Quick Summary (TL;DR)
Smart radiator valves and zoned wet underfloor heating are different hydraulic control systems. A smart TRV motor adjusts a radiator valve. A wet underfloor heating (UFH) zone usually needs a room thermostat, a compatible manifold thermal actuator, and a wiring centre or zone controller coordinating the heat source and circulating pump. A smart TRV cannot simply replace a manifold actuator or an underfloor thermostat.
Our recommendation: retrofit smart TRVs to suitable existing radiators when the boiler demand path is already understood. For a new wet UFH installation, choose a complete compatible manifold control ecosystem and plan the heat-source and pump interface before buying thermostats. Mixed radiator/UFH houses need both types of zone hardware plus coherent boiler or heat-pump demand logic. Home Assistant is useful for schedules and monitoring, but should not be the only safety-critical controller.
- Radiator-only house: compatible smart TRV heads, central boiler/heat-source controller and optional representative room sensors.
- Wet UFH-only house: room thermostats, manifold actuators, approved wiring centre, pump/boiler coordination and appropriate hydraulic controls.
- Mixed system: TRVs for radiators and separate UFH zone actuators, with a professionally designed heat-source demand and minimum-flow strategy.
- Electric underfloor heating: a different product category requiring a thermostat and appropriately rated electrical switching and floor-temperature limitation.
Smart TRVs and underfloor heating: the fundamental difference
A thermostatic radiator valve (TRV) restricts hot-water flow through one radiator. A smart TRV adds electronic temperature sensing, a setpoint and a motor. The radiator is a relatively fast-response emitter. Wet underfloor heating distributes water through long pipe loops embedded in or beneath the floor; each loop is commonly connected to a manifold with a thermal actuator that opens or closes on a call from its assigned room thermostat. Floor mass and coverings can make temperature response much slower.
Neither the radiator head nor the UFH actuator necessarily starts the boiler. That request normally travels through a heating hub, wiring centre, zone valve or manufacturer-approved heat-source interface. Heat-source modulation and safety interlocks are separate questions. A controller advertising “8 zones” may have eight thermostat inputs but a different number of actuator outputs or supported devices; check its exact specification.
| Feature | Smart radiator TRV | Wet UFH zone |
|---|---|---|
| Primary moving part | Motorised head on radiator valve body | Thermal actuator on manifold valve |
| Temperature measurement | On-head sensor or supported remote room sensor | Room thermostat; floor sensor where required |
| Typical controller | Zigbee, Thread/Matter or proprietary heating hub | Hardwired or wireless room thermostats and wiring centre |
| Heat response | Often faster; depends on radiator and water temperature | Often slower due to floor thermal mass |
| Heat-source call | Requires compatible boiler/heat-source demand coordination | Usually wiring-centre/zone-controller output |
| Hydraulic constraints | Radiator flow, balancing and bypass requirements | Loop flow, balancing, mixing, pump and minimum-flow requirements |
| Best use | Existing radiator rooms | Purpose-built wet UFH manifold zones |
What hardware do you need for a radiator-only system?
The simplest retrofit retains a correctly commissioned boiler or heat-pump control system and replaces selected compatible mechanical TRV heads with smart heads. Check the valve body thread, travel and supplied adapters. Add a representative room temperature sensorAliExpress price where the valve head is heated by its radiator or hidden by curtains. Select a Zigbee, Matter/Thread or manufacturer bridge route supported by the exact model and firmware.
The critical question is who requests heat? A smart TRV can open while the main room thermostat is satisfied and the boiler remains off. A multi-room hub may aggregate room demand and switch a boiler relay or communicate via an approved modulation interface. Do not assume Home Assistant’s climate entities automatically provide that orchestration.
| Component | Usually needed? | Buying check |
|---|---|---|
| Compatible TRV head | Per controlled radiator | Valve-body fit, adapters, battery access |
| Zigbee coordinator / Thread border router / bridge | Depends on chosen ecosystem | Local connectivity, firmware and range |
| Room sensor | Optional but often helpful | Remote-sensor support in actual integration |
| Heat-source controller | Yes, somewhere in the system | Demand aggregation and boiler/heat-pump compatibility |
| Hydraulic protections | Installer-dependent | Bypass, pump overrun, minimum flow and balancing |
What hardware do you need for wet underfloor heating?
