Grow to love the installations good way to show off the cosmetic side of the company. We just use the PVC cause its easy and how easy would all change outs be if u just had to unscrew transition and knock out PVC legs?
Thanks my boss my makes great tin trained me well. And yes we set a majority of our furnaces on 3" PVC.
That is the best thing to do to make the cabinet last, instead of setting it on concrete that is full of moisture. Have you ever thought of using 3" MIP x slip and a 3" FIP x slip and screw them together? This way you can make fine tune adjustments to get the right height of each leg. One can level up unit on uneven surfaces and even pitch furnace forward as required now days to better remove fau condensate from a Lennox furnace. We also set outdoor units on stand off's if the unit does not have them. They will last longer too.