# Chimney Draft Failure

### Re: Chimney Draft Failure

Maybe I'm visualizing this incorrectly, but isn't a negative # an actual reverse flow, or "down-draft" which would prohibit any flow outward or up?
joeq

Hand Fed Coal Stove: G111, Southard Robertson
Stove/Furnace Make: Thermopride
Stove/Furnace Model: oil fired

### Re: Chimney Draft Failure

joeq wrote:Maybe I'm visualizing this incorrectly, but isn't a negative # an actual reverse flow, or "down-draft" which would prohibit any flow outward or up?

In a natural drafting chimney (with no power vents, direct vents or combustion blowers) there are these two following scenarios :

To be technically correct, a negative number actually represents a vacuum in the flue pipe. This vacuum is created from rising warm air in the chimney which is trying to pull air thru the fire chamber.. Since the pressure difference (in this case vacuum) can't be satisfied with incoming primary or secondary air (or leaks in pipe joints or wherever), we get a reading on the manometer. This is of course, is what we want the chimney to do.

A positive number (to be technically correct) would represent pressure in the flue pipe. This positive pressure would be created when a chimney fails and gases in it try to sink back down thru it. Since the pressure difference (in this case positive pressure in the flue and stove) can't be satisfied with outgoing flue gases thru primary or secondary air controls (or leaks in pipe joints or wherever), we get a reading on the manometer the other way. There are many contributing factors that can cause this. This is bad since now carbon monoxide along with the flue gases have an opportunity to leak out of the pipe or stove..

The confusion occurs because many of us set up the Dwyer manometer "backwards" to read negative draft pressure (vacuum) on the positive side of the scale. We do this because the positive side of the scale reads higher than we will ever need, while the negative side of the scale only reads down to a -.05" WC.. And then to add to the confusion, sometimes when speaking in terms of negative draft pressure not everyone (including me) will put a "-" in front of their draft number to indicate (to be technically correct) a vacuum.

SO, usually its assumed that a .05" WC is actually meant to be negative pressure value, unless its defined in the post or thread otherwise.

That's kinda messy isn't it...
Sorry, I just woke up
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Chimney Draft Failure

well said Lee ...!
...yes... a.vacuum...by definition is "negative pressure"
like drinking thru a straw joe..
to get the liquid to rise up the straw you woud suck. (yes Im chuckling a bit)
(you are applying negative pressure to the straw)

...now-if that same straw had a hole in the side .it would act like a BARO...

unless the time is 4:20.....then it would act like a carb!
Rigar

Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

### Re: Chimney Draft Failure

Hahaha that's awesome
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Chimney Draft Failure

Lazy draft today. 61 degrees outside. 77 in the house. Wife says it's comfy lol.

Got a solid -.01 with secondary wide open and primary just a sliver. 228 degrees over the load door and 147 on top the pipe
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Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Chimney Draft Failure

Alright men. Sorry for the delay, but had to shut down the puter for a bit, to replace it with an updated one. (Which was provided by a buddy....thanx Joe). Now for our "neg". pressure discussion. Thanx for clearing up the difference between a vacuum and a pressure, (being a carburetor fan, I was savvy to it), but on my Dwyers, the scale to the right of the "0" the incremental numbers are black. To the left, the numbers are in red and labled with a "-", or minus. So what you're saying lightning, is yours isn't reading in the red, just you "choose" to call the black numbers a "neg", cause "technically" they are.
Which would give reasoning to your new avatar similar to the "Big Bang Theory". Aren't they always running around in super hero costumes? Or is it your Halloween costume?
joeq

Hand Fed Coal Stove: G111, Southard Robertson
Stove/Furnace Make: Thermopride
Stove/Furnace Model: oil fired

### Re: Chimney Draft Failure

joeq wrote: Or is it your Halloween costume?

It's rude to make fun of what somebody wears. He could get traumatized.
franco b

Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

### Re: Chimney Draft Failure

joeq wrote:but on my Dwyers, the scale to the right of the "0" the incremental numbers are black. To the left, the numbers are in red and labled with a "-", or minus. So what you're saying lightning, is yours isn't reading in the red, just you "choose" to call the black numbers a "neg", cause "technically" they are.

Yes sir, that's how it goes
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Chimney Draft Failure

In the really big scheme of things (I.E., technically) there is actually no such thing as negative pressure. All pressures are positive. You can take pressure down to near zero, but it can't ever go negative (even in the deepest and most empty space between the galaxies). Just figured I'd toss that monkey wrench into the works.

Not that you can't have pressures that go below the prevailing atmospheric pressure of course, but they are still positive....
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)

### Re: Chimney Draft Failure

lsayre wrote:In the really big scheme of things (I.E., technically) there is actually no such thing as negative pressure. All pressures are positive. You can take pressure down to near zero, but it can't ever go negative (even in the deepest and most empty space between the galaxies). Just figured I'd toss that monkey wrench into the works.

Not that you can't have pressures that go below the prevailing atmospheric pressure of course, but they are still positive....

well that will be handy information when someone builds a coal fired space ship....
till then we'll keep it relative ...as defined...as not to perplex us simple folk
Rigar

Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

### Re: Chimney Draft Failure

...and I will correct myself....i should have stated a PARTIAL vacuum by definition is neg pressure
Rigar

Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

### Re: Chimney Draft Failure

All temperatures are actually positive also.
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)

### Re: Chimney Draft Failure

lsayre wrote:All temperatures are actually positive also.

....even ABSOLUTE ZERO. ??
Rigar

Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

### Re: Chimney Draft Failure

Just like time and space, temperatures and pressures are all relative hahaha
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Chimney Draft Failure

Rigar wrote:
lsayre wrote:All temperatures are actually positive also.

....even ABSOLUTE ZERO. ??

That is unachievable, just as zero pressure is unachievable.
lsayre

Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Blaschak Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW)