Is 8" square tile flue best compromise for masonry chimney?

[MI Feller]

Ready to have interior masonry chimney built along with new construction. Talking to builder next week. Problem is I currently have a great little 30 year old stove which has a 6 inch vent but is mated to a 8 inch metal chimney and works great. Not sure how to go with the new masonry chimney. 8 inch round is rare in these parts of Michigan. 8 inch square is easy to come by and I think it probably the best way to go. On the other hand, I've heard that the newer stoves (should I buy one in a year or so) don't like 8" flues and do better with 6". Doesn't sound right to me. Am thinking 8" square is the best overall compromise. Pleasr share your opinions. Sorry this is likely something you've batted around before but am not a regular. Many thanks for your ideas.

 

[cmonSTART]

If your end goal is to install a new stove I would go with the six inch round. Also consider a masonry chimney with a stainless rigid liner if possible - doesn't have to be clay. Stainless will be much less likely to crack with age.

 

[MI Feller]

Sounds like you agree the newer beasts prefer 6 inch. I have to think the old one would do OK with round six. Will look into the stainless liner. Didn't know about it. Yes, have heard the tiles tend to crack under extreme heat. I watch the stack temp and don't let it remain above 500 degrees for long. Being interior creostote is less of a problem. The masonary will be 2-3 feet taller than the metal due to the construction. Don't know it that works in favor of a narrower flue or not.

 

[Battenkiller]

8" nominal size clay flue tile is about 7" inside diameter. That's 49 sq.in. cross-sectional area vs. about 50 sq.in. for 8" round pipe. I used to run a stove designed for a 5" flue into my 8" masonry chimney, and it was not a match made in heaven. Personally, I think my old stove would have performed better if I had dropped a SS liner down it. As it was, I had to use a flue pipe damper to keep the heat in the stove where it belonged.

You might look into a poured cement liner of a type called "cast-in-place" liner. They are supposed to last a lot longer than just about any liner (>50 years), are made of insulating lightweight refractory cement (so they will be hotter inside the flue and burn cleaner than a clay-tile liner), they are impervious to the corrosive by-products of wood burning, and they are round rather than square in cross-section. I've been told by several experts that smoke goes up a round flue better than it does up a square flue.

 

[MI Feller]

Interesting. My stove is a Tiny Moe (All Nighter Stove Works) and probably an antique nowadays. The guy who sold it recommended the 8 inch chimney and can't complain about performance. But was it really necessary??? Yep. Have been told round is best and hard to argue with the logic. Maybe the best thing would be to go with six inch (round) and if doesn't work... well...I'm due for a replacement stove anyway. In terms of longevity, I'm 63 and may not keep the house more than 10 years. Even a tile liner with decent care should last that long.

 

[MI Feller]

BTW: What type stoves still reqire 8 inch? Seems most folks are leaning to 6 inch today?

 

[begreen]

Some of the biggest stoves like the BK King, VC Defiant and the Hearthstone Equinox still require an 8" flue.