A wet UFH manifold is not controlled by radiator heads. Each heated zone normally has a room thermostat that requests heat from a wiring centre or zone controller. The controller energises the appropriate manifold actuator outputs and, where designed, operates a pump or signals the heat source. Some installations use one thermostat for several loops in the same room; other systems divide a large room into independently controlled zones.
- Manifold: sized for the loop count, with isolation, flow setting/balancing and compatible actuator valve bodies.
- Thermal actuators: correct thread/stroke, supply voltage (often 24 V or 230 V), normally-closed or normally-open behaviour and inrush/loading characteristics.
- Room thermostats: approved hardwired or wireless units compatible with the wiring centre; optional floor sensors for floor-covering protection.
- Wiring centre/zone controller: correct zone count, thermostat protocol, actuator voltage and output ratings, pump and boiler/heat-source interfaces.
- Hydraulic controls: pump, mixing arrangement where necessary, balancing, minimum-flow provision and temperature limits designed for the heat source and floor construction.
Never mix 24 V and 230 V actuators or thermostat wiring merely because the connector looks similar. An actuator may take several minutes to open; this is normal for many thermal types and should be reflected in pump and heat-source sequencing. All mains wiring and heating plant changes must be designed and carried out by appropriately qualified professionals.
Heatmiser, Danfoss and SALUS: controller ecosystem examples
Heatmiser UH8 is an example of a hardwired eight-zone UFH wiring centre with associated thermostat and actuator wiring arrangements. Danfoss Icon2 is a dedicated room-control system for hydronic floor heating with application-specific outputs and accessories. SALUS offers UFH wiring centres including the KL08RF wireless family. These are examples of system architectures, not interchangeable parts: check region, exact revision, actuator ratings, pump interface and heat-source compatibility against current manufacturer manuals.
| Ecosystem example | Where it fits | What to verify |
|---|---|---|
| Heatmiser UH8 and compatible thermostats | Hardwired multi-zone UFH | Supply voltage, thermostat inputs, actuator output ratings, pump/boiler connections |
| Danfoss Icon2 | Integrated hydronic UFH room control | Master controller revision, thermostats, actuator compatibility, heat/cool configuration |
| SALUS KL08RF family | Wireless UFH thermostat/wiring-centre arrangement | Gateway requirements, supported actuators and heat-source interface |
| Generic ESP32AliExpress price/Home Assistant relays | Supervisory monitoring or approved low-voltage interface only | Do not substitute unapproved DIY controls for certified wiring centre or plant protections |
Mixed radiators and underfloor heating: design the demand chain
Mixed houses are common: radiators upstairs and UFH downstairs. A practical architecture keeps each emitter type’s local zone control and combines demand using the heat-source manufacturer’s supported inputs or an installer-designed control centre. The radiators may need higher water temperatures than UFH, so the hydraulic design may require separate circuits, mixing or a suitably designed low-temperature radiator system. Merely wiring both systems to one thermostat does not solve water-temperature compatibility.
A heat pump generally benefits from weather compensation and stable water temperatures. Aggressively closing every room valve can reduce flow, force short cycles and harm efficiency. Before introducing occupancy-driven setbacks or individual room automations, the installer should establish minimum circulation flow, buffer or bypass strategy if needed, pump control, frost protection and priority for domestic hot water.
| Scenario | Suggested hardware approach | Common trap |
|---|---|---|
| Two radiators, no UFH | Two compatible TRVs plus existing heat-source controls | No boiler demand when main thermostat is satisfied |
| Four UFH rooms, six loops | Four thermostats, six correctly grouped actuators, suitable wiring centre | Assuming one actuator equals one room |
| UFH downstairs + radiators upstairs | UFH manifold control plus radiator zone/TRV controls and coordinated heat source | Different required flow temperatures ignored |
| Heat pump with extensive zoning | Manufacturer-supported weather compensation and minimum-flow strategy | Short cycling when most zones close |
| Electric UFH bathroom | Approved floor thermostat and electrical protection | Using hydronic manifold actuator hardware |
Home Assistant integration: what is safe to automate?
Home Assistant can schedule occupied-room temperatures, expose sensor history and show which rooms are requesting heat. It can also coordinate comfort setbacks using supported integrations. However, the heat source and wiring centre should retain their native protections and sensible fallback if Home Assistant or the network fails. Avoid making a Wi-Fi automation the sole mechanism that prevents overheating, dry running, frozen pipes or unsafe pump operation.
