Should I be worried about overdrafting?

[rayfield]

Took a few years to find a capable chimney man here in southern Rhode Island but after half a dozen pretty sorry sweeps proved useless, last year a capable chimney mason paid me a visit or took: the two big things he did were 1) removing the "bird cage" at the top of the chimney vent, doubtless the primary cause of the creosote buildup and inadequate draft, and 2) installing a cleanout just above the stove flue. So far this season I've seen a all-around huge improvement in the third season for this Woodstock Soapstone Keystone.

Maybe things have gotten a little too much better: as a consequence of the vastly improved draft, I'm getting somewhat more concerned about overfiring. Last night was the first really cold night of the season, and closing the damper all the way allowed me to burn overnight fairly effectively. However, at other times, I've seen the stovetop get quite hot -- this morning when it was around 35 F outside, even when I had the damper closed all the way, the thermometer read around 680. Maybe not in itself cause for alarm, maybe enough to be concerned how hot it gets when the outside temp drops below 20 or 10??? Should I be thinking about installing a flue damper?

 

[begreen]

Describe the chimney that the stove is venting into. How tall is it? Is there a stainless steel liner in the chimney or is this clay-tile lined. What is the size of the liner?

 

[mikey]

There are some good installers on Aquidneck Island, I don’t know if they will travel down there.

 

[rayfield]

Describe the chimney that the stove is venting into. How tall is it? Is there a stainless steel liner in the chimney or is this clay-tile lined. What is the size of the liner?

As best I can: a 7"-to-6" adapter, around 6" long, connects from the top (not the rear) of the stove to double-walled steel pipe reaching up to the ceiling - probably 10' of that black pipe - connecting to about 9-10' of shiny aluminum atop the roof.

 

[begreen]

Great. It sounds like there is about 20' of flue system on the stove, straight up. That should be ideal. I would hold off on adding the stovepipe damper. Instead, try loading thicker splits for a slower fire and see how things go at around 25º outside.

 

[rayfield]

There are some good installers on Aquidneck Island, I don’t know if they will travel down there.

It's too far for almost everyone, goes to show how big a state we live in! Called everyone I could find until I practically had to plead with a guy from Smithfield. He was nice enough - and strong enough, with his assistant - to get the stove off the truck and in here, most of the battle. But just not really very expert in chimney matters, in fact I was pretty much in touch with every sweep in RI and had half a dozen in: only this one guy isolated the problem - in fact I got my money back from the previous guy, a disciple of the South County sweep everyone seems to use.

 

[Eman85]

Sounds like the chimney had buildup and the cap was clogged. now it sounds like the stove might have an air leak. 20ft. metal chimney shouldn't be an overdraft problem. The shiney shouldn't be aluminum should be stainless.

 

[Todd]

I burned a Keystone for many years. Did you see this 680 temp with a low air setting? Many times I’ve seen 700+ especially when it was shut down too low with the cat doing most of the work. It never stayed up there long and would settle down to 600-650. This may sound counter productive but if you see these high temps give it a bit more air so there’s more flame in the box. The cat will cool down along with the stove top temp. I usually ran my Keystone around #1 and it gave me a nice lazy flame with 500-600 temps. Still it wouldn’t hurt to check all your gaskets especially the ash pan. I replaced mine every 2-3 years.

 

[rayfield]

I burned a Keystone for many years. Did you see this 680 temp with a low air setting? Many times I’ve seen 700+ especially when it was shut down too low with the cat doing most of the work. It never stayed up there long and would settle down to 600-650. This may sound counter productive but if you see these high temps give it a bit more air so there’s more flame in the box. The cat will cool down along with the stove top temp. I usually ran my Keystone around #1 and it gave me a nice lazy flame with 500-600 temps. Still it wouldn’t hurt to check all your gaskets especially the ash pan. I replaced mine every 2-3 years.

Very interesting, since my first reaction is of course is to close the damper far as it will go.

Haven't seen the problem again, but I will do some gasket work in the spring.

Here's as good a place as any to remark how unbelievably helpful this site has been, hard for me to describe just how much I've learned here - a special shoutout to @begreen

 

[fire_man]

I burned a Keystone for many years. Did you see this 680 temp with a low air setting? Many times I’ve seen 700+ especially when it was shut down too low with the cat doing most of the work. It never stayed up there long and would settle down to 600-650. This may sound counter productive but if you see these high temps give it a bit more air so there’s more flame in the box. The cat will cool down along with the stove top temp. I usually ran my Keystone around #1 and it gave me a nice lazy flame with 500-600 temps. Still it wouldn’t hurt to check all your gaskets especially the ash pan. I replaced mine every 2-3 years.

Very true. Opening the air to reduce temps is counter intuitive but on a cat stove the laws of physics seem reversed.

My Palladian has a 27' flue and I use to hit 680F Stove Top temp when the cat was brand new with the air choked down, but as the cat aged it peaks around 600F. I have seen no indication I need a damper, even with the tall 6" ovalized flue.

 

[rayfield]

Very true. Opening the air to reduce temps is counter intuitive but on a cat stove the laws of physics seem reversed.

Hmm, no engineer I, but: maybe with a smaller opening the air travels at a higher velocity = higher temp burn?

 

[fire_man]

I think it's got to due with slower draft means there is less flame in the firebox so the cat gets to eat more smoke.
Higher draft causes more flame in the firebox which burns the smoke before the cat gets it.

A cat stove is kind of the opposite of a Rocket stove or Masonry heater (draft wise), if you think about it. Masonry and Rocket stoves burn most of the smoke because they burn fast hot fires (lots of flames) with a high draft. Cat stoves operating in pure "cat mode" (no flame in the firebox) smolder the wood and feed tons of smoke to the combustor, which ignites and burns super hot, hot enough to burn the smoke.