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What we built and why
In this project, we automated a fireplace chimney system(pumps, fans, temperature sensors), added hot and cold water metering, chimney heat power production metering, implemented leak detection, and integrated everything into Home Assistant, with all core logic handled locally via a MiniPLC and WLD-521-R1 extension module.
System Diagram & ArchitectureThis system combines chimney heat recovery, hydronic heating, metering, leak detection, back-up gaz heater and indirect heater.
Key Elements of the SystemChimney Water Jacket & Air Heat Exchanger
- T1 & T2 – Water Jacket Temperature Sensors - Surface-mounted sensors that monitor the temperature of the water inside the chimney’s integrated water jacket.
- T3 & T4 – Chimney Air Temperature Sensors - Measure the temperature of air passing through the heat exchanger in the chimney’s flue.
- T8 – Fresh Air Temperature Sensor - Captures the temperature of incoming outside air before it enters the air-side heat exchanger.
- M3 (Fresh Air Fan) and M4 (House Air Fan) - Two fans used to circulate air through the chimney’s air heat exchanger — one for fresh air intake and one for indoor air recirculation.
Hydronic Heating Circuit
- T5 – Return Water Temperature Sensor - Monitors the temperature of water returning from the heating system.
- T6 – Supply Water Temperature Sensor - Measures the temperature of water leaving the chimney’s water jacket.
- T7 – Tank Output Temperature Sensor - Measures the temperature of water leaving the indirect heater tank.
- F3 – Circulation Flow Meter - Measures the flow rate in the heating loop.
- M1 & M2 – Circulation Pumps - Two pumps used to move water through the heating system and buffer tank.
- V3 – 3-Way Valve - Directs the heated water either directly to the heating circuit or through the buffer tank, depending on operating conditions.
Domestic Water System & Leak Detection
- F1 – Hot Water Flow Meter - Tracks the amount of hot water used in the household.
- F2 – Cold Water Flow Meter - Tracks cold water usage.
- V1 & V2 – Shut-off Valves - Motorized valves used to isolate the water supply in case of a leak.
- 2x Leak Sensors - Detect the presence of water in critical areas to prevent flooding or damage.
The automation system is built around two main devices:
- A MiniPLC, which acts as the Modbus RTU master and executes all system-wide control logic.
- A WLD-521-R1 module, which serves as a smart Modbus slave for all water- and leak-related I/O, as well as flow metering and thermal energy tracking.
All logic is handled locally by the MiniPLC, while the WLD-521-R1 autonomously supervises flow inputs, leak sensors, and provides data for heat energy calculations — all accessible via Modbus.
Connection & Roles
MiniPLC
The MiniPLC acts as the central controller and Modbus RTU master, executing all automation logic and system coordination.
- RS-485 Modbus Master
- Polls the WLD-521-R1 for flow, leak, and temperature data
- 1-Wire Temperature Sensors BUS1: (T1, T2 – Water jacket surface temperatures
- 1-Wire Temperature Sensors BUS2: (T3, T4 – Chimney air temperatures T8 – Fresh air inlet temperature)
- Relay1 → Pump 1 (Primary circulation pump)
- Relay2 → Pump 2 (Secondary/booster or tank pump)
- Relay3 → 3-Way Valve (heating circuit or tank)
- Relay4 → Fan 1 (Fresh Air Fan)
- Relay5 → Fan 2 (House Air Fan)
- Relay6 → Gas Heater (backup heating element)
The MiniPLC runs all core control logic for chimney operation, heat routing, pump/valve sequencing, and system safety.
WLD-521-R1 Module
The WLD-521-R1 is connected as a Modbus RTU slave over RS-485 and handles all water flow, leak detection, and heat energy calculation features.
- DI1, DI2: Leak sensors (dry-contact type)
- DI3: Heating circuit flow meter (F3)
- DI4: Hot water flow meter (F1)
- DI5: Cold water flow meter (F2)
- 1-Wire Temperature Sensors( T5 – Return water temperature, T6 – Supply water from chimney jacket, T7 – Water temperature after the buffer tank
- R1 → Shut-off Valve for Cold Water
- R2 → Shut-off Valve for Hot Water
WLD-521-R1 Internal Calculations:
Heat energy production is calculated using:
- Flow data from DI3 (F3) ΔT from T6 − T5
- Outputs: Instantaneous power (W), Accumulated energy (kWh)
This system runs fully local: MiniPLC executes the control logic; WLD‑521‑R1 handles flow/leak/ΔT/energy and exposes data over Modbus RTU; Home Assistant provides dashboards.
1) Warm‑up detection
Pump1: Start when (T1 ≥ 35 °C OR T2 ≥ 35 °C) and < 45 °C.
Pump2: Start when (T1 ≥ 45 °C OR T2 ≥ 45 °C).
2) Routing decision (3‑way valve V3)
The PLC reads a Heating ON/OFF signal from Home Assistant.
