Preventing Condensation

[Giggetty]

I've only ever used table salt which is extremely cheap in bulk bags. I only about half fill a bowl, so that as the water is absorbed it doesn't overflow.

 

The cat litter sounds like a very good idea although I've never tried it, but doesn't it contain other chemicals for neutralising urine? My wife seems to recall that pregnant women should avoid contact with it for some reason.

 

Silaca gel is also excellent if available at the right price. Calcium chloride is a very effective water absorber and de-icer, but does require more careful handling and storage than Sodium Chloride (table salt)

 

Roger

 

Fresh cat litter should be OK. If used by an affected cat could transmit toxoplasma-gives rise in non-immune women to congenital foetal infection.

[Roger Gunkel]

Fresh cat litter should be OK. If used by an affected cat could transmit toxoplasma-gives rise in non-immune women to congenital foetal infection.

 

Sounds nasty, I'll make sure we don't use any used litter then

 

Roger

[kendo]

Hi Roger. On visiting the boat, we discovered it has the hopper type windows (that another poster mentioned).

They stick out 2-3 inches proud of flush. You say these can be removed? Like the other poster mentioned, i'm

concerned that if i do that, the glass will fall out. (because they stop the top pane from opening more than 30 deg).

 

I read (in another thread, i think) that you also block up your drainage channels, so that cold air can't get in?

But i'm left wondering what you do for ventilation?

[FORTUNATA]

Worryingly I've found major damp under my matress. I can see it's where my body heat must be interacting with rising cold air from the hull which is now bedded in ice. I've lifted up the bedding to expose the wood and will try stuffing newspaper on top for the time being to absorb the damp and also airing the boards.

I use my log fire a lot but can't be on board all the time so I do get temperature fluctuation. My boat isn't really a live-a-board so with no central heating I have to do it the traditional way and use solid fuel. I can get the boat warm as toast in time but think the damp has been getting a hold in the early morning when the fire has burnt out. I leave a 300 watt radiator on when I'm out but this doesn't give out enough heat to get at all the damp.

I feel I haven't quite got the Winter situation solved and am now looking at more back-up for the log fire. A fan heater is probably the best bet and I can also turn it on those bed boards.

 

A lot of people will already know all about condensation, but for those that aren't so sure, I thought some ideas might help.

 

If you have a number of windows on your boat, then you will certainly know about condensation problems this time of the year. Double glazing will make a huge difference to the condensation on the windows as well as reducing heat loss immensely and cutting out the constant draughts due to convection. (See the double glazing thread if you want to know more LINK) That is just basic physics, but there is also the perceived idea that stopping the window condensation will increase it elsewhere. That is not neccesarily true, but is sometimes seen as such.

 

Any given mass of air will be able to absorb a fixed ammount of moisture before it becomes saturated. The higher the temperature of that air, the more moisture it can contain. The air volume of a boat is much smaller than a house, so the saturation point arrives quicker than a house would. As windows are usually the coldest surface of the boat and the biggest heat loss, they will reduce the temperature of the air next to them until the dew point is reached and the water condenses on the cold surface. If we double glaze the windows, the air will not make contact with the cold surface and the moisture will be retained as the overall air temperature will remain higher. The downside though is that the air will still contain the moisture as it hasn't chucked it on the windows, so is likely to deposit it on other cold surfaces.

 

Boats tend to be very variable in the quality of insulation, but generally, any hidden surface, under beds, behind furniture, inside cupboards, behind curtains, is going to have little access to the warmer air, which tends to rise. the colder air will reach the colder surfaces and quickly reach dewpoint giving condensation. As these areas are hidden most of the time, moisture will be absorbed into the surroundings, giving mildew and promoting rot.

 

So what can we do about it? Well there are number of things, all or any of which can make a big difference.

We need to replace the saturated moist air with drier air, so ventilation with outside drier air is essential. Naturally in sub zero conditions we tend to keep everything closed up, but certainly during the day, try to open the odd window or the hatch for a while, even if you need to boost the heat a little. A solid fuel stove always draws in air to burn, so a fresh air supply near the stove will bring air in, without creating draughts everywhere. Leave cupboard doors open where possible and leave air gaps behind furniture and under beds. One idea which works very well is to use very low power consumption computer fans to circulate air in otherwise unventilated areas. This will help to move the warmer air around the boat and prevent the closed in areas reaching dew point.

