Terra cotta flue for an 1983 Defiant II

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woodlot

New Member
Jul 1, 2010
22
south eastern PA
We are getting ready to build a masonry chimney for a 1983 defiant II, the owners manual says an eight inch flue should be used.I had the chimney block and eight inch square flue pipe delivered to my house,I noticed the flue only measured six and a half inches on the inside.Inside corner to corner it measures about eight and a half,is this acceptable.Someone told me that corner to corner is how it is measured.I plan on burning the stove with the front doors open daily for maybe an hour,I want to make sure I get good draft.The defiant II is in very good condition except for a new paint job.The mason that is building my chimney thinks i will be fine with this flue but we both want to be sure.The inside measurement of the chimney block is nine inches,I also found out that they make a eight and a half by eight and a half flue pipe.Maybe I should have got that flue instead,our main concern is building the chimney properly for this older defiant II.We are looking to get the right usage out of our stove without any problems down the road.If anyone can give us some advice it would be greatly appreciated.It would not be a problem to get the flue changed to what we need.Thank you
 
I understand the Defiant is touchy about going too small on the flue, so I'd probably make sure it's 8"x8" on the square sides. My 1980 Defiant II was installed in a massive 12x12 with a 6" thimble downstairs for the Jotul 8 (Defiant upstairs, Jotul downstairs, Defiant has inadequate flue length at only 10ft) and the Defiant drafts just good enough to burn in updraft mode, not too good with the doors open unless you warm it up with the doors closed first, but that's on the opposite extreme. At least if you go slightly larger and later on want to retrofit a 6" SS liner through (for a newer EPA-certified stove), the larger terracotta clay flue will accept the liner easier.
 
I would send the undersized flue tile back and buy an 8" round insulated stainless liner to insert in the block. Better draft, easier to clean, and lasts longer. Or nix the whole masonry chimney and install a metal class A chimney.
 
Todd said:
I would send the undersized flue tile back and buy an 8" round insulated stainless liner to insert in the block. Better draft, easier to clean, and lasts longer. Or nix the whole masonry chimney and install a metal class A chimney.

x2, with the options available today I wouldn't dream of building a terracotta flue today. Make the block part of the chimney big enough for an 8" round SS flue with wrapped insulation and call it a day. In 25+ years if you have trouble with the liner pull it out and slide a new one down.
 
The owners manual for my defiant II says a 8 inch flue is needed for that stove,I am getting ready to start building a chimney block chimney with a terra cotta flue.The block and flue have been delivered in my driveway,my problem is the 8 x 8 flue measures 8 inches on the outside and only 6 and a half on the inside.There is a 8 and a half by 8 and a half flue that is available,even if I exchange the 8x8 to the larger 8 and ahalf would my draft be ok .Flue pipe has not really changed since the 1980s, they built chimneys out of 16 inch chimney block and 8 inch flue.I cannot see why that chimney application was ok then and not now.The vermont castings dealer said I would get poor draft.The 8 and a half flue measures 7 inches on the inside,I would like some input as to what I should do to make this classic defiant burn properly. Thanks
 
Before answering, I have a couple questions: How tall is the chimney going to be? Is it interior or exterior?

I am holding myself back from asking why the heck you are worrying about a flue system for a 27 yr old stove.
 
The height of the chimney is 27 feet and it is an exterior chimney.Our mason suggested pouring perlite around the flue as he builds the chimney.With all do respect why would I not be concerned about the flue,even though the defiant is 27 yrs old, it is in excellent shape.Please let me know what you think. thanks Tim
 
logroad said:
The height of the chimney is 27 feet and it is an exterior chimney.Our mason suggested pouring perlite around the flue as he builds the chimney.With all do respect why would I not be concerned about the flue,even though the defiant is 27 yrs old, it is in excellent shape.Please let me know what you think. thanks Tim

Getting the flue right is a good thing. With a 27' insulated flue, the draft should be decent. The reason I was asking about designing for the old Defiant is that if it were me, I would probably go for a 6" metal flue which will accommodate most modern stoves. And I would do it in stainless. But then again, if it were me, the flue would be in the interior of the house.

If you are set on an exterior masonry chimney, I think the 8x8 tile will work fine with a 27' flue if there is only one elbow on the connector.
 
logroad said:
.Flue pipe has not really changed since the 1980s, they built chimneys out of 16 inch chimney block and 8 inch flue.I cannot see why that chimney application was ok then and not now.

Terra cotta can crack over time, stainless will not. Round flues also draft better.
 
Lots of folks did it with the small flues and the terra cotta years ago. The stoves smoked and the tiles cracked. The stainless idea sounds better to me...use good welded rigid pipe, such as from Heat-fab. Fasten it with multiple stainless rivets or screws. Insulate it in some way for best operation.

You can find old threads here with burning advice as well as old manuals for that stove...the manuals are in the wiki.

Here is one old conversation about burning that stove. You can search for more
https://www.hearth.com/econtent/index.php/forums/viewthread/14877/
 
You sound like you are set to build an exterior masonry chimney with a square terra cotta flue liner.

Bad idea in my opinion.

I have an exterior brick chimney with the same terra cotta flue and it is now lined with a 6 inch stainless liner and insulated with poured in insulation around it.

Do your homework on your chimney and you'll find the exterior masonry chimney of the past is NOT the way to go.

Best thing to do is listen to the veterans here, they know what they are talking about.
 
Stainless for sure! Send the flue tiles back....
 
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