ClimateSync

Developed with Plugwise Emma in mind. Source climates expose current_temperature and temperature; destinations may expose either a single temperature target or a target_temp_low / target_temp_high range.

Release 1.2.7

This release adds a downloadable Home Assistant diagnostics file. It captures the configured source and destination roles, current source health and deltas, demand state, setpoint calculation, timestamps, counters, and the latest error. It contains no credentials and does not change ClimateSync's control behaviour.

Release 1.2.6

This release adds two first-class heating-demand binary sensors. Heating Demand Active follows all configured sources, while Primary Heating Demand Active follows only the user-selected primary subset. Both use the exact same configured activation and deactivation thresholds; the primary scope does not change destination control. The setup and options flows are now a documented four-step wizard with Next buttons between steps and Submit only on the final step.

Release 1.2.5

This release retains the clearer source-health diagnostics from 1.2.4 while restoring the active idle fallback when no usable source remains. That fail-safe withdraws a potentially stale heating request instead of leaving the last destination target untouched.

Release 1.2.4

This release makes partial source failures explicit and safe. A source climate that is off but still exposes a valid current temperature is treated as a usable inactive room with zero heating demand. Unavailable or incomplete sources are reported as degraded_source_data, while healthy rooms continue to drive the destination. ClimateSync suppresses destination writes only when no usable source remains.

Release 1.2.3

This release adds configurable heating-demand hysteresis. Small positive room deltas no longer start the destination thermostat immediately; by default, demand starts at 0.3 °C and stops at 0.1 °C. The existing destination-setpoint anti-flap and rounding behaviour remain unchanged. Heating range destinations are supported by controlling target_temp_low while preserving their current target_temp_high atomically.

ClimateSync is a HACS-ready Home Assistant custom integration that implements delta-based thermostat synchronisation. It reads the heating demand (delta between target and current temperature) from multiple source climate entities (rooms) and drives a single destination thermostat by continuously adjusting its target temperature.

Why delta-based instead of copying the highest setpoint?

Instead of simply syncing the highest source setpoint to the destination, ClimateSync uses the maximum delta (largest gap between target and current temperature across all rooms) and adds it to the destination's own current temperature:

destination_target = destination_current_temperature + delta_max

This approach was designed with the Plugwise Emma in mind. The Emma is connected to the central-heating boiler (CV) over OpenTherm and internally calculates a desired CV water temperature based on its own current delta. By feeding the Emma the home-wide maximum delta on top of its own measured temperature, ClimateSync lets the Emma function as a full OpenTherm controller — it sees the "hardest working" room's demand and adjusts the boiler modulation accordingly.

Even without an Emma, this delta-based method is more accurate than copying setpoints because it accounts for how far the destination already is from equilibrium.

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Features

• Event-driven updates — reacts immediately to temperature changes.
• Periodic resync (configurable, default 60 s) to recover from missed events.
• Anti-flap: only sends climate.set_temperature when the change exceeds a configurable threshold (default 0.2 °C).
• Configurable demand hysteresis: start heating at 0.3 °C room delta and stop at 0.1 °C by default.
• All-source and primary-source heating-demand binary sensors, both driven by the configured hysteresis.
• Destination target selection: ordinary temperature (default) or heating-range target_temp_low.
• Rate limiting: maximum one service call per 10 seconds (configurable).
• Rich diagnostic sensors plus a downloadable diagnostics file for support and troubleshooting.
• No controllable entities — all control is internal via climate.set_temperature.

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Installation

Via HACS (recommended)

1. Open HACS → Integrations → ⋮ → Custom repositories.
2. Add https://github.com/Patrick1610/ClimateSync as an Integration.
3. Search for ClimateSync and install.
4. Restart Home Assistant.

Manual

1. Copy custom_components/climatesync/ to your <config>/custom_components/ directory.
2. Restart Home Assistant.

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Configuration

Navigate to Settings → Devices & Services → Add Integration → ClimateSync.

Step 1 — Source rooms

Select one or more climate entities that represent the rooms whose heating demand should be tracked. Each selected entity must expose current_temperature and temperature attributes.

Step 2 — Primary sources

Select the subset of source rooms that may enable other rooms to piggyback on an existing heating run. General destination control still uses all sources. A secondary room can therefore start heating when it falls below its own target, but it does not turn on Primary Heating Demand Active.

