Garage temperature and humidity control

[M1k3yC]

I expect that some of you have already done this, so I'm hoping for some pointers, please.

My garage gets too cold in winter (zero degrees Celsius - I don't think that it has ever dropped lower, though) and it can become too humid. The humidity is caused, I think, because I have a really wide roller shutter door so when it's open and humid outside it comes right on in! That and wet cars are sometimes unavoidable.

It's a detached construction and the ground floor measures approximately 6m x 8m. The outer wall is facing brick and the inner is 100mm Durox Supablock (according to spec) - it's painted inside, not plasterboard. There's a 50mm cavity that should be insulated (again, according to spec). There's an upstairs with a pitched roof and three roof windows. Downstairs has a window and door on one side and the large roller shutter on the other (it must be c. 5m wide).

I'd like to stop the temperature dropping below about 10 degrees - it hasn't done that yet this year, with no heating in place. I also want to drop the humidity to about 60% (it can get close to 90% when conditions are adverse). I have an electrical supply, cold water, and drainage up there.

I was considering an Ebac dehumidifier with a constant drainage option. Not sure which one yet, but probably one of the more expensive ones - I'll seek Ebac's advice, too. https://www.ebac.com/dehumidifiers/range/

For heating, I think that two wall mounted electric panel heaters downstairs makes sense. I've got plenty of plug sockets already installed so hope to just mount them and plug them in. I've got no idea where to start on that one - heaters seem to vary hugely in terms of price and function. I'd like automatic temperature control and basic scheduling (I probably don't even need days of the week, just a clock/timer function).

I'm not working to a strict budget so I can spend a bit more on a quality solution but also I don't need to spend money on superfluous features - for example I am not bothered about having a mobile app for my panel heaters! :lol:

Any suggestions/help gratefully received - thanks.

 

[B21]

We used to build hangars to house expensive helicopters (£2m+), as well as for fixed wing aircraft.

Condensation can play havoc with complex avionics and help accelerate corrosion.

So the point at which you see condensation is the dew point and that's where the air is 95%+ saturated with water vapour.

The dew point is directly correlated to temperature.

The diurnal heating cycle of the day, allied to the fact that the car being metal will cool down faster than the bricks/wood etc will be a preferential place for condensation to appear.

If you are willing to spend money on heating the garage then I would recommend that as your first point.

Ideally you want a bit of convection in the air to help move moist air away from the car.

A simple oil filled radiator with a simple temperature thermostat may give you the best / simplest payback.

If you keep the air about 10c and there is some internal circulation the car should not get condensation on it.

If you set the thermostat right you don't even need a timer..you want to avoid temperature changes if you can..but I guess the car is going in and out during the day?

In an ideal world what you would want is a heater directly under the car..the heat rising would heat the car and help convect air away carrying the moisture.

All the heat loss will be going through the roller shutter door..we used to supply insulated doors to help in that area.

I'd try the oil filled radiator first and then see how it goes, maybe then add a de-humidifer

 

[Zedebee]

Check out an air conditioning inverter from the likes of Samsung or Panasonic. It will heat, cool, humidify and dehumidify. Not the cheapest solution, but low maintenance and cheap to run. I had a system put in to heat a (two story) extension to save extending the central heating and it’s been excellent. Fully automatic and programmable.

 

[pvr]

I have the ebac units which work well to keep the humidity in check. I have it set at 60%

I have almost completed a new 12* 5 4 door garage outfit and have insulated all walls etc which raised the temperature by about 10 degeres inside during the night frost compared to the previously uninsulated state.

I have used a membrame first, then 10 cm insulation, then 22mm meliamine board for the finished look inside. I am waiting to see what the temp does (I installed remotely readable terhmostats / humidity sensors in the garage to see what it does at the various locations (low and high).

 

[Phoenixboy]

from my experience when storing high end motorcycles, it was the concrete floor that caused a lot if not all of the condensation on the bike.
I was advised to put carpet tiles under the wheels, and the problem went....Bone dry …..

