Chimney height

Chimney height

PostBy: Adamiscold On: Fri Aug 08, 2008 9:36 am

Jerry,

Do you have a minimum chimney height for the Pioneer stove? Or do you go by the chimney specs calling for a minimum of 3 feet from the roof and 2 feet over a 10 foot reference line?
Adamiscold
 
Stove/Furnace Make: Chubby Sr. Old School

Re: Chimney height

PostBy: Devil505 On: Fri Aug 08, 2008 10:01 am

Adamiscold wrote:Do you have a minimum chimney height for the Pioneer stove? Or do you go by the chimney specs calling for a minimum of 3 feet from the roof and 2 feet over a 10 foot reference line?



Great question!!

I'm sure there must be a minimum chimney height for any chimney to work correctly but I have no idea what it may be???
( Interested in the answer to that question)
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Re: Chimney height

PostBy: gambler On: Fri Aug 08, 2008 10:43 am

Adamiscold wrote:Or do you go by the chimney specs calling for a minimum of 3 feet from the roof and 2 feet over a 10 foot reference line?


Those specs are probably code for a chimney install. Although I did not follow the "code" because if I would have made my prefab chimney 2 feet taller than the highest part of the roof within 10 feet I would not be able to reach the top of the chimney to clean it unless I disassembled part of it. As it is now I have 5ft of chimney above where the chimney exits the roof and to meet code I would need another 2+ feet added to the chimney. My stove is a top vent and my chimney is directly above the stove so I have a totally vertical install. My chimney is 15ft high plus the 5ft of stove pipe connection and with the insulated prefab chimney I have no draft issues. If anything I have almost too much draft. Quite often last winter my baro was open full to keep my draft at -.05
gambler
 
Stove/Furnace Make: Leisure Line
Stove/Furnace Model: Pioneer

Visit Leisure Line Stove

Re: Chimney height

PostBy: Devil505 On: Fri Aug 08, 2008 11:17 am

I was thinking more of a physics question than building codes. I know code requires a chimney to be a certain amount higher than the roof, but how high would a chimney have to be for the physics to work at all? (ie would a 2 ft chimney work?......Hypothesis=Yes)
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Re: Chimney height

PostBy: Adamiscold On: Fri Aug 08, 2008 2:42 pm

I know mine would be high enough for code going 4' above the roof line on my flat rubber roof. But it's only going to be about 8' total height going straight up in one shot. It seems like it should work and without any issues, nothing near it to effect the wind flowing across the top of the chimney.
Adamiscold
 
Stove/Furnace Make: Chubby Sr. Old School

Re: Chimney height

PostBy: Devil505 On: Fri Aug 08, 2008 2:53 pm

Adamiscold wrote:I know mine would be high enough for code going 4' above the roof line on my flat rubber roof. But it's only going to be about 8' total height going straight up in one shot. It seems like it should work and without any issues, nothing near it to effect the wind flowing across the top of the chimney.



Here's my "layman's" understanding of how a chimney works:

Warm air rises
As the warm air rises it expands
Trapped within a chimney's walls, this air expansion is "squeezed" & since it wants to expand (but is prevented from doing so) it increases it's velocity upward to escape it's bounds
This increase in upward velocity creates a vacuum below the upward rushing air.
Since nature abhors a vacuum, it (nature) fills it (the vacuum) by sucking the exhaust out of the fireplace/stove/furnace
The higher the chimney, the greater the upward air velocity & vacuum

Thus, we have Draft!


(bows) :devil: :lol:



Any engineers out there wanna critique my analysis? :blah:





So the question is: Is there a minimum height necessary to achieve this chimney effect, & if so.......how does one formulate it?
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Re: Chimney height

PostBy: CapeCoaler On: Sat Aug 09, 2008 1:17 pm

From
http://www.chimneylinerdepot.com/lander/articles/lev2/chimney-height.asp
This link is broken, either the page no longer exists or there is some other issue like a typo.


Effective Chimney Height
Tall chimneys contain a taller column of warm, rising gases. The movement within the flue of this taller column of gases also increases the pressure difference (or draft) at the bottom of a chimney. The actual chimney height of the venting system is the critical factor, not the volume of gases contained in it.

The rule of thumb states that the total system, from the floor where the appliance is mounted, to the top, should never be less than 15 ft. Most normal installations exceed this.

Installations in cottages with shallow-pitch roofs may not. If draft problems are experienced with shorter systems, consider adding to the length to ensure adequate draft under all conditions.

Chimneys must be at least three feet higher than the highest point at which they contact the roof and two feet higher than any point within ten feet of horizontal distance from the chimney. These are minimum guidelines and may be increased if necessary.

