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Rinnai Infinity 26 gas water heater - supply conversion

I have a Rinnai Infinity 26 gas water heater that is a natural gas version. I'm wanting to know if it can be converted to LPG? Bought the NG unit because the gas company said they were going to run lines on our street but have since reneged. So just want to find out, first if it's possible to convert the unit and if so how much it'll cost. I have a plumber/gasfitter who will do the install but just doesn't know how /if the unit can be converted.