I have a 16 inch block chimney with 6" liner to accommodate a 120k btu boiler and a 35k btu HWH. I need to go up 6 or 7 block for the new second floor addition. Can I remove the block and put in double wall b vent?
Clearances needed? Thanks.
I believe we've discussed this before, but...
Unless your house is something like an unisulated 4000' house located on windswept ridge in the Poconos there's almost no way your boiler isn't ridiculously oversized for the space heating load. If there's even a remote chance you'll be replacing the boiler in any reasonable time frame installing a right-sized modulating-condensing boiler and letting it heat the hot water too would allow you to take the whole chimney out and just side vent the boiler with plastic venting.
To figure out the oversizing factor for the boiler,
run a fuel-use heat load calculation, and compare it to the DOE output (not the IBR net) of the boiler at the 99% outside design temperature. When seriously considering a modulating condensing boiler,
run the math on the radiation at condensing temperatures against the minimum-fire output of the boiler.
But to just answer the question, sure- as long as there is a 1" clearance to combustibles (it can be 0" to masonry) it's fine to do it all with B-vent. A metal firestop at every floor/ceiling penetration needs to be included in the flue chase.
