Exhaust for 2 rooms?

I am trying to figure out how to exhaust two rooms (roughly 10'x10'x9') as to not cause any problems and limit customization. Getting the vent into the attic is the easiest part, getting it out is a little bit more of a challenge since I have a tile roof. If it was a shingle roof I would think about putting in a new vent, tile, fuck that.

I do have vents on top of the roof that are louvered vents, along with copious soffit vents low (which I do not want to use do to the hot humid air coming back in.

On the roof


In the attic


I do have a 10 or 12" chimney metal duct easily accessible but I am not sure on the customization of that.

My homes construction is from the mid 2000s and is two stories. I will never have a fire in the fire place because I am too lazy, and its not cold enough (barely will get below freezing once a winter). Is it hard to modify a chimney tube and then unmodify it, easily and cost effectively? Or would I be better off exhausting out of the louvered vents on the roof (see pic, 24" half circle, they stick up from the tile roof)? Maybe creating a metal plate with then combing the two 6" exhausts into an 8" before it gets expelled, then caulk it in air tight to the metalbox (the roof felt paper is inbetween the plywood and the metal box.

Bonus if you have dealt with a 36" whole house fan in the immediate vicinity that pushes 10k CFM.

Leave the louvered vents alone, they serve a purpose.

Ideally you would add a dedicated roof vent thats not designed where air flows back in to the attic (except your duct and that can have an electric baffle on it).

A roof vent is easier to cover up later (compared to going through an exterior wall) since you can replace the roofing tiles/shingles after patching the hole.

Avoid combining exhausts whenever possible.

The metal chimney may be an option but would be more complicated if its a twin skin. But you should be able to get an adapter to match what you have. Possibly disconnect it , tap in and when you sell the house pay someone to repair it. Since you don't want a bodged fire flue killing the people that buy the house.

It will cost you at some point but it gets your grow vented properly and not doing that could cost you a lot more when you need a new roof in 10 years due to mould , rot ect.

I do have one more option, and that is a dryer vent that doesn't look more than 6" in diameter, possibly 8". I do have some smaller Black PVC going up into the roof too, but that is like 2" in diameter. Any ideas?

Any ideas on cost of putting in a roof vent on a tile roof? I am in the Sacramento area.

Jesusgrowsmygrass said:

Any ideas on cost of putting in a roof vent on a tile roof? I am in the Sacramento area.

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Go to home depot early in the AM, buy the materials and pickup some mexican roofers. Couple hours and a couple hundred bucks and done.

That does sound tempting but my roof is tile and two stories up, I don't like to be up there nor do I want the responsibility of one of those guys falling off and more likely breaking tiles. If I had asphalt shingles, no problems, but with tiles are expensive to repair along with possible burial cost of day labor(s). If someone is to actually move tiles and make holes they would have to be licensed and insured.

I keep coming back to the chimney idea, it's about a ten foot run to where the 6" vents for each room vent into the attic. Plus my chimney does not conform to the clearly posted notice of keeping combustibles at least 2 inches away. It looks like if I take out one section of the chimney right about the floor, it might be simple. The thinking is I can build a brace to keep the chimney up on the rafter that is too close to the chimney, see pic (shouldn't be too heavy right?).

Is this something I should explore more or a bad idea?

Here are some pics at the floor of the attic where the chimney comes in


Where there is not currently 2" of clearance to combustibles



Looking up in chimney structure

From a construction perspective adapting a section of the chimney duct to serve as your exhaust should be fairly simple. But if you ever need to get it back to where is was as a fireplace chimney it might not be that easy. The way the duct is stacked and held in place with flashing in may very well be layered into the roof.

My experience with roof construction is to avoid messing with that tile if at all possible, especially if you live in an area with heavy rainfall. The way roofs are layer during construction serves well for shedding water but makes it hard to make a hole in any existing roof and then get it to seal properly. Not saying it can't be done just takes extra effort.

Jesusgrowsmygrass said:

That does sound tempting but my roof is tile and two stories up, I don't like to be up there nor do I want the responsibility of one of those guys falling off and more likely breaking tiles. If I had asphalt shingles, no problems, but with tiles are expensive to repair along with possible burial cost of day labor(s). If someone is to actually move tiles and make holes they would have to be licensed and insured.

I keep coming back to the chimney idea, it's about a ten foot run to where the 6" vents for each room vent into the attic. Plus my chimney does not conform to the clearly posted notice of keeping combustibles at least 2 inches away. It looks like if I take out one section of the chimney right about the floor, it might be simple. The thinking is I can build a brace to keep the chimney up on the rafter that is too close to the chimney, see pic (shouldn't be too heavy right?).

Is this something I should explore more or a bad idea?

Here are some pics at the floor of the attic where the chimney comes in
View attachment 4438560View attachment 4438561

Where there is not currently 2" of clearance to combustibles
View attachment 4438563


Looking up in chimney structure

View attachment 4438564View attachment 4438566View attachment 4438569View attachment 4438567

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you will need some slack in that pipe to get it apart,witch means breaking the seal at the top of the fire place or the roof line. there is another pipe inside of what you are showing ya no.

I feel you there about slack in the joints, I was really hoping some one was going to say, "undo that screw there and it will all fall apart."

Wish full thinking.

Now the real thinking... The cost of a replacement stretch of chimney pipe that will be sacrificed to the SawZaw Gods (probably the least advisable and reminds me of a hold my beer idea) vs hiring a pro to come to customize this to my liking vs climbing on the roof, cutting out the original seal to create slack then go up again to reseal. All three of these options will require a contractor to change it back for the "normal people" to ensure it is up to code, since it currently is not (came stock like this).

Jesusgrowsmygrass said:

I feel you there about slack in the joints, I was really hoping some one was going to say, "undo that screw there and it will all fall apart."

Wish full thinking.

Now the real thinking... The cost of a replacement stretch of chimney pipe that will be sacrificed to the SawZaw Gods (probably the least advisable and reminds me of a hold my beer idea) vs hiring a pro to come to customize this to my liking vs climbing on the roof, cutting out the original seal to create slack then go up again to reseal. All three of these options will require a contractor to change it back for the "normal people" to ensure it is up to code, since it currently is not (came stock like this).

Click to expand...

what size is that out side galvi pipe there will be another smaller stainless pipe in side.When that pipe is installed you set fire place an stack up not built to come apart. If you don't plan on moving for a long time an don't use the fireplace I would tap in its perfect.just get a pro to rehook it back up if you move out.

By tapping in, is there an easy way or do I have to break the seal at the top of the chimney?

thumper60 said:

what size is that out side galvi pipe there will be another smaller stainless pipe in side.When that pipe is installed you set fire place an stack up not built to come apart. If you don't plan on moving for a long time an don't use the fireplace I would tap in its perfect.just get a pro to rehook it back up if you move out.

Click to expand...

As for the size I believe it is either 10.5" or 8", I say this because at the floor is this piece, ls312 (looks like with diagram https://www.dwc-k.com/product/fireplaces/sl312-12-chimney-section-detail ) and I would need to climb back up there to figure out the size.

Jesusgrowsmygrass said:

As for the size I believe it is either 10.5" or 8", I say this because at the floor is this piece, ls312 (looks like with diagram https://www.dwc-k.com/product/fireplaces/sl312-12-chimney-section-detail ) and I would need to climb back up there to figure out the size.

Click to expand...

ok its double wall not pipe in a pipe.its pretty easy to break the seal on the roof just remove the storm collar an cut the seal.