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Old 12-15-2017, 01:54 PM   #1
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2008 25' Classic
Wichita Falls , Texas
Join Date: Nov 2012
Posts: 4,275
Question about Tank Heating Duct and Bath Heating Register

While I was replacing my water pump I noticed the 2" pipe that is screwed down to the floor. There is a opening in the floor where the hose end is clamped down. I can see the top of the waste tank as the subfloor cut is larger. The hose is clamped down to a bracket that is screwed to the floor. One edge of the bracket is exposed due to the large subfloor hole.

It just occurred to me was how does the bathroom vent get heat? Does the holding tank cavity get pressurized slightly and push air to the bathroom wall heat register? I always figured the bath was heated via a 2" duct that ran under the floor but there is only one 2" duct off the hallway 4" register.

The two photos show how the 2" flexible duct is attached to the floor. This is under the hall closet between the fridge and shower. Closet floor removed.

Should I cover the exposed subfloor opening to keep more heat in the hold tank area under the subfloor?

Does this design adequately heat the water and both waste tanks?

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2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver
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Old 12-15-2017, 04:02 PM   #2
Vintage Kin
Fort Worth , Texas
Join Date: Nov 2006
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It’s cut that way for easy construction. This level of detail even Silver Streak didn’t bother with. Consider it normal.

Yes, one could get some cold air infiltration. But for heated air to flow into tank cavities, there’ll have to be an outlet. An exchange.

I suppose one could test by starting from ambient on a winter day and measuring temps at cutout. Any temp rise would be “good”.


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Old 12-15-2017, 07:36 PM   #3
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1986 34' Limited
1975 27' Overlander
Conifer , Colorado
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My 75 Overlander had a 2" spur duct into the rear tank cavity. There was enough hole in the black tank vent floor penetration to allow air exchange. The 75 has 10" by 2" sheet metal duct work from the furnace to the rear bath under the tub. I will likely run flex duct instead.

My wife's 86 Limited uses flex duct. It has a 2" duct to heat both the fresh water tank pan and the waste water tank pan. There is a 4" flex duct running under the subfloor to the bathroom in this trailer.

In both cases, the tank pans are insulated with styrofoam. I feel the furnace running may keep the tanks and dump valves from freezing on a 25 degree night. I do not think there is enough heat going down there to keep them from freezing on a cold Minnesota winter night.

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