The Perfect Garage Vent System?

laurellanestudios · #1 2006-03-08, 6:07pm

I need to improve the vent system I'm currently using in my garage, however, the more I read the more my head is spinning.

Can someone, in simple terms (I'm a former kindergarten teacher...when I say "simple" I MEAN simple!) tell me what I need?

For example...

Can I find a powerful enough hood w/ fan at Home Depot?

That hood should hang just slightly above my head, correct? And, it should vent outside using 8" smooth galvanized metal ductwork?

I notice that in several photos the workstation/hood has sides. Is that to minimize the draft?

What about replenishing with fresh air? Can I simply open the garage door a few inches? Or does fresh air need to be brought in via another vent system?

Thanks for your help.

Just Nancy · #2 2006-03-08, 7:38pm

Simple terms, and a disclaimer, I'm not a safety guru.

I have yet to find anything locally that is big enough, or that utilizes an 8" duct. I know many people who have range hoods from the home stores. I don't know if they worry about the 8" duct. Don't get a duct that has ridges (slows down the air movement). That I believe is the reason to specify galvanized.

The sides help contain the fumes so the vent works more effectively. Not everyone uses sides.

Your fresh air has to be equal to what is being exhausted. In other words you don't want to suck all the air out of the garage. (I get that one.) I've read it should come from behind you, so it doesn't cross from the open air to the vent and miss the fumes. (Probably didn't sound right but works in my mind.)

Good luck.

laurellanestudios · #3 2006-03-09, 8:01am

Thanks, Nancy.

Another question...

It would be fairly easy for me to put the propane tank outside a window and move my work space to that window area.

Could I use a rubber hose to run the propane inside or must it be metal?

Getting down to the nitty gritty here.

Thanks.

Dale M. · #4 2006-03-09, 8:49am

You can bring hose through a door or window as a TEMPORARY measure.... It must be disconnected and removed when torch session on done....

Dale

MikeAurelius · #5 2006-03-09, 8:52am

I missed this post yesterday, sorry.

As Nancy pointed out, kitchen vent hoods do have some major drawbacks, mainly CFM and vent hole sizing.

Glassworking ventilation pretty much requires a higher CFM than residental kitchen vent hoods can provide as well as needing a larger vent duct diameter.

A rough rule of thumb is to require 80 CFM per square foot of hood opening for a bench mounted, 5 sided box hood and 125 CFM per square foot of hood opening for a ceiling mounted hood.

Absolutely do not use flexible vent ducting. While it may be ok to use (although I don't recommend it ever) for laundry dryers, it is NOT ok to use for lampworking ventilation. It creates too much turbulence in the exhausted airstream and turbulence leads to back pressure, which reduces total air flow, by as much as 50%.

For your outside propane, the hose can be rubber IF and ONLY IF you run the hose through an open window or door. If you run the hose through a wall, this becomes classified as a permanent installation and under NFPA regulations must be plumbed in metal, usually black or galvanized pipe, with hard shut offs on each side of the wall (the outside shut off may be waived if the tank is within 3 feet of the wall entry point).

Going back to the ventilation for a moment, also be sure to provide the same amount of incoming fresh air as you are exhausting. Not providing a source of fresh air will lead to a decrease in air pressure in the studio area, and possible back drafting of other appliances and/or plumbing vents.

Moth · #6 2006-03-09, 10:22am

I used flexible aluminum ducting...but it is smooth...it doesn't have baffles at all. Is that ok?

Semi-rigid aluminum duct

MikeAurelius · #7 2006-03-09, 1:17pm

How smooth is smooth? Is it galvanized metal smooth or can you feel ridges?

Standard galvanized metal ducting has a surface roughness of 0.0004" (4 ten thousandth's of an inch).

"Smooth" flexible ducting has a roughness of about .2", flexible plastic ducting has a roughness of .6" (numbers are approximate).

By factoring in the surface roughness of the duct material, on an example has the following results:

360 CFM, 8 foot total straight run, 6" ducting

Standard galvanized metal, static pressure: .02"
"Smooth" ducting, static pressure: 7.79"
"Flexible plastic" ducting, static pressure: 23.37"

Most fans will "shut down" at static pressures in excess of 2-3 inches.

laurellanestudios · #8 2006-03-09, 5:51pm

Thanks, Mike.

You said the same amount of incoming fresh air is needed.

How is that achieved? Is opening the garage door a crack (in winter) sufficient or is another fan/vent needed?

