CFM and ventilation

[glassblaze]

I've been reading a few threads on ventilation (there is so much useful info here, thank you!) I can't seem to find a good equation on how to figure out how much ventilation I would need. I am converting my tool shed into a studio, it's 9x10x8 (720 cu ft). On the opposite side of my work bench is both a window and door to the outside, one of which I assume I could crack open for intake air. I am going to put a hood or fan or something on the wall infront of my torch (minor bench burner). But have found conflicting info on how much CFM and power I actually need! Do I need a hood or would an exhaust fan suffice? How many times per hour does the air need to be changed? WHat does CFM even stand for?

Also, I am running this all on a 20amp breaker and only have about 2 amps left after the O2 concentrator, kiln etc is hooked up. Does anyone know how many amps most ventilation systems run on?

Thanks!

[glassblaze]

Oh and one more thing. I live in Ontario where it is very hot in the summer and VERY cold in the winter! Is there any way to minimize heat loss through ventilation or am I doomed to work in a snow suit?

[Dale M.]

CFM is most directly related to opening size of hood... Current thoughts is about 100 to 125CFM per square foot of hood opening....

IF you have a hood that is 28x32 inches, that is 896 square inches, divide that by 144 (one square foot) and you get a figure of 6.222 square feet of hood opening .. So that translates to 620 to 778CFM of air flow required....

To keep room warm in winter and cool in summer you can duct your make up air (from outside) through bench top so flow goes through work/flame zone and then out hood. This leave most of the air-conditioned or heated air in room for your comfort.

http://www.artglassanswers.com/forum...opic.php?t=150

Edit to add...

Hood opening for our example is 28 inches by 32 inches....

28x32=896 sq. in.

896 / 144 = 6.222 sq. ft.

6.22 X 100 (cfm) = 620cfm or 6.22 X 125(cfm) = 778cfm.

Minimum blower capacity is 620 cfm or 77b cfm depending on formula used.

Hope this make more sense.

Dale

[MikeAurelius]

CFM is cubic feet of air per minute.

2 amps is not a good place to be with your power situations. An average sized fan/blower in the 650 to 750 CFM range is going to pull at least 1 amp, possibly more. I'd suggest you try to have another circuit added to your workroom if possible.

[Just Nancy]

One of the guys posted the make up air in terms that helped me. Maybe you already get this but here goes. You can only exhaust as much air as you have coming into the room in make up air.

So as I understand it, even if you have a lot of cfm but only a cracked window you will only pull the amount that the cracked window or door provides.

Good luck

[Dale M.]

Originally Posted by Just Nancy

One of the guys posted the make up air in terms that helped me. Maybe you already get this but here goes. You can only exhaust as much air as you have coming into the room in make up air.

So as I understand it, even if you have a lot of cfm but only a cracked window you will only pull the amount that the cracked window or door provides.

Good luck

Precisely.... Make up air flow source has to meet or exceed the capability of the of the exhaust system to draw air out of studio.

Dale

[MikeAurelius]

Originally Posted by Just Nancy

One of the guys posted the make up air in terms that helped me. Maybe you already get this but here goes. You can only exhaust as much air as you have coming into the room in make up air.

So as I understand it, even if you have a lot of cfm but only a cracked window you will only pull the amount that the cracked window or door provides.

Good luck

ummmmm...close. What will happen if the cracked door or window does not provide sufficient make up air is that the air will come from "somewhere", and "somewhere" is one of the following usual suspects: furnace/hot water heater exhaust stack, plumbing vents, etc. The air will come from *somewhere* and it usually is not a place where you want it to come from.

Backdrawing the furnace/hot water heater exhaust stack not only bring CO back into the house, but will also create nitric and sulfuric acid to accumulate on the galvanized metal exhuast duct. The acid will slowly eat through the duct material and you will notice it by seeing streaky rust stains on the joints of the exhaust stack.

I had this happen to a furnace in my old house about 20 years ago - back then, what had happened is that the contractor did not put in a fresh air source for the furnace and neglected to put the bottom plate in the furnace base. It was a 80% efficient (old style) furnace. It took about 4 months for the acid build up from the backdrafting to almost completely eat through the exhaust duct. The building inspector forced the contractor to completely replace the furnace and all the exhaust ducting in the house.

[glassblaze]

Originally Posted by Dale M.

CFM is most directly related to opening size of hood... Current thoughts is about 100 to 125CFM per square foot of hood opening....

IF you have a hood that is 28x32 inches, that is 896 square inches, divide that by 144 (one square foot) and you get a figure of 6.222 square feet of hood opening .. So that translates to 620 to 778CFM of air flow required....

