chase framing

[Charles2]

The metal chimney I'm installing will be close enough to a closet door that I don't want to sacrifice any space for the chase framing. What's the minimum framing I can get away with? Could I use 2 x 3 or even 2 x 2? Could I turn 2 x 4 on the flat and have 2 x 2 plates?

 

[webby3650]

The metal chimney I'm installing will be close enough to a closet door that I don't want to sacrifice any space for the chase framing. What's the minimum framing I can get away with? Could I use 2 x 3 or even 2 x 2? Could I turn 2 x 4 on the flat and have 2 x 2 plates?

Sure

 

[Charles2]

What's the minimum framing I can get away with? The ceiling is 8', BTW.

 

[Squirrel]

2" steel studs?

 

[begreen]

You must have at least 2" from any and all combustibles. That's what's important. The chase can be framed with 2x3's flat face out on a 2x2 sill, or it could be framed with steel as long as any combustible covering like drywall is at least 2" away from the pipe.

 

[bholler]

I have done them out of 3/4 plywood with no framing just keep you 2" clearance and you are fine

 

[Oldman47]

Why not use straight 2x2s internal to a 1/2 inch OSB box. Your requirement is to have a minimum 2 inch space from the flue to the wood but a 2x2 in the corner of a 12 inch opening is 12 3/4 inches from inside corner to inside corner diagonally on those 2x2s. (Yes I tried it using my CAD system and got to measure the resulting distances.) That means your distance to that 2x2 combustible corner is already 3/8 inch more than the distance from the pipe to the OSB would be in a 12x12 box. You would probably pre-build the box and then install it in place to keep the dimensions that tight. If you wanted to build in place I would at least build one side with the 2x2s along the edge of a piece of OSB that could be attached to the wall framing. After that you could build the left and right sides, install the pipe and finish it off by installing the last piece of OSB. I would not try it using just drywall because drywall itself is not strong enough to prevent those 2x2s turning into pretzels over time. This does not leave you any option for a square frame top and bottom unless you just use some 1x2s on the outside to restrain movement of the basic box shape. That should be no big deal at the top of a closet but would be a minor 3/4 inch tall obstacle at the floor.
Note, you will not get all of the OSB out of one sheet since OSB will need to be 12 inches in one direction and 13 inches in the other.

 

[bholler]

To minimize intrusion why not build a plywood or OSB box with external 2x3 framing. Start by building what will be 2 walls of OSB attached to 2x3s that are laid flat along each edge. When you are ready to put it in place screw the other 2 sides to those 2x3s so the 2x3s end up on the outside. It allows you to build a chase that is only about 13 inches in one dimension but 18 inches in the other dimension. You get to decide which direction you would rather give up the space.
Another thought is to use straight 2x2s internal to an OSB box. Your requirement is to have a minimum 2 inch space from the flue to the wood but a 2x2 in the corner of a 12 inch opening is 12 3/4 inches from inside corner to inside corner on those 2x2s. That means your distance to that 2x2 combustible corner is already 3/8 Inch more than the distance from the pipe to the OSB.

I have done it with just a 3/4 plywood box with mitered corners and the attached top and bottom with internal corner blocks that still maintain the 2" clearance like you said but there is no need for any other framing on the outside 1/2" would work fine also but it is harder to get nice mitered corners with. That gives you a 13.5" box all the way around if it was 4 sided

 

[Oldman47]

Sorry I messed you up bholler. I went back and edited with a "better" idea.
No way do I miter corners during construction. I am building my own home and so far have zero mitered corners. That will change when I start to install trim but not for something like a chase. I would just cover the chase with 1/4 inch drywall and use a couple of corner beads before mudding it. That does mean I would end up with basically your same 13.5 inch intrusion though.

 

[bholler]

Sorry I messed you up bholler. I went back and edited with a "better" idea.
No way do I miter corners during construction. I am building my own home and so far have zero mitered corners. That will change when I start to install trim but not for something like a chase. I would just cover the chase with 1/4 inch drywall and use a couple of corner beads before mudding it. That does mean I would end up with basically your same 13.5 inch intrusion though.

That would work well I was a cabinet maker in my previous profession so Mitering corners like that is just second nature I find it way easier and faster than mudding and taping. But that is my skill set for some one better with drywall than me your idea would probably be much better