How Is Your 5" Liner Working?

[Rob From Wisconsin]

I'm sure there are several users out there that were limited to using a
5" chimney liner in their flue. How is it working for you?
What model of stove is it attached to?

Thanks..

 

[rdust]

I can't comment on a 5" but my 5.5" works well hooked up to my Lopi Endeavor. It's about 27' from the thimble to the roof with another 3' of pipe in the house.

Doesn't help you but it bumps you to the top.

 

[BrotherBart]

Never seen a post from anybody using five inch but several of us have 5.5" liners. I have a 21' and a 30+ 5.5" and they are working great.

Hard to find brushes for'em.

 

[Rob From Wisconsin]

The original owners put a rectangular 6" x 10" nominal liner, and I think it is oversized.
I could put in another smaller rectangular/oval liner, but they are extremely expensive.
The only commondity liner sizer that would work is a 5" liner.
I would in effect be "double-lining" my flue - the 6 x 10 liner is concreted to the cap (not removable).

 

[laynes69]

We have a 5.5" liner in our 32' chimney. It has a large woodfurnace on it. I choose to go with a rigid liner that way I could get a 5.5" down it. The old liner was a 7x10 and with a small offset it was a tight fit.

 

[Renovation]

By going from too big to too small you may be robbing Peter to pay Paul.

Check this thread for a discussion of too big versus too small:

https://www.hearth.com/econtent/index.php/forums/viewthread/66328/

Admittedly, the Tribute is a small stove, so 5" could be a good match, though no guarantees--not sure it's worth the risk.

Why do you ask? Are you having performance problems now?

 

[nola mike]

Never seen a post from anybody using five inch

here's one. just installed, jotul 602, 27' chimney. so far, so good.

 

[Renovation]

Some more thoughts.

According to my research, and barring better information, the chief risks of a smaller-diameter chimney are smoke spillage on reload, and reduced maximum burn rate.

Basically, a narrower flue draws air at a slower rate for a given temperature when not throttled back by the stove. The flue is unthrottled when, you guessed it, the door is open or the air supply is wide open. The lower volume going up the flue with the door open means there's a greater chance of air spilling out the door. The lower volume at full throttle means lower burn rate.

Now your stove has a very small firebox and door for stoves with a 6" flue, so I'm guessing you'll be fine.

Also, the flow rate is proportional to flue cross-sectional area, which is proportional to the square of the diameter. Now (5/5.5)^2 = 83% , so the change in flue area in itself is minor.

The upshot of all this analytical overkill? I do not think you'd notice any performance degradation with your stove on a 5" flue versus a 5.5", or even a 6".

The only other consideration is whether you think you ever might want to run a bigger stove. If so, it might be worthwhile to go with a 6" flue.

HTH, and thanks for giving me the chance to check my understanding.

 

[precaud]

My Nestor Martin is working fine on a 5" liner. I've hooked several stoves up to this same chimney, all worked fine. Remember that the original Jotul 118 had a 5" chimney connector...

 

[precaud]

...a narrower flue draws air at a slower rate for a given temperature...

George, I think it is not a fair comparison to hold temperature constant. I think the constant should be the volume of gasses passing through the chimney. With that, I think you'll find the 5" chimney maintains a higher velocity and higher temperature, which at least partially makes up for the area difference.

 

[Renovation]

...a narrower flue draws air at a slower rate for a given temperature...

George, I think it is not a fair comparison to hold temperature constant. I think the constant should be the volume of gasses passing through the chimney. With that, I think you'll find the 5" chimney maintains a higher temperature, which at least partially makes up for the area difference.

It's on now!

Okay, the rest of you can ignore this if you like, for it is time to split some technical hairs! :cheese:

Interesting, Precaud

(BTW, what is the origin of your handle, anyway? Canadian Academy of Urban Design? I'm pretty sure it's not Congenital Anterior Urethral Diverticulum ).

