i know nothing of air in the water and the 180 stuff so i will just make a guess that 180 is used to get rid of air and make sure it stays (or at least attemp) to keep air out of a clsoed system. and open system will always have air in it of some sort (again just my belief--no real proof) i also believe that running your open to air OWB at any temp you like as long as it will heat your home is good..the lower temps will be more efficient in that the temp difference between your underground lines and the earth will be closer together so heat loss will be less in this area. your blower in the house will likely have to run longer to keep your room at the heat level you desire so you may use more power unless you are like me and your blower in teh house is designed to run 24/7 then this wont matter. these things are like your old car..it has a sweet spot and it is up to you to find it and you will learn to listen to it and it will tell you when something is wrong with it. i am entering year 11...i turn the thing on in october and shove wood into untill late may or june..it does what it is supposed to and i appreciate it.
i may try and build another one (and it will likley be a gasser now that there is a lot of info on here to help me in my project) but i will never throw out the old "silver bullet" until it wastes away beyond repair. I built it with little knowledge of what i was doing..it uses about the same amount of wood as most other non gasser brands and i can live with that. i have probably spent as much on machinery as i would have buying heating oil or electricity but it has not gone out the window (so to speak) i have chainsaws, a tractor, dumpwagon that i may not have ever bought if i did not heat with wood, but these things are all re-sellable and worth something when i am done with them, and the valuable family time i have spent in the bush with my sons is priceless and i know we would not have spent this time at any other "job" together. my youngest (now 26) comes home from university and the first thing he asked are if we are going to the bush to get wood!
my OWB has not only heated my house but helped make my house, my home. i know many here worry about wood consumption and efficiency and i guess, rightly so. I would like to tell you all to take time and enjoy the dam thing sometimes, and once in a while....let the thought of "high milage of your wood" go up in smoke in your mind and let its place be taken with warm happy thoughts the OWB can give you
thats my rant of the night i guess...happy burning