Double vs single wall chimney connector

[begreen]

The stack is supposed to be 500F? When the stovetop on my 30 is about 550 F my single wall stove pipe is about 280F Am I doing something wrong?

That's surface temp. The flue gases are more likely around 450-500F.

 

[bholler]

The stack is supposed to be 500F? When the stovetop on my 30 is about 550 F my single wall stove pipe is about 280F Am I doing something wrong?

Nope you are doing good pretty good. You pipe might be just a little cool so i would watch the stack but sounds pretty good

 

[Highbeam]

That's surface temp. The flue gases are more likely around 450-500F.

When I said flue gasses are 800 I did not mean surface temp of single wall is 800. Surface temp is 400 and well within the "normal" range. Did you guys assume I said that surface temps were 800? That would be very hot.

 

[Highbeam]

One is designed by the engineers that developed the heating appliance. The other is just pulling off a random unknown amount of heat off of the venting system.

Hardly random. Some of us have instrumentation and can verify that the surface temps are staying above 250 even at the end of the single wall run up by the ceiling. The furnace guys deal with much lower flue temps. Kuuma especially run only mid 300s internal which is sub 200 surface temps.

Once you realize how many technologies reduce flue temps to gain efficiency, you become more comfortable doing the same.

 

[bholler]

Did you guys assume I said that surface temps were 800? That would be very hot.

I assumed that was with a probe and it is now way to hot but to hot for sure

 

[bholler]

The furnace guys deal with much lower flue temps. Kuuma especially run only mid 300s internal which is sub 200 surface temps.

Yes and most furnaces i work on are a mess of creosote

Once you realize how many technologies reduce flue temps to gain efficiency, you become more comfortable doing the same.

You do realize i work on chimneys every day. I see the real world results of many of those technologies. Some of them work well cats and true gassifiers but many just make a huge mess of the chimney when you extract to much heat.

 

[RustyShackleford]

I think we agree but you just don't like the idea of removing heat from flue gasses to extract efficiency or increase maximum output.

I think he agreed the stack is more efficient with the single wall. I argue that as long as the stove performs properly, that means the whole system is more efficient. I am totally on board with the idea that if pulling that heat from the flue gasses causes problems, forget it and go with double-wall. But for me, it does not cause problems: I do not get smoking when I open the door (unless I jerk it open suddenly in the middle of a burn cycle without turning up the air intake beforehand), and my chimney requires cleaning less than once per year. I guess I might could be convinced that somehow the stove itself would operate more efficiently with double-wall - even given that I clearly have adequate draft without it - enough to make up for the loss in stack efficiency.

 

[bholler]

I think he agreed the stack is more efficient with the single wall.

No if you have to say it is more efficient one way or another due to the fact that the purpose of the venting system is to remove the products of combustion as quickly as possible while loosing as little heat as possible then double wall would be the more efficient choice. Yes i know very well it can be done just fine while loosing heat off the pipe but as a general rule that is not a very good approach.

 

[Highbeam]

the purpose of the venting system is to remove the products of combustion as quickly as possible while loosing as little heat as possible

This is tripping you up. That last part about "while loosing as little heat as possible", is not the purpose of a venting system. Actually, the "as quickly as possible" part is not true either.

 

[bholler]

This is tripping you up. That last part about "while loosing as little heat as possible", is not the purpose of a venting system. Actually, the "as quickly as possible" part is not true either.

I disagree with you on that completly

 

[RustyShackleford]

I think he agreed the stack is more efficient with the single wall

No if you have to say it is more efficient one way or another ...

I hate to get into "he said, you said" but in post #17 you state "Yes less heat up the stack is more efficient".

 

[RustyShackleford]

This is tripping you up. That last part about "while loosing as little heat as possible", is not the purpose of a venting system. Actually, the "as quickly as possible" part is not true either.

Well stated. I think what's he's trying to say if that if it's "too slowly" and "loosing too much heat" then the chimney won't perform properly (bad draft, smoking when opening door, creosote buildup).

But he can't seem to acknowledge that if the flue performs properly, then you're fine with single-wall, and you DO get more heat from a given amount of wood - which I call "efficiency".

We seem to be talking in circles around each other. Maybe we can get @BKVP to weigh in.

 

[bholler]

I hate to get into "he said, you said" but in post #17 you state "Yes less heat up the stack is more efficient".

yes i know but that pipe is part of the stack

 

[bholler]

But he can't seem to acknowledge that if the flue performs properly, then you're fine with single-wall, and you DO get more heat from a given amount of wood - which I call "efficiency".

I never said you where not fine with single wall in fact i said the opposite that single wall is fine in short runs with stoves that can handle loosing some extra heat through the pipe. But saying it is a good idea to rely on that pipe to increase the efficiency of your stove is just wrong. And i am positive i know what bkvp will say why do you think their manuals call for double wall.

 

[begreen]

If a setup works well for single wall then fine. There are always exceptions to the rule. The problem is that argument is for a specific installation, which may be ok because the operator is vigilant, watching flue temps and for buildup. The average person running a stove however is most often is not a stove burning enthusiast and frequently has no thermometer. Additionally, installations vary dramatically in flue configuration which may or may not make double-wall the best configuration. When in doubt, the average user is much better off following the stove manual recommendations. BK specifically recommends double-wall connector on their cat stoves for this reason. Several other stove companies recommend double wall for runs over 8ft for this reason too. The downsides if any are minor.

 

[Highbeam]

I never said you where not fine with single wall in fact i said the opposite that single wall is fine in short runs with stoves that can handle loosing some extra heat through the pipe. But saying it is a good idea to rely on that pipe to increase the efficiency of your stove is just wrong. And i am positive i know what bkvp will say why do you think their manuals call for double wall.

The BK manual does not require double wall. Recommends, sure, but that's not the same as requires. I use double wall on the BK because that appliance is already so efficient that any further cooling could lead to problems with draft or creosote. Not so on the non-cats.

Also nobody ever "relied" on the flue for additional efficiency. It's just a bonus.

 

[begreen]

There are several cases we see here where switching to double-wall has improved draft enough to improve stove efficiency. This is common in single story wall exit flues. If the chimney is not ideal or right at the minimum, using a double wall connector can mean the difference between getting good secondary burn or not.

 

[realstihl]

I know that when I went from single wall to double wall there was a significant difference in the amount of heat loss going into the room. Not a problem, just had to push the stove harder for the same amount of heat. On the flip side there is less creosote build up in the double wall. It's a give and take situation.

 

[bholler]

The BK manual does not require double wall. Recommends, sure, but that's not the same as requires.

ok fine they recommend it i misspoke. But after seeing thousands of different setup i can tell you that those with longer runs of single wall pipe have more creosote buildup generally than those with longer runs of double wall. In short runs of pipe or with less efficient stoves the problem in not as noticeable but the principle still stands that loosing to much heat from the venting system will cause more buildup in that venting system. I never said single wall was bad it is just fine in the right situation but in general double wall will make your stove run better and cause less buildup in the chimney.

 

[RustyShackleford]

I never said single wall was bad it is just fine in the right situation but in general double wall will make your stove run better and cause less buildup in the chimney.

Fair enough.