High temperature silicone or caulking - Fiberglass RV

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Old 05-17-2006, 10:49 AM   #1
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So outside my Trill where the vent for the furnace is there is a small gap between fiberglass and the vent cover. This causes furnace exhaust to vent right up the side of Eggmeon turning him rather sooty and black in thi area. So far the high temp silicones I have come across are red. Any other products out there to caulk the gap and can withstand fairly high temps??
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Old 05-18-2006, 08:26 AM   #2
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Name: Gina D.
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I would be more concerned with finding out WHY you have black exhaust.

Gas is clean burning. No soot.

Kurt.. where are you, oh Chancelor of the Chimney?

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Old 05-18-2006, 08:30 AM   #3
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Gina's right... if you have soot, you have a burner problem of some sort.

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Old 05-18-2006, 09:14 AM   #4
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Well it might just be burning off some sediment from long periods of inactivity. In any event nothing burns 100% clean in a 1980 furnace. The burner has a nice blue flame with just a touch of yellow at the top as it should be. I have read that not enough air to the gas will cause a fine carbon powder particular buildup as well while burning. Over a whole night the side is kind of black above where the crack is between the exhaust vent and the outside wall. Maybe just a lot of build up in the exhaust pipe from burning dust. In any event I still need a caulking that withstands the temp of the hot air being exhausted. So I would guess furnace cement or caulking of some sort. I have not seen a clean exhaust vent on a trailer yet, well inside the vent where you can't clean anyway.
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Old 05-18-2006, 08:28 PM   #5
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Are you averse to the high heat silicone because of the red color? Will it be seen? you can get RTV silicone high heat gasket maker that comes in grey along with black and another color, can`t remember what it is now.....good for about 625 degrees F ....I`ve used the red high heat in the outer pipe of sealed fireplace install and it is what is recommended...Benny
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Old 05-19-2006, 04:38 AM   #6
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The red does kind of bother me as it will be right outside the trailer where the vent rests against the fiberglass. But I don't need much, just a nice tight seal where whatever was there before has gone where ever these things go. tks, Pat
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Old 05-19-2006, 06:36 AM   #7
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You've got two problems; both are easily repaired and you do not need hi-temp silicone to fix it.

The exhaust vent should fit tight against the outer wall. Remove the furnace and exhaust vent, and investigate the trouble with the vent. It should be easy to repair this and make it fit properly on the outside of the trailer. When the exhaust vent is properly installed a small amount of regular silicone should seal it up nicely.

While you have the furnace out so that you can get the exhaust removed and properly installed, take a good look at the burner. 26 years old or not, if you are getting soot there is some sort of problem that must be checked out.

This is not a really big job. It takes about 30 minutes to remove the furnace in my Scamp, and that includes looking for the tools! This job should be easily competed in one or two hours. It might take all afternoon if you want to avoid mowing the lawn.

What brand furnace do you have?

-- Dan Meyer
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Old 05-19-2006, 09:13 AM   #8
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Furnace exhaust is like people, it will take the path of least resistance. Check to make sure there is no restriction anywhere in the exhaust vent. You are correct about an improper air/gas mix causing sooting. The air intake for the burner may be blocked by dust, lint, spider webs and their ability to collect debris, pet & human hair, etc. Spider webs can do a serious job of blocking exhaust. If the burner has an adjustment such as a vane or machine screw in the air path then those typically must allow the maximum amount of air when burning propane fuel. If you usually camp at altitudes over 3000 Ft. then a service center or propane dealer might change the gas orifice to restrict it so it will be balanced due to less air being available. Propane appliances must be de-rated by 20% in my community because of altitude. Manufacturers of propane RV appliances have to choose a "happy medium" since one may be camping at sea level one day and 8000Ft. altitude or more the next. Ideally one would change appliance orifices to suit the altitude location, but in the "real" world no one will devote the time or energy when they can be outside enjoying themselves.
The moral of the story is make sure the burners and venting are kept clean. Whether you feel competent to do the job, or you have a propane dealer or RV service center either teach you or simply have them do it, it should done at least annually. If you camp or drive where it is exceptionally dirty or you notice black accumulating around the vent, then the task should be done more frequently.
Keep yourselves safe and...Happy Camping
Kurt & Ann K.
One other problem could result in black appearing as you describe. If the heat exchanger has failed and developed a hole. This can prove to be deadly and requires immediate attention before the appliance is used again! Turn off the propane supply immediately, until replacement has been accomplished.

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