Natural gas is lighter than air and rises. And it can still easily explode a house. But propane gas (LP) is heavier than air and would fill a house from the flooring first to the ceiling. Propane also has a much higher BTU rating. Making it much more combustable. Thats why LP furnances have smaller orfice's. Connect LP gas to a natural gas orfice--Kaboom! Squirrel Crusher