DIY loose fill insulation?
In the course of remodeling a third-floor unit, I opened the floor near the chimney- there’s a large chase that continues down to the first floor containing a couple of 4″ ducts, not much else. Air pours up out of that chase, so I’d like to insulate as much of it as possible, for energy and sound. Can I just buy some loose-fill insulation (cellulose? fiberglass?) and dump it down there? I guess I’d have to improvise some sort of funnel, as my opening is a slot about 8″ wide.
Insulation should generally be held away from the chimney, with the distance depending on the type of chimney. Better to install metal draft stops at the top and, if possible, at each floor down the shaft.
If these are just ventillation ducts, though, and any insulation wouldn't contact the chimney, then it's not as serious a problem, though I'm betting that code still would like draft stops in there, in addition to the insulation.
If you do put insulation in there it might be worthwhile to rent a blower. Would reduce the chance of voids.
That should have firestop spacers at each floor level and NO insulation in contaact with the chimney. I have attended fires resulting from that sort of stuffing
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I think what you've got here is a building envelope issue. Usually, around plumbing stacks and the such, we use a 2 part polyurethane foam. The chimney issue is a tricky one! Roxul insulation will not burn, but allows air movement. Maybe a combination of foam up to a steel/aluminum heat allowance "baffle?" which in case could be caulked with a heat resistant gasket caulking??? Be nice to keep a good 4 inches away from the chimney. Or as much as the ducting will allow. The ducts are probably right up against the chimney. Could you caulk a piece of drywall over roxul? (mineral batt?) The name of the game is stopping air movement VS insulation. Furnace filters are made of fiberglass, and therefore all batts allow air movement!