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11-11-2006, 12:27 PM
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#1
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
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NT-30MA to NT-30SP furnace change '79 Excella 500
Hi, folks,
Over the weekend and the next few days untill it's done, I'm going to be changing out the furnace in my '79 Excella from the original 1979 NT-30MA to a modern NT-30SP. The "A" nomenclature appears to mean that the heater is a variant of the NT-30M made for Airstream. There may be other differences, but the main one I see is that the old heater has an opening in the bottom from for flexible ducting to the forward holding tank.
The NT-30M is described in the 1979 service manual, and it is a thermostatically controlled pilotless model. I am replacing it because it's been operating a little bit erractically and because it is twenty-seven years old.
The furnaces are not exactly identical, although they do share very close dimensions. The outside end does fit in the existing cutout in the interior skin, but the inside end needs to be raised about half an inch to make the inlet and outlet pipes line up.
Here's a picture of the new furnace pushed into place.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 12:32 PM
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#2
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
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And a picture of the duct detail. The old furnace had the gas inlet at the top facing rearward, and the gas line came in from behind the curve in the duct and arched over the top of it to connect. (The rear gas line is to the oven. I have it pushed out of the way here.)
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 12:37 PM
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#3
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
Here's a comparision of the inlet locations. That's it on the lower right of the picture on the new furnace. Below that is the new line that I'm going to try running UNDER the duct. Obviously, this heater is not really made to accomodate the large ductwork adapter of this application -- the inlet is too close to the duct. (We shall see. I'll put an extension pipe on it if I need to in order to get clearance from the duct.)
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 12:54 PM
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#4
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
And here's a closeup of the duct adapter and the proposed new supply line. That's no optical illusion - that's a mighty tight clearance to that inlet.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 12:57 PM
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#5
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
As mentioned above, the new furnace lacks a hole on the bottom to feed the forward tank.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 01:18 PM
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#6
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
And, uh-oh. This may have been the cause of my problems to begin with. The installation instructions specify that three of the furnace outlets or two of the outlets and the bottom punch-out are to be used. Total outlet space should be a mininum of three 4-inch diameter outlets, and outlets to "dead space" having no air return like to holding tanks are not to be counted!
When the catalytic heater was put in for a PO, the forward duct was covered. The thought might have been that this would also push more of the heat to the back. It also might have interfered with the temperature rise in the heater and might have been the cause of the erratic operation that's been bugging me. (The old furnace often failed to cycle off after a run, sometimes went into lock-out mode, and always required several attempts to start.)
My current plan is to move the cat heater upwards, maybe (grrrr!) losing the use of the little folding extension in order to place an outlet somewhere near the original location.
It never has really made sense to me to have to run the furnace to warm the back of the trailer and the catalytic heater to warm the front. I LOVE my cat heater, but it's really better at warming objects and people than it is the air, and, of course, it doesn't do a thing in the world for the holding tanks. I also don't run it when I'm sleeping.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 04:53 PM
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#7
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
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Trouble in paradise
This photo illustrates two problems. With the heater pushed back against the skin, the duct adapter is not lined up and the bottom will not expose an opening to the forward tank heater hose. Hmm... I can pull it back about two inches and expose the lower hole. This is almost, but not quite where the old furnace was installed, so I guess that's acceptable.
However, the geometry of the duct adapter is wrong for this furnace. The old one had the openinings near the bottom, and this one has them near the top. Also, the duct can move forward a couple of inches, but there is no clearance to move it aft -- it hits the wall.
Looks like I'll be modifying the duct some. What fun. (The party never ends.)
Lamar
`
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 04:59 PM
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#8
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Silver Mist
Currently Looking...
Riverhead
, New York
Join Date: Aug 2006
Posts: 3,011
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You can use 4" flex duct, cut the old stuff out, it weights like 75 lbs.
Or cut out part of it and adapt the flex pipe.
