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MG MGA - Relative Humidity

I have a standard airconditioner (not Cacoon) in my detached single brick double garage. Just wondering what others see as an optimum relative humidity level. I have lathes and other stuff so not interested in Cacoon. Also, I run the car at least once a week during the winter months to keep it aired and functioning.

The garage is fairly well sealed, no air bricks; just a few very small gaps round the electric doors, but can't do any more about them. I don't want to dehumidify the whole road so I am just looking at the balance between electricity cost and an acceptable RH. Today for example RH is 90. The air con brings it down to 80 without too much trouble, but getting it down to 75 where I currently have it set is still an unachieved target.

Thoughts?

Steve
Steve Gyles

Steve, our AC keeps our double garage at 55 -65% with no sign of rust on machine tools etc.
d brenchley

Thanks for that DB. I only have the fan on low and don't keep it running 24/7 - perhaps only a few hours a day. May be I should bite the bullet and run it continuously to get closer to your figure. The specification on my unit should do it ok.

Steve
Steve Gyles

Steve, you need a dehumidifier, not an aircon. Keeps the temp normal, just removes the H2O
Art Pearse

Steve

I live not far away, in Surrey, so experience a similar climate as you do. I have two MGs (MGA and MG TC) in a double length brick garage. The garage also contains tool chests and spares (and wine store).

I have used a Mitsubishi MJ-E14CG-E1 14 Litre dehumidifier for quite some years in this garage. It is set to start operation at 70% humidity. No rust or condensation problems experienced at all. Very good unit, and highly recommended.

Our other MG TC has lived very happily in a Carcoon for many years in part of the (separate) workshop. However having been so happy with the first dehumidifier, I have recently dispensed with the Carcoon and installed a second Mitsubishi dehumidifier to look after this car and the workshop area with its lathe etc., and tools. This unit is also set at 70% humidity switch-on.

A bonus of a humidifier is a supply of distilled water for coolant and for the steam iron.

Cannot advise on running costs but you could probably calculate from an guess at on-time ratio for the dehumidifier. Do not think it is expensive.

Cheers
Mike

M D Card

Art

My error. I meant dehumidifier. Mine is an Electrolux EXD25DN3W. Comes well recommended. Thanks for the 70% aiming point Mike. I concur the distilled water point. That's what I use.

Steve
Steve Gyles

Steve,
I dont think that humidity is as critical a factor in keeping a classic car rust free as you may expect.
The most important thing is to prevent condensation from forming on the metalwork.

Before I had my new garage built a couple of years ago, my MGA stayed in a leaky old concrete sectional garage.
It was leaked so much rainwater in through the roof that I bought an Airchamber unit to keep the car drier.
(The Airchamber is basically a clear plastic freestanding frame tent with two small computer fans built in that create airflow over the car)

The humidity must have been always close to 100% in my garage and it was unheated and the temperature varied between 35 degrees and minus 10 degrees. However, the car always stayed dry.

With the bonnet, boot-lid and windows slightly open, the gentle airflow over both inner and outer body surfaces meant that there was no temperature difference between them and so condensation did not form on them.

So in a dry garage, either heated or unheated,I would suggest that some form of gentle airflow over the car, either natural or forced, would keep the car dry and may be as effective and less expensive to run than a dehumidifier.

Which is why my Airchamber is now up for sale! :-)

Cheers
Colyn
Colyn Firth

Colyn

The dehumidifier provides that circulation of air you talk about.

At this time of the year with warm frontal weather swapping with cold frontal weather overnight, or vice versa you close the door one night with the car nice and dry. Open up the next morning and the changed air floods in. Instant change of temp on the car's surfaces and she disappears in mist and condensation.

As I said above I run the car all through the winter primarily to keep the air flowing through all parts of the car. The dehumidifier is an addition to this process and gets the garage back to 'dry' conditions quicker than nature is capable in winter.

Steve
Steve Gyles

Just ship your cars to Queensland for the winter (our Summer), and we will look after them!
Gary Lock

I used to run a dehumidifier but, even after trying to seal most of the air gaps in the garage, I was drying out the whole of Surrey. Plus, of course, in really cold damp weather the exchanger would frost up as it got too cold. I would have said that 65% would be ideal, but unlikely to be achieved in current UK weather.

Ages ago I bought an air chamber mainly to keep the muck off the car from other garage activities. It does a super job, with two small 12v fans just humming away whilst the air bleeds out through the Zips and Velcro joins.

Regards
Colin
Colin Manley

Steve,

At the beginning of last winter I bought a small Panasonic heat pump
for my not so well insulated double garage.
This unit is capable of keeping the temperature at a constant 15 deg C and the electical bill is affordable.
The RH is steady around 60%.
The initial investment is a little high, but I can highly recommend this sullution.

