What are the unused 240V breakers in my panel for?
2 x 50A for furnace implies electric heat. (If it was a heat pump, that would be combined with the 2 x 40A AC). That all points to &quot;everything electric&quot; because in most places if you have gas available then you use that for heat rather than electric. Plus &quot;2x&quot; indicates this is a large house. While you have a gas water heater now, my hunch is that your house originally had electric water heater(s) and, due to the size of the house, was wired up for 3 water heaters. That also fits with the (typical, but not universal) slower recovery time for residential electric water heaters compared to gas. One large gas water heater could easily produce as much hot water (between faster recovery and larger capacity) as 2 electric water heaters. Then at some point (my parents did this years ago, but they added gas heat at the same time), someone got gas piped into the house and replaced the electric water heaters with gas.