__________________
Bob
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11-11-2006, 05:38 PM
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#9
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
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Hi, Bob,
Thanks. Well, I pulled some duct tape off the bend in the duct and found three screws that hold it together. A 18-inch screwdriver comes in handy here. With the screws out, I can lean it and rotate it enough to make it fit without strain. Now all I need is an 18-inch drill bit to pilot in a couple of new holes and that will solve that. (I have it sitting in place now with no fasteners.)
I see what you mean. This duct is about twenty feet long and it has four right-angle turns in it. Three connections to it are made under the shower pan, though. (I've been there - had that fun.)
Oh, I found an old ink pen and a funny looking refirigerator part behind the duct. Removed them and now I can go further aft with the duct. (At least I THINK it's a refrigerator part.)
Lamar
PS - Oddly enough, that's the first time I've seen duct tape used on DUCTS.
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 05:50 PM
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#10
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Silver Mist
Currently Looking...
Riverhead
, New York
Join Date: Aug 2006
Posts: 3,011
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You can buy self tapping screws with hex heads, you can use standard 1/4 or 3/8" socket drive in a drill with an extention, they will go right in.
__________________
Bob
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11-11-2006, 05:54 PM
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#11
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
Hi, Bob,
Thanks. I like to drill pilot holes even for self-tapping screws. I don't know why - I just picked it up somewhere.
Is your furnace under the stove on the curbside? Center bath or rear? Did you run 4" flex in yours?
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 05:57 PM
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#12
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
And every job, it seems, needs a supervisor. This is Lucy.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 06:23 PM
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#13
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Silver Mist
Currently Looking...
Riverhead
, New York
Join Date: Aug 2006
Posts: 3,011
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Center bath, I'm running two 4" all the way to the rear bedroom, I put in two Y branches to the water tanks.
I think it took 20' @ $15.
More room under the skink too!
__________________
Bob
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11-11-2006, 07:21 PM
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#14
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
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Hi, Bob,
Do you get a decent puff of warm air out of the little vent under the shower opening? I checked my flex tube when I had the shower pan out. It was unobstructed, but still little or no airflow comes through that vent. (Maybe this new heater will be heartier.)
Thanks,
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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11-11-2006, 07:31 PM
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#15
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Silver Mist
Currently Looking...
Riverhead
, New York
Join Date: Aug 2006
Posts: 3,011
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I rerouted that in the sidewall under the sink which allowed a full 4" vent, instead of the factory 2" under the shower pan.
__________________
Bob
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11-14-2006, 12:47 PM
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#16
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4 Rivet Member
1979 31' Excella 500
Detroit Area
, Michigan
Join Date: Jul 2004
Posts: 498
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Did you have to remove the oven (or maybe there isn't one in your trailer) before installing the new furnace? Mine is right below the oven (1979 31' International).
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11-18-2006, 01:57 PM
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#17
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Round on both ends
1979 31' Excella 500
1975 28' Argosy 28
Rutledge
, Georgia
Join Date: Apr 2005
Posts: 783
|
Hi, Wacnstac,
One MIGHT do it without removing the oven, I guess, but it's much easier access with the oven, the bottom closeout panel, and the lawn chair cabinet liner removed.
Removing the oven is EASY. There are four screws into the countertop and one gas line to remove. Then the oven slides forward until clear of the fuel line. I actually bought this oven new-old-stock in the factory box on Ebay. I paid as much as I would for a modern oven, but it appealed to me to have a brand new 25-year-old stove.
This installation is still in progress, by the way.
Lamar
__________________
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
Klaatu barada nikto
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08-22-2007, 08:36 AM
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#18
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4 Rivet Member
1979 31' Excella 500
Detroit Area
, Michigan
Join Date: Jul 2004
Posts: 498
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Would there be anything "Wrong" with using the external shell from the old furnace with the one modifcation of cutting out a hole on the bottom for the gas line, to house the new furnace and make things line up in terms of ducts a little better?
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