Although mine does a good job of heating my house I gotta say that I would build it way different. I would lay the big tank down versus upright and use a lot bigger fire box. I've come to believe that more firebox area and less water is the key. (or should I say a better balance between gallons vs. sq. inches of firebox is the key)
Imagine trying to heat 20,000 gallons with a firebox the size of a shoe box for an analogy.
Plus if you will notice on mine the amount of firebox protruding outside the water jacket. (wasted heat)
I drew this up about a year ago and someday I may build it.
I would cut the tanks flat and weld 3/8" plate to the front for a flat surface for the doors. Working with all the round areas was a pain.