Inline water filter

General Electric SmartWater(TM) model GXWH04F inline water filter instructions say not to use with water over 100F in temperature. I want to use it to filter sediment, sand etc our of the water I am putting into my hot tub, and also as a "vacuum cleaner" filter for the hot tub. When filling the hot tub, I can control the water temperature by adjusting the hot and cold faucets. When using it to filter/vacuum the hot tub, the tub temp is usually 98-102F. The housing is heavy plastic (type 5 PP) and the fittings are PVC on the inlet side and brass on the outlet side.

Why is there a temperature limit? Is there a +/- tolerance around the limit? Would it be better if I put a plastic fitting on the outlet side instead?