Smoke exhaust fan duct material

[muncybob]

Decided to add an exhaust fan to the boiler hoping the Mrs. won't let any smoke escape when loading. Could not find 5" duct at the local Lowes so I went to a heating/plumbing supplier and they said not to use semi rigid aluminum as it will probably melt?

I think the material is rated to 400 degrees, surely the exhaust smoke does not have a temp anywhere near that? Another WG owner uses galvanized duct work but I was thinking the semi rigid stuff would be an easier install.

 

[woodsmaster]

Seems like it would be ok no longer than the door would be open.

 

[Gasifier]

Bob. You will get a soot(sp?) build up in the exhaust pipe over time. It should not happen. But. Would it be possible to have an ember get up in there and start a fire? I do not know. But have thought about that. I usually do not load until it is down to coals, so no need to worry about flying sparks/embers. But I have thrown a few more pieces in just before I go to work if it is really cold out. And the fire is going pretty strong. And have noticed the possibility how quickly a flying spark can go up into that fan and through the exhaust pipe. Something to think about with that flex pipe and temperatures. My exhaust pipe needs a good cleaning.

 

[711mhw]

Decided to add an exhaust fan to the boiler hoping the Mrs. won't let any smoke escape when loading. Could not find 5" duct at the local Lowes so I went to a heating/plumbing supplier and they said not to use semi rigid aluminum as it will probably melt?

I think the material is rated to 400 degrees, surely the exhaust smoke does not have a temp anywhere near that? Another WG owner uses galvanized duct work but I was thinking the semi rigid stuff would be an easier install.

Bob, I don't know if I'm the "another WG " guy but I did use the same 5" (I think) ridgid. It's the same size as the outside intake air duct. I would have some concerns about something flexable that might restrict air flow and allow "stuff" to collect. Unless you have a crazy way to the outside, it's not that bad running the snap together stuff. I notice that the fan will get pretty warm with an extended "open door" fiddling with the fire sometimes. Sory about my wording and spelling, currently Dr Jim Beam is helping with my knees! Congrats on the hood fan, you'll like it.

 

[muncybob]

Thanks guys, good point about an ember. Rarely have I seen one come out but it's always a possibility and with the cfm rating on that fan I'm sure it would get sucked into the duct.Keeping the pathway as smooth as possible is probably a good idea. Originally I thought about the flex duct partly because it seems an easier install but also because I'll have 2 bends to make to the exit hole in the wall. With proper planning I can make them 45 degree so that should help.

Dr Jim and his assistant Jack have helped my knees and back more than on one evening