Okay, perhaps I should have been even more geeky, and clarified by saying "a narrower flue's inherent, unthrottled flow rate is lower for a given temperature of exhaust gasses". Better?

Let me see if I follow your logic. For a given, intermediate burn, the added drag of a narrower flue will be compensated by a larger damper opening, causing identical flue *flow* rates for identical stoves burning at the same rate into different diameter flues, but higher gas *velocity* in the narrower flue. Correct?

Or perhaps your reasoning is simply that the narrower flue's reduced surface area leads to less heat loss and higher exhaust gas temps? And your reasoning is that this higher average gas temperature helps compensate for the reduced cross sectional area?

I take your point, and appreciate your insight, though draft is only proportional to the square root of temperature difference (and chimney height), but directly proportional to chimney area. This gives the counter-intuitive insight that changes in chimney diameter affect draft more than changes in height or temperature.

Granted, the flue gas temperature used in that particular model is an average one, which does not take into account the surface area effect I think you're mentioning. But that is a second-order effect.

If you're interested in the equation I'm using, you can follow this link to the Wikipedia article on chimneys, and scroll down to the "Chimney draught or draft" section, you'll find the model I'm using, which I find very useful--the illustration of chimney draft is particularly good for intuition:

The stack effect in chimneys: the gauges represent absolute air pressure and the airflow is indicated with light grey arrows. The gauge dials move clockwise with increasing pressure.

http://upload.wikimedia.org/wikiped...imney_effect.svg/220px-Chimney_effect.svg.png

http://en.wikipedia.org/wiki/Chimney#Chimney_draught_or_draft

As a "first guess" approximation, the following equation can be used to estimate the natural draught/draft flow rate by assuming that the molecular mass (i.e., molecular weight) of the flue gas and the external air are equal and that the frictional pressure and heat losses are negligible:

Q = C A(sqrt(2gH(Ti - Te)/Te))

where:
Q = chimney draught/draft flow rate, m³/s
A = cross-sectional area of chimney, m² (assuming it has a constant cross-section)
C = discharge coefficient (usually taken to be from 0.65 to 0.70)
g = gravitational acceleration, 9.807 m/s²
H = height of chimney, m
Ti = average temperature inside the chimney, K
Te = external air temperature, K.

Thoughts? Thanks for an interesting point!

I now return you to your thread, which is already in progress.

 

[CaptSteve]

WOW hh:

 

[Renovation]

WOW hh:

Yeah, I know. :red:

"Geeking out--at least it's not crack!"

I'm mostly harmless. :lol:

 

[precaud]

Thanks for your detailed post, George. You're right - diameter plays a dominant role in the formula. But I must say - I find formulas interesting only when they corroborate my experience. And my comment was based in large part on observation and experience, using stoves say 2.2 cu ft and less, that maintaining draft at lower burn rates (which is when draft is most needed) is more difficult with "too large" a chimney than with "too small". That tells me that the role of temperature loss is greater as gas velocity decreases. Maybe there's a better explanation.

This is also supported by my experience of what happens with an insulated chimney vs an uninsulated one of the same size and materials. The insulation gives a more constant draft under low firing conditions. Other than that, I see no benefit. But... the fact is that my stoves spend most of their time cruising at lower burn rates.

So, back in the real world, other factors being equal, I'd rather have a 5" chimney than an 8" one.

 

[forvols]

My head hurts........

 

[mainstation]

I have a 5" SS flex lining approx. 30' of quarry stone chimney attached to a R14 Regency wood insert. It was professionally installed and the installers indicated they had to go that way because a slight obstruction in the ceramic flue?. It runs fine, although I think it draws quicker than the 6" would and therefore I may be using a bit more firewood than I should, although my insert is 16 yrs. old.

 

[Renovation]

Thanks for your detailed post, George.

You're welcome--thanks for tolerating it.

