Jan-Åge Johnsen

lives and works in Norway, doing Azure, Power Platform and sometimes smart house things.

6 minute read

This guide walks you through connecting ESPHome Altherma to Emoncms in Home Assistant for long-term heat pump monitoring. Both local and remote setups are covered — starting with local.

ESPHome Altherma + Emoncms setup diagram

Why use Emoncms with your heat pump?

Home Assistant is excellent for real-time monitoring and control, but it wasn’t built for analyzing long-term heat pump data. Emoncms fills that gap.

What you gain:

  • Energy dashboards the built-in MyHeatpump app gives you a dedicated heat pump performance dashboard with COP, heat output, electric consumption, and temperatures over time.
  • Long-term data feeds are stored efficiently and queryable over months and years, well beyond how most Home Assistant instances are configured.
  • Calculated feeds Emoncms can derive values like heat output in watts and cumulative kWh directly from raw sensor data, without extra automations in Home Assistant.
  • Open standard your data stays on your own hardware (local install) or your own Emoncms account (remote), with no vendor lock-in.
  • Performance monitoring tracking COP (Coefficient of Performance = heat out ÷ electricity in) over time lets you spot degradation, validate refrigerant charge, and compare heating seasons.

Typical use case: You have a Daikin Altherma with ESPHome Altherma reading sensors over UART, and you want to know: is my heat pump actually running efficiently? How much heat did it produce last month compared to how much electricity it used? Emoncms answers those questions out of the box.

Install Emoncms as a Home Assistant Add-on

This is only required for running Emoncms locally.

Go to Settings → Add-ons → Add-on Store.

Add the Emoncms repository by clicking the three-dot menu (…) in the upper right corner and selecting Repositories.

Add: https://github.com/Open-Building-Management/emoncms

Then use the … menu again and select Check for updates.
Search for emoncms and install it.

Emoncms add-on in the store

From the add-on info screen, open the Web UI. You may also want to enable Show in sidebar.

Emoncms add-on info screen

Get Your Emoncms API Key

In Emoncms, go to My Account and copy the Read & Write API Key — you will need it in the next step.

Emoncms API key location

Configuration in Home Assistant

Configure the rest_command

This sends sensor data from Home Assistant to Emoncms.

Add the following to /homeassistant/configuration.yaml (you can use the File Editor add-on):

rest_command:
  emoncms_post:
    url: "https://YOU_HOME_ASSISTANT_IP:7443/input/post.json?apikey=YOUR_KEY&node="
    method: POST
    verify_ssl: false
    payload: "json="
    headers:
      Content-Type: application/x-www-form-urlencoded

Replace YOUR_HOME_ASSISTANT_IP and YOUR_KEY with your actual values.

After saving, do a Quick Reload or Restart Home Assistant for the change to take effect.

Test the rest_command

Go to Settings → Developer Tools → Actions, select rest_command.emoncms_post, and test with:

action: rest_command.emoncms_post
data:
  node: test
  payload: '{"test":1}'

Testing the rest_command

A successful response returns ok. You can confirm by opening Emoncms — the test data should appear under Inputs.

Test data visible in Emoncms inputs

Install the emonncms_heatpump_sender Blueprint

The blueprint creates a Home Assistant automation that collects heat pump sensor readings on a fixed schedule and posts them to Emoncms via the rest_command configured earlier. It runs every 30 seconds by default and skips any sensors that report unknown or unavailable, so a missing sensor won’t break the whole payload.

Two values are calculated inside the automation rather than read directly from a sensor:

  • heatpump_elec — electric use in watts, computed as INV primary current (A) × Voltage (N-phase) (V).
  • immersion_elec — backup heater power in watts, summed from the BUH Step 1 and Step 2 binary sensors and their configured power values.

Go to Settings → Automations & Scenes → Blueprints → Import Blueprint and use this URL:

https://raw.githubusercontent.com/jjohnsen/esphome-altherma/refs/heads/main/homeassistant/blueprints/emonncms_heatpump_sender.yaml

