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Old 01-04-2009, 06:56 PM   #1
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1975 25' Tradewind
Holland , Michigan
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How I installed new furnace NT24SP

The shell the old furnace was in, is part of the plenum, they are one piece and I use the term shell and plenum interchangeably throughout my little bit here.

I have no idea if the furnace in my trailer worked or not, I needed a water heater and called Palomino parts: 800-297-5830 they gave me a quote of $185.00 for water heater and so I asked about a Suburban NT24SP furnace, the quote was $285.00 if they could get one. Suburban has recently stopped production on these smaller units but they were able to find me one, $285.00 to replace a 34 year old furnace which sounded reasonable.

It was my understanding from what I have read her and from looking at the NT24SP installation manual that this should have been a drop in replacement, it is not.

This would have been much easier had I cut the old furnace shell off the plenum and used angle iron to raise the new furnace to the correct height, but I did it the hard way.

Here's what I did:

First I tore out the kitchen cabinets to gain access to the furnace. I am redoing the cabinets anyway so better to get that all out of the way.

Tearing out the kitchen cabinets:



Here is the old plenum ready for modifications:


The new furnace sat too low and too far towards the rear to match the old exterior intake/exhaust vent holes so I took the plenum out to modify it. First I had to bend one of the ribs out of the way. It would have worked to fold it inwards but I folded it towards the outside of the shell. I also had to cut the corner bracket off.

Rib bent out of the way and corner bracket removed:


I had measured earlier about where the new furnace should sit in the old shell so I proceeded to cut holes in the old furnace shell to match the venting and wiring on the new furnace also added one small hole on each side just above the plenum so I could shim the furnace up to the correct height when I did a test fitting in the trailer. Used a 4" grinder with cut off wheels.

Holes cut, this is the finished product but it does show all the holes I cut in it.


The old furnace cover, covered the front of the furnace and the plenum so I cut the old cover down to a size to cover the front of the plenum and riveted it on. I also cut a hole in it for the down draft vent.

See above photo (black piece in front):

Next I took this back in the trailer for a test fit and to shim the new furnace in the old shell to get the correct height. I had to move the the plenum about a 1/2" towards the front of the trailer to get the intake and exhaust vent to line up with the original holes in the exterior skin. The new exterior vent uses a large intake tube so I needed to enlarge the hole on the exterior skin.

Scribed line where I eventually cut hole larger:



Now that I have the correct height for the new furnace I brought it all back into the shop and cut up some hat-girt (stamped steel with the profile of a top hat) that I got from the scrap yard for $3.00 into the correct shapes I need to hold the new furnace up to the correct height. I pop riveted these to the old furnace shell using the measurements I had just gotten from the test fit.

New angle in old shell:




Brought everything back out to the trailer and made sure everything lined up with the exterior vent, then brought it back into the shop to install the down draft vent. The vent adapter I bought with the furnace was too short so I cut 3 strips 1 inch wide from the the knock-out piece I had taken out to convert the furnace to a down draft and spot welded these to the adapter to make it taller. Pop rivets would work but I have never used the spot welder that I have had for 15 years.

Vent modification:




Installed 4 round vent covers to cover the side vent holes that would not be used and covered them with foil tape. Put the furnace back in the old shell and mounted the vent adapter in.

Vent covers and vent adapter:


I should have made the angle go all the way to the front of furnace so I'd have a place to screw the furnace down, but I didn't, so I bought two 3/8-16 coupler nuts. The idea was to grind these down and use them as stand offs and drive a sheet metal screw through the furnace and coupler into the plenum, but this would not work as the gas line coming in was in the way. Instead I bolted the couplers to the plenum and found some short screws in my brothers Harley parts bin (I'm sure I'll catch hell for that) to screw the furnace to the couplers.

Stand offs and vent adapter


I needed a way to hold down the back of the furnace when it is installed for good but you can't get at the back then so I cut a few more small angles from the scrap I bought and pop riveted them at the rear of the shell, had to trim a little off the furnace to make snug fit.

Rear hold down:




All done and ready for installation:







Here I have the shell installed back in the trailer:


I slid the furnace in, screwed in the vent adapter, attached the two front screws to the stand offs, attached the wiring, gas lines, checked for leaks.
Cut some small ribbons of butyl and went around the inside perimeter of exhaust vent, heated it up with a heat gun because its cold out there and screwed the vent in.
Set the thermostat and fired it up. Boy did that thing stink for awhile.