Existing installations migrate with every existing source selected as primary, so the upgrade does not silently narrow their demand scope.

Step 3 — Destination & setpoint settings

Field	Default	Description
Destination climate entity	—	The thermostat that ClimateSync will control.
Destination target	Target temperature	Select ordinary temperature or lower target target_temp_low for a heating range climate.
Idle temperature	5.0 °C	Target temperature sent to the destination when no room has a positive delta (all rooms are at or above their target).
Maximum setpoint	35.0 °C	Hard ceiling for the destination setpoint.
Rounding mode	1 decimal	Step size used for the computed setpoint.
Rounding direction	nearest	Whether the computed setpoint is rounded down, normally, or up within the selected rounding mode.

Step 4 — Demand & safeguards

Option	Default	Description
Resync interval	60 s	How often ClimateSync checks even without state changes.
Minimum destination change	0.2 °C	Only send a new destination setpoint when the change exceeds this. It does not determine demand state.
Heating-demand activation threshold	0.3 °C	Delta required to switch either demand scope on.
Heating-demand deactivation threshold	0.1 °C	Delta at or below which an active demand scope switches off. Must be lower than activation.
Minimum send interval	10 s	At most one destination service call per this many seconds.

Options Flow — reconfigure everything via the settings gear

After setup, open the integration → Configure (⚙ gear icon) to get the same four-step wizard again. Intermediate steps show Next; only the final step shows Submit. You can change:

• Step 1: add or remove source rooms;
• Step 2: choose the primary subset;
• Step 3: change destination and setpoint behaviour;
• Step 4: change hysteresis, resync, anti-flap, and rate limiting.

Option	Default	Description
Destination thermostat	—	Change which thermostat is controlled.
Destination target	Target temperature	Select ordinary temperature or lower target target_temp_low for a heating range climate.
Idle temperature	5.0 °C	Temperature sent when no room needs heating.
Maximum setpoint	35.0 °C	Hard ceiling for the destination setpoint.
Rounding mode	1 decimal	Step size used for setpoints.
Rounding direction	nearest	floor, nearest, or ceiling rounding within the selected mode.
Resync interval	60 s	How often ClimateSync checks even without state changes.
Minimum change threshold	0.2 °C	Only send a new setpoint if the change exceeds this.
Heating-demand activation threshold	0.3 °C	Minimum room delta required to activate the destination thermostat.
Heating-demand deactivation threshold	0.1 °C	Delta at or below which active heating demand stops. Must be lower than the activation threshold.
Minimum send interval	10 s	At most one service call per this many seconds.

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Algorithm

For each source climate entity (room):
    current = current_temperature attribute
    target  = temperature attribute
    if state == off and current is valid:
        source is usable but inactive; delta = 0
    elif current or target is missing/unavailable:
        source is degraded; delta = 0
    else:
        source is active; delta = max(target - current, 0)

If no usable source remains:
    apply idle_temperature to withdraw prior heating demand

delta_max = max(all room deltas)

If demand is inactive and delta_max >= demand_activation_threshold:
    demand becomes active
If demand is active and delta_max <= demand_deactivation_threshold:
    demand becomes inactive

primary_delta_max = max(deltas of configured primary sources)
Apply the same activation/deactivation hysteresis independently to
primary_delta_max to calculate primary_demand_active

If demand is inactive:
    setpoint_raw = idle_temperature        # No room needs heating
Else:
    setpoint_raw = destination_current_temperature + delta_max
    # The destination target is set to its own current temperature
    # plus the largest demand across all source rooms. This means the
    # destination "feels" the same heating gap as the hardest-working
    # room, which is critical for OpenTherm controllers like the
    # Plugwise Emma that modulate boiler output based on their own
    # observed delta.

rounded_setpoint = round_setpoint(setpoint_raw, rounding_mode, rounding_direction)
setpoint_final = min(rounded_setpoint, maximum_setpoint)

If abs(destination_current_target - setpoint_final) > min_change_threshold:
    If time_since_last_call >= min_send_interval:
        If destination_target == temperature:
            climate.set_temperature(destination, temperature=setpoint_final)
        Else:
            climate.set_temperature(
                destination,
                target_temp_low=min(setpoint_final, current_target_temp_high),
                target_temp_high=current_target_temp_high,
            )

Home Assistant requires both range bounds in the same set_temperature action. ClimateSync therefore reads the upper target again immediately before applying a lower target, preserves it in the same action, and never controls cooling through target_temp_high.

