Ventilation Question

[Pr3ssure]

I was wondering if there is a certain diameter that the exhaust pipe has to be to get sufficient ventilation. I mean i know it can't be too small but how small is too small? I'm thinking about trying to turn a section of my basement into a temporary welding shop until I build one and when the weather doesn't permit being outside to smith. Would the exhaust pipe running outside from the air/heating unit be good? Basically hook up an exhaust and splice it to the one built into the house. Would that work?

[Daswulf]

Welding produces all kinds of nasties. I couldn't say exactly how much air flow you need, but you need air coming in and air going out, and a lot of it with welding.

you also need to have the area free of anything flammable materials. Those sparks and weld splatter go Everywhere. Even at work we quit welding at least a half hour before any quitting time to make sure nothing is smoldering. (in the body shop). Also smoke and stuff can rise going through ducts and vents into the house.

Sorry I don't have an exact for you but yeah more airflow and safer is better. Last thing you want is to be fumed out or burn the house down.

[Irondragon Forge ClayWorks]

Do not splice into the HVAC vent. Doing so would most likely send fumes into the system and house. It would be foolish to weld inside the house (basement), safety wise and you probably would invalidate the home owners insurance.

[Latticino]

Good advice so far.  Unfortunately I don't have my Industrial Ventilation text at home, so don't have a good handle on exact airflow velocity required for good weld fume capture exhaust, but the duct size is a function of how much exhaust you want to move and what size exhaust fan you plan on using with it.  With a strong enough fan you can use 3" diameter duct to exhaust a welding point of use capture hood (think a 6" diameter funnel like connection), but the airflow will be noisy and inefficient. 

You absolutely can not use your furnace vent for a welding exhaust trunk, if you still plan on using it for the furnace.  Not only is it against building code, it is also not good practice.

As Das indicated, whatever air you plan on exhausting you need to makeup, so unless your basement is as leaky as mine is (1850's era house) you will need a source of outside air to balance your exhaust.  If you keep your hood very close to where you are welding (welding snorkel) you can probably get by with an 8" opening, but I'll have to check on standard practice velocity when I can get to my text.

Bottom line is that you are going to need an exhaust fan to make this work, though another alternative may be to look into one of those portable welding capture systems.  I believe they just filter the air instead of exhausting it outside.  Might be a little pricey though.

[Pr3ssure]

Thanks for the advice so far, I was only considering using the outgoing exhaust if I put an extra blower outside the house to pull out and be sure nothing went the wrong way. I wasn't really thinking about doing it as I have other options that would be easier, like a door and window. I just thought about it and wanted to know what others thought.

[Glenn]

If you do exhaust the welding fumes, you will have all the nasty materials from the smoke in the basement, and all over everything. The debris, slag, grinding dust, etc can not be contained and will go into the house when you open a door, or walk into the house. It will also be on your clothes, hair, body, etc. You ever look at the floor or top of file cabinets in a welding shop? Ever give then a wipe test with a damp cloth? You sure you want to introduce this stuff into your home?