I have tried last year to to run 190 with 8 degree differential. What I quickly learned my boiler in undersized for my home and no matter what high limit I set it to, it will never be reached during the single digits with high wind in this old farm house. Works great when the temperature is in the mid twenties or higher, delivers hotter air to the home and the furnace cycles less. I just wanted to point out higher set point makes no difference if your heat demand is so high you will probably never reach 170 - 180, as your furnace blower just runs and runs... and when it kicks off for maybe 1 minute and back on. The people who have experienced this it will resonate hard. Sellers claim a approx square footage of heat but have no idea what your home conditions are such as insulation, windows, and other factors. If you live in a drafty old farm house, poor insulation, or had problems keeping your home warm with propane or other means you have to at least double the square foot rating. Hard lesson I had to learn... Please take my advise.. OWB are wonderful but can't create miracles.
I'm going to modify my post, my experience with a conventional boiler only... With Natural draft... When setting such high limits your going to burn more wood and if your demand is so high your boiler / blower will run wide open and wood consumption will be greater... I hope I covered myself here.
Going to modify my post once more..... Lastly Green wood can cause huge issues when the house is demanding a large heat load. For example you go outside the water is 155. crap that is getting pretty low so you throw in 3 or 4 large pieces of fresh green wood close the door and go watch football. Your game hits half time, its cold as a witches nipple outside so you decide to check the boiler temperature again...WHAT! WTF 125 degrees.. At this point throwing more wood in is going to lower your boiler temperate, and at the same time your blower hasn't cycled off in 2 hours. Your damn football game is ruined cause you have the boiler door open hoping for the Hail Marry. Yes, finally after 2 hours of the door being open I reached 180 barley any wood left, so you have to slowly add your green wood in to get a respectable fire again. You check the clock the game is over its 12:30am and you have a meeting in the morning and you start to curse the world. You been out in the cold so long sucking down too many brewskies by the time you get inside and warm up you can barley remember your name and stumble to bed, as you stumble to bed you wake up your wife she is not happy to see you trying to take off your socks, she instantly knows you drank too much. See being out in the cold for too long and drinking, when you hit warm air your body metabolizes the alcohol differently, warm air it will make you very confused... on worst occasions the warm air makes you want to pee and if you drank too much watching the boiler there is a good chance your going to pee in the corner of your bedroom, or miss the toilet and waking up to the misses demanding what the fu$@# just happened, Thinking you were partying all night but you were just trying to keep the place warm. Its happened to me, and will happen to you if heat demand is high enough and trying to recover with green wood. I can use green wood all day long in shoulder months but when the demand gets high enough you need seasoned wood. Yet, with a undersized boiler even dry wood may not be enough, and a high set point is only a dream during the coldest months. Why I wrote this I have no idea... stay warm... and keep the wife happy.