Rounding mode and direction

The rounding mode determines the step size. The rounding direction determines where the raw setpoint lands within that step size. ClimateSync applies epsilon-safe floor/nearest/ceiling rounding to avoid floating-point edge cases around step boundaries.

nearest is the default and preserves the historical ClimateSync behaviour for existing installations. If an older config entry does not contain rounding_direction, ClimateSync treats it as nearest.

Mode	Example input	Result
0.5 steps	19.3	19.5
1 decimal	19.33	19.3
2 decimals	19.333	19.33

Direction	Behaviour
floor	Always round down within the selected mode.
nearest	Round to the nearest step, matching the old behaviour.
ceiling	Always round up within the selected mode.

Plugwise Emma examples:

Mode + direction	Raw setpoint	Sent setpoint
0.5 steps + ceiling	19.1	19.5
0.5 steps + ceiling	19.5	19.5
0.5 steps + ceiling	19.6	20.0
0.5 steps + floor	19.1	19.0
0.5 steps + floor	19.9	19.5
1 decimal + ceiling	19.11	19.2
1 decimal + floor	19.19	19.1

For Plugwise Emma, 0.5 steps can be useful because Emma commonly accepts half-degree setpoints. Combining 0.5 steps with ceiling can help when small RoomMind deltas would otherwise disappear through normal rounding, for example a raw setpoint of 19.1 becoming 19.5 instead of 19.0.

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Entities

All entities are attached to a ClimateSync device. Sensors (setpoint, deltas, destination target) are regular entities; the status sensor is classified as diagnostic. Home Assistant can also download a diagnostics file from the integration or device page.

Binary sensors

Heating Demand Active — binary_sensor.climatesync_heating_demand_active

Logical regulation demand across all configured sources. It switches on at the configured activation threshold and remains on until the maximum delta reaches the configured deactivation threshold. It means ClimateSync has a qualified heating request; it does not prove that the boiler is physically firing or that the destination accepted the last write.

Primary Heating Demand Active — binary_sensor.climatesync_primary_heating_demand_active

The same independently retained hysteresis state, calculated only over the configured primary subset. Use this entity to enable secondary rooms to piggyback without allowing those secondary rooms to trigger one another. It is unavailable when none of the configured primary sources has usable data.

Both entities expose their scope, current maximum delta, leading source, thresholds, source list, and source-health diagnostics as attributes.

Sensors

Computed setpoint — sensor.climatesync_1_destination_setpoint

Attribute	Description
destination_entity_id	The controlled thermostat
destination_target	Selected destination target: temperature or target_temp_low
destination_current_temperature	Current measured temperature at destination
destination_current_target	Current target temperature at destination
delta_max	Max delta used for this computation
demand_active	Whether the hysteresis currently considers heating demand active
demand_activation_threshold	Configured room delta required to start demand
demand_deactivation_threshold	Configured room delta at or below which demand stops
rounding_mode	Active rounding mode
rounding_direction	Active rounding direction
raw_setpoint	Unrounded destination_current_temperature + delta_max, or idle temperature when no room needs heating
rounded_setpoint	Raw setpoint after rounding mode and rounding direction
final_setpoint	Final setpoint after rounding and maximum-setpoint clamp
idle_temperature	Configured idle temperature

State: the final setpoint that ClimateSync wants to apply (destination_current_temperature + delta_max, rounded and capped by maximum setpoint).

Max delta — sensor.climatesync_2_delta_max

Attribute	Description
room_deltas	Map of {entity_id: delta} for all rooms
leading_room	Entity id of the room with the highest delta
usable_source_count	Number of sources that can safely participate
degraded_source_entities	Unavailable or incomplete sources ignored for demand
inactive_source_entities	off sources with a valid measurement and zero demand

State: the maximum delta across all rooms.

Per-room delta sensors — sensor.climatesync_delta_<slug>

One sensor per source climate entity.

Attribute	Description
source_entity_id	The climate entity this sensor tracks
current_temperature	Last known current temperature
target_temperature	Last known target temperature
raw_delta	target - current (may be negative)
source_status	active, inactive_off, unavailable, or missing_temperature

State: max(raw_delta, 0) — the effective heating demand for this room.

