As long as the dehumidifier is capable of working at low temperatures then maybe heating will only be needed when we are onboard.

Is it likely to cause any galvanic problems by keeping plugged in? The 240 system is not connected to anodes just through an RCD.

Many Thanks
Ian

 

[fireball]

Before you go and buy a "marine" dehumidifier checkout B&Q or homebase - we bought ours from one of these a few years ago - it also has the internal tray or drain hose and has worked on our boat for around 6 hours a day throughout the winter.
Just by having the dehumidifier on it felt like the boat was warmer - so we didn't bother with heater whilst we were not onboard.
Our 240 system was completely seperate to the engine/hull/seacocks/anodes and we suffered no galvanic problems - but you do need to test the RCDto ensure it is working ok.

 

[Matt341]

Thanks for the reply,

I have a B & Q dehumidifier that I use in my office, that also drains out but im not sure if it works in cold weather, I think it was about £70.

Think I will have a look through some websites first.

It seems that it is definitely worth getting one, another question, are they fairly heavy on the power? We are on a metermaid and pay about 16p per unit. Also the power is limited to 13amps so do some use more power than others?

Thanks
Ian

 

[jbweston]

I agree with the advice about running a domestic dehumidifier a few hours every day on a mains time clock. That's what I do. I lash it above the galley work surface so the run-off pipe discharges into the sink. Only drawback is that I have to leave the seacock open which of course is no problem when the boat's ashore and a calculated risk when she's in her berth.

I have a cheap digital max/min thermometer / hygrometer which I check from time to time so as to fine tune the adjustment on the dehumidifier and how many hours to run it.

The result is that's she's fresher and drier in the winter than during the summer.

In addition I have a small domestic oil radiator on on a frost stat to stop my plumbing freezing. Again the thermometer helps me to get the settings right.

 

[bobm]

We also have dehumidifier draining into the sink, on twice a day for 2 hours, turned down to low operation. This is supplimented by a 60w tube heater with a thermostat set to 10 degrees, have been doing this for 8 years and has kept the boat(s) dry. The humidifier was about £99 from B&Q in 2001, made up the tube heater/thermostat myself onto a mounting board to give stability. Boat is not ventilated, only drawback is the wastepipe seacock being open but I leave the auto bilge pump on all the time.

 

[seamaster30]

What is it with Plug in Timers and De-Humidifiers????
A good dehumidifier will have an adjustable humidistat.
If set correctly it will come on required, and switch off when not - so why the timer?
If you think you can guess the expected moisture levels and use a timer, the humidistat becomes redundant.
If you are trying to save money by running it for less time, then you will still end up with mold if it's not allowed to run for long enough.
You need a small heater to help keep the temperature high enough for the dehumidifier to work - A dehumidifier cannot suck the moisture out of fabric or off walls/windows - it needs to be airborne for the dehumidifier to condense the moisture out.
A self draining model to drain into the sink is a must.

 

[fireball]

If you think you can guess the expected moisture levels and use a timer, the humidistat becomes redundant.

Generally over winter the temperature during the night time is too low for the unit to work efficiently- thus there is no point in having it running over night hence use of the timer ... QED!

 

[seamaster30]

Generally over winter the temperature during the night time is too low for the unit to work efficiently- thus there is no point in having it running over night hence use of the timer ... QED!

Hence the other part of my post about requiring a heater...
Most people (granted your post was different) seem to say they are putting the dehumidifiers for a couple of hours a day.
Yes, if you are not heating the boat, I would agree with you, but in the UK in winter, the days will also be too cold.

 

[Matt341]

Thank you all for the comments,

The dehumidifier I have in the office is controlled by humidity levels but I have found that when set to normal humidity it will run all the time constantly, So I think the timer would be the best option as I could control how long it will run for, 24 hours of constant use would use a lot of power.