Lars
L. Christiansen

I have never used anything and I am only 50m from the sea. My only rule is I take the car off the road as soon as first salting is applied to roads No problems so far and I competed my rebuild in 1979. Garage is of modern block construction with pitched wood/tiled roof.

Paul
Paul Dean

Thank you for your comments. As you can see from the photo my garage is a well built structure. I have also boarded in the roof space. to create an upstairs spares store. I don't have a problem with dampness other than the ambient damp air this time of the year that permeates all these types of out-buildings. So I am not looking for a sticking plaster to cure an existing wound; more a preventative course of action. I drive the car throughout the year and on dry days I usually have one of the main doors open, plus the small width door at the back to create a flow of air.

Steve

Steve Gyles

I ran a dehumidifier last winter set to 65%. Although the garage is pretty well sealed, built of brick etc, the unit seemed to struggle and produced gallons of water! I also suspect it used quite a lot of power but this year, having had one of the new meters fitted I should get an idea about how much it is costing.
Graeme Williams

My dehumdifier has taken almost a week to get my single garage (modern brick, reasonably sealed) down to 65% or thereabouts. It has rattled away at about 7kwhr per day and only just started to cycle. But it's rained and gone from warmish to cold so now it is running flat out again.
I'm putting the heavy use at the moment down to general moisture in the building fabric but if it is going to continue at this rate it won't be cheap to run.
Graeme Williams

I live about 500m the pacific and the humidity often climbs .The daily cycle of temps often produced condensation in my large double garage/ workshop. I bought and installed a heat pump domestic hot water storage heater about 5 years ago and that sucks all the humidity out and dumps ithe water outside . Everything has been bone dry ever since..so two birds with one stone .....economical HW (about 3 kw of water heating power for 1 kw of elect energy) and a dry garage. very please with the unit...bteer than the roof top solar HW systems ..works all the time . I have a solar elec panels as well so thee elect bill is minute......I am now a full greenie.
Neil Ferguson

Interesting
My problem living close to the sea is salt spry
My garage is underground-into the face of a hill but I have this salt problem--car is ok but the garage door cops it and I had to replace it last year as the salt ate the catch out of the door---metal roller door
willy
William Revit

I have seen references, including that by Neil, of heat pump systems. I have had a look on the web and seen a bit about them but they seem extremely expensive, especially for a detached double garage. Can someone clarify the type of system please.

Steve
Steve Gyles

Steve, heat pump is a fridge in reverse. Takes heat from the air outside and transfers it to inside air at a higher temp. Any form of heat will keep the inside air above condensing. The cooler and the heater can be split ito two separate units connected by the Freon pipes.
Art Pearse

Yes, but at what cost to buy, install and run?
Bruce.
B Mayo

Exactly Bruce, that's what I am wanting to know. Neil talks about the hot water generated with his system, but that's of absolutely no use to me with a detached garage. My house system does all that quite efficiently.

Steve
Steve Gyles

You could use a window mount A/C but face it in reverse
Art Pearse

You can get neat little units to fit into a window hole or on a wall if you have a vent outside OR a split system as Art mentioned
A lot of motels use them here for heating / cooling
Some are better than others with different operating strategies
Some / most basically run nearly all the time and vary their temp.output automatically to maintain a set temp but blow air all the time, these can be a bit expensive to run but there are one or two makes that are a bit more basic and a lot cheaper to run
My son had one of these in his house, it was a Mitsubishi and through the winter he left it running all the time on a mild temp and the lowest fan setting and it was as cheap as chips to run
I think it had about 2kw max output from memory but they use only about a third of the power a normal 2kw heater would use when running flat out,but you wouldn't need anywhere near flat out
willy
William Revit

If you look at any manufacturers' information they state that the "fridge" type dehumidifiers are not suitable for drying air in low temperature environments (like uk garages in winter). The recommendations are for the chemical dryer type.

Quote (one of many):
Refrigerant (or compressor) dehumidifier Itís often claimed that a refrigerant dehumidifier works better at higher temperatures and higher humidities, and so is the better choice for most occupied homes in Britain. Refrigerant dehumidifiers draw in air over a filter and then pass it over cold coils. Water then condenses on the coils and drips into the water tank. Desiccant dehumidifier A desiccant dehumidifier is designed to work more effectively in colder temperatures Ė the sort of environment you might expect in your typical garage or conservatory. Desiccant dehumidifiers use an adsorbent material to extract water from the air, and then the material is heated so that the moisture drips into the water condenser. Itís often claimed that desiccant dehumidifiers tend to use more energy than refrigerant dehumidifiers because of the way they use heat to warm the adsorbent material.

