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Old 04-26-2008, 10:18 AM   #1
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Replacing NT22A furnace with a NT30SP

I was not able to work outside on my subfloor yesterday. Work tried to get in the way of play! So I decided to see what I needed to do to get my new furnace ready for installation. I thought that I would share my experience.

I contacted Airstream, Inc., and they sent me a Bulletin #16 on how to replace my old furnace with a different model number (NT-30M) but it helped.

Bulletin 16.pdf

I contacted Suburban and they gave me the following response:

"Please be aware that the NT30-SP requires that at least 3- 4" ducts are used unless the unit is bottom ducted. And if the unit is bottom ducted the bottom duct must maintain at least 48 square inches throughout the run of the ducting. In some older Airstreams the bottom discharge was set up with only 2 duct line s coming off of the bottom duct plenum, if this is your situation I strongly recommend incorporating the use of at least 1 of the 4" round side discharge duct outlets by the means of 4" round flexible ducting or other appropriate ducting material."

Therefore I will need to find a location for another duct outlet on final installation.

First I made a trail fit to see what needed to be done.

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Then I pried, hammered, sawed, and said a few choice words and removed the old furnace casing from the plenum.

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The Airstream bulletin suggested cutting and bending aluminum into an angle to close up the front of the plenum but I discovered the old furnace door was made to fit. It only needed to be cut down.

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Once that was fitted I cut the rectangular hole for my bottom vent.

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A little spray paint (I used heat resistant but it was probably not necessary) and a couple of pieces of aluminum angle to hold the new furnace to the plenum and it is almost ready to install.

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On the final install it may have to be spaced up a little but it looks like it is going to fit my outside holes if I cut them out a little.

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The main reason that I wanted to use my old plenum is now my old rectangular duct work will fit! When I finally set it in place and line everything up I will pop rivet the new furnace to the plenum at the aluminum angle and duct tape where needed.

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Old 02-24-2009, 02:00 PM   #2
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1967 22' Safari
Austin , Texas
Join Date: Apr 2006
Posts: 49
Hi Vernon, Was looking at your post. I just ordered a NT30sp for my 66 safari
I'm not taking out the cabinets to do this, but will likely hack out the plenum too.
What did you do about the extra vent?. I suppose I could run a round duct somewhere in the kitchen cabinet and pop a hole in a door face. Eventually I will tear out the cabinets on an interior remodel, but not this year.

I also ordered a bottom duct kit with gasket Part number 520009. I suspect this will need to be increased in length though. In looking, none of the replacements I've seen fit without raising the unit up a few inches.

Will post if I get into too much trouble

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