MikeAurelius · #9 2006-03-10, 7:09am

It's usually not a good idea to use a powered fresh air system, especially in colder climates, you'll tend to overcompensate the system and freeze yourself out.

An 8" round duct will provide approx 350 CFM of fresh air passively.

Just Nancy · #10 2006-04-05, 6:11am

Kathy,
IF you are working near a window, can you bring in the make up air in flexible tubing that way? Run it near your torch and then exhaust it back out? That way less of the cold air is filtering through your whole room.

If you understand what I'm saying one word of caution, be sure to have the make up 10 feet or more from the exhaust point.

I have make up air coming from upstairs down 2 4" pieces of PVC to near my torch. That way in the dead of winter my make up air won't come from in full force and won't drop the temperature in the rest of the room as badly. In the good weather I may cap them off and use the windows. Haven't decided on that one yet.

Good luck.

MikeAurelius · #11 2006-04-05, 7:41am

Nancy - I'd either use larger PVC pipes -or- more of them.

As I noted above, an 8" round duct provides 350 CFM of passive fresh air.

8" round ducting is 50.26 square inches. (PI R Squared)

4" round PVC is 12.56 square inches, you have two, so that's 25 square inches, half of what's needed for 350 CFM.

funfuser · #12 2006-04-05, 7:54pm

There is a reason I didn't go into a math/science field... I am trying really hard to follow, but I just am not. I too need to figure out how to vent my garage & I think the information here is probably what I need, but it is all greek to me!
I just got a vent from a jen-air stove that I was going to hook up.... There is a grate, but I can replace with my own, if need be- Can this be used & work with the equations you were stating? Will this fan be sufficient if I use 8" solid ductwork?

MikeAurelius · #13 2006-04-06, 4:54am

It depends

Is it the fan for keeping the oven surround cool, or is it the fan from a down draft cook top?

If the former, probably not. If the latter, "maybe".

It will all depend on the CFM that the fan can generate, how big your collection hood is, and how long your duct run will be. I can do the calculations for you to see if it will work, but I do need the starting numbers.

funfuser · #14 2006-04-06, 7:51pm

It is for the range top. (The downdraft)
What numbers do you need from me, exactly?

We are running 2 torches (HH within 3 feet of eachother, if that matters)
Also, we were thinking of installing it Between the torches, because the garage door sits above us & we cannot connect to the cieling.

The run of the exhaust pipe is roughly 11-15 ft of run (depending the route we take)

Motor 15V 60Hz 3A 800/1550RPM .07HP A.0.

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PS (Propane is put outside when we run the torch)

MikeAurelius · #15 2006-04-07, 7:31am

Do you know what the CFM ratings for the fan are at the high and low settings?

What size hood do you plan on using?

The propane tank MUST be kept outside ALL THE TIME, not just when in use, especially if your garage is attached in any fashion to the house.

Just Nancy · #16 2006-04-07, 4:26pm

Mike,
The 2, 4" tubes stay because that's what's cut into the ceiling and the drywall is finished and painted. Cutting back through the insulation and getting the two holes aligned wouldn't be much fun at this point. There are still 5 other windows that can be opened. This is just to help cut down on bringing cold air in from the outside when it is 20 degrees.

For those who didn't see the original idea it came from a post at the ISGB forum. I don't recall that could have been an 8" duct. Her's dropped down outside to bring in make up air and her exhaust was just above it.

NanCy

MikeAurelius · #17 2006-04-08, 5:57am

yeeeeaaahhhh...

I don't want to rain on anyone's parade, but kind of like all the pictures you see in books with the propane tanks inside, a picture on the ISGB (or anywhere else for that matter) without design information, isn't all that good.

I don't dismiss the idea totally, mind you -- but it DOES have to be calculated so that enough fresh air is supplied.

Just Nancy · #18 2006-04-08, 8:39am

Quote:

Originally Posted by MikeAurelius

yeeeeaaahhhh...

I don't want to rain on anyone's parade, but kind of like all the pictures you see in books with the propane tanks inside, a picture on the ISGB (or anywhere else for that matter) without design information, isn't all that good.

I don't dismiss the idea totally, mind you -- but it DOES have to be calculated so that enough fresh air is supplied.

I thought someone up north designed it for her. I don't remember who, but I thought the person was named. Either way it is a good concept and if it helps someone remember to use make up air in the winter instead of skimping I thought it was worth mentioning.

funfuser · #19 2006-04-10, 12:47pm

Do you know what the CFM ratings for the fan are at the high and low settings? (From above)

No Idea, or how to figure that out.

