need new gas boiler elevated of concrete basement floor

belle

How high can a new Sentry slant fin s90 boiler be installed of a basement concrete floor. The ceiling is 74" from floor. The manual says the unit is 37"  and the vent damper is 6".  I choose the contractor because he said (and e-mailed) that this new unit could be installed     " quite high off the floor". The old boiler was 7 1/2" off the floor (cinder blocks).  (He knew the situation that the basement floods and the old unit was too low and destroyed) I went home at lunch and am very disappointed & feel bamboozled. The new boiler is only 3 1/2" higher!  I would like to know where the other 20" of space went ?  He should not have misled me, or maybe he could have done other things to install it higher? I would appreciate any input anyone has as he wants to be paid. I would like to pay him but I had other estimates that were better than the installation i received. thanks.