Garage Air Intake and Ventilation

[Grrrmachine]

Here's the little brick lock-up I do all my car work in. My BMW E30 just fits in there each day, protecting it from the -30 winters we have. It has a single 16A fused ring for sockets and lights.



Up until now, I've just done rattle-can painting and drilling in here, but now that I've got a welder and compressor, I need to sort out an air in-and-out system for spray painting and dust/fume removal. As you can see on the right, there is a 140mm square air vent, no fan, going through a 250mm thick rear wall. The doors on the left are wooden, with small holes drilled in top and bottom.

I was planning on wiring in an extractor fan (150mm, 200 m3/h, more than a Sealey extractor) to the vent, with some ducting to extract air from the sides of the garage. I will then run a smaller duct to the door end to meet a hole in the door, to feed the compressor, which, irritatingly, will be sitting just to the left of the ventilator hole. This is so that the compressor doesn't suck in any of the fumes expelled during painting. Good idea, or have I ignored some drawbacks?

 

[rtcosic]

I spray parts in my shed. It has a total volume of around 20 cubic metres.

I have an old car cooling fan in the end wall that I run off an old battery whilst spraying. According to the Kenlowe website a fan that size moves around 2000 cubic metres per hour, so I'm getting around 100 air changes per hour. That works perfectly for keeping the air clear of paint fumes. When spraying the compressor lives outside and there's a hole in the shed wall for the airline.

Your garage is around 40 cubic metres so to achieve the same thing you would need around 4000 cubic metres per hour free air flow - two car fans.

Your proposed 200 cubic metre per hour fan would only give you around 5 air changes per hour, which is less than that recommended for a kitchen or bathroom just to avoid condensation.

Your air 'entrance' hole will need to be broadly the same cross sectional area as your fan outlet. I was a little paranoid about dust in the fresh air I was drawing in. I have an old fresh air filter about 300mm square that I acquired from an old computer room which I fitted into the shed wall opposite to the fan.

 

[rtcosic]

Googling air changes and spray painting I've found:

4 air changes per minute or 240 per hour

20-30 air changes per hour just for general repair workshop

So even my 100 air changes per hour in my shed is not adequate!

 

[Grrrmachine]

Yeah, I see what you mean; those little fans just aren't going to shift the amount of air needed. 4 changes a minute is mad though; my garage would sound like a jet engine!

Maybe a car rad fan built into something like a kitchen cooker hood would channel air out of the vicinity better? My garage is only 2m high (2.1m at the door end) so it might even make more sense to vent the air out towards the door, and suck clean air in from the vent hole.

Trouble is, I'm not sure how I'd power a 12V fan off the mains. Old car battery charger?

 

[cumbriasteve]

Yeah, I see what you mean; those little fans just aren't going to shift the amount of air needed. 4 changes a minute is mad though; my garage would sound like a jet engine!

Maybe a car rad fan built into something like a kitchen cooker hood would channel air out of the vicinity better? My garage is only 2m high (2.1m at the door end) so it might even make more sense to vent the air out towards the door, and suck clean air in from the vent hole.

Trouble is, I'm not sure how I'd power a 12V fan off the mains. Old car battery charger?

All you need is a 12v transformer, they are cheap as chips and should be loads on Ebay

 

[rtcosic]

Yeah, I see what you mean; those little fans just aren't going to shift the amount of air needed. 4 changes a minute is mad though; my garage would sound like a jet engine!

Maybe a car rad fan built into something like a kitchen cooker hood would channel air out of the vicinity better? My garage is only 2m high (2.1m at the door end) so it might even make more sense to vent the air out towards the door, and suck clean air in from the vent hole.

Trouble is, I'm not sure how I'd power a 12V fan off the mains. Old car battery charger?

Yup! When the fan is running it is LOUD - exactly like a baby jet engine! It drowns out the noise of the compressor.

Read the links - they give good information on size of ducts to achieve recommended velocities for adequate dispersion. An old cooker hood is likely to have 100mm diameter outlets - FAR too small for the required volume.

If your garage has a flat roof venting straight up via a 300mm diameter vent pipe with a 'coolie hat' on top might do the trick. Do you have close neighbours? Beware of blowing paint all over them from the vent!

A typical car fan takes 20-30 amps, a battery charger typically can deliver 5 amps. I have an old battery - good for about 2 hours use, which is fine for spraying small collections of parts. For a whole day's spraying of a whole car why not collect a few old batteries, charge them all up then use sequentially. Then take a few days to recharge them all?

A transformer capable of driving two fans at around 50 amps isn't going to be cheap.

 

[Grrrmachine]

Yeah, I see what you mean, and I wasn't aware that the fans took that much juice; the car battery idea seems great, seeing as I have a few knocking around.

I should have mentioned on the pics that behind the garage is a big school playing field, and while I don't want to douse the kiddies with isocyanates, it's got to be better pumping the fumes in that direction than it is towards the door, other cars and whoever's walking past. Trouble is, I doubt I can stick a vertical chimney on my garage; it would look a bit odd compared to the other 9 garages in the row!

 

[NTwoO]

PC power supplies are strong enough to pull a car fan. One per fan and you should be OK.

 

[Omniata]

You could run the duct out through a 90° bend and down at 45° to the floor...

Wrap it in fibre glass and put some baffles, or a grate, on the end and you should be fine...

 

[eil]

Try and keep with the way your prevailing winds blow and work with them not against them every little helps.

 

[Grrrmachine]

This not being England, it's not very windy over here; a day like today is absolutely still, for example.

My preference is heading towards using car fans, but finding a way for them to dump their output through that 140x140mm vent because I'd rather not work with the garage doors open. On the other hand, building a collector hood and flue to get the air out that hole is a task compared to just hanging the fans from the ceiling by the door.

 

[Pete.]

What you need is a fan from a busted portable air conditioning unit. There should be two in each unit, they shift a good bit of air, and are quiet.

 

[Grrrmachine]

I'll keep my eye out for broken air-con units, although I'll more likely have to bite the bullet and buy some new fans with a known throughput rating, or set up a series of car fans as previously suggested.

A new 400mm fan spinning at 1430rpm will move over 4000 m3/h, so at least I know what sort of specs to be looking for. But those fans cost 100 quid each...