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Old 05-08-2017, 02:17 PM   #1
2 Rivet Member
1976 31' Sovereign
Terre Haute , Indiana
Join Date: Apr 2017
Posts: 37
Where is the heater duct to the fresh water tank on my AS? and furnace duct outlet ?

76 AS Sovereign rear bath

I'm going through every system on our AS to make sure everything works and fixing what I find.

For the furnace I found out that it has been upgraded to a NT-30SP.

Looking at the FSM I found the ducts going to the black and grey tanks, but I can't seem to find the duct going to the fresh water tank. According to the FSM it should be right up by the furnace, but I don't see it anywhere.

Does anyone have a picture of where this duct is so I can try and find it on mine?

Also, the FSM shows two lines coming off the side of the furnace and feeding into the duct that travels to the back of the AS, and one line coming off the opposite side and feeding to a short duct and then directly into a vent that blows into the front of the AS. Someone has switched this around. I have 2 ducts going forward into 2 vents (one has obviously been added), and then only 1 duct going to the rear. Where the 2nd duct should connect has been taped off.

So a couple of questions here:

1) there are 4 outlets from this unit. One going to the rear is blanked off. Should I add this duct going to the rear?

2) if I do that should I blank off one of the ducts going to the front?

thank you!!

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Old 05-08-2017, 06:29 PM   #2
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1986 34' Limited
1975 27' Overlander
Conifer , Colorado
Join Date: Jun 2009
Posts: 5,824
Images: 1
I have installed three of thee NT-30 furnaces. They are a RV staple.

The installation instructions if very clear that there MUST be at least three of the four duct outlets used, or the 10 by 3 bottom duct. There is so much square inch area required for the heat to exhaust the furnace.

There may be two "tank covers" under your Airstream, one for black and gray tanks, and one for the fresh water tank. They are likely in or around the axles.

These pans are what Airsteam heats with one of the furnace ducts. There very well could be a "Tee" in the underfloor duct that runs to the bathroom, where heated air is diverted to the tank pans.

Here is a photo of my 86 trailer fresh water tank "bay". You can see the duct from the furnace running to this area. The second photo is of the fresh water tank "bay". You can see a hole in the cross member. I had to drop the fresh water tank (ugh) to repair a plumbing leak above the tank, but below the subfloor. (ugh, ugh). The photo shows the new PEX lines, but also shows the "heat register", this 3" round hole, in the cross member for heat ing the tank area.

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