A generic Home Assistant thermostat entity combines a temperature sensorAliExpress price and a switch; it is not a certified multi-zone hydronic controller. Its software hysteresis and cycle controls cannot replace plant-level safety interlocks. The ESP32 multi-zone heating controller guide is useful for understanding control logic, but a live mains-connected heating installation requires approved hardware and qualified commissioning.
| Automation | Reasonable use | Keep native protection for |
|---|---|---|
| Occupied/unoccupied setpoint changes | Comfort and schedule management | Frost protection and heat-source limits |
| Room temperature trend logging | Finding overheated or slow rooms | Floor-temperature protection |
| Demand aggregation dashboard | Understanding zone activity | Pump/boiler sequencing and minimum flow |
| Remote override | Temporary comfort boost | Manual fallback and network outage |
| Solar or tariff-aware setback | Slow supervisory optimisation | Plant safety and hot-water priority |
Room thermostat versus floor sensor: when does each matter?
A room thermostat measures air temperature and is generally the primary comfort input for wet UFH. A floor sensor may be used to cap surface temperature, particularly where floor coverings or manufacturer specifications impose limits. It is not a substitute for correct flow-temperature design or hydraulic mixing. Sensor placement, control mode and temperature limits should be agreed with the floor and heating-system suppliers before the floor is finished.
In a radiator room, a remote wall sensor can avoid the temperature bias of a TRV mounted beside a hot radiator. Not every smart TRV or integration supports an external room sensor as its control source; some expose a calibration offset only. Confirm this before ordering several devices.
Response time, setbacks and energy efficiency
A radiator may warm a room relatively quickly after a setback, whereas a thick UFH screed can take hours to respond. Repeatedly changing a floor-heating setpoint every 30 minutes is unlikely to produce useful room-temperature control. Start with gentle, longer schedules and measure the actual response under typical outdoor conditions. The best setback depends on building insulation, thermal mass, heat source, tariffs and comfort requirements.
There is no credible universal percentage saving for either smart TRVs or zoned UFH. Zoning can reduce unwanted heat delivery, but too many short calls for heat, a high water temperature or excessive pump cycling can offset some benefits. Compare weather-normalised energy use and occupied comfort before attributing savings to the controller.
Buying and installation cost: build a complete bill of materials
For radiators, budget per smart head, adapters, any central heating hub and possibly a room sensor. For wet UFH, include thermostats, actuators for each loop, a wiring centre, any wireless gateway, electrical work, hydraulic balancing and commissioning. In a new build, the pipework, manifold and pumps are a much larger cost category than the smart controls alone. For retrofits, check whether existing wiring and actuators are reusable before replacing the entire control system.
| Cost item | Radiator smart TRV project | Wet UFH zoning project |
|---|---|---|
| Per-room device | Smart radiator head; optional room sensor | Room thermostat; sometimes floor sensor |
| Per-emitter actuator | Usually included in smart head | Often one thermal actuator per manifold loop |
| Central controller | Boiler hub/relay or existing heat-source controls | Wiring centre plus compatible heat-source interface |
| Network equipment | Zigbee/Thread/bridge if needed | Vendor gateway if needed |
| Professional work | Hydronic checks and any boiler wiring | Electrical wiring, manifold balancing and commissioning |
| Hidden costs | Adapters, batteries, radio coverage | Pump/mixing compatibility, spare actuator channels, cabling |
Commissioning checklist
- Confirm heat-source model, required water temperatures, manufacturer-approved demand input and existing safety controls.
- Count radiator valve bodies, UFH rooms and individual manifold loops separately.
- Check every actuator’s voltage, normal state, thread, travel and controller load rating.
- Verify the actual room-to-loop map, thermostats, sensors and any floor-temperature limit.
- Have the installer test pump operation, valve-opening delay, minimum-flow behaviour and boiler/heat-pump demand.
- Check what happens when the internet, Wi-Fi, gateway or Home Assistant is offline.
- Log room temperatures and heat-source cycles for several days before applying aggressive automation.
- Document manual override and frost-protection behaviour for future occupants.
