[travelin texans]

Also when opening the valve on the tank be sure to open slowly or the safety shut off will trip & you'll get no gas. To cure this close the valve, loosen the hose fitting from the tank, reconnect, then open slowly.
One other thing, a low tank should not affect furnace operation, it's regulated down to about 30 psi before the furnace, so if there's anything in the tank the furnace should function properly.