Routing your own furnace vents...
My trailer has in floor ducting. The most important of the three vents has never worked that well, and has gotten worse. Now the floor actually gets warm where the duct is likely leaking. I thought...
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I thought the same as you about the warm floor, careful examination just showed it gets warm because the duct is right up against the bottom of the floor. My furthest ducts don't provide the airflow I would like while the ones closest to the furnace put out too much. Still working on a fix for that. Am concerned if I partially block the closest vents, the furnace itself may overheat from the restriction. An added duct right at the furnace plenum is probably the best idea to carry heat to where it is needed and relieve some of the excess flow by the furnace. This would fix the issue without causing a restriction right at the furnace. I think adding additional vents would be more productive than closing existing ones and installing new ones.
