Shop Furnace Installation ?'s

[Jason Hanko]

Hi everyone,
Sorry for the novel but here goes:
We've recently moved, and I now have a 24' x 24' two car detached workshop! err...garage. Anyways, I live in Wisconsin and the winters, well yeah, you know.
I was originally going to go with a ~5000 watt electric heater, but I dont have 220v service out there (yet), and also I stumbled upon a 5 year old 50,000 btu furnace for $50. Its one of those ones designed for an apartment or other small space so it can be recessed into a wall between studs. Ive already converted it to LP since I dont want to bother with running a gas line out to the garage.
Now I just have a few questions for the collective knowledge here on SMC:

First off, I need to run the Bvent up to the roof, but now that Ive recessed it I find that Im running into the top plate with the venting (D'Oh - see pics below). I could just un-recess the unit to provide the clearance but Id rather not move it now that Ive got the hole cut in the wall. Otherwise Id need to cut a slot out of the top plate for the exhaust vent to pass through. The cutout would probably have to be about 6'' wide (OD of the Bvent) through ~3/4 the width of the plate. Im guessing that would be a bad idea as far as the structural integrity of the building?? Could I cut through the top plate to get my vent through if I braced the top plate on either side of the cutout with trimmer studs? (picture 2) Or would I still need to have more bracing against the "pulling force" on the top plate from the weight of the roof? (Picture 5) Maybe some sort of "bridge" around the front of the vent to tie the plate back together??
Anyone have any other ideas? I dont think theres enough room to put a 45° bend around the plate, and un-recessing the unit would be my last resort...

Secondly - The unit draws air in at the top where the fan is, then blows the heated air out of the bottom vent in the unit. There is no filter bracket or anything on the furnace, so I'll probably need to build some sort of box at the top of the unit around the intake. Ive read that blowing up your garage from sawdust-laden air is mostly an urban myth, but Im guessing I dont want all that sawdust going thru it anyways...
Ideally Id like to build a box that would hold multiple filters of 30, 10, and then 5 micron size - this would not only protect the furnace but also act kind of like shop air filter at the same time. Question is - would this be too much for the fan in a furnace like this? I dont want to smother the unit or burn out the fan motor as it tries to pull air thru the filters...I dunno, this isnt my area of expertise. Any thoughts?
Thanks in advance for your time and suggestions!

[Rollie Meyers]

1st you need to use BW oval vent then there is a fire stop that is needed at the top plate the plates are cut out and the firestop is used. for a view of the parts you need see this link. http://www.duravent.com/pdf/catalogs/gasvent.pdf Vent pipe manuf. are prob regional but you will get the idea.

[Jason Hanko]

Thanks Rollie, I didnt know about the firestop.
I guess my question is do I need to use the oval as opposed to the round venting? I already have the length of 4'' round pipe that I need, and Im not really running the pipe up the inside of a wall, which Im guessing is what the oval was built to do. Would the square firestop made for the roundpipe work just as well?

[Matt Ocel]

Jason -
When notching a top plate.

To be code compliant with the International Residential Code -

I.R.C. R602.6(1)
Top plate framing to accomodate piping

-16 guage x 1 1/2" wide metal tie across and to each side of the notch with 6 - 16D nails each side.

These straps are usually 16" long and you can get them in the joist hanger section at the local Big Orange Retail Giant.

[Rollie Meyers]

I only know about a oval firestop after the F.S. you can use your adapter to change to a round pipe and in response to another post, the firestop is heavy gauge galvy steel & is intended to tie the plates together.

Be sure to maintain the clearances to combustables per manufacturers instructions, I think it's 1" w/ type B gas vent pipe but check to be sure.

[Bill ThompsonNM]

I used to have one of these in my garage workshop in Massachusetts.. I used some magnets and some aluminum channel to put together a filter holder in front of the intake. You're right you don't want sawdust all over the heat exchanger.. it chars and smells and needs frequent cleaning. I think the relatively small fans these units come with would be taxed by a whole bunch of filters. I just used a high end 3M 16x 20 filter and changed it once a month. It did clear the air in the shop a lot and more importantly I only had to clean the furnace once a year.