House is c 1920, semi-rural at that time. I think it originally had a coal furnace - there's what looks like the renment of a coal bin. Currently gas forced-air furnace, c 1969.

When I replaced the water heater's vent pipe into the chimney, I found the chimney - up to about 6' from the floor - seems to be full of what I'd call compacted soot. When dug out, it wants to break into a fine, and messy, powder. The chimney's upper section seems clean; at least, 25 years ago, we rebuilt it from the attic floor, and the bricks weren't coated.

Is this a common thing? If it was to be cleared, how would that be done?

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    If it was used as the chimney for a coal-fired furnace for ~40 years, it's not too surprising that there is soot & unburnt coal dust in the bottom of the chimney. Are you currently using it as a brick chimney, or are both the HWH and the furnace going up their own steel vent pipes place inside the chimney? If they're in separate ducts, there's zero reason to even think about the gunk in the bottom unless you're replacing duct work, then it's just avoid disturbing it.
    – FreeMan
    Jan 20, 2023 at 13:49
  • Likely it is coal ash rather than carbon.. My parents apartment had a coal furnace I filled many times ; it made a lot of ash . Jan 20, 2023 at 16:44

1 Answer 1


Probably want a can type(known as shop-vacs) vacuum.

Chimneys should be cleaned at least once a year, gas can probably be clean less, but at minimum checked.

Mask, eye protection since that stuff gets everywhere.

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    There are even ones sold as 'ash vacuums' which are designed to be fit to the purpose, with a metal canister in case there are warm spots in the ash, and a finer filter to avoid spreading the ultra-fine dust everywhere.
    – KMJ
    Jan 20, 2023 at 16:01

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