I usually shut the heads sea cock, oulet & inlet as well as the sink/shower drain but have never shut the galley outlet, usually because on the previous boat it was above waterline but maybe I should shut it on this boat as it is under water level but then im going to be using a dehumidifier now.

We plan to use the boat through the winter for the odd weekend here and there, im wondering whether its worth the hassle of draining the water etc. and then refilling the system or whether I should keep a heater on. Something like this - http://www.force4.co.uk/667/Force-4-Tube-Heater---600mm---80W.html

Would this prevent the interior pipes from freezing or will something stronger be needed?

I plan to leave all lockers open and cushions propped up.

Thanks
Ian

 

[seamaster30]

The dehumidifier I have in the office is controlled by humidity levels but I have found that when set to normal humidity it will run all the time constantly, So I think the timer would be the best option as I could control how long it will run for, 24 hours of constant use would use a lot of power.

I suspect there is something wrong with it then - is is a dial or a rocker switch? - Mine is a dial, so I adjust it so it switches off at a comfortable level, and can be fine tuned if required.

I usually shut the heads sea cock, oulet & inlet as well as the sink/shower drain but have never shut the galley outlet, usually because on the previous boat it was above waterline but maybe I should shut it on this boat as it is under water level but then im going to be using a dehumidifier now.

Good point, and one you should check with your insurer, but without a permanent drain, once the internal bucket is full, there is no advantage in having the dehumidifier as the moisture will start to accumulate again.

We plan to use the boat through the winter for the odd weekend here and there, im wondering whether its worth the hassle of draining the water etc. and then refilling the system or whether I should keep a heater on. Something like this

We have a split level layout - A lower cabin at each end, then the higher saloon in the middle, I use two low wattage heaters in the cabins as heat flows upwards, and the dehumidifier is above the galley in the saloon, draining into the sink. This system works very well for me.

Would this prevent the interior pipes from freezing or will something stronger be needed?

Difficult to tell as it will depend on a lot of factors.
For peace of mind, how about getting one of those thermometers from a garden centre that measures the max/min temps? - You can reset it each time you visit, and will know if things are getting borderline.

 

[johnpye]

I have seen a dehumidifier on Force 4 website for £119, it can work below 12 degrees and can drain down the sink as well as having its own container.

Before anyone reads any more of my post, let me declare an interest that we sell desiccant dehumidifiers. Interpret my comments accordingly, but I hope the technical background that led to our product decision is a useful contribution.

Practically all dehumidifiers sold in the UK are imported as domestic appliances. They are designed for household use, and can be expected work well within the home, drying laundry etc. The task of keeping an unused boat dry throughout the winter is a rather peculiar one, because the temperature in the boat will be lower than in a normal domestic environment. Unfortunately, the specification for dehumidifiers provided by importers is usually quoted (if at all) as an extraction rate at 30 degrees Celsius. Given that the normal temperature range during the autumn and winter is somewhere below zero up to a max of 10 or 15 degrees, this is not much help in evaluating their suitability for our application, and most resellers appear to choose models to suit particular price points without necessarily looking much further.

The £119 model mentioned is a refrigerant type, as are units available in retail stores. It works by drawing moist air over a refrigerated element, so water condenses on the element and drips away to the tank or drain. As the ambient temperature falls below about 15 degrees, the water on the cold element begins to freeze rather than condense. This particular model uses a hot gas defrosting system, so it is perfectly true to say that it is able to work at a lower temperature. I'd say it is ideal for a utility room where the temperature may drop to around ten degrees from time to time.

Some posts report success with cheap (refrigerant) dehumidifiers, and others have posted that it is necessary to have a heater as well as a dehumidifier to get the air warm enough to enable the dehumidifier to work. Both viewpoints are valid. With temperature in winter seldom rising to 15 degrees, any refrigerant dehumidifier in an unheated boat is working at the extreme lower limit of its possible range.

