Propane Furnace Exhaust Sealant

[Hog3loves]

I need some advice concerning the best way to seal a gap on the outside of our 321 RSTS 5er. After many attempts (by CW) to fix our intermittent propane furnace, there is now a noticeable gap on the top side of the exhaust port where the factory caulking used to be.

I realize that whatever I use must be heat resistant and able to withstand significantly hot temperatures. I found this DAP Heat Resistant Silicone Sealant. Is this okay to use on the 5er, between the outside wall and the exhaust port? I thought I read somewhere on this forum that using a silicone sealant is a no-no.

Thanks in advance.

[NVGun40]

I have never heard using a silicone sealant is a no-no. Perhaps someone else can chime in on that; hopefully showing relevant proof as to why so we are not mislead by something someone heard sometime, somewhere.

That said (and until I hear differently), consider going to an automotive store and getting some High Temp RTV Silicone. Often used for making gaskets or adding to gaskets on engines.

[Screwby]

A big reason people shy away from silicone (especially on the roof) is that nothing sticks to silicone. Not paint, not other sealants, not putty, not even more silicone after the first layer has dried.
Continued maintenance on an RV requires new layers of sealant anywhere there is a gap or cracked old sealant. Since nothing likes to stick to silicone then you either have to cut away as much of the old silicone as possible which is a major pain in the butt, or put the second coat on thicker so it is adhering to the surrounding surface and not just the old silicone. Other things like butyl tape, DAP sealant or non-silicone caulking are easier to remove and usually are ok to reapply right over the old stuff.
Silicone is awesome, we use it a lot in construction, but it comes with it’s bad points too as said above. Campers aren’t like houses, they are constantly flexing and being shaken to death. You’ll always be fixing new cracks unless you don’t care, then you’ll be posting in the “I’ve got a leak threads”

[hoppers4]

Originally Posted by Screwby

A big reason people shy away from silicone (especially on the roof) is that nothing sticks to silicone. Not paint, not other sealants, not putty, not even more silicone after the first layer has dried.

X2

[Johnny Lightning]

I agree that nothing sticks to sillycone, but it is VERY good at lasting under high heat. I have seen silicone used for the header gasket on a race car and it was still there after the header came off a few races later. This header probably got to nearly 2,000 deg. so it will take the heat. I also know that they use it for sealing fire boxes on furnaces and boilers. Silicone is also very good at giving with flex so I don't see cracking being an issue. The biggest issue I see is possible aesthetics issues with color. The only high temp silicone I've seen is red and maybe blue. Check with your local HVAC supply an see if they have different colors. If you need to remove the residue for a repair body shops have silicone removers for body shops so they can paint over where silicone has been applied. It's been a few years since I've been around that stuff but it's called Polycracker. Good luck.

[RedHorse1]

Since the area you have highlighted is in contact with the wall (filon w foam core?) I wouldn’t expect it to be very hot. I’d suggest running the furnace a bit to see just how hot that part gets. Bedding it with butyl tape and finishing with non-sagging caulk would likely get the job done.

[RogerR]

Plumbers putty should work. It will not stain plastic and is relativity easy to remove and apply. The edge of the vent gets warm but not hot enough for whatever kind of sealant you want to use.

[JoeSenior]

Originally Posted by Hog3loves

I need some advice concerning the best way to seal a gap on the outside of our 321 RSTS 5er. After many attempts (by CW) to fix our intermittent propane furnace, there is now a noticeable gap on the top side of the exhaust port where the factory caulking used to be.

I realize that whatever I use must be heat resistant and able to withstand significantly hot temperatures. I found this DAP Heat Resistant Silicone Sealant. Is this okay to use on the 5er, between the outside wall and the exhaust port? I thought I read somewhere on this forum that using a silicone sealant is a no-no.

Thanks in advance.

I spoke with an RV service center about the same question. He recommended silicone as well, but he recommended you pay more than a couple bucks for it (don't buy the cheap stuff). Also, he said this application is the only place where silicone should be used on an RV. He didn't go into specifics, but it confirmed what I had heard from other sources. After removing the furnace exhaust, I can say with certainty that the material used was not silicone. It was more like Butyl tape, however butyl tape is not high temperature. I am contacting a Jayco dealer to confirm what is used.

Has anyone confirmed what Jayco uses in this application?

Also, anyone know what is used for other seams on the exterior joints?

[LuckyDuck]

Originally Posted by JoeSenior

I spoke with an RV service center about the same question. He recommended silicone as well, but he recommended you pay more than a couple bucks for it (don't buy the cheap stuff). Also, he said this application is the only place where silicone should be used on an RV. He didn't go into specifics, but it confirmed what I had heard from other sources. After removing the furnace exhaust, I can say with certainty that the material used was not silicone. It was more like Butyl tape, however butyl tape is not high temperature. I am contacting a Jayco dealer to confirm what is used.

Has anyone confirmed what Jayco uses in this application?

Also, anyone know what is used for other seams on the exterior joints?

When I called Jayco about what to use to caulk siding joints they said they use Geocel Proflex RV. But that stuff you see oozing from many of the cracks and joints is butyl tape.

[TWP723]

3M Fire Block is good stuff. So is Hilti.