Running two LP heaters
A 100lb propane tank holds approximately 24 gallons of fuel, each of which will provide about 90k BTUs. So, one of your 30k BTU/hour heaters will use 1/3 gallon of fuel an hour (if run at full tilt), using up the full 100lb tank in about three days.

reference: https://theadminzone.com/threads/propane-usage-calculations.118427/