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Which Furnace Heats the Bays

December 06, 2010, 08:50:17 am

I have a 1993, U300 SE. Which furnace heats the bays?

I installed a remote thermometer yesterday. It showed the water tank bay got down to 30F last night. I had the front furnace on but not the rear furnace. I always thought the front furnace heated all of the bays but now I am wondering.

Does anyone know for sure which furnace provides the bays heat or where the the heat enters the bay are?

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Re: Which Furnace Heats the Bays

Reply #1 – December 06, 2010, 09:44:04 am

Kent, it the rear furnace.

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Re: Which Furnace Heats the Bays

Reply #2 – December 06, 2010, 10:42:02 am

Jimmy, thanks for the reply. I also checked with Mark Harmon at FOT and he confirmed it is the rear furnace.

I learn something new from this forum every day.

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Reply #3 – December 06, 2010, 10:44:21 am

Its the front furnace on mine, I suppose it is different for other years and models.

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Reply #4 – December 06, 2010, 11:04:04 am

I believe in my U225 it also was the front furnace so you are apparently correct. I would like confirmation from one of the U300 SE owners that it is, in fact, the rear furnace. 

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Reply #5 – December 06, 2010, 11:11:11 am

I'm sure that I read somewhere, on the U225, it is the front furnace.  But then I only know about the U225, and not other models!

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Re: Which Furnace Heats the Bays

Reply #6 – December 06, 2010, 11:47:05 am

I checked our 1997 U295 and concluded that the rear furnace heats the bays. I set the thermostat so the front furnace was off and the rear furnace was running. Air blew from the vents in the service entrance and water pump bays. I then set the thermostat so the front furnace ran while the rear furnace was off. There was no air flow from the vents in the bays.

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Reply #7 – December 06, 2010, 12:35:54 pm

We had a freezing night here.  I set both furnaces at about 50 and went into the house.  We typically have five or so freezing nights in a year here, so I was not too concerned about the propane use.

Is there a way to regulate how much heat goes into the bay?  Is there a way to see in the bay?  Best I could tell, the only way is to remove the waste drains and work in from there.

Matt B
1994 U240

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Re: Which Furnace Heats the Bays

Reply #8 – December 06, 2010, 02:24:23 pm

Matt, even if you remove the waste drains and the FG wall there is nothing behind the white FG wall you can access. All you can get to is the wiring for the night light and the tank sensors. The black and gray tanks fill up the space completely.

It is my understanding that the heat for the holding tanks comes from the 4" X 8" vent in the bathroom at the bottom of the shower encasement. It is not forced air in the tank bay but simple air flow from bay to bay. The water tank is heated by the front furnace by forced air. The duct comes in under the access door to the fresh water fill and drain valves. The bathroom is heated by the front furnace as well and having the bathroom door closed forces some of the heated air into the vent at the bottom of the shower. I insulated my holding tank access door and the floor of the bay with 1/2" Styrofoam just as added protection. I remove the floor insulation in the summer. There is no room under the tanks behind the wall to put any insulation but you can and should caulk the wall/floor juncture in the bay.

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Reply #9 – December 06, 2010, 05:18:18 pm

My 89 280's rear furnace sends air into the basement via a vent on the passenger side. My vent is in the top of the bay. It is the same bay that gives access to the hot water heater, water pump and one end of black, gray, and fresh water tanks.

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Reply #10 – December 06, 2010, 08:53:25 pm

My 1991 Grand Villa on an Oshkosh chassis has the water tank up front between the driver and passenger seats.  It is heated by the front furnace.  The black and gray water tanks are exposed to the underside of the chassis and I don't think they are heated in any way.  Since the water in both the black and gray tanks is not pure I would expect that it would take a somewhat lower temperature than pure water.  Any suggestions for protecting the two exposed tanks?

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Reply #11 – December 06, 2010, 08:56:28 pm

Thanks Kent.  Now I know what that vent below the bath/shower is for.  I don't need to worry about anything freezing here.  We had our coldest winter in 100 years last year and I suffered no ill affects and didn't heat anything.  I doubt it went below freezing for more than a couple of hours on 10 occasions last winter.  It is supposed to dip down below freezing tonight though if you are far enough inland.

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Re: Which Furnace Heats the Bays

Reply #12 – December 06, 2010, 10:51:42 pm

Dwayne,
Aren't you in the Tampa area?  I used to live in St. Pete in the late '60s and I can seem to remember it getting down into the teens any number of times.  It was no fun being a VW mechanic in an unheated garage and picking up a wrench when the temperature was nineteen degrees!

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Reply #13 – December 07, 2010, 10:27:14 am

Temp was 21 deg in Southern Ark last night . I 'm not using the mh now but every time the weather forcast indicates it will be below freezing I turn on both furnaces and set inside temp at 55 deg. I checked my bay's this morning and they are 55 deg.  That pleases me particularly with my rig being a 89 model.

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