 

Any cold smooth area is likely to promote condensation, but one area which is often overlooked is water pipes. All year round, but particularly in the Winter, the fresh water pipes are extremely cold. As they are frequently run around the edges of the boat, they pass under beds, through cupboards, behind skirtings etc. They will be dripping with condensation if unlagged and are a large contributor to low level moisture. The dripping water will be absorbed into the surrounding woodwork and anything near them, giving mould, mildew and leading to rot. It can be stopped by using very cheap foam pipe lagging from any DIY store, over all of the pipes, hot and cold.

 

ALL smooth areas behind cupboards, under beds, lockers, should be covered with something like thin cord carpet, which should be glued firmly to the surface, leaving no airgaps behind. This should also be carried out on all closed in floor areas, to avoid the bottoms of boxes or stored clothes absorbing moisture.

 

Cut down on production of moisture, by only boiling as much water as you need. Don't leave the kettle on the stove all day, it will give you constant hot water, but also massive ammounts of airborne moisture. Boil the kettle when you need it and save any surplus in a large vaccuum flask. Try to have a window open next to where you are boiling saucepans or kettles. When possible, dry any towels or washing outside the boat. Don't let washing up drip dry, use a tea towel then dry it outside. All these things will save recirculating the same moisture.

 

Finally, you can remove some moisture from the air by using a dehumidifier if you have hookup or a plentiful power supply. Much cheaper, is a few breakfast bowls half full of table salt around the boat, which will absorb considerable ammounts of water. It can be refreshed regularly for liitle cost or even dried out and reused if you can dry it away from the boat.

 

I'm sure others will have useful additions that I have forgotten, but I hope that some of this will help to make the winter less damp and more enjoyable.

 

Roger

[Roger Gunkel]

Hi Roger. On visiting the boat, we discovered it has the hopper type windows (that another poster mentioned).

They stick out 2-3 inches proud of flush. You say these can be removed? Like the other poster mentioned, i'm

concerned that if i do that, the glass will fall out. (because they stop the top pane from opening more than 30 deg).

 

I read (in another thread, i think) that you also block up your drainage channels, so that cold air can't get in?

But i'm left wondering what you do for ventilation?

 

Hi Kendo,

 

We removed our stops, after first checking on one window that the glass wouldn't fall out. We found that the transom across the window where the bottom of the hopper glass sits, is sloped back and supports the bottom inch or so of glass at the open angle. We fount that it supports the open glass well, for the odd occasion that we may want to remove the acrylic and open for ventilation. There is also no reason why you couldn't bend up a simple wire retainer to hook in the endplate bolt hole and over the edge of the glass, or even a couple of hooks and a piece of string for a temporary retainer. In practice, we find that we get all the ventillation we need by opening the hatch and/or doors, but knowing that we can remove the acrylic and open a hopper glass if we should need to.

 

We blocked up the drainage holes in the frame, because they are there to drain condensation water from the bottom of the channel to outside the boat, rather than ventilation. If you install the acrylic carefully, you won't have condensation to drain out. Any small amounts that you may get from moisture trapped in the air between the panes, can be easily removed every few days with a tissue, although silica gel will absorb most. If you don't block the drainage holes, you will get cold outside air entering the air gap.

 

The installation the way that I outlined will give the best results from a heat loss and condensation point of view, but there will always be variations depending on how well sealed your windows are, how well you seal the acrylic, the size of the gap and your own choice of variations. Some such as Innisfree, prefer to ventilate the space between the panes, preferring to use their own variations to reduce the draught from open windows at the expense of some heat loss compared to the sealed option.

 

Our own preference is for retaining the maximum amount of heat and comfort, with the minimal levels of glass condensation, which is what we have achieved with our installation. The optimum air gap is about 1" for thermal insulation, but this is difficult to achieve on boat frames. Ours is about 1.5" and works very well, helped by the fact that acrylic is also a better thermal insulator than glass. As you increase the gap, you start to get convection between the panes and the heat retaining properties start to drop off, although sound insulation gets better.

 

Hope that all helps,

 

Roger

[Chris Pink]

Worryingly I've found major damp under my matress. I can see it's where my body heat must be interacting with rising cold air from the hull which is now bedded in ice. I've lifted up the bedding to expose the wood and will try stuffing newspaper on top for the time being to absorb the damp and also airing the boards.

 

The damp on the bottom of your mattress will be your body sweat passing through the mattress.

 

Too much information I hear you all cry.

 

The only way to combat this is ventilation under the bed (ie slats not solid boards) and turning the mattress. Newspaper will stop ventilation and keep the damp in, drying the boards by wiping them is more efficient.

[Roger Gunkel]

Worryingly I've found major damp under my matress. I can see it's where my body heat must be interacting with rising cold air from the hull which is now bedded in ice. I've lifted up the bedding to expose the wood and will try stuffing newspaper on top for the time being to absorb the damp and also airing the boards.

