Chimney Draft Test

 
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Lightning
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Post by Lightning » Sun. Aug. 10, 2014 11:52 pm

Today I was interested to see how my chimney drafted on its own without being hooked up to an appliance. I did a smoke test this morning about 2 hours after sunrise while ambient air temperature started to climb since it's nighttime low. Then I did another test 2 hours after sundown while ambient air temperature started to fall since it's daytime high. Both tests were done with no wind conditions and I also had a vent to the basement open to the outside to keep basement pressure equal with outside pressure. I should also mention that the basement door is closed to prevent any influence from the house..

I have an exterior block and mortar chimney that is 26 feet high. The top is roughly 6-7 feet higher than the ceiling of the second story and about 1-2 foot higher than the peak.

Morning smoke test....
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Evening smoke test....
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In the morning test, I see the smoke wisp away from the chimney inlet. I can also feel a cool subtle flow of air flowing out and I can smell ash residue in the air of the basement. In the evening test, I see the smoke streaming into the chimney. I can feel the flow of air around my fingers when I hold my hand in front of it, and no more smell of ash residue.

So I wondered what could be causing these two different outcomes and here's what I've concluded. During the morning test while ambient air is warming up, the chimney is still cold from the nighttime low temperature. The cold chimney cools the air inside it, making it more dense (than the air around it) and it flows downward into the basement. During the evening test while ambient air is cooling down, the chimney is still warm from the daytime high temperature. The warm chimney heats the air inside it, making it less dense (than the air around it) and it flows upward pulling air out of the basement.

I thought this information could be useful for new people curious about chimney drafting.. Results may vary based on chimney design, the materials it's made out of, it's location in the home and weather conditions.. :)


 
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michaelanthony
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Post by michaelanthony » Mon. Aug. 11, 2014 12:12 am

I have a mile high mountain just north of my house and the morning dew is pea soup...don't forget the earth's tilt is something like 66* so in the early am we're walking up hill and post noon down hill, as my friend the weatherman Al Kaprilian say's HIGH PRESSURE!!

 
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Lightning
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Post by Lightning » Mon. Aug. 11, 2014 9:06 am

michaelanthony wrote:I have a mile high mountain just north of my house and the morning dew is pea soup...don't forget the earth's tilt is something like 66* so in the early am we're walking up hill and post noon down hill, as my friend the weatherman Al Kaprilian say's HIGH PRESSURE!!

That's pretty interesting Mike :) Where I live, the Earth is tilted at 23.5 degrees. What's neat about that is that when you add 42.5 degrees longitude (our location relative to the equator) to it you get 66 degrees. Now when you subtract that from 90 (zenith) degrees you get the angle at which the sun is highest in the sky around noon (or 1:00pm depending on daylight savings time) around the first day of winter. This angle is only 24 degrees above the horizon and it must have something to do with it being cold outside.

Then 6 months later the opposite is true. Since the Earth tilts the other way we subtract our tilt from our longitudinal location and get 19 degrees. Now when we subtract that from zenith we get a 71 degree angle. This is the highest angle the sun gets above the horizon around noon on the days around the first day of summer and must have something to do with why its warm outside..

Now last night we also had a "Super Moon". Which I don't think effected my draft any but does in fact intensify the ocean tides.. This happens because the moon has an elliptical orbit and is sometimes closer and at other times further away from the Earth. Its by chance that this time the moon was closest during full moon so we see a bigger brighter moon than usual.

I'm off from work so,,,
I'll be here all week.. :lol:

https://www.youtube.com/embed/D1KKpeW231Y

 
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Post by franco b » Mon. Aug. 11, 2014 11:33 am

Lightning's findings and explanation really points out the danger period of early morning when the chimney has the greatest likelihood of reversing. Just when most are asleep. Strong argument for multiple CO detectors.

 
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Post by franco b » Mon. Aug. 11, 2014 11:43 am

michaelanthony wrote:I have a mile high mountain just north of my house and the morning dew is pea soup...don't forget the earth's tilt is something like 66* so in the early am we're walking up hill and post noon down hill, as my friend the weatherman Al Kaprilian say's HIGH PRESSURE!!
Finally an explanation of how it is possible some people claim they walked uphill both ways to and from school. It was the tilt of the Earth all along. Those on the other side of town walked downhill both ways.

