Draft Checks
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Any time the velocity of a gas increases, it’s pressure decreases.
Any time the velocity of a gas decreases its pressure increases.
That’s all we need to understand
Any time the velocity of a gas decreases its pressure increases.
That’s all we need to understand
- Sunny Boy
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- joeq
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Scotty, are you quoting Bernoullis theory again? I don't think our stoves will be "lifting off" any time soon.
So Lee, you asked about the flow or mano reading placed in the ash pan area, for a little more "understanding?" of stove performance. Maybe I'll, conjure something up this afternoon, just for ..... and giggles. any predictions?
I have-ta head out here soon,but be back later. OFN.
So Lee, you asked about the flow or mano reading placed in the ash pan area, for a little more "understanding?" of stove performance. Maybe I'll, conjure something up this afternoon, just for ..... and giggles. any predictions?
I have-ta head out here soon,but be back later. OFN.
Last edited by joeq on Sat. Feb. 17, 2018 11:04 am, edited 1 time in total.
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Heat differential being the source of draft, the closer to the fire any bends are, the less they effect overall draft. Away from the fire in the smoke pipe resistance becomes more critical as velocity decreases.
- Sunny Boy
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But it's resistance to flow is offset somewhat because as the exhaust moves further from the fire it is also loosing heat and condensing, therefore loosing exhaust gas volume. As the volume decreases, that's making it increasingly less prone to resistance to flow.
Case in point, many old stoves in large buildings that had extremely long pipe runs, which should have greatly increased flow resistance with such long distances for the exhaust to travel, drafted fine.
Paul
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If a stove has a manual pipe damper built into the breech of a stove, will it be more sensitive or less sensitive than one identical in size installed further on in the flue path? At the stove breech velocity is higher and further away both velocity and volume are lower.Sunny Boy wrote: ↑Sat. Feb. 17, 2018 12:11 pmBut it's resistance to flow is offset somewhat because as the exhaust moves further from the fire it is also loosing heat and condensing, therefore loosing exhaust gas volume. As the volume decreases, that's making it increasingly less prone to resistance to flow.
Case in point, many old stoves in large buildings that had extremely long pipe runs, which should have greatly increased flow resistance with such long distances for the exhaust to travel, drafted fine.
Paul
Those long pipe runs in churches and stores usually had stoves fired very hard with high stack temperatures to make long pipe runs possible.
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Yeah just stick the probe thru the primary air opening during a well established fire a couple hours after clearing ash and see how the reading compares to the CC. My observations showed a slightly stronger negative pressure under the grates. For example, a pressure of -.03 in the CC showed -.035 under the grates.
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Damn, here I am, still using a candle & showing a draw of "it's goin up the chimney" LOL
- Sunny Boy
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Not the stove in the Manetto Hill Church at Old Bethpage Village Restoration, that had a very long stove pipe that ran from the stove in the rear of the church between the entry doors, to a chimney that was above alter, when my father was tending the stove while he was "interpreting" the part of the minister. He started and kept a low fire in it and it drafted fine. Nor the one in the Layton store that ran the length of the store, when he was the interpreter there. I got to experience, first hand, how these mid-1850's heating systems defied "modern" stove rules, 50-60 years before the time of our even more efficient base heaters were designed.franco b wrote: ↑Sat. Feb. 17, 2018 1:05 pmIf a stove has a manual pipe damper built into the breech of a stove, will it be more sensitive or less sensitive than one identical in size installed further on in the flue path? At the stove breech velocity is higher and further away both velocity and volume are lower.
Those long pipe runs in churches and stores usually had stoves fired very hard with high stack temperatures to make long pipe runs possible.
Paul
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At the very least I would expect a decent pitch to the pipe. The vertical design of the stoves was also easier drafting than low modern stoves. Obviously they worked.Sunny Boy wrote: ↑Sat. Feb. 17, 2018 4:44 pmNot the stove in the Manetto Hill Church at Old Bethpage Village Restoration, that had a very long stove pipe that ran from the stove in the rear of the church between the entry doors, to a chimney that was above alter, when my father was tending the stove while he was "interpreting" the part of the minister. He started and kept a low fire in it and it drafted fine. Nor the one in the Layton store that ran the length of the store, when he was the interpreter there. I got to experience, first hand, how these mid-1850's heating systems defied "modern" stove rules, 50-60 years before the time of our even more efficient base heaters were designed.
Paul
- joeq
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OK gents, were're off and runnin again. So Lee wanted to know about the draft under the grates.
I 1st wanted to know the temps in that area of the stove, and the outer castings of the stove, didn't register any higher than 85-90°, so I guessed it was safe for common materials.
I found a small section of 1/4" copper tubing, which I had to adapt some plastic hosing to connect to the Dwyers mano rubber hose. All the connections are tight, but think there's almost 8' of run from the ash pan chamber below the drawcenter, to the mano itself. Not sure how influential that is. It was tricky getting the bend to be under the grate, while externally resting outside the stove. Once it was resting securely on the boot rail, this is how it all looked. I couldn't experiment with primary openings, cause you see how the tube obstructs the slide. So all tests were done with that 3/8ths primary adjustment.
The stove was "hot" and relatively clean. You can see the glow in the clinker window, but there was a bit of greying under the grate. I unplugged the CC hose, and plugged it off. (That's where the Dwyers mano was.)
