Questions about screws for double wall pipe and T6

[aussieblake]

Ok I have two questions first topic,

I purchased some Metal Fab DW pipe to grow from the stove to the Manufactured chimney's ceiling support box. The instructions say to secure the sections together with screw, but it did not come with screws and the shop I purchased it from does not carry them. So what type of screws work best, what length of screws (I assume the intent is to only penetrate the outerwall of the pipe and not the inner wall). Do you pain the heads to blend in (the Pipe manual says Stove Bright 1990). Should the DW section of stove pipe screw to the stove pipe chimney adaptor, and what about the top of the stove.

Now I just set my T6 in place, and my question is this, I do not plan on using outside combustion air, so do I still need to Knock out the 4" Knock out on the bottom of the stove? My interpretation is "NO" it is not required, but I may be wrong.

I realize there are several questions in the above paragraphs, your experiences and opinions are greatly appreiceated.

aussieblake

 

[Metal]

#6 or #8 size 1/2" long self tapping screws are recommended. They will look better if you paint them before putting them in so you don't have to worry about overspray. You should screw it in both ends but I wouldn't put any screw in the adjustable lengths (if used).

 

[thechimneysweep]

Put screws in all joints, excluding the stove collar. We use tec screws, 8-18 x 1/2". They don't penetrate the inner layer of the double-wall pipe. Ours are pre-finished in black, but if the only screws you can find are unfinished, hit them with Stove Bright 1990 when you're done.

Knock out your knockout. This is a multi-use plenum, but on the Alderlea the knockout hole is the only way for combustion air to enter.

 

[aussieblake]

Thanks for the reply's and please keep them coming.

I will knockout the 4" KO for the air I was concerned it may be the only way for combustion air to enter the stove.

Where do you get the pre painted screws? I was at Lowe's today and they had white and brown. I thought about using the Black screws for metal stud framing, they are #7--7/16" in length. I might try ACE Hardware. Are the self drilling (drill bit end tip) everyone's choice of the self piercing (pointed end tip).

I do not live in a manufactured home, but is outside combustion air something to consider for efficiency?

Again Thanks,

aussieblake

 

[mikeathens]

I bought stainless steel screws at Lowes - a box of like 10 of them, maybe 1/2" or 5/8" and they had black phillips heads on them. I had to pre-drill the holes.

 

[thechimneysweep]

Outside combustion air can be beneficial in some instances. Some folks swear by it, and others think its a bad idea. You can read both sides of the debate online at (broken link removed to http://www.chimneysweeponline.com/hooa.htm)

 

[Highbeam]

I like my outside combustion air. Works great.

My double wall expansion piece was used just as you describe between the top of stove and the ceiling support box. It was installed by a professional and inspected/approved by my county with particular attention to the screws on this slip joint. The ONLY screws used were to secure the overlap in the middle and that was three screws equally spaced around the pipe. No screws to the stove collar and no screws to the ceiling box.

The double wall twist-loks in place to the ceiling box and expands onto the stove so it can't really go anywhere. On the stove end you can imagine that screwing into the stove collar can't be done with 1/2" long screws since that would only pierce the outer shell and not the inner. How can you even screw into the stove collar? I've been trying to find a photo of that for a long time.

 

[Carl]

I like my outside combustion air. Works great.

My double wall expansion piece was used just as you describe between the top of stove and the ceiling support box. It was installed by a professional and inspected/approved by my county with particular attention to the screws on this slip joint. The ONLY screws used were to secure the overlap in the middle and that was three screws equally spaced around the pipe. No screws to the stove collar and no screws to the ceiling box.

The double wall twist-loks in place to the ceiling box and expands onto the stove so it can't really go anywhere. On the stove end you can imagine that screwing into the stove collar can't be done with 1/2" long screws since that would only pierce the outer shell and not the inner. How can you even screw into the stove collar? I've been trying to find a photo of that for a long time.

On the stove I just purchased (Yosemite) and the previous one, jotul 3, both had predrilled holes in the stove collar to secure it to the pipe. I would think this is the hottest joint so it would be the most critical one for expansion and shrinkage which would need fastening. I put no screws into the slip section at the ceiling as it needs to slide as the pipe heat and cools. If your stove installation was inspected then it must be ok.

edit: I used single wall pipe and see you used double wall so this may not work on your pipe. I have never used double wall in the house.

 

[aussieblake]

Knock out your knockout. This is a multi-use plenum, but on the Alderlea the knockout hole is the only way for combustion air to enter.

