Sealing / Caulking Vent Piping Question (and first post to the forum)

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MarkF48

MarkF48

Feeling the Heat
Nov 14, 2011
270
Central MA
Did my install of a new Harman XXV and have a few questions about sealing/caulking the vent piping.

Fired up the stove with nothing caulked as of yet. Noticed some obvious smoke leaks around some of the joints and odor of smoke as well. I plan on using the high temp silicone for most of the joints near the stove and possibly high temp tape further from the stove. I am considering on just the main vent pipe joints using O-Ring clamps with some kind of gasket material, possibly strips of silicone rubber that can take the heat or maybe aluminum foil folded to several layers that could compress into the joint. I did try the aluminum foil idea on one of the joints and appearance wise it doesn't look too bad, the clamp screw is behind the pipe out of sight, but not sure how effective it may be as a seal. This would allow for fairly easy disassembly to clean the the piping if needed. Any thoughts on the O-Ring clamp idea on the main joints?

Open to suggestions on best way to apply silicone sealer. Is it generally adequate to apply externally to the joints or is there any reason to glop up the fitting internally?

A lot of the pics on this forum show use of a red high temp silicone for joints. Local store has some high temp in black. Any difference in using red versus black? I'm planning on painting the piping black, so thinking black silicone may be easier to blend/hide.
 
I used the red silicone available at most stove shops and hardware stores. Not sure about the black stuff. If it says it is made for high temp applications including stove pipes it should be okay. I gooped the pipes inside and out for a good airtight seal.

Mine is a Harman P35i fireplace insert. Below is a pic of my vent pipe connection to the insert frame.

They also make a foil tape specifically for stove pipe joints (also available at most stove shops and hardware stores) which would make disassembly/reassembly easier.

What type of pipe are you using? Maybe you could use pipe like this that has its own built in gasket and does not require RTV or tape. Be sure to follow the manufacturers directions in the manual for vent piping type and local fire/building codes.
 

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MarkF48 said:
Did my install of a new Harman XXV and have a few questions about sealing/caulking the vent piping.

Fired up the stove with nothing caulked as of yet. Noticed some obvious smoke leaks around some of the joints and odor of smoke as well. I plan on using the high temp silicone for most of the joints near the stove and possibly high temp tape further from the stove. I am considering on just the main vent pipe joints using O-Ring clamps with some kind of gasket material, possibly strips of silicone rubber that can take the heat or maybe aluminum foil folded to several layers that could compress into the joint. I did try the aluminum foil idea on one of the joints and appearance wise it doesn't look too bad, the clamp screw is behind the pipe out of sight, but not sure how effective it may be as a seal. This would allow for fairly easy disassembly to clean the the piping if needed. Any thoughts on the O-Ring clamp idea on the main joints?

Open to suggestions on best way to apply silicone sealer. Is it generally adequate to apply externally to the joints or is there any reason to glop up the fitting internally?

A lot of the pics on this forum show use of a red high temp silicone for joints. Local store has some high temp in black. Any difference in using red versus black? I'm planning on painting the piping black, so thinking black silicone may be easier to blend/hide.
Click to expand...

Welcome aboard! XXV is a great stove, you'll enjoy it.

Try to find Permatex red, I believe it's rated at 650 where the black is 500. Both are probably sufficient, but a little extra heat resistance is always good.

If you are using double wall pipe (typical), then aluminum tape on the joints will give you a good clean look without too much trial and error. You can paint the tape as well.

Silicone inside the joints might make the pipe unservicable, your call.

Lots of silicone on the appliance adapter and fittings connecting the stove to the pipe. Since you can't see it, a healthy amount will prevent any little annoying leaks. Even if it makes some of these joints unservicable, you don't want to skimp here. I also find that it's easier to clean when there's excess to grab on to while you try to remove it. For servicing, I plan to remove the 3 bolts holding the cast flange to the stove. This way the piping can stay in tact.

Finally, once you're done, inspect the piping at night, all lights off, with a flashlight to insure you don't see any traces of smoke. Best to do at stove start up as this is the smokiest time. If you over-prime the pot with pellets this too will generate LOTS of smoke (don't get too carried away).

If all goes well, zero smoke and zero smoke smell.
 
Make sure the Black is not Stove cement. Other than that, they make Red, Black, and Clear RTV High temp silicone. Anything rated for 500* and over is sufficient. Definitely seal the stove appliance adapter well. As for the joints, sealing internally may cause you problems down the road if you need to get them apart (as stated above). Seal the outside of the joint, or use the High temp 3M tape (stated above alsp).

Welcome to the Forum. Do you have your pellet stash yet?
 
Ended up using the red silicone as it did have a higher heat rating than the black. Also bought the 3M high heat tape for the upper joints that are not near the stove. It's all coming together slowly and looking good.

When I purchased the stove the dealer "included" 2 tons of pellets and that's now stashed in the barn.
 
I used clear RTV High temperature silicone in a thin bead inside the pipe joint where the pipe sections twist lock together. None squeezed out and the installation looks real clean. The stove adapter is just a Whitfield slip joint with a sheet metal screw in it to lock it in place. I gooped the RTV all around the stove section and pushed the adapter over it. The RTV didn't squeeze out of that joint either, but it sealed well too.

It has been my experience, in other applications, that RTV silicone has pretty poor adhesive qualities and joints with silicone sealant in them will come apart easily, if I ever need to disassemble the parts.

Dave
 
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