Just my opinion and my situation, not suggesting for OP topic. I installed OWB when we built our house, then added garage heat to attached garage and then ten years later added it to new shop 24x32. Also heat domestic hot water. Surprisingly, with using high dollar insulated pex, I haven’t noticed a real measurable increase in wood consumption with the adds. Mine is using fan/heat exchanger since I didn’t have sufficient time when the builds happened or I would done in floor pex. I can’t be more pleased, much better experience crawling around on 70•F concrete working in things.