I am in no way doubting or second guessing this information and definitely plan on doing it. But one would think PE would remove this from the factory to avoid potential problems (DIY'er install, or professional installer forgetting to remove it).

aussieblake

 

[Highbeam]

Yep, double wall is the sticking point here. No brainer with single wall. The outer shell of the double wall shields the predrilled holes in the stove collar and even if you could find those holes, you couldn't tighten the extra long screws for fear of crushing the outer shell. I don't think it gets screwed, nor did the installer or the inspector. Folks on this site and even manufacturers catalogs don't show screws there with double wall.

I see no need to allow for expansion and contraction of the slip pipe. My stove isn't getting taller and my ceiling isn't getting lower. That said, if the top and bottom of the slip piece were secured with screws somewhowthen there should be no need for the screws in the middle.

 

[Carl]

Yep, double wall is the sticking point here. No brainer with single wall. The outer shell of the double wall shields the predrilled holes in the stove collar and even if you could find those holes, you couldn't tighten the extra long screws for fear of crushing the outer shell. I don't think it gets screwed, nor did the installer or the inspector. Folks on this site and even manufacturers catalogs don't show screws there with double wall.

I see no need to allow for expansion and contraction of the slip pipe. My stove isn't getting taller and my ceiling isn't getting lower. That said, if the top and bottom of the slip piece were secured with screws somewhowthen there should be no need for the screws in the middle.

Your ceilings or stove aren't changing height but when anything is heated it does expand and when cooled it does contract. Probably the only time this would happen enough to pop the pipe out is when you have an overheated stove or a chimney fire. Then if there is no room for expansion and no screws it could fly apart. Just the physics of things.

 

[thechimneysweep]

I am in no way doubting or second guessing this information and definitely plan on doing it. But one would think PE would remove this from the factory to avoid potential problems (DIY’er install, or professional installer forgetting to remove it).

aussieblake

PE's air plenums are mass-produced on a big, computer controlled metal stamper. Several of the other models in PE's lineup can get combustion air in more than one way, so the machine is designed to create knockouts which may be removed or left in place depending upon the desired source of combustion air.

In the case of the Alderlea models, the knockout must be removed regardless of the air source. This may seem like a needless hassle, but removing the knockout only takes a second, and it saves the expense of reprogramming the stamper and running separate batches just for plenums to be used on Alderleas.

Regardless of who installs the stove, PE trusts that he or she will follow the instructions in the installation manual that comes with it. Instructions to remove the knockout are on PG 14 of your manual, under COMBUSTION AIR: Item 2, Room Air Supply.

There is also a built-in failsafe of sorts: if you don't remove the knockout, you won't be able to start a fire.

 

[BrotherBart]

There is also a built-in failsafe of sorts: if you don't remove the knockout, you won't be able to start a fire.

Then you get on hearth.com and everybody will tell you that your wood isn't dry enough. :lol:

 

[thechimneysweep]

Same manual, page 15.

 

[begreen]

I am in no way doubting or second guessing this information and definitely plan on doing it. But one would think PE would remove this from the factory to avoid potential problems (DIY’er install, or professional installer forgetting to remove it).

aussieblake

Regardless of who installs the stove, PE trusts that he or she will follow the instructions in the installation manual that comes with it. Instructions to remove the knockout are on PG 14 of your manual, under COMBUSTION AIR: Item 2, Room Air Supply.

Read the manual? That cuts out about 25% of the public right there.

 

[Highbeam]

Thanks Carl, I was wrong about my thoughts and didn't visualize the pipe expanding when hot. I considered it a fixed length.

So all of the folks with telescoping sections... are your slipjoints fixed or free to slip? The need would be the same whether single or double wall pipe.

 

[thechimneysweep]

I've always felt that the slip joint should be left free to slip as the connector pipe expands and contracts, but NFPA calls for three screws per joint, and our local Code Authority interprets that spec literally, requiring screws in the slip.

The result can be seen in my own home installation. I've got about 20' of single-wall connector pipe from the stove to the painted manufactured chimney, which sticks down about 36" below the vaulted ceiling. The chimney trim collar attached to the ceiling touches the chimney on the high end, and when there's no fire in the stove you can see a 1/2" shiny area where the paint has been scraped off the chimney. When we're burning, the shiny area disappears! What this tells me is, the connector pipe grows longer as it heats up, and pushes the chimney upwards about 1/2". The wing suport that carries the weight of the chimney allows this movement without compromising its function, but there's always that little shiny smile to look at in the off-season, where the paint has been scraped off the chimney.

 

[Metal]

The adjustable lengths should not have screws as they are not considered "joints" and are there for expansion. Be sure to have the two parts engage at least 2 inches ( or whatever overlap the manufacturer's installation instructions call out.