If Heating = ON: set V3 = Direct (send heat straight to the heating loop).
If Heating = OFF: set V3 = Tank (charge buffer) if T7 < T6 with hysteresis.
If T7 ≥ T6 (tank can’t absorb heat), set V3 = Direct.
3) Air‑side recovery (fans)
If (T4 − T3) ≥ 28 °C, enable Fan1 and Fan2. (The setpoint at 28 °C can be setted via HA dashboard)
4) Gas assist (backup heat)
If Heating = ON and (T1 < 35 °C AND T2 < 35 °C), enable the Gas heater (Relay 6).
Disable gas when chimney heat recovers above 35 °C (with a little hysteresis).
5) Energy & metering
The WLD‑521‑R1 computes Power and Energy from F3 and (T6 − T5).
F1/F2 provide hot/cold water rates and totals.
PLC/HA display live graphs and history.
6) Leak protection (instant)
On any leak (DI1 or DI2):
WLD closes V1/V2 (shut‑off valves).
MiniPLC — Logic & MappingWarm‑up detection in ESPHome:
time:
- platform: pcf8563
id: pcf8563_time
address: 0x51
on_time:
- seconds: /10
then:
- if:
condition:
lambda: return id(chimney_water1).state > 35 || id(chimney_water2).state > 35;
then:
- if:
condition:
lambda: return id(chimney_water1).state < 35 || id(chimney_water2).state < 45;
then:
- switch.turn_on: relay_1
- switch.turn_off: relay_2
- switch.turn_off: relay_6
else:
- switch.turn_on: relay_1
- switch.turn_on: relay_2
- switch.turn_off: relay_6
else:
- if:
condition:
switch.is_on: heating
then:
- switch.turn_off: relay_1
- switch.turn_off: relay_2
- switch.turn_on: relay_6
else:
- switch.turn_off: relay_1
- switch.turn_off: relay_2
- switch.turn_off: relay_6
Air‑side recovery (fans):
climate:
- platform: thermostat
name: "Thermostat Climate Controller"
visual:
min_temperature: 18
max_temperature: 35
temperature_step: 1.0
sensor: sensor3
min_cooling_off_time: 60s
min_cooling_run_time: 60s
max_cooling_run_time: 60s
supplemental_cooling_delta: 5
min_idle_time: 30s
cool_action:
- switch.turn_on: relay4
supplemental_cooling_action:
- switch.turn_on: relay5
idle_action:
- switch.turn_off: relay4
- switch.turn_off: relay5
default_preset: Home
preset:
- name: Home
default_target_temperature_high: 23 °CConnecting Modbus external package for WLD module:
uart:
id: uart_modbus
tx_pin: 17
rx_pin: 16
baud_rate: 19200
parity: NONE
stop_bits: 1
modbus:
id: modbus_bus
uart_id: uart_modbus
packages:
wld:
url: https://github.com/isystemsautomation/HOMEMASTER
ref: main
files:
- path: WLD-521-R1/Firmware/default_wld_521_r1_plc/default_wld_521_r1_plc.yaml
vars:
wld_prefix: "WLD#1"
wld_id: wld_1
wld_address: 6
refresh: 1dWLD WebConfig — 1-Wire setup:
This screen is where I register the temperature probes on the WLD-521-R1. After clicking Scan 1-Wire, the module lists ROM IDs under Discovered devices. I assign a friendly name and click Add so each probe moves into Stored sensors (flash) with a numbered position (#1…#n). Those positions are later selected in the Heat/ΔT configuration (e.g., A = supply, B = return).
The 1-Wire Live Temperatures table auto-refreshes with current readings and error counters. Here you can see Outside temperature and Boiler T1/T2/T3 updating with 0 errors—handy for confirming wiring and sensor order before enabling heat-energy calculations on the flow input.
Note on names vs. main schematic: in this screenshot the labels don’t match my main scheme. The correct mapping is:
- T3 = Supply water (from chimney jacket to loop)
- T2 = Return water (back from loop)
- T1 = Water after tank (tank outlet to loop)
The Outside temperature probe is included for visibility on the main dashboard only; it is not used in the control logic.
Water leak detection in WLD module:
WLD WebConfig — DI3 (Flow + Heat/Energy):
This card shows IN3 configured as a Water counter for the heating loop flow meter.
- Pulses per liter: 396 (meter constant).
- Calibration: both Total × and Rate × at 1.000000 (no scaling).
- Live values: Rate ≈ 4.697 L/min, Total ≈ 86.874 L.
- Buttons: Reset pulses (raw counter), Reset total (moves the liters baseline), and Calc from external (derives Total× from a known external volume since last reset).
