I was recently looking for a way to estimate power consumption in Home Assistant without buying any additional hardware. I already have a Kill-A-Watt, so it’s easy to just go around and start collecting data for 24/7 devices and devices with on/off states in Home Assistant.

PowerCalc ties this data together with an easy to use integration.

Intro ⚡

So why am I doing all this? First I want to shout out the amazing developers behind HydroQC which brings in data from Hydro-Quebec directly into Home Assistant. It’s much faster, and updates more regularly vs Hydro’s own website. Our Landis+Gyr Gridsream RF meters seemingly have a Zigbee radio inside, but it’s disabled ☹️

So with this data in Home Assistant what more could I ask for? I want to know which devices are contributing to the totals I get from Hydro-Quebec.

That’s where PowerCalc comes in. It creates virtual power sensors with your own data, or from their library.

24/7 Devices 🔌

For devices that are always on like your home network, you can create a Daily Energy sensor.


  • Value: 50
  • Unit: W
  • Defaults to 1 day

I measured each device like my router, access points, switches, etc. I keep track of them in a spreadsheet so I can create a total value for the network power sensor.

For appliances that cycle on and off like a refrigerator, connect it to your Kill-A-Watt and measure over several days to calculate an average power. The more hours you measure, the more accurate it will be. For example 12 kWh / 48 Hours = 0.25 kW.

Static loads with on/off states in Home Assistant 💡

For example a smart light switch with 8x 4 Watt LED bulbs.

Virtual Power (manual)
Source Entity: switch.living_room

Fixed Config
Power: 4

Advanced options
Multiply Factor: 8

Gaming PC with Steam 🎮

I wanted to try something more advanced, how much power is my PC using, and how much more when I’m playing a game.

First I set up Wake on LAN to get the on/off state for my PC. You could also use the Ping integration.


  - platform: wake_on_lan
    mac: AA:BB:CC:DD:EE:FF
    name: PC

Then I hooked up my PC to a Kill-A-Watt and measured power consumption under normal use, and to make it more interesting, I tested in different games.

With the Steam integration you can easily create a Power Template in PowerCalc to map games to different power levels.

Power Template

{% if is_state_attr('sensor.steam_user', 'game', 'BattleBit Remastered') %}
{% elif is_state_attr('sensor.sensor.steam_user', 'game', 'Counter-Strike 2') %}
{% elif is_state_attr('sensor.sensor.steam_user', 'game', 'Microsoft Flight Simulator') %}
{% elif is_state_attr('sensor.sensor.steam_user', 'game', 'Aimlabs') %}
{% elif state_attr('sensor.sensor.steam_user', 'game') is not none %} # All other games
{% else %}
{% endif %}

You can also use the WoL sensor to trigger other fixed power devices like displays and other peripherals.

Heat Pump 🥶

For heat pumps you can get a rough estimate of the power consumption by using the following formula:

BTU ÷ SEER = Watts

For example 24,000 BTU ÷ 10 SEER = 2400 Watts

If you have a smart thermostat you can easily trigger off that, or else you need to set up a temperature sensor and some helpers. You could also trigger off a light sensor if your machine turns on an LED when it’s running.

Set up a Derivative helper to watch a temperature sensor placed on a register reporting every minute. My settings are Precision: 2, Time Window: 2 minutes, Time Unit: Minutes.

Then set up a Template Binary Sensor helper with the following template:

{% if states('sensor.vent_derivative') | float <= -0.25 %} # On when temp drops -0.25 C / minute
{% elif states('sensor.vent_derivative') | float >= 0.25 %} # Off when temp increases 0.25 C / minute
{% elif states('sensor.vent_temperature') | float <= 16 %} # Steady state, hold on
{% else %} 
{% endif %}

You may have to tweak this for your own HVAC system.

Vent Sensors

Come back in 6 months when I have to modify this for the winter to see how to actually do this properly 😉

It requires some additional logic to account for defrost cycles that I need live data to test with.

Honestly just buy a smart thermostat or see if your system has an LED you can attach a light sensor to and avoid all this nonsense. For an accurate reading there are current clamps you could use instead.

Final Thoughts

PowerCalc is a fantastic addition to Home Assistant, I wish I heard about it sooner. I’m looking for other ways to integrate stuff like my washer, dryer, hot water heater, etc, but I think current clamp sensors might be more realistic. And Hydro-Quebec gives me hourly data anyways so is it really necessary to go through the hassle.