 

[Pondrew]

Unless you can pretty much seal the garage; ie roller shutter, rafter spaces, eaves, everywhere, a de-hum will be a waste of time. A heat pump unit same. It is unlikely a detached garage, if it was built as one, will have insulation in the cavities, unless it is attached to the house. The floor will also not be insulated.
A garage doesn't need to be insulated for building regs so builders/ developers don't do it. Also check whether you have a DPM (damp proof membrane) under the floor. There should be one, but again not all builders put them in as it is not a 'habitable' space. Look in the corners where the floor meets the walls, you can usually see the plastic (
90% humidity is VERY high for a domestic garage. You say you have a water supply. I would check for any leakages in that first, as any leakages under the floor or in the walls could cause you humidity issues.
A simple help is to paint the entire floor with a specific sealant based floor paint and put some old carpet down over the top. Oil-filled rads are good to 'take the edge off' the temperature, but can be expensive to run for long periods.
Air movement will also help. Even a relatively small fan can help a great deal.

 

[BeeEmm]

Is there anything against installing hot water radiators (normal gas fired house radiators) if the garage is attached and built to a similar spec as a bedroom? I appreciate that a large garage roller shutter door is a weak point for heat loss etc.

 

[earthdweller]

I have a detached double garage with double glazed windows and a thermal insulated door

I have a dehumidifier in there that also puts out a bit of heat and even in the wild wet weather we get here it keeps the humidity at around 60%

Coupled with that I have a garage heater with a thermostatic control that activates as a frost prevention mechanism and kicks in at around 4*

Works absolutely fine and isn’t expensive to fit or run

 

[pvr]

Which garage heater is that? That is the one thing I need to add yet

 

[earthdweller]

Which garage heater is that? That is the one thing I need to add yet

These are what I use both bought from Amazon

 

[pvr]

Yes, similar dehumidifier to what I have, works well.

Will have a look at the heater, what are real life costs for running it, my garage is 65 square meters

 

[Pondrew]

my garage is 65 square meters

'rule of thumb' is 35-40 watts/m3 for heating (to raise the temp by 6-10 deg c) in an averagely insulated space.

 

[M1k3yC]

It is unlikely a detached garage, if it was built as one, will have insulation in the cavities, unless it is attached to the house. The floor will also not be insulated.
A garage doesn't need to be insulated for building regs so builders/ developers don't do it.

Thanks for the detailed reply - I know that you're in (or were in) the trade.

The spec calls for insulation, and it should have been built to spec - my builder can't remember but my dad thinks that it was insulated and he was around whilst it was being built. The spec notes, as you say, that the insulation is not required for building regs but the cavity insulation description is very specific: 50mm cavity totally filled with 50mm Crown Dritherm 32 Wallbatts..... etc.

Also check whether you have a DPM (damp proof membrane) under the floor. There should be one, but again not all builders put them in as it is not a 'habitable' space.

Both DPM and DPC listed in detail in the spec, it's a suspended ground floor slab because of a level difference. Beam and block underneath and should be well ventilated.

90% humidity is VERY high for a domestic garage. You say you have a water supply. I would check for any leakages in that first, as any leakages under the floor or in the walls could cause you humidity issues.

90% is on the extreme end. It hit over 90% today because it's 88% outside, the roller shutter door was open, and I was using a pressure washer on my car. It quickly dropped below outside humidity (to low 80s) with the door part closed and the window open for ventilation.

A simple help is to paint the entire floor with a specific sealant based floor paint and put some old carpet down over the top.

The floor was levelled and tiled so that isn't really an option, but thanks.

Air movement will also help. Even a relatively small fan can help a great deal.

That's a good shout. I was thinking when I was in there earlier that if I'd had a fan running then humidity would have dropped much more quickly.

 

[M1k3yC]

I'm pretty sure that the roller shutter door is insulated as well - it's a good quality remote operated electric one that rolls up into a box.

 

[M1k3yC]

[ref]B21[/ref], thanks for your input - yes, sometimes cars have to go in and out in the wet or at any time. I suspect heat and air circulation will help a lot, but a dehumidifier might still be useful for when things get really wet such as when a wet car has to come in or if I'm washing cars in cold weather.

I hadn't considered driving the cars over heaters. That's interesting.

