Heating a garage - best method?

Guvnor

I am looking to raise the ambient temperature in a 700sq ft garage by a few degrees.

Just a little history -

The garage is 700sq ft with twin electric insulated doors and has a cavity wall - 4-6inches not sure exact depth.

I got a dehumidifier on the 23rd and it has helped - it has dropped the RH % from an average of 80% to mid 50's% and the average temperature in there would now be about 7 degrees C. Without the dehumidifier it could be 3 degrees or less if very cold outside.

I am going to get blown insulation into the cavity wall before the end of the month and am thinking of putting in a ceiling as there is no usable space above the beams. Would it be wise to put spray foam in the space above the ceiling?

It has a concrete floor - nice and level and surprisingly smooth - I was thinking of putting some rubber matting down like you'd see in gyms for some extra insulation between floor and garage. Would this make any difference?

The 50 litre dehumidifier does not like working out there in 7 degree weather despite saying it can work down to 0 degrees, the refrigeration coils cannot defrost themselves which requires carting it into the house for a few hours before putting back out.

Now to help heat the place and ensure the dehumidifier can work on and off - more off than on from a cost perspective I have been looking at:


Fan heaters
Space heater
Oil filled radiators
Ceramic infra red heaters
Quartz heaters
Radiant infra red heaters
Storage heaters.


As I said I have no desire to have the garage heated like a house - if could average 10-11-12 degrees that would be more than enough with a possible boost if I was out there etcetera.

I was thinking that space or fan heaters would be my best bet but not sure of the size. Now I am on single phase so this will limit me but my thinking was that a 6kw fan or space heater would be more effective at raising the temperature than a 2kw left on three times as long?

I do not expect miracles from the blown insulation or the ceiling but perhaps it would add 3-4 degrees without much difficulty?

Any views or thoughts appreciated.

Pete67

Any form of electric heating will be expensive long term. Have you considered a paraffin heater? Modern ones have thermostatic controls and are very safe to use.

Something like this:

Even better if you already have oil fired central heating and use kerosene as you can just take a few litres from the oil tank when you need it.

Adding a ceiling and insulating above it will make a big difference as you reduce the heat loss to the roof space. Use a vapour barrier or foil coated plasterboard to prevent condensation and make sure there is sufficient ventilation at the eaves to prevent the roof space becoming damp.

Guvnor

Thanks Pete.

I never considered paraffin - would of assumed it was just too dangerous!

Will look at the inverter, cheers mate!

Reyman

Is the garage detached or attached to the house? I.E. How many sides are exposed to the elements?

You need to know exactly what the walls are made of eg. they could be 9" block in which case they can't be easily insulated.
It's also possible they're two leafs of 4" solid block with a spacing cavity. You need to know before you do anything

Guvnor

Hi Reyman,

It is a detached garage so all four sides are exposed.

It is red brick on the exterior all around as with a house and internally it is grey concrete block.

I have included a picture of the garage externally. This is an old picture but it's pretty much still the same.



A more recent external shot here:


Here is an internal picture.


I am not sure of the correct term but it appears to me that it is suitable for blown insulation.

I am looking at kerosene/diesel space heaters but without a flue there must be fume issues.

Any help appreciated.

Pete67

From the flue and the oil tank location, I'd hazard a guess that your central heating boiler is located in the garage? In that case, why not just add a radiator with a thermostatic valve on it to keep the temperature in the garage around 12 to 15 degrees. By all means insulate the garage as much as possible to reduce the heat loss, if it's a true cavity wall then inject insulation as you suggested, otherwise you will have to dry line the walls. Add the ceiling and insulation as well and you should be able to keep the chill off it without spending a fortune on heating.

Reyman

I don't know what you have below the slates in the ceiling but I'm assuming you just have a roll of felt above the cross beams.

