Originally Posted by northstar1960
that's what i said the mesh screen is the cold air in . the hot air comes from the furnace
and is forced into the ducts . with the panel off the hot air is forced straight out instead of being pushed through the ducts . the furnace has openings on both sides that allows cold air in . i've modified mine to blow straight out sealed off between the furnace & cabinet front opening and now the cold air return is the hot out out . Sealed off where the ducts attached and now the vents [which where only 4 very small ones ] act as cold air returns to the furnace . much more efficient this way for those furnaces that were to small to begin with for the units size they were installed in . along with the piss poor installation of the furnace ducts and uninsulated dryer vent hoses.
The problem with this is you now have one heat "source," probably near the "center" of your TT, and the cold air returns are now probably out near the ends of the TT somewhere (at least if your's is anything like my last 2 - one in the bathroom and one out of the dinette).
This is backwards from the way anyone heats their house (or camper). If you have hot air heat in your house, you'll know that the hot air registers are at the walls (usually below the windows) and the cold air returns are in the center of the house.
Imagine if you swapped these in your house. Now you have a hot heat source in the center of the house and cold air at the walls. Makes for a large temperature gradient from center to walls. NOT EFFICIENT, hence not usually done.
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