How far off the floor must the bottom of the unit be?

This Modine Hot Dawg HD 60,000 BTU Natural Gas Garage Heater needs to have a clearance of 1' from combustible materials on the top, bottom, access side and non-access side. it will need a 18" clearance on the rear side. The vent connector will need a 3-4" clearance. If you have any further questions we recommend that you give us a call. Thanks!