If this is right you're losing about 2/3 of the total heat through the ceiling. If you put in a ceiling with 8" of fibreglass on top you'll notice a big difference. The heat loss there will be effectively zero. The temperature should then rise several degrees with the dehumidifier

Leave the walls till you sort out the ceiling. The rubber mats would also help. But do one thing at a time

Guvnor

Pete67 wrote: »

From the flue and the oil tank location, I'd hazard a guess that your central heating boiler is located in the garage? In that case, why not just add a radiator with a thermostatic valve on it to keep the temperature in the garage around 12 to 15 degrees. By all means insulate the garage as much as possible to reduce the heat loss, if it's a true cavity wall then inject insulation as you suggested, otherwise you will have to dry line the walls. Add the ceiling and insulation as well and you should be able to keep the chill off it without spending a fortune on heating.

Thanks Pete was thinking something like this tbh, just was unsure how difficult it would be to install a radiator or how much effect one radiator would have in a 700 sq ft room?

Guvnor

Reyman wrote: »

I don't know what you have below the slates in the ceiling but I'm assuming you just have a roll of felt above the cross beams.

If this is right you're losing about 2/3 of the total heat through the ceiling. If you put in a ceiling with 8" of fibreglass on top you'll notice a big difference. The heat loss there will be effectively zero. The temperature should then rise several degrees with the dehumidifier

Leave the walls till you sort out the ceiling. The rubber mats would also help. But do one thing at a time

Cheers Reyman - good advice on the ceiling - suppose you would have to drop all the electrics or would/could you put the ceiling above the beams? The ceiling would also help it from getting too hot in the summer - not likely an issue but...:D

The dehumidifier does not work outside - looks like it's kaput in less than 2 weeks! Damn that large chain beginning with a B.

In the house it works no issue but in the garage despite being 7-8 degrees it cannot defrost the coils to keep working. It's going back tomorrow!

Now I am thinking if a more expensive 'industrial' one would work any better?

Cheers guys for the advice!

Reyman

Hi Guv.

I'd leave the electric cables up in the loft (above the glass fibre). Put in a small trap door so that you have access.

On the dehumidifier - don't forget it's expensive to run 24/7 - maybe use it on a timer. Let us know how you get on.

Guvnor

Reyman wrote: »

Hi Guv.

I'd leave the electric cables up in the loft (above the glass fibre). Put in a small trap door so that you have access.

On the dehumidifier - don't forget it's expensive to run 24/7 - maybe use it on a timer. Let us know how you get on.

Cheers Reyman.

The dehumidifier uses 1kw per hour - in an ideal world it should only come on when the humidity hits a set level and then switch off which would mean a mere 4-6 hours per day but it looks like it's not going to work again properly outside - still within my 28 days to return it so may well avail of this.

Will definitely let you guys know what happens - I have a remote thermo/hygro out there so can accurately see what the temp is. It hit 10 degrees today and since removing all the moisture the RH has not risen above 60% even with the dehumidifier not working which to me is a good sign - means the place is reasonably air tight.

Guv

Gingerspice99

What about one of thos workshop stoves?/

Pete67

Guvnor wrote: »

Thanks Pete was thinking something like this tbh, just was unsure how difficult it would be to install a radiator or how much effect one radiator would have in a 700 sq ft room?

Its fairly easy to do the heat loss calculation - you would design for a slightly lower difference in internal / external temps than you would for a house, as you are only looking for background heat. Say 15 degrees. Then calculate the heat loss for each wall, including doors, windows, add in the heat loss through the ceiling / roof and floor and you come up with a kW rating to maintain 15 degrees when it's 0C outside. Then select one or two radiators to give this output based on a 70C flow temperature and a 60 degrees return temp. The plumbing of the radiators would be straightforward. If it was me I'd add a motorised valve controlled by a timeswitch and a room stat to avoid overheating the garage. You could set the room stat to 10C when the garage is not in use and this will prevent condensation. You won't need a dehumidifier then.

As Reyman says the first step is to put up the ceiling and 8" of fibreglass insulation above it. Use foil backed plasterboard (foil side up) so that there is a vapour barrier. You will need at least 2 people to handle the plasterboard sheets as they are 8 x 4 ft and you have to support them when nailing to the rafters. Shout if you want the heat loss calcs done.

