Thread: finish room fans

OK, this may seem off the wall but it is worth consideration.

Back in the ancient history era, I had a photographic darkroom. I did the developing and printing of B&W pictures.

Dust specs were killers. The dryness of Arizona made it even worse. The philosophy was positive pressure as it would push dust deeper into the cracks. That said, there was no need to exhaust any fumes.

I think that if I were to build a finishing room it would be positive pressure and only a filter for the exhaust portal in an effort to keep the pressure positive. For the intake, definitely filtered air. I don't know if the exhaust port should be high or low. I guess it depends upon the density of lacquer thinner vs. that of air.

But then spraying lacquer is different than developing and printing B&W photos.

I have advised a few Mens Sheds (Community shops) on their paint booths.

The fans in the window and on the inlet need to be boxed up so their fan boxes seal up the opening otherwise these fans will draw some of their intake air from around the sides of the fan and not ventilate correctly and reduce flow through the room.

To maximise roo ventilation efficiency the inlet and outlet need to be diametrically opposite each other ie on opposite walls.

I see you are in the USA. In that case I would use large squirrel cage fans (SQFs) since they are, efficient, relatively quiet and can provide the capacity you require.

Putting small filters over these fans will slow them down so the choice of filter media and the size of the filter/opening (needs to be large I would shoot for at least ~3 sq ft) is critical

If you want a positive pressure inside the room, then the input fan needs to be able to turn slightly faster than the output fan so having a variable speed fan will be useful. Single phase SQF speeds can be controlled using HD light dimmers. Some level of control will be possible by slightly blocking the output fan.

On the intake side it's better to push air through the filter so build a large shallow box (called a plenum) into the wall with a fan that pressurises the box and put the filter on one side of the box inside the room.

You may also need a coarse filter on the output to prevent paint droplets from making a mess outside the room.

If you buy a proper industrial fan then you should be able to adjust the pitch of the blade to suit your application/size of room. Unfortunately proper ones with backup/support are not cheap. Sometimes it’s try/error and repeat, it took me awhile to get my spray booth up and running. Yet to have the pressure monitor installed but so far so good

Originally Posted by BobL

I have advised a few Mens Sheds (Community shops) on their paint booths.

The fans in the window and on the inlet need to be boxed up so their fan boxes seal up the opening otherwise these fans will draw some of their intake air from around the sides of the fan and not ventilate correctly and reduce flow through the room.

To maximise roo ventilation efficiency the inlet and outlet need to be diametrically opposite each other ie on opposite walls.

I see you are in the USA. In that case I would use large squirrel cage fans (SQFs) since they are, efficient, relatively quiet and can provide the capacity you require.

Putting small filters over these fans will slow them down so the choice of filter media and the size of the filter/opening (needs to be large I would shoot for at least ~3 sq ft) is critical

If you want a positive pressure inside the room, then the input fan needs to be able to turn slightly faster than the output fan so having a variable speed fan will be useful. Single phase SQF speeds can be controlled using HD light dimmers. Some level of control will be possible by slightly blocking the output fan.

On the intake side it's better to push air through the filter so build a large shallow box (called a plenum) into the wall with a fan that pressurises the box and put the filter on one side of the box inside the room.

You may also need a coarse filter on the output to prevent paint droplets from making a mess outside the room.

Bob,
great info, thank you! If I were to get a SQF put in a box on one side of the room (high on the wall, and then on opposite wall install a filtered passive output (Filtered open window), would that suffice? Is there a need to also have an output fan, if I have a crossflow like this? I know the fans are expoensive, and if I get a spend the $ to get a nice sqf, I'd rather not also spend the $ to get an explosion proof output fan if not needed.
For a 10x10x9' room, all I am going to be spraying is mostly cabinets, tables, and small furniture items. Recommendation on size fan needed?
Thoughts? Very much appreciate the input and advice!!
Dave

Originally Posted by flydjb

Bob,
great info, thank you!

No worries.

If I were to get a SQF put in a box on one side of the room (high on the wall, and then on opposite wall install a filtered passive output (Filtered open window), would that suffice?

Yep that would be OK

Is there a need to also have an output fan, if I have a crossflow like this?

Nope

I know the fans are expoensive, and if I get a spend the $ to get a nice sqf, I'd rather not also spend the $ to get an explosion proof output fan if not needed.

Sure, It would also be better to put all you money into one decent fan than two ordinary fans.

For a 10x10x9' room, all I am going to be spraying is mostly cabinets, tables, and small furniture items. Recommendation on size fan needed?
Thoughts? Very much appreciate the input and advice!!
Dave

Well you said you need 1800 CFM, but don't just go and buy an 1800CFM rated fan, as any fan rated at 1800 CFM will be without filter resistance.
You might need to buy a 2400 CFM fan to makes sure it delivers 1800 CFM with filters. Maybe even 2800 CFM - it depends how fine a filter you use.