You're right - diameter plays a dominant role in the formula. But I must say - I find formulas interesting only when they corroborate my experience. And my comment was based in large part on observation and experience, using stoves say 2.2 cu ft and less, that maintaining draft at lower burn rates (which is when draft is most needed) is more difficult with "too large" a chimney than with "too small". That tells me that the role of temperature loss is greater as gas velocity decreases. Maybe there's a better explanation.

I believe your experience, agree with your assertion of better heating of a narrower flue, and believe that yes, there is an additional explanation--drag.

I agree completely that theory and experience should compliment each other. The equation I used does not seem to explicitly include drag effects at high temperature differentials, which mean high gas velocity.

Your experience affirms my theoretical conclusions--that the chief risks of narrow-flueing (for lack of a better term) are spillage on reload and lowered maximum burn. Drag comes into play as burn rate and exhaust velocity increase. A narrow flue's drag--due to higher gas velocity--will increase faster than a wide stack's, and make a narrow flue perform less well. This is easily demonstrated by blowing gently through a straw versus a snorkel--they are about the same if you blow very gently, but very different if you blow hard.

So theory agrees with your experience--a narrow flue will have a relative advantage at low to moderate burn rates with the stove door shut, where it exhibits all it advantages, and none of the cooling/draw issues of a wide flue.

Thanks for putting up with that.

This is also supported by my experience of what happens with an insulated chimney vs an uninsulated one of the same size and materials. The insulation gives a more constant draft under low firing conditions. Other than that, I see no benefit. But... the fact is that my stoves spend most of their time cruising at lower burn rates.

And mine will too. Yessir.

So, back in the real world, other factors being equal, I'd rather have a 5" chimney than an 8" one.

There you go, and there's where personal preference and risk tolerance come into play. I'm still on the fence on my 6" versus 8" choice, and probably will be until I actually nail one in. If I knew I could operate a King on a 6" flue without smoke spillage on reload, and get approval from my inspector and insurance company, I'd go for the 6" in a snap. I just don't think I can tolerate a moderate risk that I end up going with the King, and I get my new baby installed after all this planning and work to find that it belches smoke every time I open the door. :sick:

Thanks for the conversation, PC. I hope someone found it as useful and educational as I did. Happy burning!

 

[Renovation]

My head hurts........

You need to sit in front of a nicely burning stove, with your favorite refreshment.

 

[Rob From Wisconsin]

Wow, all this is starting to sound like a college physics class!!
But, in all sincerity, I feel my flue is too big - larger than an 8" circular.
I see too much build-up in the upper feet of my flue (20" long).
I can't help but think that smaller will improve my draft & somewhat
reduce the junk build-up in the upper part of my flue.

 

[precaud]

Yeah, but I think George's concern and question doesn't reflect your circumstance, Rob. Your Tribute has a 1.2 cu ft firebox, and will work fine into a 5" chimney. As I said above, the original Jotul 118 is larger than that and came with a 5†chimney connector from the factory. I don't see any reason not to do it.

 

[Renovation]

Yeah, but I think George's concern and question doesn't reflect your circumstance, Rob. Your Tribute has a 1.2 cu ft firebox, and will work fine into a 5" chimney. As I said above, the original Jotul 118 is larger than that and came with a 5†chimney connector from the factory. I don't see any reason not to do it.

+1 Agreed, as I said before my analytical tangent.

In a nutshell, the main concern with a narrow flue is smoke spillage on reload, and with your small firebox that is not likely to be a problem. And as Precaud said, the increased temps and velocity should lessen creosote.

Good luck, Rob!

 

[Rob From Wisconsin]

One interesting note....
I've been looking at a lot of European Stoves in my time,
and it seems that a lot of them are sized for metric 5" flues
"from-the-box", and then have a 6" adapter placed on them when
they hit the States. It seems in general that European stove design
leans toward small flues.
Do they know something that we don't???

 

[precaud]

From what I can see, 5" (125mm) was the standard in Europe until they finally caved and went 6" like us. Those stoves with 5" connectors are more than likely old designs. Plus, stoves tend to be smaller there.