A laser burns/vaporizes to cut material, which means lots of smoke and nastiness coming off the laser bed, which needs to be vented away not only for optical reasons (a laser shooting through smoke gets scattered and loses power) but for health/sanity reasons. Originally I was going to put the laser in the basement workspace but after realizing I'd need to be present during cuts for safety reasons, I decided I'd rather spend that time in my office rather than the freezing ass cold basement. So... how to vent/exhaust a laser out of my office... I found this great "Laser Exhaust Systems Basics" article very helpful.
The FSL 40W 5th gen hobby laser I've ordered has a 4 inch exhaust port on the back, which can be seen in this YouTube video. They offer an exhaust fan for $250 as an accessory. I know I could get one for half that, and even FSL suggests as much mentioning the one from Harbor Freight I'll talk about below. The exhaust will come out of the laser via metal 4" flexible ducting (dryer hose style) and pass through a 4-Inch Blast Gate in a window seal probably made of painted wood. From there I'll probably run metal vent pipe down to the exhaust fan outside of the house in a weatherproof box (doghouse? plastic tub? something like this but much nicer?). This will keep most of the noise outside of the house and the blast gate will allow me to keep the cold air off the laser tube when the system is off and control the airflow when needed to a finer degree than the speed controller. Nice negative pressure system sucking air through the laser bed and venting outside. But what fan to use...?
After reading way to much about exhaust fans on the forums... I settled on a couple of options.
This thread on the FSL forums recommends an in-line bilge fan, specifically a Rule 240 Marine Bilge Blower, which is $33 (plus a $17 power adaptor... it's 12V after all). That's cheap! Noise level reports are all over the map. You could easily put a dimmer switch on it to control speed. It's rated at 240 Cubic Feet/Minute (CFM).
The other more popular option on all the forums is the 1HP Mini Dust Collector at Harbor Freight, referred to as "the red one". It's $99 (easily $80 with HF coupons) and can be speed controlled with a router speed controller for $20. So supposedly much more powerful but much more expensive. I like the easy speed control that will also allow me to turn the fan on and off remotely. Con is that it uses a brushed motor so the reports are that the brushes have to be replaced fairly often with regular use and that they are hard to find. The other popular option is this "green one" from Harbor Freight, which is brushless so it'll last a lot longer with less maintenance, but it's soft start so it can't be speed controlled. It's supposedly much quieter, though "the red one" is supposedly pretty quiet when not at full power.
So I'm going for the red one with speed controller as of now. (Ordered on 2/20/2013 with blast gate and 9" level from HF)
The whole negative pressure thing could be interesting. As the Exhaust Systems Basics article mentions, a system like this needs "make up air"... or air to replace all that air you are sucking out of your space. A 500 CFM setup will suck all the air out of a 8' x 8' x 8' room in one minute, creating a vacuum. You are also pumping out all of the heat/cool of your room/house depending on the season. So in winter I'm basically blowing all my heat out the window. I'm going to set it up and see how it goes. I might have to set up an outside air feeder system or just end up putting it in the basement workshop where that's not a concern. We shall see...