Gray,
Energy is one of those areas in which I feel well qualified to
answer, but to get the best answer I need a little bit more information. Where do you live and what are your average temperatures and humidity like? Can you give me any idea on the temperature of the steam outside? Even if you can give me just a rough idea like it is warm, cool, etc. The reason I ask these is that it is possible that your system is quite efficiently transferring heat from the steam to your floors (and heated floors feel wonderful by the way). If this is the case, then it is possible that the real waste here is not energy but water, but this is highly dependent upon the climate and your temperatures and humidity. How common/scarce is water in your region? When I dry my clothes in the
dryer (not very Permie--I know) I see "steam" coming from my dryer vent, but I know that this is not truly steam but condensation and it is most visible on humid days.
For heating purposed, there are advantages to propane. As long as you are not counting
CO2, it does indeed burn clean. It can be turned on and off and this factor alone makes its use relatively frugal. If you are counting CO2 emissions, then for reasons of complexity, I will answer this in another post.
On the other hand, water may be the resource that is being most wasted, and as James pointed out, it would not be too difficult to create a little condenser coil to recover distilled water. Using the steam in a
greenhouse is a perfectly valid idea, but only if you really have ambitions to use that green house. Otherwise it will become an expensive, excessively humid place that will likely need repair and is full of mold--thanks to all of that steam.
I can go on, but this is a start. Give me a bit more information and I can be more precise.
Eric