I have no idea if this is safe first of all or how to begin to go about it.
Can you convert a natural gas wall heater to propane.
Using the wrench remove the hose from your natural gas source and make sure that it is capped or shut off.
Most space heaters are no longer convertible you must by the unit on the gas that you are using at your home.
Step 1 remove old hose.
If you can safely convert an appliance or furnace then switching to propane as a fuel source requires some appliance modification including replacing parts using a conversion kit.
Converting a natural gas grill.
I have a vent free natural gas heater made by procom.
You can convert some appliances but others are designed to burn only natural gas.
People i have talked to say it is easy to convert to propane which would be much easier i think than running gas lines to the greenhouse.
They either come with the hose assembly required or you are able to order it through the manufacturer.
A lot of grills are already ready for a propane conversion.