I connected up the wiring from the thermostat and powered up the furnace. Taped interlock switch for the front panel. After studying the wiring diagram I realized that part of the LP conversion kit there is pressure switch added to the furnace so it won't turn on with no gas pressure. I connected up my 20lb gas tank to the furnace to see if it would start and it did.

I only momentarily let the furnace run not knowing if the gas pressure from a 20 lb gas tank would have enough gas pressure (or to little) to fire the furnace.

Question: For testing purposes-- can I run the furnace on a 20lb tank? Should I have a regulator on it?