 

[Pondrew]

One thing that may help; which I have done before (not in a garage, in a home recording studio; basically a sound insulated shed) is to cut an extract fan into an external wall, controlled by a humidistat. If you are heating, cut it in at low level, as heat rises! If you were to go this route, a fan able to 'change' the air a minimum of once an hour would be ideal. Always base calcs on m3, not m2; volume is the key. There are mainstream fans available with 'built-in' humidistats (a large bathroom extract fan). The air will then be made up by natural infiltration at a lower %RH (relative humidity).
If your space is 6x8x(average)3.5m = 168m, a fan capable of 168m3 per hour would definitely help. HTH

 

[B21]

[ref]B21[/ref], thanks for your input - yes, sometimes cars have to go in and out in the wet or at any time. I suspect heat and air circulation will help a lot, but a dehumidifier might still be useful for when things get really wet such as when a wet car has to come in or if I'm washing cars in cold weather.

I hadn't considered driving the cars over heaters. That's interesting.

Just brainstorming but if you could get these lined up these are a safe -ish way of heating under a car ?

https://www.amazon.co.uk/Tubular-Heater-Inbuilt-Adjustable-Thermostat/dp/B08PKYRQH2/ref=sr_1_1_sspa?adgrpid=53680612936&gclid=CjwKCAiA1aiMBhAUEiwACw25MQWHRwGWpttFntnASRtrcVPeAdYmKAbikc7rwKrfNfm_Av4LzSu5tRoC5yMQAvD_BwE&hvadid=259155665428&hvdev=c&hvlocphy=1007326&hvnetw=g&hvqmt=e&hvrand=4454354830128086435&hvtargid=kwd-21699046&hydadcr=25113_1834925&keywords=tubular+heater&qid=1636496828&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExOEJNRk1IS0JFWUhPJmVuY3J5cHRlZElkPUEwNjI2MjY5T1Y3S0tTQzk0UjFLJmVuY3J5cHRlZEFkSWQ9QTAyNTYxMzAzMkVKT0JMMzIyRDMmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

People seem to have had good experiences with de-humidifiers so why not ?

If the door is insulated that’s a major step..

 

[Pondrew]

If the door is insulated that’s a major step..

starting to think that the garage may be 'over insulated', as it stands. With a B&B raised floor, cavity wall insulation and an insulated roller, there is possibly nowhere for the moisture to go, except condensing out when it hits 'dew point'. If this is the issue, getting rid of the humid air is the best way to solve it.

 

[PerryGunn]

If the door is insulated that’s a major step..

starting to think that the garage may be 'over insulated', as it stands. With a B&B raised floor, cavity wall insulation and an insulated roller, there is possibly nowhere for the moisture to go, except condensing out when it hits 'dew point'. If this is the issue, getting rid of the humid air is the best way to solve it.

+1 on this

Anyone who is looking at dehumidifying/heating a detached garage should look at ventilation first - it might well save them a few £££

My garage is concrete base, brick walls, detached, uninsulated and my workshop is attached to the rear - air can get around/under the garage doors and the workshop has vents in the walls. As a consequence there is continuous gentle airflow through both the garage and the workshop. The only time I use any heat is a quick blast with a small fan heater in the workshop to take the chill off if I'm working in there on a cold day.

I have never had any condensation issues in either the garage or the workshop and no issues with surface rust on tools.

Unless you live somewhere with extremely cold winters, cars don't need a heated garage, just one that doesn't leak and is well ventilated.

 

[M1k3yC]

Thanks for the additional suggestions and input, much appreciated.

Yes, the automatic roller door is insulated - I've checked. [ref]Pondrew[/ref], moisture becoming trapped is likely, I agree. A humidity controlled extraction fan is an interesting idea. However, I spoke to a friend last night that has done some work controlling humidity and temperature on an industrial scale. He pointed out that the extracted air has to be replaced and at this time of year the outside air is likely to be a very high humidity so it won't work very well.

A dehumidifier looks like the best first step, but I'm still researching them. I think that a good desiccant dehumidifier would be the right choice because of the potential for low temperatures in the garage and the fact it will generate some heat when in use as well.