This rule saves a ton of money by only allowing the water heater run during off peak hours. You can modify to match your power company's off-peak/on-peak schedule.
It also has a "set it and forget it" feature to flip a virtual switch anytime during the week, and the water heater will come on at the off-peak hour (here, it's 7:00PM) for 90 minutes. This is nice if you think you'll need a shower in the evening and don't want to spend big bucks during on-peak hours (here, on-peak hours are M-F, 3PM-7PM).
The second rule limits the amount of time (30 minutes) the water heater is on during on-peak hours, if someone manually turns it on between 3PM-7PM.
If you added a temp probe buried under insulation and touching tank wall you could maybe take this a step further. Then you could raise your set temp higher to say 140 degrees (from typical 120 degrees) and treat that upper limit more as a fail-safe upper end and then control tank temp with a temp probe and cycling power to the elements. You might want a solid state relay (with zero crossing feature) instead of contact type relay which might burn out over time.
Then you could do things like:
Ramp tank up to higher temp for morning demands, showers etc. while in off peak time.
Set a floor temp for peak periods such that water is heated in high demand times if the temp drops below that level. Maybe set a lower target temp say 100-110 degrees when this peak heating is required to keep it economical.
If you have certain laundry days factor that into the heat schedule.
If you run dishwasher daily at a certain time you could set a certain target for that usage.
anyway just some thoughts. Just be sure to keep a fail-safe mechanism in place in case Hubitat locks up and keeps the heater powered up.
An additional benefit of setting a higher temp, like 140F, is that it ensures the water heater doesn't become a breeding ground for Listeria monocytogenes. The latter being especially likely when a heater is permitted to reach temperatures below 120F.
I'm always nervous that my definition of 3PM might be different than the power company. If I was super paranoid, I'd program in a 30 minute difference to be sure. It probably doesn't matter much, even if you are off a few minutes, it's just a few minutes of high usage.
I have a similar setup, but done to control the noise from a power vent gas water heater and not for cost reasons.