As for the hood, I am going to make that or buy, depending on what I need...

MikeAurelius · #20 2006-04-11, 5:56am

You'll need to find out - it's one of the "magic" numbers...

The size of the fan (CFM) is determined by the size of the hood (Sq Ft).

funfuser · #21 2006-04-12, 5:23am

OK. Got some work ahead of me, I will try to figure out, or maybe I will scrap this idea & get an entirely new fan/hood system....

Juliac · #22 2006-06-03, 7:37am

Thanks for this post. I'm like you. I get all confused at the technical numbers. But this is pretty plain speak. Mike, any suggestions on a hood for a small home studio? Mid range plus torch, and i use mostly the minor. And, I was looking here to find info on connecting my gas line instead of using a propane tank.

MikeAurelius · #23 2006-06-03, 2:35pm

Pretty much *any* kitchen hood will work with modifications - the mods needed are usually completely gutting the hood and making a good round hole in the top that ducting can attach to.

What's needed is the measurements of the hood coverage area so that the fan CFM's can be calculated. Then I need to know the length of the run and the number of 90 degree bends needed to get to the outside.

Roseanne · #24 2006-06-09, 5:30pm

okay, so if you can't or shouldn't use flexible duct work. Why does Glasscraft include it with their "lampworker hood vent"? There are a ton of people out there that have their hoods. I'm so confused.

MikeAurelius · #25 2006-06-09, 7:13pm

Just because they sell it doesn't mean it's good.

I have no idea why they do it, they shouldn't.

Roseanne · #26 2006-06-09, 7:51pm

Have you thought about educating them as to why they shouldn't?

MikeAurelius · #27 2006-06-10, 6:41am

I had planned on discussing with them when I see them at the Gathering, yes.

judysare · #28 2008-08-14, 12:24pm

I have saved an old kitchen hood from over the stove. It is 8 1/2 inches high, 18 1/2 inches deep, and 36 inches wide. Where it would hang, the ducting could come out of the top, make one 90 degree angle and then go out the wall just within a foot of the hood. Mike, could you tell me what CFM size in line fan I would need to buy? Is the 8 1/2 inch height of this hood a problem, so that it would be better to invest in another hood?

The fan should hang slightly in front of the torch, right? How far? And not include the area over the head of the lampworker?

The incoming air, does it need to be from behind you? The two windows are to either side and slightly behind this area.

Thanks, Shirley

Lorraine Chandler · #29 2008-08-14, 7:11pm

Kathy, I know what you are going through! Here is my set up. We may sell our home and go into an RV so we do not want anything permanent.

I bought this fan at Home depot. It has 3 speeds and sounds like a jet engine at take off. CFM at high speed is around 2000 CFM and low speed is 1100.

We tested it and it really moves the air out and away from me. The fence at the end of the drive is where DH stood and the smells were very strong even at that distance.

I have the back door open behind me so makeup air is plentiful. Works for now.

I wear noise canceling headphones and a half mask respirator with frits and silver glass, etc. Not fun, pretty or comfortable, but it is safe. If I cannot open the doors and torch because of heat, cold or wind or storms, I just do not torch and go to the studio room in my house and put jewelry together or make earwires etc.

Good luck.
Lorraine

imagesinglass · #30 2008-08-15, 10:38am

Mike said: "Pretty much *any* kitchen hood will work with modifications - the mods needed are usually completely gutting the hood and making a good round hole in the top that ducting can attach to.

What's needed is the measurements of the hood coverage area so that the fan CFM's can be calculated. Then I need to know the length of the run and the number of 90 degree bends needed to get to the outside."

Hi Mike,
I have a kitchen hood fan I've been using for 1 year as my ventilation. Now I'm getting concerned about how well it is actually working. It's 350 cfm on high, which I always use. The hood measures 30 x 19-1/2" and has 2 90 degree bends and is 5 feet long. The ducting is 6" round smooth ducting. I've closed the space under the fan on three sides with plexiglass (so I don't feel claustrophobic). My torch is a minor and does not sit totally under the hood...most of the flame is directly under the hood. I also wear a half respirator when I'm working just as a secondary precaution.
Is my ventilation adequate?
I also recently bought a 440 cfm canfan but it's very big and heavy really loud. My workshop is only 10 x 8 and I can't take the noise...
Thanks for any assistance you can provide.

Suzanne