Issue: I make lots of bad smells in my shop; I weld & grind, spray paint small bits (when it's not spraying weather outdoors), I use solvents and glues, burn moxa and incense, cut metal with cutting fluids which make weird chemical-sweet smelling stenches, and I or the occasional gues also occasionally smoke weed or a cigar, at least when it isn't pleasant outside.
(my shop is the official smoking lounge for Owl House;
we don't allow smoking in the house - small amounts
of soldering fumes and the occasionally incense excepted,
on account-a-because there is an asthmatic in da hizzouse)
Issue: My wife's medical practice office & treatment room is attached to the garage and shares the furnace and circulating fan with the shop. (the parking section of the garage is not heated)
In warm(ish) weather, I have an improvised exhaust fan which does a good job of pulling air and pollution through and out of the garage and shop. But through the cold winter months, this is seldom an option. For some years now, I have been pondering various ways of dealing with shop pollution in the winter time, including:
- converting the cutting grid section of my existing welding table to a downdraft welding table with filtered exhaust
- adding a general-purpose shop air cleaner - commercial or DIY - which simply circulates and filters all the air in the shop. Probably ceiling mounted.
- adding a Point-Of-Use exhaust system similar to a dust collection system which exhausts a smaller total amount of air at higher speed with greater effectiveness.
I'll talk about each of these solutions in turn. Since I've been either underemployed or unemployed for years, commercial solutions for any of thise weren't likely, but of course I'm nothing if not a DIY sort...
1. Downdraft Welding Table
This is still a future project I fully intend to implement. I even thought about it when I was building the table, so while it remains an unimplemented option, it's not difficult to add, just expensive.
How expensive? Depending on how cheaply I can obtain the expensive part - the blower - I guesstimate between $100 and $1000, the latter only if I win the lottery and just buy a fancy blower. And that would STILL be cheaper than buying an actual commercial downdraft welding table - the real things are breathtakingly expensive!
What is needed includes: a blower capable of not less than 1,000 CFM @ several inches WC (it must overcome resistance so a simple fan won't do); some filters and metal (wire) window screen, and some sheet metal to enclose the part of the bench under the grid.
Unless and until I either score a bunch of free sheet metal and a fantastic blower, or more money comes in, this project remains on the back burner.
2. General Purpose Shop Air Cleaner
These exist commercially in various forms, the two most noteworthy being: wood shop air cleaners designed to filter fine floating dust from the air, and "Smoke Eaters™" (including the brand of the same name plus imitators) designed specifically to remove either or both of greasy vapors from restaurant environments and cigarette or cigar smoke from bars and smoking lounges (an increasingly rare space, these days).
The former cost anywhere from $150 to $600 depending on quality and features, the latter start around $1,000 and go up fast from there. All of these tend to mount in or under the ceiling.
There are various ways these things can be DIY'd, but you still have to come up with blowers capable of not only overcoming the resistance of the filters you are trying to push air through, but doing it fast enough to actually make a difference in the shop. For something that simply sits in the middle of the ceiling and cleans the air, you need a minimum air flow of 300CFM, but more is always better.
Even if you have the scratch to go right out and buy one, you will find it necessary to compromise between noise level and performance. For a general-purpose room air cleaner, we need CFM more than anything else, with just enough pressure to overcome some very basic filter media, so a direct-drive squirrel-cage blower with the motor mounted inside the impeller is ideal. For filter media, I recommend buying two types: very cheap "spun fiber" furnace filters as large as one can fit inside the cabinet (to catch large dust) followed by a high-grade, very fine "allergen" type furnace filter such as the 3M Filtrete MPR2200 product. You can set a large filter at an oblique angle inside the cabinet to minimize the height.
This type of filter box will not remove organic vapors, some welding fumes, etc. For those, you need a charcoal filter, but those require a much higher pressure blower, and the combination will inherently flow less air, so they are best suited for...
3. Point-of-Use Exhaust (or filter) Hood
To remove solvent fumes, all welding fumes including ultra-fine metal vapors, non-particulate aromas, farts, etc, we have to go to Activated Charcoal, ideally with a fine dust filter ahead of it so the AC's pores aren't clogged uselessly / prematurely by dusts.
Small so-called "activated charcoal" filters on home room air filters exist. Thise are typically a plastic foam coated with a thin layer of what is sometimes actual, real AC and sometimes isn't. That media is very thin and ineffective even when it's the real thing, and there is so little of it, that it is rapidly saturated, requiring very frequenty replacement.
However, it turns out there is a big market for very large activated charcoal air filters, along with the quiet, high-pressure, high-flow fans required to shove air through them: indoor gardening. Regardless of what you are growing indoors, indoor gardens need a lot of fresh air. The same air filtering gear they use is perfect for a Point-of-Use air filter. The filters and fans both can be bought from indoor growing supply houses (for the most competitive prices).
My personal favorite for quality vs price are Vortex's basic (VTX PowerFan) series. For this application, you would NOT want the suffix -L models which run at lower speeds for lower noise. No-name brands will cost less, be a little noisier, and won't last as long because cheaper bearings. YMMV.
I just happened to have some of this equipment left over from an indoor gardening operation. The photo shows what I installed over my workbench in my shop, over the last few days. The blower is very quiet, but it leaks sound in various ways which can all be addressed, if I cared - there are highly effective mufflers which can be DIY'd cheaply to go between fan and intake hood, the two pieces of flex hose could be replaced with solid metal duct, and the duct and fan body could be sprayed with truck bed-liner.
It turns out that a 4 inch fan is only just barely enough for this hood (which is about 24" sq); a 6" fan would be much more effective. The 4" blower is only good for 100CFM or so when pushing through a filter.I do have a 6 inch fan, and a muffler for it, but I don't especially want to uninstall it from the infrastructure it is currently built into... for now. I might change my mind later, if I aquire the money for a 6" filter - but that is a large and expensive item.
The filter I'm using has a 4" inlet, is about 10" x 24", weighs about twenty pounds, and in Denver, and costs about $100.
They are, unfortunately, not cost-effective to refill, so they either become art or landfill. (small amounts of spent AC may be used in outdoor gardens or compost, but air-filter AC is the wrong pore size for water or pool filters, sadly)
However, a 6" filter is a big boy, and costs several hundred dollars. That said, it will probably last years depending on how stinky your shop is.
On noise: the majority of sound coming from these inline fans is emitted into the ducts. Soft flex hose leaks sound badly, so use solid metal ducting for connections.
The exhaust is effectively muffled by the filter. The sound from this 4" fan is not audible when my shop's Background Noise Suppression System (AKA "stereo" or "hi-fi") is engaged, but it's certainly noticeable when the music is off.
The intake of large fans pretty much require a sound muffler.
To make a highly effective muffler for 6" or 8" fans, use a 5-gal plastic bucket with a hole in top and bottom, caulk in place two duct launch collars in said holes, then line the inside of the bucket with gray "egg crate" shipping type foam rubber.
Seal all joints with tape and for the last bit of sound suppression, either a) wrap all metal surfaces of the ducts and the fan housing with self-fusing rubber mastic / tape (electrical) or b) spray them with many layers of aerosol truck bed liner to kill the last bit of noise radiated through the metal.
Believe it or not, this can result in a system which is nearly silent.
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