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Furnace and duct work questions

I've taken out my old furnace and Pentium.  I'm planning on putting in a new furnace.  The old one was 40,000 btu, and there is only one furnace.  What is the setup on the coaches with two?  Where are they, and what size are they?  Do they each have there own zone?  Would two 20,000 btu furnaces be more efficient than one 40,000?  The duct work is a mess, partially collapsed where they tried to bend it through small spaces, disconnected from the outlet registers, and a bit on the rotten side.  It's the corrugated stuff that looks like sewer hose.  There must be a better way to distribute heat.  Is there a higher tech duct material out there now, smaller, smoother, more flexible?  Running new stuff will not be easy, especially to try to just replace with the existing type stuff.
1996 U270
Build #4846

Re: Furnace and duct work questions

Reply #1 –
Quote from: Gayland Baasch –
I've taken out my old furnace and Pentium.  I'm planning on putting in a new furnace.  The old one was 40,000 btu, and there is only one furnace.  What is the setup on the coaches with two?  Where are they, and what size are they?
Our coach is a 1997 U295 36'. A 35000 BTU furnace is driver side at the middle of the coach. It has five 4" ducts that serve private toilet room, kitchen/dining, and living/driving area. A 16000 BTU furnace is passenger side and a bit forward of the rear wheels. It has three 4" ducts that serve shower/sink area, and bedroom. There are two 2" ducts that serve service entrance bay and water pump bay.
Quote
  Do they each have there own zone?
Each furnace is on a separate thermostat. On our coach the thermostats are incorporated into the climate control system with a control unit that manages furnaces, air conditioners, heat strips, and fans.
Quote
Would two 20,000 btu furnaces be more efficient than one 40,000?
I expect changing ducts, propane supply, cabinets, etc., is not something you would want to do. There are lots of safety issues to consider. Those issues were accounted for in the original installation.
Quote
The duct work is a mess, partially collapsed where they tried to bend it through small spaces, disconnected from the outlet registers, and a bit on the rotten side.  It's the corrugated stuff that looks like sewer hose.  There must be a better way to distribute heat.  Is there a higher tech duct material out there now, smaller, smoother, more flexible?  Running new stuff will not be easy, especially to try to just replace with the existing type stuff.
Our duct material is similar. It is a fabric with a wire "frame." It is designed to withstand the heat and rigors of serving air from the furnace. You could probably improve the flow with careful placement of similar material.
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Furnace and duct work questions

Reply #2 –
Quote from: J. D. Stevens –
Quote from: Gayland Baasch –
  Do they each have there own zone?
Each furnace is on a separate thermostat. On our coach the thermostats are incorporated into the climate control system with a control unit that manages furnaces, air conditioners, heat strips, and fans.
My '94 has two furnaces, one in the bedroom and one under the couch.  and a thermostat in the bedroom for the bedroom furnace and the other in the kitchen for the couch furnace.
1994 U225
build #4514

Re: Furnace and duct work questions

Reply #3 –
How did you remove your furnace and where was it located in your coach?  Does it come out from outside or inside?

Re: Furnace and duct work questions

Reply #4 –
Quote
What is the setup on the coaches with two?  Where are they, and what size are they?
One is under couch (drivers side) other is under bedroom closet (pass side) for my '91 40 ft coach.  Both are 30,000 BTU.  Bedroom unit seems oversized.  I've contemplated changing the blower motor and LP orifice to a smaller size (same as a lower BTU configuration) to make it quieter .  I would agree with J.D. about converting to two units - just not worth the effort.  Just guessing, I would say a single unit is actually more efficient if your heating the whole coach.  Two things I don't like about furnaces: 1. Noisy (especially the higher BTU units)  That's another plus for a single unit - it's likely located mid-coach and farther from the bedroom where the noise matters most. 2. No insulation:  (when not running) it's a hole in the wall with metal conducting heat from the inside out.  If you add a second unit it will be yet another hole in the wall.

You might look through the options in McMaster-Carr catalog for ducting:
McMaster-Carr  But I'm not sure any would work better than the OEM stuff.  And you need to make sure it can handle the heat (not sure what the max. temperature the ducting would see)
If I had to replace any of mine today I would probably just get it from FT.
If you really want to study it more you can start by seaching "HVAC duct wiki" and read the wikipedia article on it.  It covers stick HVAC systems but talks about materials and such.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Furnace and duct work questions

Reply #5 –
Barry - the furnace is located under the refrigerator, (mid coach, driver side.)  I did get the furnace out the outside door.  That part was fairly easy.  Getting the Pentium out was a bit more difficult, the duct work seemed impossible to disconnect from the outside, so I ended up removing the refrigerator and cutting a hole to get at it.  I just have a small household type fridge, so that was easy to do.  This Pentium is about as others here have described as far as hookups, but I'm think it must be a FT modified setup.  It doesn't look like anything like the new setups in the catalogs. This project all started from the fan motor squealing problem.  The "book" says you can change the fan motor out without taking the furnace out, but that must be a different model than I have, even with it out on the bench I still haven't been able to get it apart.  The fans are rusted on and difficult to get at to apply any sort of force.  So I decided, 15 years old, probably just as well to replace the whole thing anyway.  Of course, one thing leads to another.

