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Community and Q&A

Unlined masonry chimney – replace with metal?

TimL_in_ND | Posted in Energy Efficiency and Durability on

This is part of the 1910 attic insulation project describe in:

As with any renovation, expect the unexpected.

There is a brick chimney that runs through the center of this house, rectangular with 2 chambers:
Main column: 20 x 28
Just below the roof: 28 ½ x 37 ½
Above the roof: 31 x 38

The larger chamber is square and was originally used as the flue for an oil burning water heater and forced air furnace. Have now switched to electric water heater and high efficiency propane forced air. the flue does have a small homemade wood burning stove piped into it in the basement. This flue is UNLINED best I can tell. It is very thick however. No fire danger in my opinion. We used this chimney a lot growing up and never had an issue.

The smaller chamber is a bit of a puzzle; not sure its original use. Currently, it is used as a heating duct to get warm air from the furnace in the basement to the 3rd floor. Running air through a brick duct; can’t be a good thing. It is blocked from the outside above the heating duct by ?? I’ve removed the loose debris but now poking up hits something more solid…

There is an active bee hive in the smaller chamber. Been there for several years and begins 2′ below the top of the chimney where the large and smaller chambers are split. The size of the hive can only be approximated; best guess is 5 to 7 feet. I’ve tried killing off the bees by suffocating with 20 lb cylinders of CO2 gas (capping chimney in plastic, blocking larger flue). Killed some bees but plenty still there. I’ve talked with a few bee keepers on how to kill and still harvest the honey. Soapy water or a pesticide is next option. Could break open the hive in the dead of winter and freeze them. Either way, we will need to clean all traces of honey from the cavity in order to prevent other bees and insects from being attracted to the leftover honey.

Another separate issue is that the chimney’s passage through the floor/ceiling areas show the chimney has risen compared to the rest of the house and this is apparent on all 3 floors. Not sure why, doesn’t matter since it’s not likely to reverse itself. Basement floor seems to have risen a bit, been a wet decade up here and water has been in the basement frequently over the last few years (renters not keeping close eye on the basement). Because of the plaster and lathe construction, the plaster of the walls, ceiling and chimney locked the chimney to the walls and floor and that is why the floor in the 3rd floor has been lifted, 1.5 to 2 inches when the chimney rose. Would have been better to have the chimney ‘floating’ but that’s not how constructed. The vertical plaster joint between chimney and wall at the 1st floor shows a large crack as well.

Options we are considering:
1) Leave chimney, clean out the bees best we can and then seal the chamber so no insects can enter. All the debris and hive would be pushed down to the heating vent hole in the 3rd floor. May remove some more bricks temporarily to make catching the debris and (water used for cleaning) and direct out of the house. Then fill the chamber with? and re-seal at the top and bottom of where the bees were.

2) Take down the entire chimney. LOT of work plus would mess up the walls in a bedroom and bath on 2nd floor as well as the dining room on the 1st floor. would then run a proper metal forced air duct to the 3rd floor and a new metal chimney if a wood burner was kept in the basement.

3) Remove just the top of the chimney, and transition to a metal flue in the conditioned space of the 3rd floor, maybe a few feet above the floor.

For this option, isn’t the metal going to conduct the cold into the conditioned space faster than the brick – won’t there be frost forming on the metal when its 20 below and the wind is howling? Is there a thermal break possible with a metal flue? I’ve read some articles but not finding the answers.

Thanks for reading another long post. Any other options we should consider?


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  1. GBA Editor
    Martin Holladay | | #1

    The best solution, as I'm sure you know, is to completely remove the chimney.

    The standard solution for homeowners who can't afford to remove a brick chimney is to line the existing unlined flue with a stainless-steel liner. Contact a chimney sweep -- they do this kind of work all the time.

    I'm no expert on bees, but you have to figure out how to kill them or move them.

    If you want to continue to use one of the flues as a duct, you'll need to line that flue with stainless-steel as well (and figure out how to connect the ends of the stainless-steel liner to standard ductwork, top and bottom).

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