Exausting LP forges from shop.

[Jeff Mack]

After deciding the hurdles in getting a coal forge up and running indoors for winter were more than my budget could handle, I started to think about a propane forge. Dodge made the tail end of a LP burner for me this weekend, so that part is coming along.

Now I'm wondering about what kind of exaust I need for LP. I was thinking about mounting an old kitchen stove hood, with a blower attached, a few feet above the forge, and running the exaust through a thimble in the wall. Is that going to be enough? Any thoughts on what kind of CFM I need to look for in a blower to exaust all that?

I'm planning on a second, smaller blower to pull air from outside the other side of the shop in along the floor.

Any thoughts would be a great help.

Thanks!
Jeff

[rthibeau]

Jeff, the kitchen hood idea sounds good and almost any size blower that comes with it would be sufficient. You only need to vent the CO2 from the forge exhaust and any enhanced air flow would do. I have a wall exhaust fan primarily over the coal forge, but it works for the gasser, too. Most shops I've seen don't have a specific venting system set up and they seem to get by, though most of them are pretty drafty naturally. Continuous air movement and venting to the outside should keep the air fairly clear.

[Chris Pook]

I bough a co2 detector from homedepot a few years ago and found that having a good blast of fresh air coming in from outdoors did more good then an exhaust fan.

[Dodge]

Jeff,
Keep in mind that the heat wave from the "dragons breath" will extend a good distance from the mouth of the forge before rising. I'm assuming, unless corrected, that the CO2 fumes will follow that path. If you are going to run a rear opening too, you'll need a good sized (commercial kitchen?) hood.

[irnsrgn]

Carbon Monixide (CO) in my opinion is much more dangerous than Carbon Dioxide (CO²)

[rthibeau]

Jr caught me, I should have said CO and CO2. Good eye Jr.

[Jeff Mack]

Thanks everyone! I'll be sure and get a CO and CO2 detector installed too.

Jeff

[Dodge]

Richard,
CO2 is correct in relation to propane. There is CO also pesent in propane exhaust but not nearly as much as in fossil fuel emissions. Thats why its ok to run propane burning forklifts inside buildings like meat lockers and such

[Marc]

I've got a dept. store type pedestal fan that exhausts out my garage door window during the winter. I still need the opposite door's window open for the fresh air intake. In the summer, the fan points at me with all the doors open. That keeps my CO meter down at 0.

Funny thing about the CO from the forge. It does seem to vary. Some days it never gets above 0, even with no fan and doors closed. Other days I need the full fan and window thing. I think I'm consistent in the fuel/air supply, but obviously not.

[frogvalley]

A kitchen hood is not good enough. The volume of air mixed with combution gases is exponentially larger than what goes in so do your calculations carefully. See Boyles law on gases when heated.

Dodge is right about watching the dragons breath, it can make the gases flow past your hood.

Anecdotally I can tell you that my propane forge inside the main shop(we have three propane and two coal in various parts of the shop and under shed roofs outside) will heat up the building to 15 degrees above ambient in under an hour. Thats with door closed, almost that much with door open but fans off. Shop is 20x24 with open trusses from 8 foot wall at edge to 12 foot at center height.

We keep the building drafty to allow for combustion gases and Vent with a 20 inch exhaust fan at the and a window or more open when we are working. There is a heat shield 5 feet high over the forge with 4 inch clearance between it and the wood trusses. This "deflector" keeps the wood from catching fire and was designed to be where the dragons breath meets the truss.

Your mileage may vary