I was asked, and so I'm asking- Flue pipe question

[Beetle-Kill]

I don't know what to tell him. My buddy is going to install my Timberline in his totally unfinished basement( 1700 sq.ft.), totally open w/dirt floor. It's a modular built into a hillside, with concrete foundation on 3 sides, low side is stud framing. There will be no negative pressure issues, as the upper half is not connected to the basement yet, and he built in a barn door, so air flow will be gentle. His plans- Stove, 4' of vert. dbl. wall, 2- 45 degree's to a horizontal(about 24") through a thimble, to a "T". Verticle for 14' after that, leaves 3' above ridge line. Question is, since the 14' of exterior pipe will be on the cold, windward side, CAN it be necked down to 6", to keep the thermal velocity up? Or should it stay at 8" for the entire run? His plan is to run it at night only, which will give him a 10hr.(avg.) burn.

 

[Corey]

My thought would be to leave it all the same size. Any increase in 'thermal velocity' will come at a reduction in flow. Think about capping your thumb over a water hose...the water does come out faster, but the flow is less. The stove runs on overall air flow - it doesn't care if the gas is coming out the flue at 1 mph or 100, as long as the cfm is there to get proper oxygen to the fire. If a reduction in pipe size has to be made, I'd say make it right at the stove and still keep all the pipe the same. Either way, I think a reduction half way up the flue, especially cutting nearly 45% of the cross sectional area going 8">6" would have bad results.

 

[fossil]

If the stove flue collar is 8", I'd run 8" all the way to daylight. Rick

 

[Beetle-Kill]

Thanks for the responses, I'll pass it along to him. With the caveat that he scrub the exterior, verticle section at least , what do you think?- 2 times a month at least? Means he'll get to it twice a year. Now for the wrench in the works. This stove is a converted(secondaries added), pre-EPA. The secondary air-flow is unregulated, while the primary air can be reduced via the twin screw knobs on the doors. Once the stove was up to temp.(550+), I could almost shut off the primary air, to the point that both knobs had a 1/16" or less clearance. I know the secondary tubes were active, from trial and error(Plus yanking open the doors fast, to have a nice flame rollout, then back in while the wood showed no active flame. Tough to describe). From top of stove, with a dampner right off the stove collar, could he go to a reducer and still generate decent draft with 6" pipe?