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Old 11-26-2007, 12:57 AM   #1
BigBoy2U
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Join Date: Nov 2007
Location: Tacoma, WA
Posts: 24
Furnace...since were talking about them air return filter?

Since I been working on my furnace one thing seems to bother me a lot. In my old Avion the furnace was in a compartment that was sealed off from the other areas of the underbelly and was only able to draw return air into the furnace from inside the coach. It had a return under a cabinet. If you wanted you could make a filter to fit in this area. On my 05 MS I noticted the blower sits in the housing for the furnace and its open to the underbelly area. It draws in from the underbelly and I guess it might pull "some" interior air from the cabin. But I noticed the hot air output to be much much less than my 35K BTU Atwood in my Avion. It would put out really HOT air...the Suburban in the MS puts out warm air. So I have concluded that the blower is drawing cool air from the underbelly and not really drawing much from the cabin causing a much higher rise to occur. Not to mention all the road dust, mouse crap and whatever is floating around in the under belly is being blown into the cabin. So a few questions. 1. Has anyone sealed off that area to create a better flow from furnace to cabin and back? 2. Has anyone taken a thermal temp of the heat output of the vents in the cabin to give me an idea of how hot the air is? 3. Has anyone made a filter to fit over the end of the blower intake to filter the air into the cabin? I think there is a so called filter above the pocket door. But it really doent filter much since the pocket door is open and the access panel to the electric is open along with the underbelly. My point is the furnace doesnt really draw much air back into the furnace from the cabin. Seems it draws more from the belly area than anything. Why would you want to move unfilterd air from the belly area into the cabin? Sorry I was just really suprised to see how poorly this was constructed. To have the furnace sitting in the belly area and pulling air from that area into the cabin. I just dont find it healthy when you store stuff that is dirty, road dirt and dust and critter crap along the smells of any chemicals, holding tank and whatever else is in that area. If you left the non sealing slidding door to the access open then your also pulling in all the air from the storage area. There must be a better way to do this?
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Old 11-26-2007, 03:01 PM   #2
bstark
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My answer is hypothetical at best but here's my take on this: I believe DT has done it this way to ensure that the tankage and service area gets heated by the air in the trailer being drawn down into the basement to be reheated by the furnace. In this manner sub-zero temps can't freeze your tanks or valves etc., and neither area is affected by a positive or negative volume problem as a "ducted" basement would result in air being fed to basement area and air inflitration occuring above in the coach area to replenish net loss. I don't presume to know what DT designers were thinking but that's my guess.

I completely removed my furnace from the rig and rebuilt rear support platform to stabilize it and keep it off the tank underneath it and also replaced the wooden cabinetry with insulation on the backside of panels around the electrical panel to ensure less air leakage and, more importantly, noise from furnace was substantially reduced.
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Old 11-26-2007, 05:27 PM   #3
BigBoy2U
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Well I only have my 94 Avion to go by but they used two methods, one was a single hose to heat the basement and a trick used by many was to cap this off and put a few small holes in the flex duct to cut down on the heat put into the basement. Second just the uninsulated duct work gives off enough heat to prevent freezing of the tanks in above 0 temps. Now I dont stay where its more than in the low teens so this might be enough for me.

I did think about the positive pressure of the cabin and the return air flow. Think I am inclinded to make a 1/2" wire mesh cover to go over the blower intake and stick a woven fiber filter material to it. Pull it off to clean and pop it back on. Really a simple bend and fit over the end of the blower. Only the bracket for the board is in the way. To bad they didnt make a slip in filter to cover the blower intake and then they could charge you $10 per filter and make you change it every 3 months....LOL
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Old 11-26-2007, 10:28 PM   #4
bstark
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Experimenting first would be wise as the sail switch inside the furnace requires a certain amount of airflow to function without hiccups. Restricting the airflow with a filter material right over the vent holes in furnace body may reduce volume of air enough to trigger the sail-switch while building a framework around the furnace and using multiple rigid furnace filters to encase the furnace in a larger cavity of filter material may not.
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