Read more: http://www.which.co.uk/reviews/dehumidifiers/article/how-to-buy-the-best-dehumidifier - Which?
Graeme Williams

When I stored my MGA in the "Airchamber" tent, I found that regardless of how humid the air was in my leaky garage and how cold the air temperature was (and it was pretty damp in there!), I could put the car into it wet-through after driving in heavy rain and the car would be completely dry after a couple of hours.

Those two tiny computer cooling fans did their job perfectly.

So stop worrying about keeping the garage warm, just make sure there is airflow over the car.

Colyn
Colyn Firth

Colyn

Whilst in total agreement about air circulation there are other factors. For instance my garage doubles up as a general workshop and I like to keep working in it (not just MGA related work) throughout the winter months. So heating also has to be addressed. It's all a balance between dryness/heating/cost. I have not found the best answer yet for my requirements.

Steve
Steve Gyles

I must admit that it is nice to work in a warm workshop Steve.

My new garage isnt heated but I clad the entire inside including the roof with 30mm "Kingspan" insulation and if I switch on a 2kw heater, it warms up to 20 degrees in about 10 mins.
After that, especially if I am working on something, it hardly needs any more additional heat at all.
Colyn
Colyn Firth

Very nice Colyn. I have floorboarding on the rafters. I am minded to put that stuff on the underside. I have so much stuff on the walls it would be an absolute pain to line them, but one thing at a time. As heat rises I guess the ceiling would make the most difference. How did you fix the kingspan?

Steve

Steve Gyles

Having written a full explanation of the physics, as they seem to have been missed, I then lost it so I will just give you the conclusions and some pointers.

1) If you wish to stop getting condensation on a car used in winter you need to keep the garage at near outside temperature. Warmer the garage the worse condensation will be. it is just like a glasses wearer coming in doors and steaming up.

2) If you aren't happy with this solution it is important, as Colyn said, that you have good air circulation around the car and into the garage, and you get the car up to garage temperature as quickly as possible. I have air bricks and I keep a window ajar, but I don't use the car once salt is on the road. A good solution would be fan blowers aimed under the car which achieves both objectives. Clearly this also works if the car comes back wet.

3) If you wish to heat the garage as a workshop that is fine as the car will warm up with the garage so there is no temperature differential issue. But let the garage cool down before you take the car out (and bring it back).

4) The other issue mentioned is when the atmosphere gets to over 100% humidity, i.e. fog. Personally I don't think this is that big an issue but applying minimum heat should solve this, and don't take the car out!

I won't rewrite my stuff on the theory but it is all about dew point for water in air and the fact humidity is relative. Air at 100% relative humidity contains around 3 times as much water at 20C than it does at 0C. The interesting point here is that if you bought a car at OC into a garage at 20C and the garage was anywhere above a very low 33% relative humidity you could get some condensation. Its all simple physics.

Paul




Paul Dean

I am with Paul on this one Steve, preventing condensation forming is the main thing that matters

However, if you need the workshop to be warm then insulating it will help.

I fitted the kingspan between the roof trusses and a few galvanised nails easily
secured it to them.
The Kingspan cuts easily with a Stanley knife or a handsaw.
As it was a new garage I decided to hide the insulation under some 1/4" plywood.
I does look a little like a sauna but it looks better and is warmer than brick.
Cheers
Colyn
Colyn Firth

Colyn

I am not for nor against anyone on this topic. I do not suffer condensation any more or less than anyone else i suspect. I am more than happy with the theories and practical issues around the causes of condensation, dry/wet adiabatic lapse rates, the fohn effect and goodness knows what having spent half my working life flying through warm/cold sector depressions and a lot more. All I am trying to achieve is that compromise solution that lets me keep working throughout the winter in the garage, exercising the car at least once a week or so but not having to take out a second mortgage to achieve it.

Steve
Steve Gyles

Sorry Steve,
didn't intend it to sound like I was taking sides against you.
Just my ham-fisted way of saying that IMHO, I think you don't have to go to any great lengths or expense to keep your car dry.

I would use a blower heater when you need heat, and only a small fan when you don't.

I would just keep the cars windows, bonnet and boot lid open a little in the garage to let the air to circulate and your car will be just fine.

I will now go get a mince pie, a glass of port and try take the advice of the Boyzone track that just happens to be playing on my radio.
"You say it best when you say nothing at all!" 😁

Have a great Christmas.
Cheers
Colyn

Colyn Firth

Colyn

Car windows open? Mmm.......

Steve
Steve Gyles

Ok, I forgot that you don't have a soft top or use side screens and that therefore, your windows are continually open!

I have to keep my vinyl soft top erected when the car is stood for any time as it tends to shrink and is then almost impossible to fit to the screen.

