I'm going to be building some type of garage in my backyard or maybe a portable car port on top on a slab of concrete.

I am looking at creating positive pressure to push the fumes out and do not want to use any exhaust fans because I have read they can ignite the paint fumes and blow the whole thing up!

So how many box fans would be ideal to create positive pressure?
And where would be the best place to place the fans? Equal amount of fans on each side or all in the back?
Will creating positive pressure be blowing the fumes all over the booth though and making a mess on the paint job?

I'm thinking I am going to put 2 filters on each fan. One outside and one inside.

And how many exhaust ports with filters only, no fans should I have?
Thank you!

For positive pressure your exhaust filter bank needs to be slight smaller than your intake filter bank.
If you want to do this right here are some calculations:

To calculate the amount of exhaust air needed for the booth, a simple calculation is used.
CFM = Booth Face Area in square feet multiplied by the required flow (typically 100 FPM)
For example, and 8 X 10 filter bank (80 square feet) would require an exhaust of 8000 CFM (100 X 80) to achieve the required 100 FPM velocity.
To calculate the existing velocity knowing the exhaust volume the following formula is used:
Velocity = Exhaust in CFM divided by the booth filter area.
For example, a fan that exhausts 9000 CFM with a 10 X 10-filter bank would have a velocity of 90 FPM.

Note: To reduce turbulence in your booth a larger intake filter bank is the way to go. (talking positive pressure here) Think of it as pushing a wall of air from the intake side through the booth and out the exhaust side. You want good airflow so you cannot have the exhaust filter bank way smaller than the intake filter bank or air will continually swirl in the booth waiting to get out.

Thanks for the reply '68.
I looked up filter banks and from what I see it is one duct coming in or going out of a paint booth that then turns into seperate filter banks correct?

Thanks for the posted formula.

I should be looking at the CFM created by a fan to calculate how many fans I will need for whatever size intake/exhaust filter bank I am going to use?

So the intake should be on one side of the booth and the exhaust side on the other side of the booth?

And the exhaust filter bank a bit smaller than the intake side.
Since the exhaust bank will be smaller. Should I have the fans CFM add up to the exhaust bank?
I hope my questions are making sense.

Generally you will have cross draft booths and down draft booths.
Cross draft moves air from one end to the other of the booth usually from the front to the back or the back to the front.
Down draft or semi-down draft booths move air from a central location on the ceiling to exhaust banks directly under the vehicle (down draft) or to exhaust running along each side of the booth at floor level (semi-down draft).

Yes you will need to calculate CFM out put of fans in order to insure the proper air flow you will need. You will find the CFM requirement is costly to meet and you need to buy something besides home box fines. I am using squirrel cage fans from home furnaces for the intake side of my booth.

Thanks again.
I am going to go with a cross draft booth.

I've seen the fans you use somewhere on here. I forgot where.
It looked like your fans were directly on the wall and just drawing air in from the outside and it didn't look like an intake bank.

This is what an exhaust/intake bank looks like right?
http://m.ebay.com/itm/PAINT-EXHAUST-FIL ... 1543745941

If it does, is it better to have individual ports for each fan directly on the intake wall sucking air in And pushing it out of individual exhaust ports on the opposite side?

Or is it better so set up an intake bank like the one in the link posted?
One port with ducting going to 3 fans sucking all the air in from one outside port?

Do I need an exhaust bank if I am going with positive pressure? Or will individual exhaust ports with only filters on the wall work?

Sorry for so many questions. Just want it to work well.