Wall thimble against ribbed metal siding?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Barnguy

New Member
Dec 18, 2020
4
CNY
Hi all, new here. I've been scouring the internet, Youtube, and called several manufacturers to no avail. I'm putting a pellet stove (TSC90 PelPro) in my new construction pole barn. I cannot for the life of me find out what the appropriate solution is for abutting the external section of the wall thimble (Duravent pellet stove kit from TSC) to the ribbed exterior siding. Traditional boxed rib with the larger ribs being 9" on center. External fascia of Thimble is 9" wide. To get it to sit flush you'd have to cut through at least one large rib. If I cut a 3" circle to accommodate the pipe, the face won't sit flush. If I cut a 9 inch square, that'll leave the rib open won't it? Would I do a square with Flashing and seal all around with high temp silicone? Going in circles here. Appreciate any and all input. Thanks! Happy Holidays!
 
Just like you trim a window, and water runs down hill, and if me, I would cut a separate piece of flat metal square bigger than thimble and a hole in center that fits the pipe and seal it over the thimble, but under the upper siding, and "Z"ed (flanged) 3/4" deep so the lower edge is over the lower siding rib. Or you could cut this piece so the lower edge is even with the lower siding cut, and use a piece of "Z" trim that starts under the piece covering the thimble, but over top of the lower siding. Seal the sides to siding with clear or colored RTV as it ain't gonna get but so hot. Water runs down hill.

Picture is an attempt to draw my idea, section view and looking straight into pipe view. Hope it helps.

FLASH.jpg

Is there a significant overhang above?
 
Last edited:
  • Like
Reactions: johneh
Thank You!
I think I follow But the ribs run vertically.
I spoke to an installer who said it was ok to alter the face plate of the thimble such that it fits between the ribs. Then just seal it in.

Does this sound accurate? Plausible? Insane?

Thanks
 
Thank You!
I think I follow But the ribs run vertically.
I spoke to an installer who said it was ok to alter the face plate of the thimble such that it fits between the ribs. Then just seal it in.

Does this sound accurate? Plausible? Insane?

Thanks
I drew the ribs vertically. They are just about 3/4" high and have angled sides and rounded to, total near 1-1/2" wide at the base, you said the pipe was going to exit in a rib's line.
Water coming off a rib from above needs to fall outside of the thimble's face, not behind it.
Water off the thimble's face needs to run onto outside of any ribs & siding below.

Sounds like he wants to cut slits (narrow notch) at the base of the rib and slide the face plate into it, but that doesn't seal the top of that cut rib?
 
Ah! Ok, making sense. I got The response via email without the diagram. Thank you so much for such a detailed explanation!
 
  • Like
Reactions: tbear853
We just did one. cut the hole the correct size for the thimble to go thru the wall. slide thimble in and make sur it works. Square up the outside piece and mark the rib top and bottom. pull thimble back out make a slice in the rib. (We used a Rotozip with a diamond blade). Slide thimble back in and it will set flush with the wall and secure it and seal with silicone.
 
  • Like
Reactions: tbear853
We just did one. cut the hole the correct size for the thimble to go thru the wall. slide thimble in and make sur it works. Square up the outside piece and mark the rib top and bottom. pull thimble back out make a slice in the rib. (We used a Rotozip with a diamond blade). Slide thimble back in and it will set flush with the wall and secure it and seal with silicone.
This is how i did mine i notched the thimble for the ribs and used a good quality sealant to seal it to the house. Still leak free after 4 years...
 
  • Like
Reactions: Ssyko and tbear853
Great advice! Thanks! What sealant do you guys recommend?
Metal to metal outside like siding, your favorite color or even clear RTV or Polyurethane sealant, if stove pipe I like was orange, now it's red Permatex high temp RTV from like Advance Auto.
 
Great advice! Thanks! What sealant do you guys recommend?
We use the clear silicone around the thimble and pipe. It is a higher heat rated type.
 
  • Like
Reactions: tbear853