Gas Dryer Duct Reccomendations?

[EmbellishAthletics]

We are about to install a new Mini-Sprint dryer and keep hearing we need double walled duct.  It makes sense to me since I would assume the exahust will get pretty warm when running for 8+ hours although there doesn't seem to be a consensus.  M&R doesn't give reccomendations as they don't know the local codes. 

Will single wall (galvanized) work or do we need the double walled?  Can we use single wall and wrap with insulation or will it get too hot for the insulation?

Thanks
  Bret

[cvreeland]

Double-wall it as high up as you might expect anyone to come in incidental contact with it, say 7-8 feet, then go single-wall the rest of the way up. Then, you might want to wrap that with some insulation. I can personally testify that you will burn the crap out of yourself on the singe-wall ducting coming off of a Sprint. Don't ask me what I was thinking when I was up on the ladder next to the dryer that one time -- not a good place to put a soft, fleshy hand. I think I was hanging lights over the outfeed, & went to steady myself. Ouch!

[ScreenFoo]

I'd seriously consider double wall the whole way--unless heat isn't a problem in the summer.  Definitely improved temp issues here.

Not to mention the added safety benefit, as mentioned ^^.  I'd be willing to add corroborating testimony.   

[chubsetc]

I just did this with a new mini sprint.  I went single wall from the dryer straight to the roof and then double wall just through the roof.  The vent side of my dryer runs along a wall with enough room to walk but will not be a place people will be going through so I am not worried about accidental contact.  For what it's worth I touched the pipe the other day to see how hot it was after about 2 hours at 350 degrees and it wasn't hot enough for me to even have to take my hand off immediately.  This works for me now but i havent been through a hot summer yet.

Eric

[Gilligan]

I bumped against Ted's (old) Interchange and I am pretty sure it was single wall.  QUICKLY left a whelp on my arm!

[EmbellishAthletics]

Sounds like we. Need to just go with double wall but it is pricey. Luckily we only need about 15 ft.

[ericheartsu]

double wall, type b!

[alan802]

Can someone explain why double wall is better than single wall with insulation?  Our vent is insulated, room temperature to the touch and was way cheaper than going double wall all the way.  Seems like we accomplished the exact same thing, maybe even better insulated than double wall but at half the cost.

[inkman996]

Can someone explain why double wall is better than single wall with insulation?  Our vent is insulated, room temperature to the touch and was way cheaper than going double wall all the way.  Seems like we accomplished the exact same thing, maybe even better insulated than double wall but at half the cost.

Good question Alan, double walled is usually used where there is not a lot of clearence or where the pipe will pass through walls etc. The air between the two walls is insulation which will keep the outer wall cooler, in a hot climate probably nice to not have extra heat being dunped in your place. Our pipe is single walled till before exit then double walled per code.

[tonypep]

Double wall all the way up. Just plumbed this Mini on Monday.

[tonypep]

And heres the pic!

[Binkspot]

Double wall is just a pipe in a pipe. The air gap between the two acts as insulation. It's the same concept the dryers use to maintain a cool skin. IMO use the double wall at the penetration through the wall or roof as per most codes, standard the rest of the way with insulation and lagging if you want to keep the heat out of the shop. Check the ratings but most fiberglass insulation will be fine at the oven temp. Secure it with bailing wire then wrap with lagging. The lagging is cloth impreginated with a plaster, wet it with a spray bottle and smooth with your hand. When it dries it will be a hard surface that can be painted with a high gloss paint so its easy to clean. Or you can have removable blankets made for it, some supply houses have them pre made to fit diffrent size pipe including bends.  If you are worried about someone getting burned get a sheet of expanded metal and make a cage around the pipe (with a gap) to keep people from touching it. My exhausts are single, the heat is nice in the winter, not bad during the summer.

[EmbellishAthletics]

Anyone have a supplier to get the double wall Type B?  I found a few places and it looks like 15 ft will cost approx.  $750+.  That is just for the pipe and no roof flashing.

I had a local HVAC come in yesterday and he said it should be double wall all the way up according to local code as we are venting "combustable gas".  Still waiting on a quote from him to do the work.

[ericheartsu]

We get ours from hvac supply places. Usually Johnstone or Johnson Supply