stumper clone exhaust question

Posted: Sat Jan 14, 2012 3:41 pm

I built a large clone. It works really well with my exhaust leaving about 3/4 ways up the cooking chamber with a really long exhaust (8ft stack of a mack truck). Once the pit is heat soaked it drafts well and my fan doesn't come on often. Now I have noticed that most stacks come out at the top. Is that better or does it lose heat to quick. I'm gonna put a shorter permanent stack on and was wondering before I finalize everything, if maybe I should rethink the location of my exit point. I have plenty of fan to force air through, but I think it could be more fuel efficient with a good draw. I don't mind the tall stack, but it looks crazy. Any advice from the Guru's?

Posted: Sun Jan 15, 2012 12:34 am

Look at the FEC's, they're exhaust is 1/2 way down and they work. I'd leave it like you have it if it's working for you so far. Wish I'd have done that so when it starts raining I don't have to put a pie tin on the top shelf to act as a water tray.

Posted: Mon Jan 16, 2012 9:14 am

The newer Stump smokers are also with the exhaust out the back instead of the top. I think some of the reason for this was to prevent the drippings from the exhaust from falling back down onto the meat. That can be some nasty stuff.

The next smoker I build will have the exhaust out the back or side (towards the top of the smoker) instead of the actual top.

Posted: Tue Jan 17, 2012 9:00 am

Hi Krawfish
You posted "Once the pit is heat soaked it drafts well and my fan doesn't come on often".
I am trying to decide if I want to setup a closed loop temp control system or go with a naturally aspirated system and your post sounds to me like your setup is a naturally aspirated system with a power boost as needed to maintain temp.
My question is, is this the way your setup works or is it a testament to your stack location working very well to help hold the heat?
Where is your temp sensor in relation to your exhaust exit point?
Perhaps some of the multiple clone builders will chime in on this valid post as there are many variables that can be at play here.
Thanks for the post.
Ed

Posted: Tue Jan 17, 2012 10:14 am

Excellent questions. My thermostat is on the opposite side of the box from the exhaust and my thermometer is on the door centered. My idea behind locating my exhaust further down is that heat rises and will rise into the void area above the exhaust outlet allowing for a more uniform temp across the cooking area. I know that works well on my stick burner but it has a lot of btu and really tall exhaust for drafting. Now the clone doesn't move air very fast, so not a lot of exchange without the draft or fan. Now with all that said, The problem I have with my set up is that most of the air intake is blocked by the fan sitting in it. If it were not there I would think it would aspirate sufficiently. I noticed some experimenting with two ball valve intakes. One for the fan and one for the natural aspiration. I would like to know how well that works with the fan running and the other valve open.. Or should it be shut during fan operation.
Now naturally the idea behind the clone and temperature control is to make it easier on the "pittmaster". With my system I'm not to concerned about natural aspiration because I am more concerned that if I leave it naturally aspirated the temps will fluctuate too much. But I'm considering a new build, a smaller one and am looking at different options to make it more back yard friendly. Sorry for the long post!

Posted: Tue Jan 17, 2012 10:24 am

One more thing on the exhaust. The location of the exhaust doesn't matter if the exhaust is long enough to off set how low your mount it. As long as its above the heat inlet. For a naturally aspirated system one could experiment with variable lengths of exhaust to cause more or less draft. But as the pit gets hotter, the draft will increase. I was curious for the new build; I didn't really want a tall stack and was thinking of placing it higher on my cooking chamber. Just wondering at how well they cook evenly across the board.

Posted: Tue Jan 17, 2012 10:31 am

[ sounds to me like your setup is a naturally aspirated system with a power boost as needed to maintain temp.]

Yes that bout sums it up. Worked really well for the 2 all day cooks I've done so far.[/quote]