I can control most, possibly all functions of my Stiebel Eltron heatpump through a HACS plugin, but I've found that once it was dialled in it doesn't actually need controlling and just manages itself. So I use it purely for energy reporting.

Hot water heater? Yes, I did find it.

I specifically bought a Rheem ("Performance Platinum" model) last year because I can control it with Esphome.

Little M5Stack Atom controller with rs485 module plugs right into the port on the water heater, using a simple old-school modular phone cord. I do not use the water heater's wifi or Rheem account/cloud service.

It works great completely local from HA. I automated it to boost the thermostat setting extra high during lower electricity rate time of day, and lower the thermostat during peak billing time. So I can bank extra stored heat, for less cost.

I added a thermostatic mixing valve on output, to ensure regulated safe temperature to pipes and fixtures.

https://github.com/esphome-econet/esphome-econet

I have a Panasonic heatpump and use HeishaMon to control it. It works.

Look for something with OpenTherm connection. You can use you own local ESPhome thermostat with any of them

An example of ours https://github.com/jellewie/esphome-opentherm-thermostat

mitsubishi's ac/heat pumps, that have a cn105 connector (the connector is on each indoor unit; it should also work for the water tank indoor unit) can be integrated with esphome, but you have to connect each indoor unit seperatly. If you run jysty cable from each indoor unit to a central point you can use 1 esp32 for 2 indoor units. From my experience it works very well, but i have my esp on wired ethernet.

I don't have the water heater indoor unit, so that's part of my air indoor unit esphome config:

logger:
  baud_rate: 0

external_components:
  - source: github://echavet/MitsubishiCN105ESPHome
    refresh: 0s

climate:
  - platform: cn105
    id: hvac_eg
    name: "HVAC EG"

    horizontal_vane_select:
      icon: 'mdi:arrow-left-right'
      name: EG Horizontal Vane
    vertical_vane_select:
      icon: 'mdi:arrow-up-down'
      name: EG Vertical Vane

    supports:
      fan_mode: ["AUTO", "DIFFUSE", "LOW", "MEDIUM", "HIGH"]
      swing_mode: ["OFF", "VERTICAL", "HORIZONTAL", "BOTH"]

    uart_id: hvac_eg_uart

    update_interval: 500ms

sensor:
  - platform: uptime
    name: Uptime

uart:
  - id: hvac_eg_uart
    rx_pin: 5
    tx_pin: 17
    baud_rate: 2400