Most draft problems have to do with inadequate gas temperature. They say that the flue should be the same size as the appliance flue collar. Venting systems that are over sized for the appliance they serve are common, partly because people used to think that bigger is better. Now it is clear that bigger is not better when it comes to sizing. A given volume of flue gas flows faster and has time to lose heat in a smaller flue than in a larger one.
CapeCoaler
 
Stoker Coal Boiler: want AA130
Hand Fed Coal Stove: DS Machine BS#4, Harman MKII, Hitzer 503,...
Coal Size/Type: Pea/Nut/Stove

Re: Chimney height

PostBy: bustedwing On: Sun Aug 10, 2008 3:51 am

Try http://www.woodheat.org They have an all about chimneys section,a chimney don't care what the fuel is.Also the NFPA(national fire protection assoc.)nfpa.org has info or links to it that explain how they come up with these codes etc.,links to info on chimneys,fire codes,a lot of their stuff they want $$$ for,but a lot of insight can be gleaned just by surfing around. RichB
bustedwing
 
Stove/Furnace Make: LeisureLine
Stove/Furnace Model: Pioneer

Re: Chimney height

PostBy: Adamiscold On: Sun Aug 10, 2008 7:49 am

Damn 15' :notsure: I'm going to have to move this darn thing to a new spot.
Adamiscold
 
Stove/Furnace Make: Chubby Sr. Old School

Re: Chimney height

PostBy: CapeCoaler On: Sun Aug 10, 2008 3:17 pm

Just add some height. Chimney will need support after 5 feet.
CapeCoaler
 
Stoker Coal Boiler: want AA130
Hand Fed Coal Stove: DS Machine BS#4, Harman MKII, Hitzer 503,...
Coal Size/Type: Pea/Nut/Stove

Re: Chimney height

PostBy: Adamiscold On: Sun Aug 10, 2008 6:51 pm

My problem is securing it to the flat rubber roof and being so high. If I go straight up in the corner I want to go in and if I have to go 10-12 feet then I'm more then likely going to be hitting a tree branch. It wont be a problem next year as we are going to have the trees cut down but it might be a problem this year with the inspector. Being so high up I would have to question how good one of those brackets are with the two legs being so long from the chimney to the roof is going to be?
Adamiscold
 
Stove/Furnace Make: Chubby Sr. Old School

Re: Chimney height

PostBy: cArNaGe On: Sun Aug 10, 2008 7:14 pm

Soooooo.

If my EFM requires a 8x8 flue of 15 feet.

Would a 6x6 flue of 45 feet work?

What the calculations to figure it out?
cArNaGe
 

Re: Chimney height

PostBy: coaledsweat On: Sun Aug 10, 2008 7:30 pm

Devil505 wrote:Here's my "layman's" understanding of how a chimney works:

Warm air rises
As the warm air rises it expands
Trapped within a chimney's walls, this air expansion is "squeezed" & since it wants to expand (but is prevented from doing so) it increases it's velocity upward to escape it's bounds
This increase in upward velocity creates a vacuum below the upward rushing air.
Since nature abhors a vacuum, it (nature) fills it (the vacuum) by sucking the exhaust out of the fireplace/stove/furnace
The higher the chimney, the greater the upward air velocity & vacuum

Thus, we have Draft!


(bows) :devil: :lol:



Any engineers out there wanna critique my analysis? :blah:





So the question is: Is there a minimum height necessary to achieve this chimney effect, & if so.......how does one formulate it?


Yes warm air rises because its lighter but actually a chimney should work without the warm air rising thing. The reason being is that it works not because of air temperature, but air pressure. At the bottom of a 30' tall chimney, let's say the air pressure is 14.7 PPSI. Now if you climb the chimney, you may find that the air pressure only produces about 14.4 PPSI Because there is 30' less air squeezing it down. The draft is created by a long cylinder seeking to equalize pressure through out its length. So any long length of pipe stood up should create a draft of sorts even without a fire. It's Bernoulli's law! :)

It's the engineer in me. :D :roll:
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Chimney height

PostBy: coaledsweat On: Sun Aug 10, 2008 7:42 pm

cArNaGe wrote:Would a 6x6 flue of 45 feet work? What the calculations to figure it out?


The only thing you need to figure out is how big of a baro that beast needs.

Near the bottom there is a sizing chart. It looks like 7-8" but it is hard to tell with that height chimney, I would call Field Controls Tech Support as they have a very helpful staff.

http://www.fieldcontrols.com/draftcontrol.php
coaledsweat
 
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

Re: Chimney height

PostBy: Devil505 On: Sun Aug 10, 2008 7:55 pm

coaledsweat wrote:es warm air rises because its lighter but actually a chimney should work without the warm air rising thing. The reason being is that it works not because of air temperature, but air pressure.



Interesting! I never realized that...Thanks for the info. :)
Devil505
 
Stove/Furnace Make: Harman
Stove/Furnace Model: TLC-2000

Visit Leisure Line Stove