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 on airforums 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:
