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Old 11-12-2008, 07:49 PM   #1
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1976 31' Sovereign
Blairsville , Georgia
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Furnace Ducts

I've been working slowly on my '76 International rear bath 31' Airstream. Today I fired up the furnace for the first time and it worked fine. Looking in the service manual at ductwork diagrams I see two small ducts that seem to go into the floor at the rear bath end and one going into the floor at the front end. Is this right? Are these for warming the tanks? If I'm not going to use the fresh water tank, can I close that duct off so as to get that heat into the living area instead?

Also, is there any heat getting into the rear trunk area at the back behind the sink? There is a lot of plumbing there which seems like it will be vulnerable to freezing temps.

Thanks for any help with this stuff.

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Old 11-12-2008, 08:36 PM   #2
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On my '77 rear bath, there is a vented section on the right side of the toilet that allows warm air to enter the rear trunk and keep the plumbing from freezing. The ducts going through the floor do keep the tanks from freezing so the best thing is to leave them alone. If ya drain the fresh tank consider re directing the hose instead of closing it off. Additional flow from the hose flowing into the main area would be much better than the minimal amount added to the remaining vents if you block that one off.

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Old 11-12-2008, 08:43 PM   #3
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i`m not real familiar with larger units, mine a 73 trade winds 25`. my experience is that nane of your heating from the furnace goes under or into any area of the trailer except the living space. you should have some insulation in the walls and the floor to somewhat protect water pipes but always drain tanks and pipes when not in use. the ducts you see going in floor should tie to a trunk line feeding back to the furnace.
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Old 11-16-2008, 10:10 AM   #4
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Pelzer , South Carolina
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I just replaced the furnace in my Soverign 31, the old NT32 Suburbans heat exchanger was burnt out, when I put the new NT30 in I noticed it was running much to hot. I don't think the two vents are enough, so I added a 3rd using 3 inch flex pipe. Cooled it a lot.
I check the exhaust temp, before the new vent, I could not hold my hand near the exhaust, after I notices a big decrease in the temp of it. I think the NT32 was burnt out over the over temp.
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Old 11-16-2008, 03:03 PM   #5
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Puyallup , Washington
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There are small flexible ducts (about 1 1/2" in diameter) that come off your main furnace duct to blow warm air on your holding tanks.
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Old 11-16-2008, 04:21 PM   #6
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1976 31' Sovereign
Blairsville , Georgia
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Thanks very much for the responses. Jim, I too noticed how hot the exhaust is on mine. Maybe I'll try adding an extra vent like you did. Iwas really happy with the amount of heat it puts out but that super hot exhaust worries me.
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Old 11-24-2008, 10:21 AM   #7
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1976 31' Sovereign
1963 16' Bambi
1971 21' Globetrotter
Marbletown , New York
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I've just finished a sucessful furnace replacement. I'd like to replace the flexible 4" ducts. On my A/S the original flex ducts seem to be made of fabric with coiled wire and a silver coating. It has the outside appearance of duct tape.

Does anyone know where I can get some?
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Old 11-24-2008, 10:42 AM   #8
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Stone Ridge- I'd think you'd be better off with the new mylar, insulated ducts that are available in any hardware store.

By the way, I'm just down 209 from you, near Port Jervis.
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Old 11-26-2008, 05:49 AM   #9
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What about adding a inline fan for airflow to rear of trailer ? . Any one you do that or suggest it ?
1976 Airstream Sovereign International Landyacht (renovating)(found DOM plate said 1976)
1968 Airstream Caravel 17 footer

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Old 11-26-2008, 08:10 PM   #10
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1976 31' Sovereign
Blairsville , Georgia
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As I posted on another thread, when I tore out all the under sink cabinetry I found that the shelf was laying right on top of the furnace. This completely blocked the top return air hole so that only the side one was able to take air into the furnace. With the shelf removed I have much more hot air getting to the bathroom and the furnace exhaust is much cooler. I'm betting this is a common and often undiscovered problem. The less air in, the less air out. I just finished new cabinets under the sink and range today. All easily removable if the furnace needs to come out.

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