Destination current target — sensor.climatesync_destination_current_target

Shows the destination thermostat's actual current target temperature in real time, making it easy to compare against the computed setpoint without switching to the destination device.

Attribute	Description
destination_entity_id	The controlled thermostat
destination_current_temperature	Current measured temperature at destination

State: the destination's current temperature attribute (its active target).

Diagnostic

Status — sensor.climatesync_status (most important)

States:

State	Meaning
ok	Everything is in sync, no issues.
rate_limited	A setpoint update was suppressed because the last call was too recent.
destination_unavailable	The destination climate entity is unavailable or unknown.
degraded_source_data	One or more sources are unavailable or incomplete, but at least one usable source remains. Valid rooms continue to control the destination.
missing_source_data	No usable source remains. ClimateSync applies the configured idle fallback until a source recovers.
apply_failed	The climate.set_temperature service call threw an exception. Check last_error.
mismatch	The destination's actual target deviates from the desired setpoint beyond the threshold. ClimateSync will attempt to correct this on the next cycle.

Attributes:

Attribute	Description
last_update_time	ISO timestamp of the last evaluation
last_service_call_time	ISO timestamp of the last climate.set_temperature call
last_desired_setpoint	What ClimateSync computed as the ideal setpoint
last_applied_setpoint	What was last actually sent to the destination
current_destination_target	The destination's actual temperature attribute right now
rounding_mode	Active rounding mode
rounding_direction	Active rounding direction
raw_setpoint	Last unrounded setpoint
rounded_setpoint	Last rounded setpoint before maximum-setpoint clamp
final_setpoint	Last final setpoint after rounding and clamp
mismatch_seconds	How long (seconds) the desired and actual setpoint have been diverging
mismatch_since	ISO timestamp of when the mismatch started (null when in sync)
resync_count	Number of periodic resyncs since startup
apply_attempts	Total service call attempts since startup
apply_failures	Total service call failures since startup
evaluation_count	Total evaluation cycles since startup
skipped_anti_flap	Times a setpoint update was skipped because the change was within the threshold
skipped_rate_limit	Times a setpoint update was skipped due to rate limiting
last_error	Last exception message, if any
source_count	Number of configured source climates
usable_source_count	Number of sources currently safe to use
degraded_source_entities	Sources currently ignored because data is unavailable or incomplete
inactive_source_entities	off sources that remain valid measurements with zero demand

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Troubleshooting

Destination is not accepting the setpoint

Some thermostats (e.g. Plugwise Emma) only accept specific temperature steps. Use the 0.5 steps rounding mode in that case. If small RoomMind deltas are rounded away, use Rounding direction = ceiling so a raw setpoint such as 19.1 is sent as 19.5 instead of 19.0.

mismatch_seconds keeps growing

An external automation or the user may be overriding the destination's target. ClimateSync will keep trying to reapply on every evaluation cycle and resync. Check if another integration or automation is fighting over the thermostat.

rate_limited appears frequently

The source rooms are changing temperature very rapidly. Increase min_send_interval in the Options Flow to reduce chatter.

missing_source_data

No selected source currently provides usable data. ClimateSync actively applies the configured idle temperature so an earlier heating request cannot remain in effect. Restore at least one source with a valid current_temperature and temperature, or an off source with a valid current_temperature.

degraded_source_data

At least one source is unavailable or lacks a required temperature attribute. Other usable rooms continue to be processed. Inspect degraded_source_entities and each delta sensor's source_status attribute.

destination_unavailable

The destination thermostat is offline. No service calls are made. ClimateSync will recover automatically once the entity becomes available again.

apply_failed

Check last_error in the sensor.climatesync_status attributes. Most likely the climate entity does not support the climate.set_temperature service or the entity id is wrong.

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Compatibility

ClimateSync uses only the standard climate.set_temperature service and reads standard climate entity attributes (current_temperature, temperature). It works with any climate integration that follows the standard HA climate platform contract, including but not limited to:

• Plugwise Emma / Smile
• Generic Thermostat
• ESPHome climate components
• Z-Wave thermostats
• Zigbee thermostats (ZHA / Zigbee2MQTT)
• Google Nest (via the Nest integration)

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License

MIT — see LICENSE.