What to do with an unused, shared, chimney? – GreenBuildingAdvisor

Hi!

I’m Leib, and I’ve been trying to figure out what to do with a chimney that I can’t remove.

The house is in New York City (zone 4), and is built of mass masonry.

There is one party wall, in the center of which is a 3 foot square chimney, from the basement through two floors to the flat roof, shared between the two houses (each detached on the non-chimney side).

In planning insulation and energy upgrades, we’re looking at the outer walls (side, back) getting exterior insulation, and the front wall getting interior closed cell.

The shared wall will get interior mineral wool. 

But it’s not clear to me what to do with the chimney. Unlike the rest of that wall, it’s not up against conditioned space in the other house. Its current function (for both houses) is to house flues for the combustion heating in the basement. On our side we’re planning on switching to heat pump hot water, but the neighbor is still burning gas and needs to vent.

What’s the best strategy for insulating around the chimney? Main concerns are maintaining the tight envelope we’re aiming for on the rest of the house, and not introducing any mold issues.

Also, is the (soon to be) empty space in the chimney appropriate for running services through? Thinking about conduit for roof-top solar; roof-mounted split pump service lines; ERV input and/or output.

Thanks for any advice – I wasn’t able to find anything about specifically shared chimneys.