Furnace Replacement (and I have NO idea what I'm doing)

[OldEdBrady]

The furnace in the Alfa is just about dead.  Since SWMBO has declared the trailer WILL be used this winter, I have to replace the furnace.  No choice.  And I have NO idea what I need to do, what I need to know, etc.

I'm sure the furnace in there is the original.  Don't even know what kind, model, none of that stuff--and, old as it is, there probasbly is nothing to tell me any of that stuff.

I know it ain't gonna be cheap.  But I'd like to hold everything to under $1k.

C'mon, guys.  You all have the experience.  Guide me.   

[OldEdBrady]

In my seraches on the boards, there are plenty of recommendations for replacement.  That doesn't help.  I nee3d the "how to" stuff.  I can always yank the old one out and stuff a new one in, but what the devil am I doing?

What's actually involved?  I mean generically, of course.  No two furnaces would be the same, even if they were from the same manufacturer.  I know that.

What do I need to watch for?  What do I need to plan for?  I'm at sea here, people.

And I'd better be ready to start this project this coming weekend, too.  Or I'm probably toast around here.

[RV Mech Tech]

Ed - replacing a furnace or any other RV appliance is usually an easy job- for furnaces things to look for are  a) measure the size of the area your  furnace is located   b)  note the location of the propane line and fitting type  c)  are there any hoses attached to the furnace for air distribution ?  the smaller furnaces usually do not have hose connections but as you go up in BTU sizes you get removable covers on the sides and top for connecting hoses -  d) is there a decal or metal plate with the specifications including the BTU size on your furnace ? -  if there is you can match the size with the new furnace - e) here are the two most common RV furnace manufacture websites   - 1)   www.atwoodmobile.com    -they have a products link at the top of the home page  and   2)  - for Suburban furnaces   - www.rvcomfort.com/suburban   - when the page comes up go to the site map link and then select  furnaces  - both sites give the specs including dimensions, BTU rating , gas line connection location (some furnaces have front and back connection points)   - usually you can get  a new furnace that will have the connection close to the original - if not its  usually easy to modify or add fittings to the gas line and don't forget to test the gas line connections for leaks after installation  f) make sure you leave some room around the furnace for air intake  for the air distribution - you do not want combustionable materials close to the sides of the furnace case   g)  make sure that you have an open air intake for the furnace air distribution - I have seen some brand new RV's that have a furnace under the stove in an enclosed cabinet that would cause problems - one of those problems is that if the stove top burner plates(s) were on and the furnace was started the flames would actually  get pulled downward  instead of up because the furnace blower would try and pull air from the top of the stove -( this is in an enclosed kitchen cabinet setup - Gulf Stream 'Amerilite' trailers had this problem ) this was solved by putting a hole somewhere in the side of the cabinet near the furnace (and covered it with a grille) and the furnace would then pull air through the grille instead of the stove-  -   h)  the furnace combustion pipe(s) go through the side of the trailer body and there may be one or two pipes on your original furnace - the system on the new furnace may be different from what you have so check for this as well - the two pipe system is air intake and combustion gas exhaust and is sealed from the interior -  you may have  to modify  the opening to match the new furnace -  let us know what you find.     

[OldEdBrady]

Thank you!  That's an excellent start!

Since there aren't any topics on this on the boards, I'll try to keep this updated as I go for future reference for others.

[tiredtraveler]

I would bet it bolts in and out and there is hose clamps on the ducting

[Oz]

You may want to look at the Free Manuals & Diagram section, Ed.  I believe some of the furnace manuals include installation instructions.  These may give you a general idea of the physical and electrical set-ups.

[DaveVA78Chieftain]

New furnaces are DSI models.  Most likely your old unit is a pilot model.  If you have not glanced through the following thread, then you should.  There is a tremendous amount  of operation as well as mechanical drawings.  Hookup of the 2 types is the same.   How they operate is the difference.

Dave

Anatomy of an RV Furnace
http://www.classicwinnebagos.com/forum/index.php?topic=2640.0

[OldEdBrady]

Uh, oh.  Now i have to tell the females it will have to wait while I go back to school and learn how it's dfone!   