A desiccant dehumidifier works in a completely different way. The air is passed over a desiccant, which is recharged and continuously re-used. The desiccant is at ambient temperature (actually a bit warmer after recharging), and because it doesn’t have to cool the air to precipitate moisture, the process is significantly more energy-efficient, and practically all the energy consumed by the unit is converted into heat that warms the air while it is working. Even more importantly, there is little loss in efficiency throughout the operating range, including the crucial 1 to 15 degree range. (At zero, moisture freezes out of the air anyway). Our model’s extraction rate of ten litres per day is maintained over its entire working temperature range of 1 to 40 degrees.

We have more information on our website, including more detailed technical specifications.

Having said all the above, if you are using the boat regularly during the winter, then you will need some heating anyway, and you might find a refrigerant type is OK, even if less efficient.

As the boat is nearly 2 hours away from home it is difficult to bring all the cushions & upholstery home so I would prefer to leave them onboard through the winter and hope the dehumidifier would keep them damp free.

When we stay onboard I try to keep as much ventilation as possible with the hatch on vent, windows open etc. I think the main problem is that we use the shower onboard so that causes a lot of moisture in the air as well.

If the bedding is staying on board all winter, I'd definitely run a pretty meaty dehumidifier.

PS, if the bilges are not dry, any dehumidifier will be an expensive way of emptying them

 

[Seanick]

Dehumidify, dont heat.
Set the humidistat at about 70%
Some part of a winters day will be warm enough for it to work well.
Close all other vents or the machine will run contiuously.

Run a seperate power lead down a vent or cockpit locker to avoid any risk of not having a prop in the spring.

Keep your boats ring main switched off.

We do this on 6 or so boats and it works well.

Finally, a small boom tent will protect your sprayhood, if you leave it on, and keep some frost of the deck.

 

[Marsupial]

(At zero, moisture freezes out of the air anyway)


Correct!



"Our model’s extraction rate of ten litres per day is maintained over its entire working temperature range of 1 to 40 degrees."

So the device is defying the laws of physics - if it has been working there wont be 10 litres left in the air at 1deg! IF there is then it hasnt been working!

Consult the steam tables as used by HVCA for determining the size of air conditioning and dehumidifying plant

QED

 

[seamaster30]

PS, if the bilges are not dry, any dehumidifier will be an expensive way of emptying them

Why? - A dehumidifier can only extract moisture from the air - it will not 'suck it out of the bilge' - so if there is water evaporating from the bilge, then would you not need a dehumidifier to get that excess moisture out?

 

[seamaster30]

Close all other vents or the machine will run contiuously.

Only if closing the vents make your boat 100% air tight - I think not.
If it's running continuously, it's set too high.
You need it set lower than the outside air humidity level, but higher than the level that is reached in the confines of the boat when trapped moisture (bedding, condensation on windows etc) evaporates into the air.

 

[johnpye]

Why? - A dehumidifier can only extract moisture from the air - it will not 'suck it out of the bilge' - so if there is water evaporating from the bilge, then would you not need a dehumidifier to get that excess moisture out?

Yes, agreed completely, but water in the bilge adds to the load for the dehumidifier. As the dehumidifier dries the air, more moisture evaporates from the bilge and has to be removed. Keeping the bilge dry just reduces the work that the dehumidifier has to do.

 

[seamaster30]

Yes, agreed completely, but water in the bilge adds to the load for the dehumidifier. As the dehumidifier dries the air, more moisture evaporates from the bilge and has to be removed. Keeping the bilge dry just reduces the work that the dehumidifier has to do.

OK - That makes sense.
Although, because the bilge is so cold, I would expect the evaporation levels to be extremely low from there.
Unfortunately for me, one of my bilges is designed to be wet (the shower drains into it) so it would be impractical to dry it after every use.
I did think about inserting some kind of sump for the shower, but there really isn't any room, and it would add another level of complexity and another point of failure.
I also like the idea that the bilge pump is getting a regular workout and not sitting there seizing up for the occasion when I may really need it.