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.
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.
Then I pried, hammered, sawed, and said a few choice words and removed the old furnace casing from the plenum.
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.
Once that was fitted I cut the rectangular hole for my bottom vent.
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.
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.
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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