I use my log fire a lot but can't be on board all the time so I do get temperature fluctuation. My boat isn't really a live-a-board so with no central heating I have to do it the traditional way and use solid fuel. I can get the boat warm as toast in time but think the damp has been getting a hold in the early morning when the fire has burnt out. I leave a 300 watt radiator on when I'm out but this doesn't give out enough heat to get at all the damp.

I feel I haven't quite got the Winter situation solved and am now looking at more back-up for the log fire. A fan heater is probably the best bet and I can also turn it on those bed boards.

 

The damp on the bed boards is not so much caused by cold damp air under the bed, but rather the moisture and warmth that your body produces while you are laying on the matress. This moisture permeates the matress and condenses out on the coldest surface which is the bedboard. If you insulate with newspaper, you will find that the paper will get damp and will produce black mould and mildew along with the bottom of the matress. The small internal volume of the your boat also means that the air will saturate very quickly.

 

The best solution to bedboard damp, is to remove the boards and use slats instead, or if that is not possible, get a hole cutter about 1-2" and cut holes into the entire bedboard about 1 hole diameter apart. That will allow air to circulate under the matress if you keep access to the under bed area open. Rather than using a fan heater to circulate air, providing your stove provides enough heat, it would be more economical to use a couple of 12v computer case fans to circulate air into cooler damper areas.

 

(edited to say my long winded answer was pre-empted by Chris's quicker one.)

Roger

Edited December 23, 2009 by Roger Gunkel

[kendo]

a couple of hooks and a piece of string for a temporary retainer

doh! i was worried about the weight of the glass pressing against the perspex, and the

possibility of it all coming tumbling down. thanks for the common sense and affordable

suggestion, Roger. we'll also try experimenting with open and closed off drainage channels

to see what works out best.

 

Thanks for the tips, and i hope you have a happy xmas.

[sueb]

Worryingly I've found major damp under my matress. I can see it's where my body heat must be interacting with rising cold air from the hull which is now bedded in ice. I've lifted up the bedding to expose the wood and will try stuffing newspaper on top for the time being to absorb the damp and also airing the boards.

I use my log fire a lot but can't be on board all the time so I do get temperature fluctuation. My boat isn't really a live-a-board so with no central heating I have to do it the traditional way and use solid fuel. I can get the boat warm as toast in time but think the damp has been getting a hold in the early morning when the fire has burnt out. I leave a 300 watt radiator on when I'm out but this doesn't give out enough heat to get at all the damp.

I feel I haven't quite got the Winter situation solved and am now looking at more back-up for the log fire. A fan heater is probably the best bet and I can also turn it on those bed boards.

We have a layer of foam under our mattress. It seems to work.

Sue

[Mat B]

I have a Webasto air blower.

 

The installation manual implies that if heating air is drawn from outside, rather than recirculating internal air, then humidity is reduced.

 

Anybody tried this?

 

m@

[Justme]

I have a Webasto air blower.

 

The installation manual implies that if heating air is drawn from outside, rather than recirculating internal air, then humidity is reduced.

 

Anybody tried this?

 

m@

 

 

Whilst it would be true I would think that it would struggle to heat the incoming air if it was chilly outside.

 

Specs

(for the 5000 model)

 

Variable Heat Rating:

Output:

From 5,100 Btu/h (1.5kW)

To 17,000 Btu/h (5.5kW)

 

And an air flow of

 

Hot Airflow (unrestricted):

From- 81 cfm

To- 128 cfm

 

 

using

 

Temperature rise © = heater size (kw) / air volume (m3/s) x 1.25

 

full power full flow

5.5 / 0.0604 x 1.25 = 113.8c rise (do they get that hot?) in temp at max power & max flow.

 

low power full flow = 31c rise in temp

 

Look like they are strong enough to work that way.

 

That did surprise me.

 

 

Do they work that well in real life?

 

I guess the 3m3 per min flow still takes a while to heat a large boat?

[sueb]

I have condensation on my spuds and the wine bottles in the cupboard

Sue

[Lady Muck]

I am wondering if the mode of heating makes a difference. We never used to get condensation problems (except in the unheated bathrooms) when we had houses with solid fuel heating. We did experience serious problems in a house that was well sealed but had central heating.

 

The heating on our boat is from a Morso Squirrel centrally located with a back boiler feeding three radiators. The stove is situated close to the bathroom and there is a big radiator in the bathroom which room is also well ventilated. Somertimes the large mirror will mist up when one of us is having a shower but as the mirror is above the radiator, it soon clears.

