I have an older Rheem furnace and would like change the filter. Appreciate any help for me to know what the correct filter is and where it is to be placed. Also, if anyone has a manual or instructions for this model or know where to get one - that would be very helpful. I tried the Rheem site but my serial number is 15 positions and didn't match the types it listed. Again thank you.

In a previous thread several people recommended calculating the load when looking at new furnaces. The house involved is 1 1/2 stories with a finished basement. The supply ducts have no dampers. In the winter (sometimes down to 25 below F), electric baseboard heating in the basement does a good job keeping those rooms warm as needed. The gas forced air furnace warms the main and upper floors adequately in the winter, but my thinking is that manual dampers in the ducts would be nice. In the warm months, the basement is always cool, never needs AC. So much cold air gets down there through gravity and registers (even if fully closed) that it is too cold whenever the AC is on. The main floor can be kept comfortable by the AC, but when quite warm the 2d floor requires so much cooling that the main floor is overly cool and the basement frigid. When calculating load, shouldn't you take into account that the basement needs no heat or AC from the furnace and coil? Also, do you need more tonnage to push more AC to the 2d floor, or can you accomplish that with dampers or motor HP? When looking at new furnaces, what feature would you focus on to get enough heat to the 2d floor? The ductwork lacks dampers and the supply registers are in the floor and returns in the upper walls; I expect these issues affect efficiency quite a bit. All of the room registers can be opened and closed, but wouldn't in-duct dampers help? P.S. Are there tricks to adding manual dampers, so that it could be done DIY? All the basement ducts (rectangular and round) are reachable. Thx.