After import click on the tree dots and select +Create Automation:
alt text

Blueprint inputs

Input Typical ESPHome Altherma entity Notes
Emoncms node — Name used in Emoncms. Default: ESPHome_Altherma
Interval in seconds — Default /30 (every 30 s). Must match the feed interval in Emoncms
heatpump_primary_current INV primary current (A) Combined with voltage to calculate heatpump_elec
heatpump_voltage Voltage (N-phase) (V) Combined with current to calculate heatpump_elec
heatpump_flowT Leaving water temp. after BUH (R2T) Used to derive heatpump_deltaT and heat output
heatpump_returnT Inlet water temp. (R4T) Used to derive heatpump_deltaT
heatpump_outsideT Outdoor air temp. (R1T) —
heatpump_roomT Room temperature Typically a separate sensor inside your home
heatpump_targetT LW setpoint (main) —
heatpump_flowrate Flow sensor (l/min) Used to calculate heat output in Emoncms
heatpump_dhw 3-way valve (On:DHW / Off:Space) Binary sensor — sent as 1 (DHW) or 0 (space heating)
heatpump_dhwT DHW tank temp. (R5T) —
heatpump_dhwTargetT DHW setpoint —
BUH Step 1 BUH Step1 Binary sensor for backup heater stage 1
BUH Step 1 power — Watts to add when Step 1 is on. Default: 2000 W
BUH Step 2 BUH Step2 Binary sensor for backup heater stage 2
BUH Step 2 power — Watts to add when Step 2 is on. Default: 4000 W

The Interval in seconds here should match the interval you set on each Emoncms feed.

Configure all the blueprint inputs. ESPHome Altherma should already be running and will populate most of the sensor fields.

Blueprint input configuration

Configure Emoncms

Emoncms Inputs

heatpump_elec

This input must produce both electric use in watts and cumulative electric use in kWh.
Click the wrench icon and under Process, ensure Log to feed is selected.

heatpump_elec input

Set the interval to match the Interval in seconds configured in the Emoncms heat pump sender automation (default: 30 s).
Click Add:
Log to feed process setup

To add the cumulative feed, select Power to kWh, set the process name to heatpump_elec_kwh, set the correct interval, and click Add.

Your heatpump_elec process list should now look like this:
Completed heatpump_elec process list

heatpump_heat

Heat output in watts is calculated from flow rate and temperature difference using:

Heat (W) = flowrate (l/min) × ΔT (°C) × 69.78

Where: 69.78 = specific heat of water (4.187 J/g·°C) × 1000 g/L ÷ 60 s/min

Step 1: Create heatpump_deltaT

heatpump_deltaT = flow temperature − return temperature.
It does not exist as a direct sensor, so we derive it inside Emoncms.

Open the heatpump_flowT input and configure the following process steps:

  1. Log to feed use the default name, set the correct interval, click Add.
  2. - input select heatpump_returnT as the input, click Add.
  3. Click the log button next to Add process, change the name to heatpump_deltaT, set the correct interval, and click Add.

Click Changed, press to save, then Close.

The process list should look like this:
heatpump_deltaT process list

Step 2: Create heatpump_heat

Open the heatpump_flowrate input and configure the following process steps:

  1. Log to feed set the correct interval and click Add (this logs the raw flow rate).
  2. × feed select heatpump_deltaT, click Add.
  3. Calibration: × enter 69.78, click Add.
  4. Click log next to Add process, set name to heatpump_heat, set the correct interval, click Add (this is the heat output feed in watts).
  5. Click kWh next to Add process, set name to heatpump_heat_kwh, set the correct interval, click Add (this is the cumulative heat feed).

Click Changed, press to save, then Close.

The process list should look like this:
heatpump_heat process list

Remaining inputs

The remaining inputs all follow the same pattern:

  • heatpump_returnT
  • heatpump_outsideT
  • heatpump_roomT
  • heatpump_targetT
  • heatpump_dhw
  • heatpump_dhwT
  • immersion_elec

For each: click the wrench, select Log to feed, set the correct interval, and click Add.

Simple Log to feed process setup

Verify Inputs

The complete input list should look like this:
Complete Emoncms input list

Configure Feeds

Set the correct units for each feed:
Feed unit configuration

Verify

The complete feed list should now look like this:
Correct feed units

Configure the My Heatpump app

The My Heatpump app is an Emoncms built-in app purpose-built for heat pump performance monitoring.

Setup

From Apps -> +New select My Heatpump.

My Heatpump app selection

Map the app inputs to the feeds we just created:

My Heatpump app feed mapping

Check Enable daily pre-processor to split the daily view into space heating and domestic hot water, giving you separate COP and energy figures for each mode.

Click Launch App and enjoy ;)

My Heatpump dashboard in Home Assistant

Tips

  • Click on a bar in the daily chart to jump to the power chart for that day.
  • Click COP in the stats panel to toggle between COP 30 min (smoothed average) and COP Now (instantaneous).
  • For deeper analysis, the app also tracks data quality percentages for each feed, so you can see if gaps in data are affecting your COP figures.

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