 

We get barely any either and our layout/set up is similar to yours. The mushroom vent above the bath has an extractor fan above it - we put the fan on before we get in the shower and leave it on until any steam has cleared.

 

When I'm cooking I open both portholes in the kitchen and also the pigeon box, if theres gonig to be lots of steam I open all the window, and the back hatch.

 

We don't seem to suffer from damp around the mattress like some people report. But my bed is raised and underneath I keep spare clothes/blankets and shoes in eight mesh plastic crates. I use vacuum bags to store things in these crates to ensure that nothing gets damp.

Edited December 26, 2009 by Lady Muck

[nb Innisfree]

I have a Webasto air blower.

 

The installation manual implies that if heating air is drawn from outside, rather than recirculating internal air, then humidity is reduced.

 

Anybody tried this?

 

m@

 

I and many others have done it lots of times by putting a car's heating on recirculation to warm up the interior faster only to find windows steaming up, this is rapidly cured by switching heating to fresh air intake.

[Smelly]

I have condensation on my spuds

Sue

 

 

thermals are definitely in order!

[sueb]

thermals are definitely in order!

Good job I got thermals for christmas as well as a tesco turkey

Sue

[NB Alnwick]

Has anyone used these for preventing damp patches under the bed?

 

http://www.marinebedding.com/bedFlex.php?P...2509765eca31a61

[soggy]

Gardeners use a product called Perlite to soak up water. It is dug into the soil as a precaution against drought. I wonder if it might be of use to absorb condensation on a boat? It also goes by other names, it is a granular, whitish product that comes in bags like fertilizer bags.

 

As to damp mattresses, a cheaper alternative to 'special' bed slats is to use broomstick handles. Cut them to length and tie them together to make a bed slat base that will keep the mattress aired. This is not uncomfortable. In cold conditions, such as when the heat is turned off for several hours at night, then a well aired mattress is going to get cold and could be cold enough to disturb one's sleep.

[Roger Gunkel]

In cold conditions, such as when the heat is turned off for several hours at night, then a well aired mattress is going to get cold and could be cold enough to disturb one's sleep.

 

We've found in practice, that it takes as much, if not more fuel to bring the boat back up to temperature after letting it get cold, than to just keep the heat going at a reduced level overnight. The other side of letting the boat get cold, is that moisture will condense onto various surfaces as they cool down, giving more moisture associated problems.

 

Roger

[casper ghost]

I leave my boat for a while at a time. It can take a couple of days to properly heat the boat up. The air warms quickly but surfaces remain cold and i do suffer from condensation dripping.. This winter the condensation on the windows froze..

[nb Innisfree]

In our experience it takes an absolute minimum of 3 hours to thoroughly heat our 60' nb. probably more like double that.

[Mat B]

..........

Temperature rise © = heater size (kw) / air volume (m3/s) x 1.25

 

full power full flow

5.5 / 0.0604 x 1.25 = 113.8c rise (do they get that hot?) in temp at max power & max flow.

 

low power full flow = 31c rise in temp

 

Look like they are strong enough to work that way.

 

That did surprise me.

 

 

Do they work that well in real life?

 

I guess the 3m3 per min flow still takes a while to heat a large boat?

 

Thanks for the calculations. Work fine for me on a 24ft cruiser

 

"113.8c - do they get that hot?" Not sure, just checked a teaspoonful of water on the ducting , it evaporated in 2 seconds!

 

I and many others have done it lots of times by putting a car's heating on recirculation to warm up the interior faster only to find windows steaming up, this is rapidly cured by switching heating to fresh air intake.

 

Good point, it is a modification I am probably going to implement in the summer.

 

m@

[Lady Muck]

I have just moved this topic here at Rogers Suggestion.

 

Thanks Roger for raising this important topic!

 

LM

[Naughty Cal]

I leave my boat for a while at a time. It can take a couple of days to properly heat the boat up. The air warms quickly but surfaces remain cold and i do suffer from condensation dripping.. This winter the condensation on the windows froze..

 

We have found this through the cold snap. We leave Cal a week at a time with just the frost heaters on and upon our return she is chilled to the bone (well wuld be if she had bones) It takes a good 24 hours to fully warm her through with the diesel heating. Thank goodness for the electric blanket

[Oldboater]

Has anyone used these for preventing damp patches under the bed?

 

http://www.marinebedding.com/bedFlex.php?P...2509765eca31a61

 

 

Bought our 'Dry Mat' from www.shipshapebedding.co.uk, it's expensive but it does resolve the problem of sweating mattresses.