Should I Baffle Grandma ?

[Strange82]

Hi folks.
Just joined here, but I've been looking around for a few years.
I heat my old farmhouse with a grandma bear, but compared to my parents smaller Cozy Comfort it just never seemed to put out the heat. I'm leaning heavily towards a baffle install sounds like the ticket to more efficiency.

 

[coaly]

Welcome to the Forum !
It does help a lot, but tell us about the stoves and installations. I want to make sure you're comparing apples and apples.
If you mean Kozy Komfort, they are very much like a Fisher with a Timberline top. (large cooking surface in the rear with much smaller lower portion at the front)
Is theirs a single door stove with 6 inch pipe and flue compared to your 8 inch possibly?
Are they both vented the same from top or rear?

 

[Strange82]

Their stove is a single door 6" rear vent into a 8" tile lined 2 story chimney.
My stove is 8" top vent, into a 10" tile, 3 story chimney. Although my connector pipe does choke it down to 6", it was available and free.
I just couldn't get my stove to put out as much heat as the Kozy, I can get it hot but it seams as though my pipe is where most of the heat is going.

 

[Strange82]

Oh, I'm a two stove guy. I also run a jotùl 3 in my living room.

 

[coaly]

As I thought, your stove is venting into a larger flue than necessary. Your stove suffers more since you have reduced to 6 inch which is 28.26 square inches increasing to 100 square inches (if that 10 inch is square) Even 10 inch round is 85 square inches which is too much even if your pipe was the full 8. If you're going to reduce to 6, it has to be 6 all the way. I've found expanding flue gas drops in temperature from 300 to 170* increasing from 6 to 8. You probably have 500 going down to that. It won't work.
You don't want to baffle yours since you have to leave so much up to make good enough draft to get air into it now. Cooling the flue more weakens draft and slows fire. You absolutely need a insulated liner plus yours is taller requiring even more heat. A taller chimney improves flow capacity, but not in direct relationship to height. Doubling in height gives a 41% increase in draft, and as it goes higher, decreases the gain even more.
Opening your stove up with 8 inch connector pipe will help get yours hotter, but burn more wood.
Get each other liners for Christmas !!

 

[Strange82]

So no baffle, and you suggest a 8" insulated liner. Ok. Thanks. Probably not gonna happen this year but it'll go on the "to do" list. Do you have a liner you suggest?
I will however get rid of the 6" pipe soon.

 

[Strange82]

Oh, is the insulated necessary? Here's my reason for questioning. My chimney is in the middle of my home, so it's not (except to top 4') exposed to outside air temperatures. It's nice to have the warm chimney.

 

[coaly]

No, it's not required with the indoor chimney. But it's better for the stove.
I would use 6 inch, not 8 all the way. With the indoor chimney, that will work fine.
If you were going to just dump into the larger chimney like it is now, I'd enlarge to 8 inch pipe.
The exterior of the chimney is not going to get as warm with the smaller liner, but the output of the stove is much more. (less heat loss due to chimney not radiating as much up through the roof as well) Then you can baffle it being careful you don't take too much heat away from the liner without insulating it.

 

[Strange82]

Ok, so if I'm not going to line it right off, make the switch to 8" to the chimney. When I do line it run 6" all the way and then add the baffle. Insulating the liner is the better option for the stove? Could you explain? I'm not questioning just wondering. Thanks for the input by the way.
I've been inspired by the site, I finally got around to replacing the firebrick in Grandma today after three years saying that I wanted to do it. I did manage to destroy the nail on my pointer finger in the process. Oh well.

 

[Strange82]

Oh also, is it possible to extend the clean out plug lower than the tee? My thimble is about 3' above my clean out door.

 

[coaly]

Yes, as long as any opening into flue or pipe is capped so it doesn't leak indoor air in it's fine.

Here's the basics;
The chimney is the engine that drives the stove. Hot rising gasses are hotter inside flue than out. The more temperature differential, the faster they rise. This is draft. The first purpose is very clear, to expel smoke and unwanted byproducts of combustion. The second and most important is why the insulated flue is best. The rising gasses create a low pressure area in connector pipe and stove. This allows atmospheric air pressure to push into the stove feeding the fire oxygen. So the hotter the flue inside and the colder outside, (outdoors at chimney top) the stronger the push into the stove. The smaller 6 inch flue is almost half the size of the 8. Those two inches in diameter almost doubles the square inch cross sectional diameter. So the larger flue takes almost twice as much heat (waste) to get the same results of air pushing into the intake. The insulated flue stays hotter inside much easier making the stove more efficient using less wood. The other advantage with an insulated flue staying hotter is less creosote. 250* is the temperature you must stay above all the way to the top. At 250* water vapor from combustion condenses on the flue walls causing smoke particles to stick. This is creosote. So the insulation requires less heat to be left up to keep clean. That's why it can then be baffled to put the heat to stove top instead of needing it up the chimney.
Now you can see why your parents stove needs the correct size and preferably insulated liner as well.
Any opening into flue other than the stove through intakes also allows atmospheric pressure to leak in. This cooler air cools the flue gasses which slows draft since there is less temperature differential allowing water vapor to condense before it gets out.
There is no way to have enough heat loss up your 6 inch pipe to heat the huge chimney flue you have. At least with 8 inch outlet and pipe you're only expanding from 8 to 10, but that still isn't good. The drop in temperature allowing flue gasses to expand reduces draft, reducing oxygen into stove. That's why you might feel it's "sluggish". It needs the heat up the stack instead of in the house.

 

[Strange82]

Thanks! I appreciate the lesson. Insulated liner is in my future for sure.

 

[coaly]

Once you understand the theory and principals it all makes sense. I copy and paste a lot of that all the time. You'll find the basic principals on threads for newbies to burning, where people that have burned many years don't read. Then they have a problem and the basics they never understood makes what they've been doing wrong all those years quite clear.