Looking back at the preamble of the 2015 NSPS, EPA mentions the idea of requiring a minimum efficiency for OWB's (Hydronic heaters). Their goal being to reduce PM2.5, the OWB's can burn quite a bit of fuel, but to be fair, each installation has to be reviewed upon it's own merits. If a home has a tremendous heat loss factor and the owner isn't willing to upgrade things like windows, doors, siding, insulation, then a larger amount of heat production will be required.
Often in forum folks ask about age of house, types or number of windows, doors, r-value etc. One factor we should all remember is the human factor! My wife wants it 72 in the summer and 82 in the winter....go figure.
Our home was built in 1895. But is has received (thanks to Covid knocking back my travels last year) a vast upgrade. All walls were 2 x 4 are now 2 x 6, R34 (versus the
nothing! that was in the walls), 5/8" OSB, Tyvek House wrap and then new concrete siding. We reduced our wood consumption from 4.5 cords to 3 cords and that really was noticeable.
If EPA were to implement a minimum efficiency, it certainly would scale back the number of available units for consumers. The pellet models seem to do quite well in the eyes of regulators are seem to produce less PM2.5 You might look at a pellet furnace.
You have two stoves doing the job for you. You have lots of seasoned wood which means you have lots of time to evaluate your options. These forums are great for those that have the time and dedication to learning. You're on the right path!
Oh, I also built a new hearth and put a King 40 in the corner. P.S. The boards on the wall are NOT wood, but concrete, so do not worry about my clearances.