Now its back to my mince pie and Port

😁
Colyn
Colyn Firth

Hi Steve

I am sure you are ok with your dehumidifier but if you go 'natural' as Colyn suggests you really would need to add some ventilation into the garage. I have air bricks and leave the window ajar although my new roller doors are better sealed. My main winter problem is that the car gets dusty, but clearly I don't take it out.

Paul

Paul Dean

You could always move to Australia - Melbourne temperature for Christmas Day is forecasted to be 36C!
Mike Ellsmore

Paul & Colyn

I don't have airbricks. I just have a few gaps in hinge areas of the electric doors and along the base in places. I do have rubber seals along the base on the outside but there will always be small air gaps. One of the doors is opened every day for the wife's shopping transport (bicycle), plus the access door behind the photo is always being used both by myself for general workshop access and by the wife for raiding the additional chest freezer. So, the air in the garage is forever changing.

Steve

Steve Gyles

How about a 500W solar panel on the roof, connected directly to a resistance heater in the garage? You have to get the right arrangement of series/parallel cells to maximize the heat output. No mains connection.
Art Pearse

Arts suggestion sounds a reasonable one, if the cost calculations work out.
You would have to compare the cost of installation against the long term costs of running a similar power 500 watt blower heater.

On ventilation, I think your garage is ventilated enough Steve, my tiny pair of computer fans kept my car dry in my old damp garage that was ventilated about the same as yours is now.

When I built my new garage I originally intended to cut a couple of vents with tiny computer fans built into them into the walls at one end to act as extractor fans.
I was also going to cut an air vent at the other end with some sort of air filter over it to keep the dust out.

I havent gotten around to doing this yet, it is on my to-do list for sometime in the future, but so far the the car appears to stay dry enough without them.

Cheers

Colyn


Colyn Firth

Sounds like you have enough activitiy to get the ventilation. I can go up to a week without going in the garage.

Paul
Paul Dean

My answer is to keep the cars outside - all mine live out all year round and therefore remain at ambient temperature and humidity.

The only problem I have is on a cold day when the passenger insists on breathing , but a few minutes with the heater on (yes mine work) and even that isn't a problem.
Chris at Octarine Services

Am I alone in chuckling, as the title of this thread conjures up a picture of steaming relatives over the Christmas holiday?

Shane
Shanerj

Shane

Up to now probably yes. Good one.

Reminds me of an electronic Xmas card I received a couple of days ago. It said "Looking forward to an exiting 2017". I responded "Perhaps. Might 'C' you there."

Steve
Steve Gyles

Colyn

I have just priced out the ceiling insulation for my double garage. My local Travis Perkins does a Kingspan equivalent, 50mm thick. £273.00. Always a quandary whether to spend this sort of money on the hardware or just accept the equivalent spend over a period of time on electricity.

I asked them about fixings. A builder standing along side me at the counter said just to cut a few mm wider than the joists and push up into place against the floorboards above.

Steve
Steve Gyles

I used 30mm insulation Steve which was available then but may well have been superceded by the 50cm stuff.

I also accepted "seconds" quality which meant that there was the odd small dent in most of the panels and I paid less than half what you paid to cover three walls of my garage and also the underside of the tiled roof.

I just put the dented side to the inside so that only the good side was on show.

It is better to secure the foam in the roofspace with some 3" nails hammered in sideways into the joists so that the foam rests on them.

Otherwise in high winds it is possible for a strong gust of wind to dislodge the foam panels so they fall out.
Colyn
Colyn Firth

Ebay have 30mm panels (2nds) 2.4m X 1.2M
for £9.00 per panel.
How does that compare with your supplier Steve?

Colyn
Colyn Firth

Great to hear from you Chris Betson, glad to see that you are still active in the world of MGs.
How are you enjoying retirement?

Wondering if we should maybe report you to the RSPCMG for leaving your MGs outside in all weathers😁!
Colyn


Colyn Firth

Colyn

Thanks for the heads-up. That size but 50mm from TP is £22.75 +vat a sheet! I need 10 of them.

I could not contemplate leaving mine outside for more than the occasional night. With only the tonneau for weather proofing I think deterioration would soon set in. Would not help my insurance premiums either.

Steve
Steve Gyles

Thumbing through some old EMGs I came across an article in the March 2014 edition about a dehumidifier fire in a garage leaving the plastic casing in a molten heap on the garage floor and a lot of heat and smoke damage on a 14/40.

The dehumidifier was made by Ebac but the model number is not given. It was within its 5 year guarantee.

I don't recall seeing any follow-up of this incident or the resulting compensation from Ebac or the house insurer, although the vehicle insurer will pick up the tab for the car.

Cheers

Dave
Bolney Coupe

This thread was discussed between 22/11/2016 and 03/01/2017

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