The "heat pump, the water heater" are high wattage devices, and are likely 220vac too.
It looks like the best X10 module can do 4400 watts.
ActiveHome Pro: X10 Pro Switch
Is your hot water heater under that limit?
To use X10, it seems like you would need to add plugs to your hardwired appliances. Will they still meet code?
I'm curious if the 220 switches both sides of the line?
Since some 220 appliances use both 110 & 220, so a single switch may not do the trick.