Chris CJ
Well-Known Member
Bought a seago dehumidifier, works really well, what is a reasonable RH setting to leave it on whilst not on board
Dehumidifier- what setting to RH
- Thread starter Chris CJ
- Start date
billcole
Well-Known Member
I can't remember where, but I think I once read somewhere that mould needs RH of 60% to grow, so I set mine at 55%
Scubadoo
Well-Known Member
55% is best, if set any lower you could risk it becoming too dry which could affect woodwork if you have any.
thinwater
Well-Known Member
Just below 60% is the common advice. But there are two more factors.
If the boat is relatively cool compared to outside that helps. An unoccupied, unheated boat.
Insulation and double glazing helps with condensation, but most boat score poorly and will drip at 60% RH when heated and occupied. I double glazed the windows in the winter, in part to save heat (more even temperatures) but also to stop drips.
If the boat is not heated, 60% is more than good enough, certainly no lower. If the boat is occupied, the determination is usually drips, and the solution is well thought out insulation and vapor barriers. Until that is done, you may have to go lower.
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The other thing to consider in the winter is deumidifier freeze-ups. Most expereince icing below about 50F. Some this can damage, others not. But best to have them cycle off during the day so they can defrost.
- How great is the inside/outside temperature differential?
- How well insulated is the boat and the windows?
If the boat is relatively cool compared to outside that helps. An unoccupied, unheated boat.
Insulation and double glazing helps with condensation, but most boat score poorly and will drip at 60% RH when heated and occupied. I double glazed the windows in the winter, in part to save heat (more even temperatures) but also to stop drips.
If the boat is not heated, 60% is more than good enough, certainly no lower. If the boat is occupied, the determination is usually drips, and the solution is well thought out insulation and vapor barriers. Until that is done, you may have to go lower.
---
The other thing to consider in the winter is deumidifier freeze-ups. Most expereince icing below about 50F. Some this can damage, others not. But best to have them cycle off during the day so they can defrost.
GEM43
Well-Known Member
We’ve a dessicant dehumidifier, Meaco DD8L, I leave it on the one drip, low fan setting. It maintains a constant 66%rh on board whilst unoccupied. No problems with mould or damp experienced. Below is past 24hr graph, the lower graph shows the frequency of dehumidifier cycle on/test/off.
Halo
Well-Known Member
I do exactly the same as Gem43. The boat feels fresh and no woodwork issues in 12 years of doing this from September to March. Make sure the drain tube has a steady angle which will not airlock and seal her up
Close vents
Cling film over the head
Empty kettle etc
The only downsides are a small electric bill and any crisps or biscuits tend to go dry and brittle if left for long periods
thinwater
Well-Known Member
I run the dehumidifier year round and use the boat (daysailing not live-aboard) year round. This includes temps from above 90F to below 20F. Keeps it simple. If not needed, it does not run much. Obviously, it is off when actively cruising for a week or so here and there, although we may run AC occasionally. As a result, not even the pillows get stale.
Momac
Well-Known Member
I find the dehumidifer stops making water around early April so that's when it comes off the boat for filter cleaning and storage. It goes back on board sometime in October or maybe early November.
I have the Mesco dd8l and as said above also find the lowest setting does the job.
If we are on board the bost heating and plenty of ventilation is used and not the dehumidifier.
I have the Mesco dd8l and as said above also find the lowest setting does the job.
If we are on board the bost heating and plenty of ventilation is used and not the dehumidifier.
Chris CJ
Well-Known Member
Many thanks for all these very useful answers, we will shut the dorade vents , cling film the louvred washboard and drain the toilet dry . Open cupboards and lay seat backs down to minimise isolated non vented voids. Take coats and wet weather gear home . Then set the dehumidifier to an RH of 60 draining into the sink . Probably start this process towards the end of October . Monitor the situation, hopefully no evidence of mould and the dehumidifier is working and draining ok with reasonable electricity costs.
Chris
Chris
Momac
Well-Known Member
The greatest risk of condensation is when temperature swings are large as in well above freezing in the day and night frost.
Constant temperature no problem.
To economise a little on power I sometimes just have the dehumidifier on a couple of days a week but if I feel there is greater risk of condensation I may have it on longer. I am perhaps fortunate in that I can get to the boat easily as its less than a mile from home.
Sealing up vents while using the dehumidifier in an unoccupied boat makes a big saving in energy use.
Constant temperature no problem.
To economise a little on power I sometimes just have the dehumidifier on a couple of days a week but if I feel there is greater risk of condensation I may have it on longer. I am perhaps fortunate in that I can get to the boat easily as its less than a mile from home.
Sealing up vents while using the dehumidifier in an unoccupied boat makes a big saving in energy use.
Halo
Well-Known Member
You can get humidity indicators off the internet. It’s really good to look at the reading when you arrive.