[VAL] furnace replacement recap

[Chris Koehn <timberguides@xxxxxxxxx>]

All-
Thought I'd recap my recent experience replacing the furnace in our 
1979 @ 31' International. After a few servicings and a year of 
temperamental behavior I decided it was time to go.

At the time we were in Vermont and I was referred to Colin at GSM 
vehicles. After speaking with Colin and doing some research (Thanks 
Colin for your time and advice!)  I decided to tackle the job myself. 
First stop was at the local RV dealer, who offered to order a furnace 
for $650 (or more- they couldn't say until they'd ordered it). Their 
catalog helped me pin down the model I needed- the Suburban NT-24SP was 
the exact size of the original Suburban furnace. Within 10 minutes on 
the Web I found the furnace from a brick and mortar shop (Hawk 
Engineering) in MO selling on EBay for $450 shipping included.

The RV furnace supply in the U.S. is very tight right now due to all 
the trailers being built for hurricane relief. We had to wait a couple 
of weeks for it to arrive: by then we were in PA. The dimensions of the 
new furnace matched those of the old exactly. However in the 
intervening 26 years Suburban has changed the location of the gas inlet 
to the lower front right corner from the upper front right; and the 
duct outlets moved up accordingly. The old copper line (which was not 
tinned) could not be relocated to the new inlet. After three attempts 
to bend and flare new copper into the precise configuration required 
(with the correct tools)- and install it without kinking- I decided to 
abandon copper in favor of flex stainless, available from an LP shop. 
Flex made the job MUCH easier, and since it's entirely hidden from view 
(except for under the belly) and at least as durable as copper I found 
it to be a suitable substitute. (As an aside, I'm sure the furnace was 
originally installed early in the assembly of the kitchen; the rest of 
the cabinetry was installed around it, making soft copper much easier 
to bend and install unobstructed).

Adjustments to the ductwork required fabricating a couple of simple 
adaptors from sheet metal. Roughly 1/2 hour with a hand break and a 
straight and a right hand snips. Turns out the centers of the 3" ducts 
was changed ~ 3/4".
The only other modification I had to make was to drill a 2" hole 
through the bottom of the cabinet with a bimetal hole saw for the flex 
duct that keeps plumbing below the belly skin warm.
I also added 1/2" of foil faced insulation behind the furnace against 
the outside skin. The inside skin is removed (by Airstream) to allow 
the furnace to use the wall cavity space; however it's clear that this 
is a major spot for condensation. Since the furnace is rated for zero 
clearance I am comfortable with this addition.
So far we are thrilled with the new furnace and happy with our 
decisions.

Hope this info helps someone considering a similar adventure.

Chris Koehn
1979 @ 31' International Sovereign Land Yacht
at the Vintage rally near Salisbury, NC, heading for Charleston, SC