there are so many vague or omissions in this I don't know where to start, first you have to specify what kind of diesel heater. if your talking about the expar type (real or Chinese knock offs) , which is probably the most common one put into a rv, then you need to edit a bunch of stuff.
first they do not need windows open, just like a propane furnace, as they are sealed combustion so they can't leak any co2 into the rv unless you have a window open right above the exhaust.
they are a little more efficient, in both fuel and power but not a crazy amount, but it makes a difference over time.
they don't put out any more heat than the equivalent sized propane heater a btu is a btu no mater what the fuel source is so if you have a 16000btu propane heater and a 15000 but diesel heater they will keep you warm the same. one big difference is if the diesel heater is sized correctly then it will just run on a low setting when it is cold out keeping the heat more constant inside the rv, but if you buy to big of one, which most do then you can't do that and it shuts off in-between cycles and give you the same type of temp swing a propane furnace does, the biggest difference the diesel heater will have a tighter swing as it has a digital thermostat. so a simple answer to this is to put a digital thermostat on your old propane heater and it will have a tighter swing also.