Furnace installed and running:





Exhaust vent:
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Old 01-04-2009, 07:19 PM   #2
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Very nice write-up, Bruce! Incredible detail with all the pictures. It'll be very helpful for me as I embark on this with my '75 Safari. I purchased a new Suburban NT-30 to replace my NT-24. Ours is almost identical to yours but with the water fill and the furnace swapped.

We want to retain the original cabinetry as is. Can the job be done without taking a near complete removal of the cabinets? Looking back at how yours were constructed, do you have any advice on how to take them apart? I.e., just get the fronts off?

Thanks!
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Old 01-04-2009, 08:35 PM   #3
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Great work Bruce, glad it all worked out so well and thanks again for the parts. We were very pleased with Palomino as well, and once we get further along new water heater, range and refrigerator will be on order there.

Definately a clean install though, very impressed.
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Old 01-04-2009, 09:28 PM   #4
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1975 25' Tradewind
Holland , Michigan
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More info

DPeakMD,

Unfortunately there is no way to take just the front off but it is was not that difficult taking the cabinet out, took me about 1/2 hour.
I don't have a scanner right now or I would scan some pages from the service manual, hopefully some other member may do that for you or I'll post them next week.

Here is what I did:

Oven removal:
Shut off gas
Disconnect gas from oven, connection under burner cover
Remove 2 screws located in bottom end of side trim and 4 screws under burner top attaching oven to galley.
Remove oven from galley.

Counter top removal:
Disconnect drain pipes
Disconnect water lines from sink, service manual say to cut these lines and sweat them back together but I just disconnected them from the faucet. My faucet is a replacement so the PO may have had to do that when he replaced the faucet.
My counter was replaced also so yours is probably different. My counter top was attached at the back, underneath to aluminum angle at the wall and there were a few screws in the front. Opened the short tambour door and used a mirror and stubby screw driver to get them out.
Lift the counter to off.

Remove the galley:
There were 2 screws securing the side of the galley (between the oven and partitions wall) that had to be removed from the bedroom side.
Then I pried the panels out of the extrusions that are screwed to the walls and floor. The cabinet comes out as one piece and is quite flimsy once out.
The panels on the galley cabinet are held into the extrusion on the wall and floor with Tinnerman clips.
See this post for a picture. http://www.airforums.com/forums/f46/...ons-46881.html
I had to grab the whole cabinet and give it s sharp tug to get the panels out. some of the clips stayed put some came off with the panels and some went flying who knows where.

If you need more detail or pictures let me know.

If you do tear out the cabinet could you post a photo of your water pump, mine is missing and I would like to know where and how it is mounted.

Anybody know of a part number for the Tinnerman clips, Inland RV has some but I need more than they have.
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Old 01-05-2009, 07:27 AM   #5
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Quote:
Originally Posted by bmklawt View Post

Unfortunately there is no way to take just the front off...
Well, OK. I couldn't find any fasteners to free up just the front, either. Unfortunately, the heater is larger than the opening and the horizontal bottom tambour door track blocks the heater's egress from the compartment.

Interestingly, the heater in our '78 Excella was replaced in a similar fashion to how you accomplished it--sliding a new unit into the old housing!
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Old 01-05-2009, 07:44 AM   #6
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Great job on the retro fit and thread.

FYI - I replaced my ol NT20 with a new(er) NT30. With a little bit of imagination and a jig saw I was able to keep the base of the old furnace as a down draft plenum. I used some of the sheet metal from the old furnace to fill in a couple of spaces. I had to raise the new furnace about an inch and over about an inch to match up with the intake/exhaust ports in the skin. I used some scrap wood and silicone in between the old base/ new plenum and base of the furnace. It has been in place for about 2 years and no problem with the wood or caulk and furnace heat. But for insurance I also put in propane, CO and smoke detectors.
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Old 01-05-2009, 07:51 AM   #7
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Bruce, here are some photos for you that show the water pump. The original Jabsco/PAR has been replaced with a ShurFlo. The location is original. (Recall that in my Safari this is offset from your Tradewind). Excuse the messy wiring. I was in the process of installing the switch for the electronic ignition on the Atwood.



The pump is mounted to the Airstream original thin veneer ply which is in turn screwed down onto the duct work for the furnace. Where the ply abuts the aluminum sidewall there's a 1/2" plywood board extending down to the floor. Not beautiful, but it works. I found a similar arrangement in our '72 and the '78.
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Old 01-17-2009, 05:37 PM   #8
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Here I am thinking I'm all clever with my furnace install.
This would have been a butt load easier.
http://www.airforums.com/forums/f427...0sp-41537.html
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