- Heat/ΔT enabled on this input
Heat calculation is turned on so the WLD can compute thermal power/energy from the same flow plus two 1-Wire sensors:
- Sensor A (supply): Boiler T3 → TA = 39.50 °C
- Sensor B (return): Boiler T2 → TB = 29.63 °C
- ΔT: 9.88 °C (= A − B)
- Fluid properties: cp = 4186 J/kg·°C, ρ = 1.0 kg/L, Calibration × = 1
Outputs (live): Power ≈ 3236 W, Energy = 2, 638, 810 J (≈ 0.73300 kWh)
Home Assistant IntegrationData is exposed (temps, flows, leaks, etc) in HA
This panel shows the values the MiniPLC reads from the WLD-521-R1 over Modbus and exposes to Home Assistant:
- 1-Wire temperatures (#1…#10): live °C values from the WLD’s 1-Wire list (e.g., Temp1 ≈ 10.875 °C, Temp2 ≈ 20.063 °C, Temp3 ≈ 20.313 °C, Temp4 ≈ 21.813 °C; unused channels report 0.000 °C).
- Heat channels (Heat1…Heat5): each provides Energy (kWh), Power (W), and ΔT (°C) for a paired flow+temperatures input.In this snapshot, Heat3 is active: Power ≈ 5, 122 W, ΔT ≈ 13.938 °C, Energy ≈ 1.523 kWh; other heat channels are idle.
- Flow counters (Flow1…Flow5):Rate (L/min) and Total (L) from pulse inputs.Here Flow3 shows ≈ 2.121 L/min and 161.422 L total; Flow1/2/4/5 are at 0.000 L/min with their respective totals (e.g., Flow4 total 8.220 L, Flow5 total 0.003 L).
This view is handy for quick health checks: temps are updating, the active heat channel’s ΔT/Power align with Flow3, and any zero/flat readings are obvious if a sensor or meter goes offline.
Home Assistant — Chimney & Water Automation Dashboard
This is the single pane I use to monitor and validate the whole setup: chimney, hydronic loop, buffer tank, air heat-exchanger, and gas backup.
- Top status chips: live states for the chimney, heating demand, Pump 1 and Pump 2, Fan 1 and Fan 2, and the gas boiler (including burner status, modulation, and hours). At a glance I can see the chimney is active, both pumps and fans are running, and the gas boiler is off.
- Warm-up trend (center graph): real-time curves for water temperatures as the burn progresses. Supply rises, the return stays lower, and the spread between them shows the heat being moved.
- Hydronic bars: Water inside 1 and 2 (jacket temperatures); Water supply and Return (loop); To indirect tank 1 (from chimney) and 2 (from solar collector) plus Inside tank (buffer status); and Heat-water flow in L/min from F3. These tell me whether routing is direct or via the tank and whether flow and ΔT look healthy.
- Air heat-exchanger section: Air inlet versus Air outlet 1 and 2 shows the temperature gain across the chimney exchanger when the fans are on.
- Quick controls (bottom right): setpoints for fan start triggers.
Why it’s useful: this layout mirrors the automation flow—warm-up, 3-way valve routing, air-side recovery, and gas-assist lockout—so I can verify in one view that the PLC is doing the right thing and that the WLD meters (flow and energy) match the temperature behavior.
Home Assistant Energy
Adding parameter to the Energy dashboard:
Energy dashboard:Energy & Water Dashboard
Home Assistant doesn’t (yet) have a native “heat energy by source” card for my setup, so I’m using the Energy view to visualize everything together:
- Gas for heating consumption — energy produced by the gas heater for space heating.
- Gas for hot-water consumption — gas used only for DHW.
- Chimney heating energy — heat produced by the chimney (from WLD calorimetry using F3 × (T6–T5)).
- Solar collector energy — contribution from the solar loop (can be a little negative on recalcs/offsets).
- Cold/Hot water consumed — totals from the F2/F1 flow meters; shown with a daily/period total.
This lets me compare how much heat the gas heater provides vs. the chimney (and solar), and also track water usage in the same view.
Pump2 fail-safe on PLC/power loss:
- M2 (Pump2) is wired through the NC contact of Relay2.
- In ESPHome, Relay2 is configured inverted.
Result:if the PLC fails or loses power, Relay2 de-energizes → NC path closes → Pump2 turns ON automatically (emergency circulation).
High-temperature mechanical thermostat (90 °C)
A mechanical thermostat on the chimney circuit is set to 90 °C.
On trip, it directly switches ON Pump2, independent of the PLC (hardware override).
Automatic jacket cooling valve
The chimney has a mechanical thermostatic cooling valve with an external temperature probe in the water jacket:
If the jacket overheats (or if pumps/flow stop), the valve automatically opens cold water to cool the jacket and prevent boiling.
Thermo/pressure relief valve (≈98 °C/4 Bar)
A mechanical temperature/pressure relief valve opens at about 98 °C to discharge hot water from the jacket.
Displaced volume is replenished from the expansion tank, maintaining system fill and preventing vacuum.
Notes:
These protections are hardware-level and work even if software control is unavailable.
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