Indoor forge and hood question

CWendling

CWendling

Joined
Sep 10, 2005
Messages
518
Finally building a dedicated 24x30 shop and plan on putting the forge inside. Propane forge. I would like to see photos and/or plans on how others have vented or put hoods on them. Is a fan necessary to vent out heat/fumes? Obviously I will have CO2 alarms.
 
Forget the CO2 alarms.
You know it's going to be EVERYWHERE!! And lots of it. They'll be going off before your forge even gets up to heat.
If you have a 24 x 30 shop, I wouldn't be too concerned.
That's the same size as mine. With 10 foot ceilings.
And I have forged in much smaller for over a dozen years.
Crack a door or a window.
Here in northern Minnesota, even when it's -30, I can have the entire shop up to 80 degrees before I get done forging one knife. That's just to give you and idea of the volume of air being exchanged in the room.
Now that my forge area is at the back of the shop, I did put in a furnace squirrel cage fan in the ceiling to pull air out of the shop and replace it with new air through a front door.
Ventilation is a good thing.
 
I know it seems pedantic, but getting it wrong can leave you dead.

CO2 is Carbon Dioxide. It's what you breathe out naturally and is not usually too much of a problem on it's own, though it certainly doesn't do to get complacent. It is heavier than air. When CO2 gets high, it is usually because the Oxygen in the air has reacted with something containing Carbon (Propane, coal, etc) and the low Oxygen is the big risk.

CO is Carbon Monoxide. It's the stuff that will kill you (It binds strongly to the sites in your blood that are intended to carry Oxygen around to where you need it and doesn't readily let go of them) It is lighter than air.

It's worth noting that the lighter/heavier than air bit is mostly unimportant for us, as the effect is masked by having hot air, cold air and ventilation all stirring the air up.
 
thijsco19 said:
One thing I can add, from what I have read and heard.

Put the CO2 alarms near the floor or somewhere in the middle of the wall. CO2 is lighter than air and will 'sink' down.
Click to expand...

Wrong, CO2 is much heavier than air...which is why it "sinks down". The other info is correct.

CO2 alarms are fine, but a far more important alarm is a CO alarm. CO2 is not deadly in itself, CO is. Both are normally located about two feet from the floor. Using these in a shop with a forge running can cause false alarms to sound, so picking where they should go is somewhat of a trial and error situation. They are best used as monitors instead of alarms.

Air exchange and ventilation should be a part of a shop air-flow plan. The air is best coming from behind you, and the exhaust is best from both high and low positions.

If building a ceiling "hood" type vent for the forge gasses, a good size is 8X4 feet, and should be ducted to the outside. A small "duct fan" ventilation blower or "draft inducer" fan is all that is needed to create good air flow.

The shop should have a separate air vent fan to exchange outside air for inside air. This should force air into the shop, not draw it out ( positive vs negative air pressure). This is important, as using it to draw air out a vent would likely make the ceiling hood draw air in, not exhaust gasses out. By creating positive air pressure, the ceiling vent will be self venting, and would not really need a draft fan ( but it is a good idea).

The air exchange ratio is best achieved by having a forced air intake port that is half the size of the air exhaust ports. For example - If the fan has a 200 sq.in. intake port ( roughly 14X14"), there should be a total of 400 sq.in. of places for the air to leave (20X20").
 
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