Reyman

Guvnor wrote: »

Cheers Reyman.

The dehumidifier uses 1kw per hour - in an ideal world it should only come on when the humidity hits a set level and then switch off which would mean a mere 4-6 hours per day but it looks like it's not going to work again properly outside - still within my 28 days to return it so may well avail of this.
Guv

I hope it's not using 1kwhr per hr that would be mighty expensive - close enough to €2,000/annum running 24/7. I used to know humidifiers fairly well, but I've forgotten the detail--- do they not switch on and off with humidity levels?

Guvnor

Gingerspice99 wrote: »

What about one of thos workshop stoves?/

Cheers Ginger, not enough off cuts or sawdust if any to make this viable, now if they would burn junk mail!:D

Guvnor

Reyman wrote: »

I hope it's not using 1kwhr per hr that would be mighty expensive - close enough to €2,000/annum running 24/7. I used to know humidifiers fairly well, but I've forgotten the detail--- do they not switch on and off with humidity levels?

Hi Reyman,

The max usage would be 1kwhr however to maintain the garage at around 55% then you would set the dehumidifier to say 60 and it turns on when IT reads 63% and shuts off at 57%. The area around the dehumidifier is always a touch more humid as it is pulling the air in etcetera. I would say in an ideal world the machine would be on no more than 3-4 hours per day maximum - this would still run you €250-300 per annum.

It's on the blink anyway - was running from about the 22nd of December to the 29th pretty much 24/7 but this did get the humidity down from 80-85% to 49-55%.

It looks like that to maintain 55-60% is pretty comfortable once the levels are down.

This was from the CO's trade section - £250 and can extract upto 50 litres per day and designed for building sites etcetera. I am surprised it's packed in so soon. The air filter was spotless even after the 7-10 days out there so the environment was not that tough on it. I was thinking of getting an ebac or a www.calorexx.com however I am not sure if they will be any better at doing what they say on the tin so to speak, they would be a lot more expensive.

I am right in thinking a dehumidifier that can operate down to freezing should not have an issue in 7-10degrees?

Guvnor

Pete67 wrote: »

Its fairly easy to do the heat loss calculation - you would design for a slightly lower difference in internal / external temps than you would for a house, as you are only looking for background heat. Say 15 degrees. Then calculate the heat loss for each wall, including doors, windows, add in the heat loss through the ceiling / roof and floor and you come up with a kW rating to maintain 15 degrees when it's 0C outside. Then select one or two radiators to give this output based on a 70C flow temperature and a 60 degrees return temp. The plumbing of the radiators would be straightforward. If it was me I'd add a motorised valve controlled by a timeswitch and a room stat to avoid overheating the garage. You could set the room stat to 10C when the garage is not in use and this will prevent condensation. You won't need a dehumidifier then.

As Reyman says the first step is to put up the ceiling and 8" of fibreglass insulation above it. Use foil backed plasterboard (foil side up) so that there is a vapour barrier. You will need at least 2 people to handle the plasterboard sheets as they are 8 x 4 ft and you have to support them when nailing to the rafters. Shout if you want the heat loss calcs done.

Cheers Pete. I did use an online calculator for the BTU and came up with a figure of 13-21 depending on the height of eaves etcetera. 13,000 was based on having a ceiling. Would appreciate an accurate heat loss calculation done mate if you have the time.

Even when the garage did drop to it's low of 2.9 degrees inside and having high 70's humidity there was no condensation. There are a few plastic tubs and things out there and they were cold but then it was down to 3-4 degrees at night and upto maybe 6 during the day but no condensation which surprised me tbh.

I'll take another shot of the roof tomorrow and get cracking on getting this done and take fresh pictures - ceiling makes a lot of sense!

Cheers mate!

Pete67

No problem, send me a PM with accurate dimensions of walls, doors and windows and I'll run the numbers.

If it's a cavity wall can you determine the width between the inner and outer walls?