200 year old chimneys and forced hot air furnace

[whosthat]

hey all I've recently bought a new to me house (1830's) that has 3 very tall chimneys, the house is a cape.

anyways 2 of the chimneys are unused and the one that is used is a code violation as it has the furnace and woodstove hooked up to it and its a single flue. I would like to run a stainless liner down one of the other chimneys and hook the furnace up to it but the one I have in mind is a little funky, all it has in the basement is a cleanout door and no room to install a thimble is it acceptable to come through the cleanout door with the liner and then add a "T" for a cleanout? I also was wondering if I needed an insulated liner or not, the chimney is in respectable shape and I would think the masonry and tile inside would insulate it enough that it shouldn't be an issue, not to mention this is a furnace not a woodstove so creosote shouldn't be a anywhere near as much of an issue. on the other hand Maine winters can get pretty cold but any input would be appreciated thanks.

 

[brenndatomu]

Howdy Who. Sounds like you just need to cut a hole into the chimney at the height you need. Leave the cleanout to be used as a cleanout. That can be done buy putting a section of liner on the bottom of the liner tee (the tee will now be at the height where you just cut your new flue hole through) instead of a cap when you put it in. Put the cap on the bottom of the liner...it can be removed for cleaning as needed through the cleanout door...that's what I did, it works great.
And I would definitely put a liner in, insulated if there is any way it will fit. Insulation is the only way most old chimneys with liners will actually pass code believe it or not.
As far as creosote, some wood furnaces are better at making it then wood stoves are, so no advantage there!

 

[whosthat]

Howdy Who. Sounds like you just need to cut a hole into the chimney at the height you need. Leave the cleanout to be used as a cleanout. That can be done buy putting a section of liner on the bottom of the liner tee (the tee will now be at the height where you just cut your new flue hole through) instead of a cap when you put it in. Put the cap on the bottom of the liner...it can be removed for cleaning as needed through the cleanout door...that's what I did, it works great.
And I would definitely put a liner in, insulated if there is any way it will fit. Insulation is the only way most old chimneys with liners will actually pass code believe it or not.
As far as creosote, some wood furnaces are better at making it then wood stoves are, so no advantage there!

Well heres the thing with that, theres no room above the cleanout door in the basement to cut in a thimble, and if i did squeze one in it would be way to close to the underside of the floor. i would have to cut out the floor and follow the chimney up and that would be a whole new host of problems. also it is an oil fired furnace sorry forgot to mention that

 

[maple1]

Can you post a pic of the cleanout & chimney bottom area?

 

[brenndatomu]

Well heres the thing with that, theres no room above the cleanout door in the basement to cut in a thimble, and if i did squeze one in it would be way to close to the underside of the floor. i would have to cut out the floor and follow the chimney up and that would be a whole new host of problems. also it is an oil fired furnace sorry forgot to mention that

Ok, so maybe you use the existing cleanout as your breech and then put a new one in down lower...you need a cleanout in the bottom of the chimney IMO. I would think it would be too easy for soot/creosote flakes to block off the bottom of the liner if you didn't have a "drip leg" or cleanout area for some debris to accumulate in. Liners tend to self clean somewhat as they go through heating/cooling cycles and you can actually hear flakes falling inside the liner as you build a new fire and things heat up. That needs to have somewhere to go other than just blocking the flue off.
Maybe our resident chimney guru @bholler can inject some wisdom here...

 

[bholler]

Yeah just use the clean out ass your crock you don't need a clean out for an oil furnace. We still put them in if we can but it is not necessary at all. I woould still use a tee inside the cleanout though it will allow for a little room for stuff to accumulate. As far as needing an insulated liner by code you do not but it will reduce condensation and make the draft more stable making the furnace run a little more efficiently..

 

[brenndatomu]

Oh, this is an oil furnace? I missed that part...