Good afternoon fryedaddy.
My OWB is a NCB 175. It holds close to 175 gallons of water. I keep it set at 150 degrees off 135 on. The only time i go any higher is when temps drop into teens and single digits. Then i usually bump it up to 115-160. Circulating pump to plated heat exchanger runs continually so water is always circulating through OWB.
Made some changes to boiler first year I had it. Insulated bottom of boiler and enclosed it. Came from factory with no insulation on bottom, hard to believe. lol. Installed better temperature controller. Modified fan, and built new fire grate. One that gave it a more uniform burn and i could use to burn coal if i wanted to. factory grate was not much in my opinion.
True AHU fan does run a little longer at lower temps but the wood i save out weighs fan running.
I use OWB in summer to heat domestic HW. Burn scrape soft wood most of the time in summer. Poplar, Pine just whatever.
Add wood in winter twice a day. Morning and just before bed. Only add enough to keep fire until next loading time. I Try not to overload.
Best Regards,
Mike