OP
OP
When it's raining (like now!) wouldn't a fan be drawing damp air in through the vents??
Wet cars and garage ventilation?
- Thread starter BTB 500
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StMarks
MB Enthusiast
It will be drawing air flow.
Granted, if the weather is high humidity that air will (obviously) carry some moisture.
However..
The air will be drawn in, not raindrops.
Even if there is very high humidity, humid air is "less wet" than the water that is dripping from the bottom of your car isn't it ?
Any air flow should help remove that imported moisture, even if the air is humid it is unlikely to be saturated (except for fog or mist ) and will therefore still absorb some moisture as it passes.
OP
OP
It's raining now and the relative humidity outside is 99% according to our weather station thing. I assume the RH would remain high for some time afterwards as surface water evaporates?
StMarks
MB Enthusiast
I understand what you are saying, I'm sure someone more knowledgeable in meteorology can explain that reading properly to us.
However from a personal perspective I would like to point out that swmbo dries our household washing outside on a line all year round. As well as the line over the rear lawn, we also have one that can be strung across the front of my barn. This places the hung washing fully in the open, but without falling rain being able to land on it. Using the barn line the washed clothes dry out just as well, albeit it takes a bit longer.
Hth.
OP
OP
As I understand it ...
At 100% relative humidity air is fully saturated and cannot absorb any more moisture. So washing on a line won't dry at all (even if under cover and protected from the rain), and no matter how much ventilation you have in your garage water on the floor (or anywhere else) simply cannot evaporate. The RH here has been 99% all day (that may be the maximum value my weather station can display), so ventilation wouldn't make any difference - it would just replace the saturated air inside with saturated air from outside. A fan triggered by humidity would just run continuously. A dehumidifier would work of course, but ideally you'd want no ventilation at all (otherwise you'd be wasting energy drying damp air coming in from outside).
At lower RH values (most of the time) ventilation is important though - it stops the air inside from becoming saturated by replacing it with drier air from outside, allowing evaporation to continue. Same applies with washing on a line - a breeze prevents the air immediately around the washing from becoming saturated as the moisture in it evaporates.
We have three washing lines - one at ceiling level in the utility room (which has an extractor fan), a normal outside line, and one under cover in an open-fronted barn. I've never owned a tumble dryer
D2028
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I think you're all overthinking this , try the simplest solution (trickle vents) . If that doesn't work then consider expensive to buy and run dehumidifiers and extractor fans. After all it is a garage, not a liveable space. I would understand if it was storing millions of pounds worth of vehicles but I don't think this is the case.....or have I missed something.
MrGreedy
MB Enthusiast
Cost of dehumidifier:
£80 upwards.
Cost of running dehumidifier on solar panels on garage roof:
£zero.
Cost of trickle vents? Not sure myself.
But the delta between the dehumidifier option and the trickle vent option can only be £80+ IF trickle vents are given away and installed for free (which I suspect is a poor assumption on my part).
Time to set up dehumidifier?
5 minutes to order and 5 minutes to unpack and plug in.
Time to install trickle vents?
Probably a lot more than 10 minutes?
But if trickle vents do it, once installed they are a maintenance free option.
OP
OP
I've spotted mould on much of the plasterboard ceiling, and found that an old grandfather clock I have in there was covered with it. So I need to do something ASAP - the cars are OK at the moment but the last thing I want is mould on/in those or anything else that's in there (the SL's hardtop, centre row seat from the Vito, etc.).
I've ordered a portable mid-sized (20 litres per day) humidifier which was £200 delivered - we have solar panels, so I can run this during the day for nothing as needed. When I get the garage window replaced it will have trickle vents in the frame and a fanlight that can be locked partially open. In warmer & drier weather this extra ventilation should keep things in check, but not when it's cooler and humid and the C Class gets put away wet.
The oldest part of our house is late 1700s with solid walls and floor and in colder/damper weather I'll probably run the dehumidifier in there as well from time to time.
Are the walls to your garage double skinned ??
OP
OP
Not sure ... total thickness is 10" / 25 cm?
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That’s 4-2-4 (2” cavity)
Walls should be OK then. Floors still might be the problem, pour a few litres of water on to it and see if it just stays on the surface or seeps into the floor.That’s 4-2-4 (2” cavity)
OP
OP
There are puddles under the C Class when it's been put inside wet. Not sure whether/how often concrete needs re-sealing though? There is a big drum of sealant in there which I assume was used by the previous owners (who had the garage built).
What type of dehumidifier did you go for?
The compressor types are more efficient but don’t work well in cold weather.
Desiccant types work better in these sorts of environments but cost a little more to run.
You don’t need to run it down to a really dry humidity setting - I should think taking the worst of the dampness out of the air and preventing puddles from forming would be enough to improve things satisfactorily
OP
OP
What type of dehumidifier did you go for?
The compressor types are more efficient but don’t work well in cold weather.
Desiccant types work better in these sorts of environments but cost a little more to run.
You don’t need to run it down to a really dry humidity setting - I should think taking the worst of the dampness out of the air and preventing puddles from forming would be enough to improve things satisfactorily
I got a compressor one .... it won't run below 5C but that's OK. In 'auto' mode you can set a humidity level between 30-80% for it to maintain - I will have a play when I get it but was thinking of 60-70% maybe.
If the dehumidifier works well I would maybe consider looking out for a second one (desiccant type) for occasional use in the cold winter months? Doesn’t need to be brand new if it’s just for the garage and you’d probably pick one up for buttons on eBay this time of year
Meaco DD8L is decent - I’ve got a couple. I use one occasionally on the boat to keep things under control in the winter. And it surprising how effective they are for keeping the humidity down in the home as well. Useful bits of kit
My garage is nearly identical to yours except that it's attached to the house , external walls have 38mm insulation in the cavity and ceiling, and my main boiler is in a room at the back, no other source of heating.. Both cars are always put in the garage after every trip , wet or not. I've never had a problem with mould, apart from some some discolouration above the doors.
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You may get enough heat soak from the house and boiler room to just take the edge off the temperature in winter? Our garage has nothing other than the inverter for the solar panels ... don't think that puts out much heat (certainly in winter when the solar panels don't do as much!). What ventilation do you have?
You're probably right about the heat soak, temperature rarely goes below 8-10 degrees.. No ventilation at all, there are no windows except for the toplights in the garage doors.
Main factor re ventilation is that both cars are in and out of the garage regularly, which is probably enough to extract the dampness in the air.
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