To keep room warm in winter and cool in summer you can duct your make up air (from outside) through bench top so flow goes through work/flame zone and then out hood. This leave most of the air-conditioned or heated air in room for your comfort.

http://www.artglassanswers.com/forum...opic.php?t=150

Dale

Oh god, numbers, did I mention I multiplied 7*7 to get 14 yesterday? This is why I need good ventilation, to protect those few brain cells I have left..

Okay, so let's say I had a hood that was 6 sq ft, and it said on the box it was 100CFM, does this mean it draws out 100 cubic feet per minute, or do we multiply that by 6 to get 600 CFM? And seeing that my space is only 720CFM, wouldn't that suck nearly all the air out of my entire room in one minute?

Do you think a simple oven range hood at around 100 CFM is sufficient?

I checked out that link Dale but can't see the pics, I've registered though so hopefully that will help.

Mike I agree 2 amps is kinda low to be playing with, I'm going to get an electrician in I think to put some wiring out there. I suppose 40 amps would be good for most studios?

Thanks so much for all the help everyone, it is very overwhelming trying to get this all figured out!

[glassblaze]

Dale,

I finally can see the picture in that link and it is very useful, I think it would work really well in my space! One more question, could I use that with the enclosed box fan method in this link:

http://www.artglassanswers.com/forum...ht=ventilation

Or is the hood better? And if I made the enclosure, and vented fresh air right up through my bench into the enclosure, how much CFM do you think would be sufficient?

[Just Nancy]

Originally Posted by MikeAurelius

ummmmm...close. What will happen if the cracked door or window does not provide sufficient make up air is that the air will come from "somewhere".

All I know is if I forget to open my window before plugging in my exhaust it operates at a low speed. You're right, pulling what air it can from around the outlets etc. In my case and that of many of the sheds or garages being used, there isn't much 'somewhere' to draw from. When I open the window the fan quits straining and runs as usual.

I've talked to a lot of people who figure that if the exhaust will pull the proper amount from somewhere that all is ok.

[MikeAurelius]

Originally Posted by glassblaze

Oh god, numbers, did I mention I multiplied 7*7 to get 14 yesterday? This is why I need good ventilation, to protect those few brain cells I have left..

Okay, so let's say I had a hood that was 6 sq ft, and it said on the box it was 100CFM, does this mean it draws out 100 cubic feet per minute, or do we multiply that by 6 to get 600 CFM? And seeing that my space is only 720CFM, wouldn't that suck nearly all the air out of my entire room in one minute?

Do you think a simple oven range hood at around 100 CFM is sufficient?

I checked out that link Dale but can't see the pics, I've registered though so hopefully that will help.

Mike I agree 2 amps is kinda low to be playing with, I'm going to get an electrician in I think to put some wiring out there. I suppose 40 amps would be good for most studios?

Thanks so much for all the help everyone, it is very overwhelming trying to get this all figured out!

Last first, yes, at least one more 20 amp circuit would be a good thing, and if he can pull two for 40 amps total, it would be even better.

100 CFM is nowhere near enough air movement for any size hood, let alone a duct that was 6 square feet. The 100 CFM number is per square foot of hood "face" or functional opening. If the hood is 6 square feet, you should have, at a minimum 600 CFM.

Don't worry about the small space you are working in - if your fresh air supply is near or in the workspace (ducted to the bench top for example) very little room air would be pulled out by the fan. Most, if not all of it would come from the fresh air duct.

[Dale M.]

Originally Posted by glassblaze

Dale,

I finally can see the picture in that link and it is very useful, I think it would work really well in my space! One more question, could I use that with the enclosed box fan method in this link:

http://www.artglassanswers.com/forum...ht=ventilation

Or is the hood better? And if I made the enclosure, and vented fresh air right up through my bench into the enclosure, how much CFM do you think would be sufficient?

The system will work.... I can't vouch for efficiency as it is a thing that Bill B. developed.... I personally would prefer a hood.... I find that the window is never exactly where I need it to be... Besides I like windows that are not blocked by anything...

Dale

[MikeAurelius]

The problem that I have with that particular enclosure is that:

1) Wood was used to construct the framework. Wood should never be used anywhere near an open flame.

2) The insulation board is not designed to be exposed to an open flame. If it begins to burn, it will generate poisons gases that will most certainly cause significant medical issues. Even though the board is covered by foil, it will still melt and quite possibly ignite if a torch is directed on the board face accidentally.

The only safe material to construct any kind of enclosure is metal or any non-flammable material. Additionally, any supports for the ventilation must also be metallic - so wood and plastic should not be used at any time.

[glassblaze]

Okay, it's starting to make a bit more sense to me now! I think I will try to do a hood with incoming air vented to the bench like Dale suggested. Thanks!