I'll do more studying on the feasibility of adding a second furnace, but off hand I'm not seeing the safety concerns.  These things are all self contained, zero clearance, outside vented.  Chop a couple holes, run a gas line and some duct work.  What am I missing?  :)) Again, the main reason I would consider it is for redundancy since I live in cold country.  Noted the comment from JF about outside holes.  For what it's worth, this did have some insulation around the compartment.

 
1996 U270
Build #4846

Re: Furnace and duct work questions

Reply #6 –
Gayland,

I believe we have similar coaches, I have 4831.  I had a similar problem on an SOB.  Not only did the fan bearings squeal, the fan actually stopped and we were very cold on that trip.  Pulled out the furnace to see if I could change the fan and also found a crack in the burner housing, so I think you are doing the right thing to replace it.  If you don't like the duct work you could replace that too.  Some of it goes under the shower pan.  Mine seems to heat the coach okay, but have not been in any real cold weather.  If you were happy with it before the problem, seems like a lot of work to install a second furnace.  Two furnaces may drain the battery faster when dry camping. 
Jerry Whiteaker former owner 96 U270  36' #4831 Austin,TX-Owner Mods LCD TV w/front cabinet rebuild - LCD TV bedroom - Dual Central AC, either can cool coach w 30 amp - Skylights at roof AC openings - Drop ceiling for ducting of AC - Shower skylight white gelcoat/wood/epoxy frame - Air Springs/Shocks replaced - 2014 CRV - 8K Home Solar - Chevy Volt

Re: Furnace and duct work questions

Reply #7 –
Our old furnace works just fine after replacing the "board" in it last fall.  I changed out the 12 volt fan motor about three years ago.  The secret is high quality long reach T-handled hex/allen wrenches.  The stock furnace burns a lot of propane, uses a lot of battery power to run and mostly heats the outdoors.  The thing is VERY inefficient.  We elected to install two propane outlets in the coach for auxiliary heaters.  One outlet is tied into the existing furnace and the other outlet is plumbed by pipe from the propane bay.  Both outlets are valved and have quick disconnects.  The heater that is tied into the furnace connection is placed in front of the furnace cold air return below the refrigerator.  It is a Camco 3000 Catalytic which operates at 1200/3000 btu and keeps the spouse toasty when she is sitting in the dinette area early in the morning.  The other heater, a Mr. Heater Big Buddy operates by sitting on the dash table (when needed) and operates at 4000/9000/18000 btu and has a small fan for moving the air.  We also use an Fantastic Fan Breeze portable unit to move more air when needed.
These heaters are very frugal with propane and the Mr. Heater unit puts out a LOT of heat if you need it.  We have NOT been using our forced air furnace and are glad to do without it as our batteries last much longer, we use a lot less propane, and we don't have to put up with furnace NOISE.

Gayland, if I were you, I would put the same size or slightly larger back in as a supplemental unit and then use portable units.  We definitely have redundancy and are able to add a larger heater in place of the Camco if we feel we need it.  We normally do NOT stay in areas where night time temperatures go below 32 degrees.  Of course, if you feel obligated to stay in the frozen north then you may need to put in two 40K btu units.
Good luck with your project.  Keep us informed as to how it goes and your long term results.
Regards,
JON TWORK KB8RSA
Full Time RVer (10+ Years) & Dedicated Boondocker
Retired, Unemployed, Homeless Transients
1996 Foretravel U270-36 w/24' Timberwolf Trailer
I firmly believe that tomorrow holds the possibility for new technologies, astounding discoveries, and a reprieve from my remaining obligations.
Welcome to WeRV2 (Under Construction)
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The Second Amendment is in place in case they ignore the others.
 

Re: Furnace and duct work questions

Reply #8 –
GMTA (That's "great minds think alike!)  I'd just been reading up on catalytic heaters.  I've been using one mounted on a bottle for heat while working inside with no furnace.  I thought it would drive the detector crazy, but haven't heard a peep from it.  Also thinking back, I once had a Avco, which I understand at one time had some sort of attachment to FT, and that's all it had for heat.  I didn't live in cold country then.  I know there's some concerns for safety, but used properly I think they're fine.  Of course there's the problem of keeping the bays from freezing but if its that cold the furnace would have to help anyway. 

The long handled allen wrench worked fine for the large fan.  There were access holes and everything.  But the small fan had no such holes.  No way to get at the screw other than from the end.  I did finally mange to get it loosened using the short end of a "regular" allen wrench, but the corrosion still has kept me from getting the fan to slide off.  This furnace had obviously been out before, so who knows exactly what it is now.

1996 U270
Build #4846