You will need to change out the burner nozzles. Best method is to remove existing nozzles and measure the orifice size. Using this and the required NG pressure, you can determine what size to use for propane. This table can be found on AF website.
The other changes will be on the gas pilot for the roaster. It will also need to be removed and replaced with one setup for propane. you would need to identify the style and the size and replace it. You can find this information from Honeywell, or whoever made the gas valve (the last Ambex we converted used honeywell for the pilot.)
The last change will be the spring inside the modulating gas valve. Based on the model of the valve, you can usually order the conversion kit. Your industrial supply house in town for HVAC would likely sell this and could tell you based on the part number of the valve.
If it has a gas regulator, that may need to be switched, but usually that would be on the "utility" side connecting to the roaster.
Nothing crazy expensive, but if you can't get part number from Ambex, you will have to figure it out.
"The cubic foot unit of measurement pertains to both natural gas and propane in their vapor forms. Provided that 1 cubic foot of propane contains 2,516 BTU and 1 cubic foot of natural gas contains 1,030 BTU, it is accurate to say that propane contains over twice the usable energy content per cubic foot (2.44 times more). "
