I have a Rinnai 21,000 BTU LP gas ventless space heater and would like to change it to natural gas. Can this be done.

Possibly. Contact a Rinnai dealer for parts.

Most gas appliances come set up for natural gas and have a propane conversion kit included, small orifices. Did you buy it set up for natural gas and then you converted to LP?

Most gas appliances come set up for natural gas and have a propane conversion kit included, small orifices. Did you buy it set up for natural gas and then you coverted to LP?

Rinnai has to be converted usually by a professional because of critical adjustments. This has to do with the oxygen depletion sensor which is a safety device so the heater does not kill you with CO.

Most gas appliances come set up for natural gas and have a propane conversion kit included, small orifices. Did you buy it set up for natural gas and then you coverted to LP?

No, it was manufactured that way.

It possibly saved me from making a fatal mistake.

Yes, go with the professional. There is no margin for error with a ventless heater. If you don''t have a CO monitor, get one.

Labman's comment about the CO monitor is right on the money. Even though the heater has an oxygen depletion sensor it is not 100% safe. Get a CO detector, now required by law in many areas.