Ventilation - connecting to existing exhaust

[Joann]

My first post! I'm new to lampworking and all the posts on ventilation have been so helpful, but I didn't see anyone address my particular question.

I have an exhaust fan (just 80 cfm) in my studio already that vents out through the roof and I just got the 650 CFM exhaust hood from Glasscraft, Inc.

Can I chain these together or will that restrict the CFM from the hood? Basically, do I need to rip out the existing fan?

Thanks!

Joann

[MikeAurelius]

No. Don't do this. Most likely the existing fan does not have a large enough duct size to handle the larger air movement of the new fan.

Additionally, because the original fan is so "small", even if it was running, the new fan would actually force air past the other fan, causing recycling of the exhaust plume.

When you have multiple fans, you need multiple exhaust ducts.

Don't forget, with the larger fan, you are also going to need a larger source of fresh replacement air.

[Joann]

Ah, it figures. Glad I asked first before trying it! I think I'll do a window setup to vent to the outside.

I do have a crawlspace so I could theoretically try to do setup similar to yours to have a vent in the table for replacement air, but that would be too close to the vent going outside, right?

Maybe I'll just open the window in another room.

Thanks so much for your help!

[MikeAurelius]

Replacement air "source" has to be a minimum of 10 feet from the exhuast duct. It's always best to duct the replacement air - if you don't you risk drawdown of the air pressure in the entire house, which can have some unpleasant results, the least of which is a sewer smell from the plumbing vents...