Class A Chimney Recommendations - How Tall?

[MrKenmore]

Hi everyone! I have a Jotul Oslo. Before the winter season I will be installing all new class A chimney pipe. How tall should I go with the chimney? My ceiling (flat) is 9'2" and I have two 45 degree elbows on the run of single wall pipe. I planned on a total of 9 feet of chimney pipe. About 3 feet is in the attic space so 6 feet would be outside. I plan on using Metalbestos materials. Do I need to go any higher?

Note: I already properly clear any nearby structures/roofs with the proposed height.

Thanks!

 

[webbie]

Sounds about right - a total of 15 feet from the stove to the top. Situations like this usually work out well, with the exception being if there are strange wind gusts across the top of the roof. Personally, I'd go for it and take my chances.....if the stove has a choice of top/read flue outlet, definitely choose the top.

 

[MrKenmore]

The stove is actually already installed but connected to an 8 inch chimney pipe (and only 8 feet of it). I am using the top exit on the stove BTW. I didn't have the money or weather to do this last season.

 

[elkimmeg]

Assuming the stove is 2’ tall you have about 13’ of chimney factoring in the friction of the two 45 degree elbows you need to add 5 more feet to that chimney.
edited Here is the entire section concerning chimney height
According to your manual
“2.4 Chimney Height
Whether a masonry chimney or prefabricated metal chimney is
used it must be the required height above the roof line.
The requirement is:
The chimney must be at least 3 feet higher than the highest point
where it passes through the roof and at least 2 feet higher than
the highest part of the roof or structure that is within 10 feet of
the chimney, measured horizontally. See figure 3.
Chimneys shorter than 14 feet may not provide adequate draft.
This could result in smoke spilling into the room from the stove
when loading the stove, or when the door is open. In addition,
inadequate draft can cause back puffing, which is a build up of
gases inside the firebox.
Other times, chimney height can create excessive draft which can
cause high stove temperatures and short burn times. Excessive
drafts can be corrected by installing a butterfly damper. If you
suspect you have a draft problem, consult your dealer.

Excuse the cut an paste it did not format all that well


14 plus 5 you need 19’ of vertical height

 

[webbie]

“When installing the Jøtul F 500 into a masonry chimney "

He is not using a masonry chimney.

In my experience a top vented straight up (top vent) stove should work in that config. Notice the Jotul quote says masonry chimneys and "could" and "may"..... one improvement you could make would be to use less than a 45 degree (adjustable els with less angle) if that works, but either way I think a chimney as you mention should work fine. If you have problems, add another couple feet or it might be that problems are related to certain wind currents, and a different chimney cap would help.

Translating Jotuls figures, since it is impossible to vent into a masonry chimney without at least one (and usually two) turns (either out the back straight in or out the top, one el, then into the chimney and turn upwards), you will end up vastly better than that.

But, you didn't give up one important piece of information - how is it working now with the 8"? And is it installed the same way (offsets, etc.)

If it is not working well at all with the existing setup, then I doubt adding one foot and downsizing to 6 will make a vast difference. Again, there are many factors which determine draft. If it is "close" - that is, working pretty good by could use a little push - well, then the smaller flue and slight height gain may do the job.

Be sure to seal up the interior black pipe well with furnace cement...those little leaks can kill the draft. Another thought is to use double wall interior pipe, which will create more draft (but cost more, and radiate a little less heat into the room).

In any case, you can hardly go wrong - worse case, you can add more (and if you do, you must place extra support brackets on the roof to stabilize it).

Tell us about your existing 8" - is it very old? Does it smoke?

 

[MrKenmore]

I'm resurrecting this old post of mine as I am getting ready to order my new class A chimney pipe. Just to refresh......my big gripe is my short burn times. I know my wood is well seasoned (norway maple and black birch with some cherry). I can pack it and only get around 3 hours before the temp goes down. During regular operation, the stove is around 500-550. With my pipe replacement, I hope to extend my burn times significantly. Other posts on the board have told me my draft was insufficient based on my current setup. Any final thoughts would be greatly appreciated.

Thanks everyone!

 

[KeithO]

Sounds like too much draft rather than too little. Did you have the primary air closed well down ? No leaks on the stove (door gasket, ash pan door, glas to door gasket etc) ? Perhaps the wood is too dry or maybe it was standing dead wood that was cut down ?

I have been burning wood from standing dead trees the past week. I find that wood which has any indication of punkiness has a dramatically reduced BTU content and a lot less volatiles.

 

[Gooserider]

Shorter than normal burn times for a given stove tend to indicate excess air, either to much draft pulling more air past the controls and secondary air inlet, or air leaks allowing to much air to enter the stove w/o proper control. (assuming good wood, etc.)

Insufficient draft tends to give smokier / smoldery fires that may last but don't put out much heat, difficulty in lighting / keeping lit, and possibly back puffing or excess smoke spillage when opening the stove doors.

What is your current setup like?

Gooserider

 

[MrKenmore]

Here is the piping setup:

About 5.5 feet of 6 inch single wall pipe (with two 45 elbows) transitioning to 8 inch single wall for 1.5 feet and then 8 feet of 8 inch class A double wall insulated chimney.

If I attempt to damper down once the stove reaches around 500 degrees I sometimes get smoke out of the stack. At the high temps (500-550), its clean (no smoke). My temperature also drops when I damper down too much.

I definitely understand what you guys are saying about possibly having too much draft. I never get any puff back and its very easy to light.

To replace all the required components will run me $800. I would hate to do all this work and discover it was for nothing!

The main things I am looking for are the long burn times and a clean burn. I am only on 1/4 acre and I don't want to smoke out all my neighbors

 

[Gooserider]

Here is the piping setup:

About 5.5 feet of 6 inch single wall pipe (with two 45 elbows) transitioning to 8 inch single wall for 1.5 feet and then 8 feet of 8 inch class A double wall insulated chimney.

If I attempt to damper down once the stove reaches around 500 degrees I sometimes get smoke out of the stack. At the high temps (500-550), its clean (no smoke). My temperature also drops when I damper down too much.

I definitely understand what you guys are saying about possibly having too much draft. I never get any puff back and its very easy to light.

To replace all the required components will run me $800. I would hate to do all this work and discover it was for nothing!

The main things I am looking for are the long burn times and a clean burn. I am only on 1/4 acre and I don't want to smoke out all my neighbors

Unusual, as that setup seems like it would be on the short side if anything... 5.5' + 1.5' +8' = 15', minus the theoretical 5' penalty for the bends would leave you with a virtual 10' stack, which is very short since most stoves require about 12-15' per their manuals... The 6-8" transition also shouldn't be helping things any.

I would not think you'd be hurt by going to an all 6" setup, which I assume is what you are planning? However I don't know that it would help your burn times. Have you gone over the stove with a fine tooth comb to make sure you don't have any air leaks - door and ash pan gaskets, any assembly seams, etc? That might be causing your short burn times by giving more air than you should be getting.

Gooserider

 

[MrKenmore]

To install a complete 6 inch stack is what I was planning. About 7 feet of 6 inch single wall and 9 feet of 6 inch class A chimney pipe.

I'll have to check the stove for any leaks.

 

[MrKenmore]

I have attached some pics of the stove running at 500 degrees.

Within 30 minutes of starting it, I was up to 425 degrees, At this time I set the intake from 2/3 open to 1/2. At 45 minutes it was up to 550 degrees,

I am thinking I may need to adjust my burn habits to see what that does. Bigger spits and really pack the heck out of the firebox to get the long burn times. All my burning tonight was very clean (naturally at the high temps).

Thanks for any help!