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Author Topic: Venting Furnace Through Bay Door  (Read 2729 times)
Doug1968
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« on: November 16, 2010, 06:47:37 PM »

Fellows,

I'm looking for good ideas for venting a propane furnace through a bay door on my 102a3. Has anyone installed a furnace in the bay with a vent design that goes out the door when closed but allows normal operation of the door when opening?

Doug
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1986 MCI 102A3 - 8V92 - 5 speed
Vancouver, Washington
fe2_o3
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« Reply #1 on: November 16, 2010, 07:43:10 PM »

Doug; Are you trying to heat the bay or save space in the living area? I wouldn't be comfortable with an exhaust that wasn't sealed. I would be more inclined to vent through the floor of the bay...Cable
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Sofar Sogood
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Everett, WA.
Doug1968
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« Reply #2 on: November 16, 2010, 07:55:54 PM »

I would like to vent through the bay door. The Suburban manual says that venting must be out the side and not through the floor.

I am not heating the bay but want to vent the furnace exhaust and intake. I would like to design the system so that when you close the bay door it makes a tight seal for the furnace. On these buses if you are installing the furnace in the bay there are not a lot of options for venting without going through the door?
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1986 MCI 102A3 - 8V92 - 5 speed
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« Reply #3 on: November 16, 2010, 08:12:35 PM »

Instead of through a door. How about through the forward or rear bulkhead into the wheel area. This would allow a sealed exhaust vent...Cable
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Sofar Sogood
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desi arnaz
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« Reply #4 on: November 16, 2010, 08:18:22 PM »

i had a [before it froze and blew up] propane instant tank-less cold water heater in the bay with a 90 on top that fit into a 3 inch hole i drilled into the bay door with a kitchen strainer glued to the outside. the 90 hit the outer skin of the door when closed and worked fine.
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thomas f  Bethlehem n.h
robertglines1
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« Reply #5 on: November 17, 2010, 04:44:27 AM »

where is combustion air coming from? Beware any unsealed carbonmonoxide that might be in seep into bay from loose fit!  or sucked thru collar for combustion air...Safety first    Bob PS would install carbonmonixide detector inside coach at least!
« Last Edit: November 17, 2010, 04:57:32 AM by robertglines1 » Logged

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desi arnaz
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« Reply #6 on: November 17, 2010, 04:48:36 AM »

bot much of a worry for combustion air as the bay doors are rather leaky.
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thomas f  Bethlehem n.h
bevans6
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« Reply #7 on: November 17, 2010, 05:01:31 AM »

Suburban furnaces just have a two tube system for intake and exhaust of combustion air.  You don't really need to seal it to the door perfectly, just stick it through the door by an inch or so.  On my bus the rear bay has a side wall to the rear of the door that is about 18" deep, that's where my furnace is, the tubes come out through that side wall.  The hard part was building a sealed cold air return from the inside of the bus down to the cold air intake on the furnace.  I didn't want the furnace pulling in cold bay air (it's in the bay with my water tanks and there is often a black tankish smell in there).  I used flexible insulated furnace ducting to duct the hot air around.  Doing it a second time I would not have put the furnace in the bay.  They are designed to be in the interior of the unit, and I think the install would have been a lot better up there.  I dread having to service it. 

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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TomC
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« Reply #8 on: November 17, 2010, 10:29:53 AM »

To elaborate a bit on Bevans6 point, any of the Propane furnaces-whether it be a Suburban or Atwood, need to be mounted inside the living space.  They are made to recirculate the already warmer air on the inside rather then bringing in the cold air from the storage bay and burning excessive propane to try to heat the cold air.  Also, the motor on those furnaces are like the ones in the car A/C's which would be pretty slow to start on a 0 degree weather.  One way you could mount it in the storage bay is to make a completely enclosed box, mount it to the ceiling or under floor and have a direct return vent cut through the floor for the air you want to heat. 
I mounted my 34,000btu Atwood in my kitchen cabinets and raised the tow kick to 6" so I could run the insulated ducts under the cabinets but above the floor.  Works well, although it is noisier then I like.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #9 on: November 17, 2010, 12:22:33 PM »

Tom has it right.  It was a PITA building the cold air return.  Lots of heat lost inside the bay that could be helping keep the bus interior warm, and routing the hot air runs through the bay was a pain.  It does keep the water tanks nice a warm, though.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
4905 doc
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« Reply #10 on: November 17, 2010, 01:01:28 PM »

I vented mine through the door. no problem. I guess mci's are more or less the same. As someone else said, they don't have to be a super tight fit to the door.


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Doug1968
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« Reply #11 on: November 17, 2010, 06:25:35 PM »

Fe2_03

My holding tanks are located in the rear bay, no room to install the furnace there. I have maintained the OTR heat/air so I can't go out the front of the first bay.

Tom

You are correct. Suburban does state that the unit should be installed inside the coach but it seems, like you mention that it would work good to design the system installation with it mounted to the bottom of the floor, in top one of the bays, and design the return air duct so that it is short and tightly sealed to prevent leakage or the possibility of pulling in cold air from the bay.

4905 Doc

Using the mounting I mention above and venting the combustion air and exhaust to the outside through the bay door like you have done seems like it makes sense?

I am also wondering about the furnace size. I hear that the 40k BTU furnace is noisier and less efficient than the 35k BTU unit but I am concerned about having enough heat when needed.

I could install some good quality insulated ducting and try to minimize heat loss into the bays.

Doug

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1986 MCI 102A3 - 8V92 - 5 speed
Vancouver, Washington
jmblake
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« Reply #12 on: November 17, 2010, 06:42:41 PM »

Doug1968
I have the 40,000 suburban mounted and ducted up in the interior, and if I had to do it again I would do 2 smaller furnaces, 1 for the front and 1 for the rear. The big furnace is loud and mostly roasts you out in the back and cooler up front. With 2 furnaces you could control your temprature better. Jason
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« Reply #13 on: November 17, 2010, 09:02:21 PM »

On the specs that I have seen for RV furnaces, the output was listed as 75% of the input BTU. This was for both small and larger furnaces. The difference was in the fan current; the smaller the furnace, the higher the fan current.

As I saw it, the smaller heat exchanger used more air to maintain the efficiency. Of course, this means more noise. If I have the room, I will choose to use the larger furnace every time.

For what it's worth.

Tom Caffrey
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Tom Caffrey PD4106-2576
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TomC
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« Reply #14 on: November 18, 2010, 08:46:27 AM »

I recently replaced my 35,000btu Atwood furnace (left the old one on for 2 weeks-the fan motor didn't like that).  The old one was noisy inside and had an annoying whistle to the outside combustion fan.  The new one has a new design on the fans that is much quieter.  Plus the new one turns on immediately with the thermostat, whereas the old one had a delay.  I will use either the Atwood or Suburban, but with the remote mounted combustion breather-my present Atwood-I had to cut a hole in the side of the bus the size of the furnace to slide it in from the outside.  Both make remote mounted combustion breathers so you can mount the furnace from the inside.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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