Class A Install: which installer is "right?"

[Charles Bourque]

Talked to two guys who install class A chimneys. One guy says, "the ceiling support box has to extend 18" below the ceiling." The other guy says, "nah, since you're only going through 1' of attic, just use a
24" ceiling support, put it 3" below ceiling, let the top of it out through roof, screw it in to framing, then cut the excess above roof in several places and nail down the flaps." Second guy says that eliminates need for attic insulation shield.

Who's righter? Second guy makes me nervous, but if he's right, I like his approach.

 

[webby3650]

The second guy is right. Most manufacturers require the box to extend only a few inches into the room. The amount changes only changes if it's a cathedral ceiling, the steeper the ceiling, the farther the box needs to extend into the room.

 

[Holiday]

My install manual says 3" below the ceiling.

 

[Delta-T]

i bet there are some differences between manufacturers...I'd reference the particular manufacturers literature.

 

[webby3650]

i bet there are some differences between manufacturers...I'd reference the particular manufacturers literature.

There is a little difference, but it's never 18"! This shows a lack of experience on the part of the potential installer. He think the stovepipe needs to be 18" from the ceiling measured vertically. Thats incorrect.

 

[webby3650]

.I'd reference the particular manufacturers literature.

Above all, this is the most important.