Monometer Install and Baro Location

At the point of exit at the top of the chimney is the highest exhaust gas speed, in the chimney. This is because the gas finally gets to rapidly expand, giving up most all of its remaining heat. When a gas expands, pressure drops and velocity increases....increasing draft If you can keep more heat in the chimney, (not by increasing stove exhaust temps) the difference between atmospheric temps & chimney gas temps will be greater, increasing the operational capabilities of the chimney.

This is the single best reason to have a properly sized, insulated chimney. Be it masonry or SS.

Gases expand when they loose heat? I've only know them to contract when they cool down

None of this is making sense to me lol.

When a gas expands, pressures drops hmm, that does not compute. You mean when pressure drops then the gas expands right?

Really I'm not trying to be difficult. But when something seems to violate fundamental principals, I like to stop and take a look at it.

Lightning wrote:Gases expand when they loose heat? I've only know them to contract when they cool down

The gasses expand right at the outlet of the chimney because they come in contact with the colder ambient air. You can see the little space sometimes right on top of a chimney where there is no smoke (think wood stove) then you see the cone shape of the expanding condensing/cooling gas cloud.

Inside a chimney they are not in contact with ambient cold air.

When the gasses expand the pressure drops and the velocity increases. It's the same way an airplane wing develops lift.

None of this is making sense to me lol.

When a gas expands, pressures drops hmm, that does not compute. You mean when pressure drops then the gas expands right?

Same thing.

Really I'm not trying to be difficult. But when something seems to violate fundamental principals, I like to stop and take a look at it.

There are no stupid questions Lee, really.

Without drilling more holes to set up my velometer, or calculate the velocity with the manometer and pitot tube, and attempt to factor in the changes of flue gas density as it rises, cools and expands ......... here is what I got

Wow, it almost sounds like I'm starting to grasp this thread !

I piped in permanent the magnehelic guage on the left into the elbow exiting my stove below the barometric damper. My chimney is two story flue lined, masonry construction.

It is 67* here and windy. The magnehelic guage on the right is tied in with a test hose and magnetic port.

What I am seeing is a pretty consistent -.04 below the barometric damper. As the wind picks up and the baro damper opens , the upper port rises to -.06 & -.07 and the lower port maintains its -.04 The lower guage will bounce to -.05 for less than a second on a high gust of wind and I attribute that to the reaction time of the baro and the sensitivity of the guage.

Paulie

Pauliewog wrote:What I am seeing is a pretty consistent -.04 below the barometric damper. As the wind picks up and the baro damper opens , the upper port rises to -.06 & -.07 and the lower port maintains its -.04 The lower guage will bounce to -.05 for less than a second on a high gust of wind and I attribute that to the reaction time of the baro and the sensitivity of the guage.

Neato, what do the mags read while the wind is calm?

Lee , Both are reading -.04 with no wind.

Paulie

Pauliewog wrote:Lee , Both are reading -.04 with no wind.

Paulie

Is that with the baro door completely closed? Or is it limiting draft?

Lightning wrote:
Is that with the baro door completely closed? Or is it limiting draft?

That is with the baro door completely closed

Paulie

OK, I imagine it's too warm out right now for the chimney to draw strong enough for the baro to limit without wind gusts. Thanks partner

scalabro wrote:

Lightning wrote:Gases expand when they loose heat? I've only know them to contract when they cool down

The gasses expand right at the outlet of the chimney because they come in contact with the colder ambient air. You can see the little space sometimes right on top of a chimney where there is no smoke (think wood stove) then you see the cone shape of the expanding condensing/cooling gas cloud.

Inside a chimney they are not in contact with ambient cold air.

When the gasses expand the pressure drops and the velocity increases. It's the same way an airplane wing develops lift.

None of this is making sense to me lol.

When a gas expands, pressures drops hmm, that does not compute. You mean when pressure drops then the gas expands right?

Same thing.

Really I'm not trying to be difficult. But when something seems to violate fundamental principals, I like to stop and take a look at it.

There are no stupid questions Lee, really.

Yes, there are Scott - the questions that don't get asked because someone thought those questions were "too stupid" !

But,...... all bets are off when it comes to stupid answers.

Paul

Outside temp cooled off enough last night for the baro to do its thing. I drilled a hole in my new pipe (dammit lol) downstream of the baro and did some measuring. On the side by side pick below you can see the reading upstream of the baro (left pic) and downstream (right pic). Close scrutiny does reveal a quarter mark (.0025) increase on the downstream side, which is what I've seen in the past. It was close enough for me to call the same.

Then I also did a video going back and forth since I only have one manometer. Video starts with mano reading upstream of baro, then downstream and finally back to upstream again. Notice baro door is pitched at 60 degrees, 90 degrees would be closed.

The interesting part was when I pinned the baro shut it took about 10 minutes for the mano reading to climb up to -.07.

So Scott, we may be both right. During no wind, the cool air makes the chimney incapable of drawing more than the baro limit, which pinning the baro closed showed me. Then during gusts the baro shows limit upstream while downstream is higher which was Paulie's observations.

Here's the video link

https://youtu.be/UvPCf6H8fGc

More pics. Pinned closed, it slowly climbed to -.07 over the course of ten minutes.

So, to sum it up, if willing to ignore wind gusts plumbing the probe downstream of the baro could be usable. But who wants to do that? Plumbing the mano probe upstream of the baro is the better location

Depends on what upstream is? Some may be confused

To sum it up in layman's terms, put the manometer tap between the stove and barometric damper.

Plus I don't think you can ignore wind, gust maybe but what if its steady at 20 plus mph.
I'm following guys with great interest and could help out but its just to warm to fire my Channing, the kast stove that I am using now is in a fire place opening and I can't connect a second mano to it