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Unread 09-23-2013, 01:55 PM   #11443
Got rid of the matchlight.
Join Date: 08-16-12
Location: Lewisville
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Originally Posted by bvbull200 View Post
What are your opinions on a single 4" exhaust? No adjustment, just a capped/uncapped sort of situation.

Actually, let me rephrase that. I took the vent out of the lid I have for this UDS (it was a 22.5" Charbroil dome). I made a hole out of it and put in a 4" 90* ducting because that is what fit. I can make some little adjustments to the opening inside the lid to shrink it down if necessary, but there are no plans to make it adjustable on the fly.

The intake is 3 3/4" pipe nipples with removable caps and 1 3/4" pipe nipple with a ball valve on it. Will the intake adjustment be enough to tame a 4" opening or do I need to plan on making the exhaust a little smaller?

For the record, the ducting is galvanized. I've read all I can on the subject and feel confident that it will be just fine after hitting it with the weed burner.
I just finished up an experiment this weekend with one of my new UDS builds. I actually went with the 8 holes in the lid instead of using the existing 2 inch hole and noticed that the variance in temperature across the grill was greatly reduced.

With the single 2 inch exhaust I was seeing a 30 degree difference between the side of the barrel where my thermometer was and the center of the grill. I also saw another 20 degree difference higher where the exhaust was.

With the 8 exhaust holes I saw about a 15 degree difference between the side of the barrel and the center of the grill and the hot spot was gone altogether.

Based on that I would say the eight holes helps to distribute the heat across your grill compared to using a single exhaust.
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