Unfortunately, you can not, RE4400DS-HTD burners are not compatible with propane.
The low turn down fully modulating model we use is not compatible with propane. Furthermore, Midco only makes a standard modulating version that has a much higher startup BTU rating, which detracts significantly from the user experience when operating the brewhouse during a rolling boil and to prevent scorching.
With that type of system, the burner would be forced to turn on and off to prevent boil overs, or super heating the kettle. We just didn’t design our brewhouses with that type of burner in mind, so for now, the only option is NG.