Too much ventilation?

[TTreasures]

I just installed a vent hood from Home Depot over my torch that has 3 speeds. When I put it on anything but the 1st speed, it makes my flame go wild! Is there a proper height that the hood is supposed to be over the torch? It is 350 fan, and should not be too powerful for my room which is about 10' x 11'. I would like to run it on a higher speed to get maximum fume removal but can't figure out what is wrong? This was a project my husband and son worked on all day and I hate to tell them it is not right. Any suggestions would be appreciated. Thanks, Pat g

[Starrr]

Where is your fresh make up air coming from? The height from the table top should be 28 to 30"s but that will depend on your fan draw, make up air, the type, width and diameter of your ducting .
Can you explain your room set up and your vent hood in more detail?
Have you done a search on this board, WC, and the ISGB board for ventilation? Try searching for "baffles", you don't need to exhaust the whole room, just the area where your torch is, so enclosing the space where the torch is lit will prevent the flame from going wild. Your fan is not too powerfull, it just needs to be contained to a specific area, over your table.
PM me your email if you need a pic.
Edie

[MikeAurelius]

You need as much space over the torch as is required to work and move safely. Baffles (or side sheets of metal) bring the effective area of the vent hood down to better enclose the work area - they should extend down the sides at least 12-14 " and back all the way to the table top.

You also need to provide a source of fresh air exactly the same amount as your vent hood is exhausting.

What are the air movement speeds for the various settings, and what is the dimensions of the vent hood itself?

Did you use smooth sided galvanized metal ducting (what size?) or did you use flex tubing?

You don't necessarily need to run the fan on the highest speed to get effective fume removal - it just needs to move the correct amount of air, and that can only be calculated by knowing how big the vent hood is and the size and type of ducting you've used.

[TTreasures]

Thanks for your replies and help. I had my husband review what he had done and he was using the flexible ducting with no enclosures on the sides or back of the hood. We will change to the smoothe non flexible duct work this weekend and get some walls up around the torch similar to the Barley box. I think that will make a big improvement on the air flow being exhausted. Thanks for all the help. Pat g