I would like to install an intake louver in my shop to allow the booth fan to draw in outside air while running. Currently, I just open the bay door a bit in the winter so the fan can pull the air through. I am aware that this is not ideal, cold air and negative pressure, but heated air makeup is not in the cards. My question is, would a 30" louver provide enough fresh air? The fan and exhaust stack are 30".

We have an 8' wide open face booth and do exactly as you describe. Works fine.

We have the intake at the opposite end of the building so the air mixes with the shop air to help pre-warm before it hits the finish booth. Shop floor is about 2000sqft with 18ft ceilings.

The fan will pull air from every leak you have if the intake air supply is not sufficient. It will also pull air back through the chimney on your shop furnace if you have one, while the furnace is running. Be careful! Since I don't know the capacity of your fan, nor what the louver is attached to, I can't say what opening is correct. Many shops have a variable speed fan to slow it down while the finish degasses.

My shop had an electrically operated louver already installed, (though unfortunately not working), when I moved in. One thing that I would likely not have thought of, but seems pretty clever, is that it's directed in and then straight upward towards the ceiling, (very tall ceilings at roughly 28' peak). So there's no cold breeze going across the shop!

As far as size I can't help you, but my thought is if it's the same size as the outlet your more than fine. The vacuum created by the exhaust will pull in as much air as is needed to replace what's going out. Although I've never measured, I think my intake is the same size as the exhaust.

good luck,
JeffD

Next to my spray booth, I installed an exhaust fan backwards so that it draws air in. I have the pulleys sized so that it puts in a little more air than the booth draws out. I built a box that goes across the top front of the booth so that the air flows out at the top and into the filters. This creates an air flow that draws the over spray into the filters.

We do the exact same thing as JM. Heating make up air may be more than you think, it was for me. I had an engineer bro of mine do the calculation for a heated gas forced air return. The first calculation was the scary one. How much air a 30" exhaust is actually removing from your building. It was some years ago but I do remember it was over (6) complete recycles an hours. Meaning all the air in my facility was being recycled that many times an hour. The calculation is basically impossible for my place. I am in a building that is 97 years old it leaks terribly. We open a garage door about 70-80 yards away. I have an 11K square foot building.

Rich C is also exactly correct. We asked our local fire department to come help us. Since it involved the spray booth that they absolutely hate they agreed. We are zoned heavy industrial so there is nothing they can do but bitch and help but they do not like the booth. We try to involve them as much as possible as a curtsey. We asked them to check all our gas furnaces like everyone in the world has. They were being back drafted horribly as Rich mentioned through he chimney. We simply opened the door more while the continued to check and when I stopped the back draft negative air flow that became our standard.
I also priced what the heating system would cost. About 12 years ago it was $19.00 an hour. Pretty pricey. And the heating contractor warned me of the issues with moving that volume of air, cleaning it is a major problem he said. With so much air being pushed at the spray booth is was like a whirlwind and would always be picking up tons of dust along the way.

I believe we all struggle with the same situation. I know some very big boy shop in my city doing the exact same thing.

Good Luck

DJB