 
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Post by freetown fred » Mon. Aug. 11, 2014 1:03 pm

Holy crap Richard, that clears up something that has befuddled me all these years! :bighug: :clap: toothy

 
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Post by Berlin » Mon. Aug. 11, 2014 11:22 pm

I would be interested to see what happens when you add two more tile sections to the top of stack and repeat the tests. just set them up there and use moretite to seal the gaps (easily removed). I think you would be surprised.


 
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Post by Lightning » Tue. Aug. 12, 2014 9:03 am

franco b wrote:Lightning's findings and explanation really points out the danger period of early morning when the chimney has the greatest likelihood of reversing. Just when most are asleep. Strong argument for multiple CO detectors.
I agree Richard.. It also explains why I need to add copious amounts of secondary air during warm weather burns while idling the fire down to maintain draft. The chimney needs the extra secondary warm air to contradict a relatively cool chimney during the day.

 
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Lightning
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Post by Lightning » Tue. Aug. 12, 2014 9:24 am

Berlin wrote:I would be interested to see what happens when you add two more tile sections to the top of stack and repeat the tests. just set them up there and use moretite to seal the gaps (easily removed). I think you would be surprised.
I wish I had a couple sections to try it.. :) I'm sure it would help draft go up thru the chimney while the chimney is warmer than the ambient air.

I don't doubt your expertise when it comes to chimneys.. You inspired me to rebuild the top of mine after my first year with the stove pipe chimney disaster :lol: And I'm so glad I can use it!! I do wish I had added another section though. It's usable but I'm sure there is room for improvement.

Which reminds me lol.. When sun would hit my black stove pipe chimney it would draft like mad. As soon as the sun fell below the horizon it immediately weakened. I saw it happen a number of times.

 
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Post by Erik Carstens » Sun. Dec. 27, 2020 10:44 am

Lightning wrote:
Tue. Aug. 12, 2014 9:24 am
I wish I had a couple sections to try it.. :) I'm sure it would help draft go up thru the chimney while the chimney is warmer than the ambient air.

I don't doubt your expertise when it comes to chimneys.. You inspired me to rebuild the top of mine after my first year with the stove pipe chimney disaster :lol: And I'm so glad I can use it!! I do wish I had added another section though. It's usable but I'm sure there is room for improvement.

Which reminds me lol.. When sun would hit my black stove pipe chimney it would draft like mad. As soon as the sun fell below the horizon it immediately weakened. I saw it happen a number of times.
There is certainly alot of inFLUEncial conditons in regards to chimneys....

 
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Post by freetown fred » Sun. Dec. 27, 2020 11:29 am

BUT------------------- with the stove going, it will produce enough heat to keep the draft. I live in one of the windest parts of CNY & have been up on the roof during sub-zero temps & wind blowin like a banshee--the pipe opening still had warmish draft coming through the top. Course I hate complicatin sht & was younger then---All that is just an old farmers experience.

 
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Post by Lightning » Sun. Dec. 27, 2020 12:18 pm

freetown fred wrote:
Sun. Dec. 27, 2020 11:29 am
with the stove going, it will produce enough heat to keep the draft.
Right... that is normally what happens until you slow the stove down to the point that outside influences take over, which is the problem at hand here.

 
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Post by coalder » Sun. Dec. 27, 2020 2:16 pm

Berlin wrote:
Mon. Aug. 11, 2014 11:22 pm
I would be interested to see what happens when you add two more tile sections to the top of stack and repeat the tests. just set them up there and use moretite to seal the gaps (easily removed). I think you would be surprised.
Lee, this is what I have been saying. The closer a flue is to the ridge, the more external influence IE: downdraft could be occurring. The easiest & most likely only fix in such circumstances is to raise the flue/chimney.
Catch 22... The flue is cool because it can't draft properly; Raise chimney= increased draft=warmer chimney=a better functioning safer appliance. Anything else is circumspect.
Jim

 
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Post by freetown fred » Sun. Dec. 27, 2020 2:38 pm

Says the guy that's only been messin with chimneys for 40 yrs. or so--what the hell does he know!!!!!!!!!!!!!!! LOL Couldn't help myself my friend!! :)

 
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Post by Lightning » Sun. Dec. 27, 2020 3:33 pm

Maybe raising the chimney would help, especially if some kind of weird thing is going on because of wind turbulence off the roof.

I would love to hear from people that have actually raised the chimney, what the circumstances were, and how successful it was with maintaining a better draft. I'd like to know if said persons were having draft failures during low and slow burns and that this absolutely fixed the problem.


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