Troubleshooting: common failures
| Symptom | Likely checks | Safe next step |
|---|---|---|
| UFH thermostat calls but floor stays cold | Actuator output, opening delay, pump, manifold flow, air or balancing | Check status indications; ask installer to inspect hydraulics and electrical outputs |
| Radiator valve says heating but radiator is cold | Boiler demand absent, stuck valve body, trapped air, flow balancing | Confirm central heating is enabled; avoid forcing valve pins |
| Several UFH rooms overshoot | Thermal lag, sensor location, excessive supply temperature | Review schedules and professional flow-temperature settings |
| Heat pump starts and stops frequently | Too few zones open, flow restriction, demand logic | Installer review of minimum flow, buffer and weather compensation |
| Home Assistant offline stops all heating | Control path improperly dependent on automation | Restore native heat-source fallback and manual operation |
| Wrong room warms up | Manifold loops or thermostats mapped incorrectly | Recommission room-to-loop mapping with installer |
Frequently asked questions
Can I fit smart TRVs to underfloor heating?
Not as a drop-in replacement for manifold actuators. Wet UFH normally needs thermostats, compatible manifold actuators and a zone controller. Some proprietary systems offer specialised UFH controllers, but ordinary radiator heads are not manifold hardware.
Do I need one UFH actuator per room?
Not necessarily. Actuators usually correspond to controlled manifold loops. One room can have several loops linked to one thermostat, depending on the hydraulic design and wiring-centre capacity.
Can Home Assistant control a UFH manifold?
It can supervise supported thermostats and zone controllers, but a general-purpose software automation should not replace the installer-approved pump, boiler, electrical and thermal protections.
What is the difference between a 24 V and a 230 V actuator?
They require different supply voltages and matching controller outputs. They are not interchangeable. The normal open/closed state, current draw and mechanical fit also matter.
Are normally-open and normally-closed actuators interchangeable?
No. They produce opposite behaviour when de-energised. The zone controller and fail-safe design must explicitly support the chosen type.
Can radiator TRVs and UFH share one boiler?
Yes, with a properly designed heat-demand and hydraulic arrangement. Different water-temperature requirements and minimum-flow constraints may require separate circuits or mixing.
Is underfloor heating always more efficient?
No. Performance depends on insulation, water temperatures, heat source, installation and controls. Low-temperature UFH can pair well with heat pumps, but no universal efficiency advantage can be claimed.
Do I need floor temperature sensors?
Sometimes, particularly to enforce limits for certain floor constructions or coverings. The system designer and flooring supplier should specify whether a sensor and maximum-temperature function are required.
Should I use weather compensation with a heat pump?
Often yes when supported and correctly commissioned. Weather compensation helps match water temperature to building heat loss; aggressive room zoning can interfere if minimum flow is not preserved.
Can a smart TRV request heat from a boiler?
Only through a compatible heating controller or deliberately designed demand system. A standalone radiator head usually cannot fire a boiler.
Can I use Zigbee radiator valves with a wired UFH controller?
Yes as separate subsystems, but heat-source coordination requires a supported hub or professionally designed interface. Zigbee pairing does not create electrical compatibility.
What happens if Home Assistant goes down?
A robust system retains native heating schedules, frost protection and manual controls where provided. Verify the real offline behaviour rather than assuming automations continue.
Is a manifold wiring centre the same as a smart thermostat hub?
Not necessarily. A wiring centre distributes approved electrical control signals to actuators and plant outputs. A hub may only provide network connectivity or scheduling. Some products combine roles.
Should I use a DIY ESP32 relay board for my heating pump?
Not as an unapproved replacement for a certified pump/boiler safety controller. ESP32AliExpress price projects are useful for telemetry and suitably isolated, approved supervisory interfaces.
Final recommendation
Buy the control architecture, not just the thermostat. Radiator retrofits usually start with compatible smart TRVs and an existing heating-demand controller. Wet UFH starts with a manifold, correctly specified actuators, room thermostats and a wiring centre. Mixed systems need a deliberate interface between both types of zone and the heat source. A Home Assistant dashboard is an excellent final layer once the underlying heating system works safely and predictably on its own.
Further reading and official documentation
- Home Assistant Generic Thermostat — software climate control and its limits.
- Home Assistant ZHA — Zigbee integration and model-specific compatibility.
- Heatmiser — UH8 wiring-centre and compatible thermostat documentation (check exact revision).
- Danfoss — Icon2 hydronic floor-heating control documentation.
- SALUS Controls — KL08RF and other manifold controller manuals.
- Uponor — wet UFH manifold and room-control resources.
- ESP32 multi-zone heating controller — relevant local project.
- OpenTherm gateway with ESP32 — modulation and interface context.
- Per-appliance energy baselines — measuring system energy use.