Can you guy's settle a debate, does it make any difference in draft if 2 45's are up at the ceiling support box or down at the stove collar on the interior run of double wall about 6 ft. long?
Settle a debate
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If shouldn't. My basment stove has a 90 degree in it up by the ceiling, about five feet from the top of the stove. Out through the wall and then a 90* connected to 25 more feet of liner. Drafts like a Hoover.
This is a stretch but I have to go for it.
The only difference I can see is that you are turning hot air (closer to stove) vs turning cooler air (closer to peak). Will that make any difference on build up? What kind of distance "difference" is there? But I most likely would have to concur with BroB. You would probably have to have equipment to detect the difference.
The only difference I can see is that you are turning hot air (closer to stove) vs turning cooler air (closer to peak). Will that make any difference on build up? What kind of distance "difference" is there? But I most likely would have to concur with BroB. You would probably have to have equipment to detect the difference.
burntime
New Member
jtp10181
Minister of Fire
With gas direct vent, more straight up venting right off the unit gives you better draw and more releaxed restrictions on venting. I would assume the same applies to wood but I can't say for sure.
Actually the elbows are better at the top. Why? Well the stove has already started its draft and that 6 ' allows momutun to let it get going.
Conversly a bend right above the stove no momentum and instant friction at the start One starts witha lazy draft right out of the stove.
Naturally in vents that are apt to overdraft this could be good Normal or weeker drafting systems the opposite is true that 6" straight run will promote better draft enough momentun to power threw the elbow friction
Conversly a bend right above the stove no momentum and instant friction at the start One starts witha lazy draft right out of the stove.
Naturally in vents that are apt to overdraft this could be good Normal or weeker drafting systems the opposite is true that 6" straight run will promote better draft enough momentun to power threw the elbow friction
elkimmeg said:
Yeah, the fellow that designed my stove was concerned when I told him that it had a 45* coming out of the flue collar into the liner. Until I told him it was 21 feet straight up from there.
Highbeam
Minister of Fire
The smoke is hotter and so less dense and so moving at a higher velocity closer to the stove than at the top in order to maintain continuity of mass flow. So I would lean towards the elbows hurting you more at the bottom. How much more, well, not huge. I think they look better up higher too.
I knew Elk would come through, so a short run it would probably make a difference, and a long one probably not. With the understanding that in the northern hemisphere the smoke would swirl clockwise when viewed from above and in the southern hemisphere counter clockwise when viewed from below, right, or was it the other way around. ;-P
hearthtools
Moderator Emeritus
with Direct vent most manufactures will say a min of 9" off the unit before an offset.
I always try to have some kind of rise before I offset.
WOOD OR GAS
I always try to have some kind of rise before I offset.
WOOD OR GAS
stoveguy2esw
Minister of Fire
while any change of direction from straight up will cause a reduction in momentum, the diffence would likely be not noticable. ELK is dead on also the bends should be up off the unit to allow building of momentum and your location should be best case as youy will have stack above to regain that momentum. bottom line , i'd be amazed if anyone could see the difference in the fire.
webbie
Seasoned Moderator
I have to say this is the first time I heard the "bends are best higher up" theory. Is there anywhere this is in writing? Seems that it would be somewhere if it was common practice.
This may make some sense in poor chimney situations, but in a normal setup where the draft of the chimney is coming from the top (not from the stove!), it would not seem to make any difference. In other words, if these els cut down on the draft, then the smoke and heat can't get a "head start" no matter where the els are located since they are cutting down on the draft from above. I'm thinking of it like a vaccum cleaner - it doesn't matter where the kink in the hose is, either way the suction is affected in the same way. Momentum cannot build in a situation where the air is not flowing right!
But I would love to see the science on this one!
This may make some sense in poor chimney situations, but in a normal setup where the draft of the chimney is coming from the top (not from the stove!), it would not seem to make any difference. In other words, if these els cut down on the draft, then the smoke and heat can't get a "head start" no matter where the els are located since they are cutting down on the draft from above. I'm thinking of it like a vaccum cleaner - it doesn't matter where the kink in the hose is, either way the suction is affected in the same way. Momentum cannot build in a situation where the air is not flowing right!
But I would love to see the science on this one!
There ain't a dime's worth of difference in having a 30* or 45* elbow coming out of the top of a stove and the few million inserts burning in this country that have the liner curved back coming out of the flue collar at at least 30* before angling up into the masonry chimney. Said angle up usually being least 30*.
That's my story and I am stickin to it. Those cute pictures in the liner ads showing the liner shooting straight up from the insert are from another planet.
That's my story and I am stickin to it. Those cute pictures in the liner ads showing the liner shooting straight up from the insert are from another planet.
webbie
Seasoned Moderator
I never heard that theory before. I still haven't, although I will check out any links you provide....at least those with a valid scientific basis. It would not surprise me if it were true...it sounds feasible, but again.....if draft is considered as being pulled from the top, it would not make any difference.
Gooserider
Mod Emeritus
Not to mention the rear-exit stoves, that usually go right into either a "T" or a 90* elbow to get the smoke headed up... At least for us, that setup works great.
Gooserider
Gooserider
webbie
Seasoned Moderator
John Gulland agrees with the ceiling premise mentioned by Elk and others....here is his take. Keep in mind that this is all opinion, although informed opinion. I don't think any actual tests have been done on it, since there would be no $$$ reason to do so (who would pay?)
From John:
"What brought all this home to me was almost 25 years ago when CMHC in Canada was developing a computer model of flue gas flow in gas furnaces and water heaters. The model clearly showed the way hot flue gases creep along the highest level of a horizontal or near-horizontal section and when they finally reached a vertical section and began to rise, draft and therefore flow increased dramatically. As a result, I have always pitched the idea that elbows or offsets should be placed as far away from the appliance flue collar as possible. Same goes for increasers, which should also be placed at the chimney rather than right at the stove in order to create a higher flow rate, shorter dwell time, smaller surface area and higher flue gas in that portion. "
From John:
"What brought all this home to me was almost 25 years ago when CMHC in Canada was developing a computer model of flue gas flow in gas furnaces and water heaters. The model clearly showed the way hot flue gases creep along the highest level of a horizontal or near-horizontal section and when they finally reached a vertical section and began to rise, draft and therefore flow increased dramatically. As a result, I have always pitched the idea that elbows or offsets should be placed as far away from the appliance flue collar as possible. Same goes for increasers, which should also be placed at the chimney rather than right at the stove in order to create a higher flow rate, shorter dwell time, smaller surface area and higher flue gas in that portion. "
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