Chimney advice for re-doing 18" diameter metal chimney needed!

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Mt Ski Bum

Minister of Fire
Feb 23, 2011
Dillon, Mt
Hi all,

At work, I have been put in charge of a big fireplace remodel project- we are putting an Avalon Olympic insert in the fireplace of our 100 year old lodge. This involves A. pulling the horribly inefficient old metal "insert" that was put in the masonry fireplace ~40 years ago (it barely heats the room at all no matter how large of fire we get roaring in it, and it spills chit tons of smoke on start up), and B. doing something to the 18" diameter uninsulated metal chimney.

I am stuck on what do to for B. The chimney is ancient, and totally uninsulated, and hasn't been cleaned for years (decades? 😬) I have 2 main ideas:

option 1. use a liner. clean the chimney (is there any brush big enough to even clean it?) and then drop a 6" pre-insulated liner down it (since this chimney is so large and uninsulated would it be beneficial to add an external insulation blanket to the liner too, even though the liner is pre-insulated?).

option 2. tear down the entire metal chimney and replace with new 6" Class A chimney (probably from Selkirk's Supervent line). This might be a bit more expensive due to the need for multiple wall braces, roof supports, and possibly a couple elbows if needed.

Any advise or input would be greatly appreciated! 🙂




Minister of Fire
Jan 13, 2015
That old steel chim would be scrap imo. Guessing almost any new insert/stove and venting will out perform the existing setup. Supervent is still at a great price. I just recieved some yesterday that I ordered online and it had not changed price since my last order. PM if you want more info. on where I ordered. Some retailers have gone berserk on pricing the same product. Crazy.

Keep in mind any new stove will require very dry well seasoned fuel to perform. Anything less will have you/employees scratching your head in frustration.

Bad LP

Minister of Fire
Nov 28, 2014
Northern Maine
Scrap the 18.


Minister of Fire
Jan 19, 2019
SE North Carolina
Make it right and safe. Here is your chance. Class A all the way. Not sure how you would even clean that. Rotary from the bottom I guess. It’s not looking stable enough to be shoving a liner down so it would have to go up through the fireplace then how are you going to put the top plate and cap on? Room for a man lift? If you are going to that amount of time can and expense just spend the extra to get it done correctly.