[OldEdBrady]

I started on the project today.  Using the information I've already been given, I noted the make, model,cetc. of the furnace in the Alfa.  It was probably the original, so I didn't even expect something close.  I was right.

I ended up with a Suburban.  The old one was 24k BTU.  This one is 30K BTU.  Close enough for me.

Then I started pulling out the old furnace.  First, disconnected all the wiring, noting which went to the thermostat, and which to the "business" area.  Didn't want to burn the wall by flicking the thermostat on house power!

Then, because the wiring colors are a bit weird in the trailer, I started looking for positive and negative.  Only blew one fuse, but that helped me find the information.

Pulled about 40 screws out to remove the thing, and found about 3" of dirt and dust in there.  Cleaning that out took over an hour.

Ductwork.  If the furnace was original, then the ductwork. probably is, too.  So I'm replacing that before I hook up the new furnace.

AND, I note that I have to put some kinda wood under the furnace to lift it up to the outside vents.  And those vents are another problem.  The old furnace had side-by-side vents.  These are over and under.  Cosmetically, I think I can take care of it.  Actually doing that, though, will probably bring me a multitude of surporises I'm not ready for.  We'll see.

[RV Mech Tech]

Ed - since you are replacing  some or all of the ducting you may want to put some wrap around it if the ducting is solid - many of the larger RV's/trailers loose a lot of heat from the factory setups that have the cheaper aluminum type  hoses - any way you can insulate the ductwork/hoses etc will give you more heat at the outlets - there is newer type of insulation available for this at most supply stores for houses-  as I said those combustion and air intake vents can be different between the years -  usually easy to fix with cosmetics being the hard part - also in some cases I have been able to eliminate some 90 degree elbows in some of the ducting and this made a definite improvement in the air flow - in some larger trailers with long runs of ducting you can also install flaps to restrict certain areas or outlets and force more air to the outlets furthest away from he furnace.   

[RV Mech Tech]

The furnaces of the mid to late 70's are more compact and half the size- that's why you can match up a replacement furnace very easily - the furnaces and appliances of earlier years  are larger moe dificult to replace in some cases and in some cases require other modifications to install - the whole RV industry was like this as many members have found out when doing repairs.

[OldEdBrady]

I never posted this info, so I should now.

The old furnace had, as I said before, horizontal outside intake/out-take.  The new one had vertical ducts.

First, I took off all the outside metal shielding.  Then I tried putting the new furnace in where it had to go.  The new ducts were a bit off--particularly on the bottom.  So, I put in some 2x4 to raise the furnace.

Once I got that in, I tried again with the furnace.  It pretty much fit the old hole (on only one side, of course).  There was some minor sanding/scraping to get the lower one in, but it finally worked.

Then I fastened the new furnace to the 2x4s with short bolts through the hols provided in the furnace.

Naturally, I THEN found out that the new furnace was too close to the right side of the area I had to put it in to connect everything, so I had to take the bolts out and move the furnace over a bit to hook up minor stuff like the gas line and the electrical connections.

The gas line was a task in itself.  I had a flare tool, and tried to flare the end of the line.  No go.  I kept making a mess of it, and figured I'd have to replace the entire line from the junction to the furnace.

But, finally, I actually LOOKED at the tool (there were no instyructions) and saw that the line should not be any higher than the shoulder of the tool itself.  Then I flared it.  Prefect!

Hooked that up, and then the electrical.  Put the furnace back where it had to go (struggling with the gas line a little bit) and bolted it in.

Then the smoke test.  It worked!

Now, this isn't the whole story, of course.  There was the duct work.  But I've already covered that on the Miscellaneous board in my "Now I Get To Start Over" thread.
The outside.  OK.  I had this BIG hole now.  The plate I took off had two holes side by side.  I only needed one.

So, I cut a small piece of aluminum and put silicone on it then screwed  it onto the plate.  The other side, I more or less measuired and cut the hole bigger to accomodate the new setup for the ducts.  It looked terrible.

But, I put it in place anyway.  Then, the furnace came with a duct cover for the outside, and I screwed it in.  Fit perfectly.  Finally, I picked up those screens they have in RV parts stores and covered the vents to make certain I don't get "visitors" like wasps, etc., in the ducts.

That's the story.