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Old 05-16-2018, 08:30 PM   #1
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1968 28' Ambassador
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Running furnace ducts near gray tanks

Hello!

I'm trying to figure out the best way to run a furnace duct from the front of our 68 Ambassador (inside the door and immediately to the left) to the rear of the trailer so that there's a hot air outlet near the bathroom/bed area.

Here are some pictures of what I'm thinking would work well, running the duct along the frame rail through the crossmembers, but I don't know

1) how hot will the duct get?
2) will the heat of the duct affect/deteriorate the gray tank over time? It's the gray tank from Vintage Trailer Supply. Made of polyethylene. https://www.vintagetrailersupply.com...-p/vts-851.htm

Any help or guidance would be much appreciated!
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Old 05-16-2018, 08:42 PM   #2
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I'd wager no more than 120* at most. I'd be asking the question of whether your heat loss to the underbelly is going to be too great to warm the end of the run. So, to eleviate both concerns, I'd insulate the ductwork with plastic backed duct insulation.
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Old 05-16-2018, 08:44 PM   #3
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I'll be watching the replys. I've been planning doing that exact same thing on our 69 ambassador
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Old 05-16-2018, 08:46 PM   #4
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I think i have a little more room for the pipe on the 69
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Old 05-17-2018, 05:15 PM   #5
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I'd recommend that you use fiberglass flexible 4" duct (about 6" actual OD) This can be compressed in tight quarters. The 1" insulation will will take care of the heat loss and will be very easy to run. It is also very quiet. The polyethylene can handle up to 200+ degrees F. You do want some heat loss to help keep the tank from freezing in cold weather camping. I would let the duct next to the tank be metal with no insulation and the rest of the run be the flex duct,

Happy streaming
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Old 05-17-2018, 06:21 PM   #6
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I think I remember that the furnace outlet temp is about 180 degrees F. Your furnace may have 3 outlet ducts from the plenum. By the time the hot air reaches the tank, it will be much less that 180, maybe 100 or less. The polyethylene tank can handle that temp, no problem. Actually, heat loss in that metal duct will help warm the tank compartment to keep it from freezing. Airstream typically heats the tank compartments to reduce freezing.

David
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Old 05-21-2018, 06:54 PM   #7
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Quote:
Originally Posted by dznf0g View Post
I'd wager no more than 120* at most. I'd be asking the question of whether your heat loss to the underbelly is going to be too great to warm the end of the run. So, to eleviate both concerns, I'd insulate the ductwork with plastic backed duct insulation.
Thanks! What do you mean by plastic backed duct insulation?
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Old 05-21-2018, 07:11 PM   #8
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Thanks! What do you mean by plastic backed duct insulation?
There is 4" insulated flexible duct material available.
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Old 05-22-2018, 06:32 PM   #9
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Here is the outfit I purchased my 4" flex ductwork from. I didn't get the insulated one as I didn't have room for the extra diameter. I ran my ducts close to my holding tanks with no insulation and no problems.

https://www.dwincorp.com/

Here is a photo of the underfloor ductwork I did on a 66 Trade Wind. The duct on the left dumps right into the holding tank compartment to keep it from freezing on a cold Minnesota night.

David
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Old 05-22-2018, 06:45 PM   #10
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Here is the outfit I purchased my 4" flex ductwork from. I didn't get the insulated one as I didn't have room for the extra diameter. I ran my ducts close to my holding tanks with no insulation and no problems.

https://www.dwincorp.com/

Here is a photo of the underfloor ductwork I did on a 66 Trade Wind. The duct on the left dumps right into the holding tank compartment to keep it from freezing on a cold Minnesota night.

David
Thanks, David! Do you know how that ductwork would hold up to the beating it'll get being towed around? I can't tell what it's made of but I'd be worried that over time it might deteriorate or the cross member would rub a hole in it?

Nick
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Old 05-22-2018, 07:50 PM   #11
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I feel it will outlast the trailer. Our 86 Limited 34' has this same stuff in it throughout, both above and below the subfloor. No worries.

David
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