I confirmed "0" on the gauge, and then I connected the gauge to the primary hose.(Under grate)
At 1st, I had the stove in BH mode, with MPD almost closed. The pipe draft was registering -.025. Once I hooked the hose to the dwyers mano, where the end of the copper tubing was located barely an inch under the outer diameter of the grate, the reading barely went up a tenth. So I opened the MPD, and the pipe draft went to -.04-05, but the base chamber barely was affected. Even with the stove in DD, there wasn't any noticeable difference. At least as far as tenths were concerned. Not sure if hundredths of an inch reading make a difference in stove performance.
As a last extreme, I flossed under the grates and got the area to glow red orange, and retested, W/O any significant changes or readings. So it doesn't appear there's much drafting going on down there. not sure if this would be considered normal or not.
I 1st wanted to know the temps in that area of the stove, and the outer castings of the stove, didn't register any higher than 85-90°, so I guessed it was safe for common materials.
I found a small section of 1/4" copper tubing, which I had to adapt some plastic hosing to connect to the Dwyers mano rubber hose. All the connections are tight, but think there's almost 8' of run from the ash pan chamber below the drawcenter, to the mano itself. Not sure how influential that is. It was tricky getting the bend to be under the grate, while externally resting outside the stove. Once it was resting securely on the boot rail, this is how it all looked. I couldn't experiment with primary openings, cause you see how the tube obstructs the slide. So all tests were done with that 3/8ths primary adjustment.
The stove was "hot" and relatively clean. You can see the glow in the clinker window, but there was a bit of greying under the grate. I unplugged the CC hose, and plugged it off. (That's where the Dwyers mano was.)
I confirmed "0" on the gauge, and then I connected the gauge to the primary hose.(Under grate)
At 1st, I had the stove in BH mode, with MPD almost closed. The pipe draft was registering -.025. Once I hooked the hose to the dwyers mano, where the end of the copper tubing was located barely an inch under the outer diameter of the grate, the reading barely went up a tenth. So I opened the MPD, and the pipe draft went to -.04-05, but the base chamber barely was affected. Even with the stove in DD, there wasn't any noticeable difference. At least as far as tenths were concerned. Not sure if hundredths of an inch reading make a difference in stove performance.
As a last extreme, I flossed under the grates and got the area to glow red orange, and retested, W/O any significant changes or readings. So it doesn't appear there's much drafting going on down there. not sure if this would be considered normal or not.
- Sunny Boy
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In that Church there's enough ceiling height to get some pitch, but many of the stores and houses had low ceilings, so often it was just horizontal runs of pipe that was all there was headroom for.
Yes, the pipe collars were often out the top of the stoves. The large Round Oak 24 that my BIL has was one of two that was in a local church. The exit collar is on top of the barrel - about 6 feet from the floor.
But as you go back in time many were small, low-built boxy type stoves - common in the mid 1800's.
The long runs of pipe were their way of extracting as much heat indoors as possible, before the days of long flues inside the stoves.
Paul
- Sunny Boy
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joeq wrote: ↑Sat. Feb. 17, 2018 7:44 pmOK gents, were're off and runnin again. So Lee wanted to know about the draft under the grates.
I 1st wanted to know the temps in that area of the stove, and the outer castings of the stove, didn't register any higher than 85-90°, so I guessed it was safe for common materials.
I found a small section of 1/4" copper tubing, which I had to adapt some plastic hosing to connect to the Dwyers mano rubber hose. All the connections are tight, but think there's almost 8' of run from the ash pan chamber below the drawcenter, to the mano itself. Not sure how influential that is. It was tricky getting the bend to be under the grate, while externally resting outside the stove. Once it was resting securely on the boot rail, this is how it all looked.
grate draft 003.JPG
I couldn't experiment with primary openings, cause you see how the tube obstructs the slide. So all tests were done with that 3/8ths primary adjustment.
The stove was "hot" and relatively clean. You can see the glow in the clinker window, but there was a bit of greying under the grate. I unplugged the CC hose, and plugged it off. (That's where the Dwyers mano was.)
I confirmed "0" on the gauge,
grate draft 001.JPG
and then I connected the gauge to the primary hose.(Under grate)
At 1st, I had the stove in BH mode, with MPD almost closed. The pipe draft was registering -.025. Once I hooked the hose to the dwyers mano, where the end of the copper tubing was located barely an inch under the outer diameter of the grate, the reading barely went up a tenth.
grate draft 002.JPG
So I opened the MPD, and the pipe draft went to -.04-05, but the base chamber barely was affected. Even with the stove in DD, there wasn't any noticeable difference. At least as far as tenths were concerned. Not sure if hundredths of an inch reading make a difference in stove performance.
As a last extreme, I flossed under the grates and got the area to glow red orange, and retested, W/O any significant changes or readings. So it doesn't appear there's much drafting going on down there. not sure if this would be considered normal or not.
The incoming air is close to room pressure because it is moving slowly. If you could restrict the primaries more - say like covering some openings with aluminum foil - it would have to speed up. Then you might see an increase in mano readings ????
Remember that what Scott said about gas velocity is part of what's accounting for mano readings. But without also using a flow meter, we are unaware of the changes in velocity as the mano pressure readings change.
FYI for anyone interested, Dwyer sells a probe kit to use mano's to measure gas velocity, too.
Paul