Quick Summary (TL;DR)
Choose an air-to-water heat pump for a well-designed low-temperature heating system, not simply because a smart thermostat can connect to it. Its key control is typically a manufacturer-designed, weather-compensated heating curve, which adjusts water temperature as outdoor conditions change. A modern condensing gas boiler can also use weather or load compensation, often through its proprietary controller or a compatible modulating thermostat. Home Assistant should usually supervise and monitor either system rather than replace its safety controls.
- Heat pump: normally favours long, steady, low-flow-temperature operation, with room influence, hot-water management and minimum-flow protections designed into the system.
- Gas boiler: often suits conventional radiators and timed heating; performance improves when a modulating controller lowers flow and return temperatures without compromising comfort or cylinder safety.
- Smart home access: a cloud app, local Modbus registers, OpenTherm interface and simple on/off contact provide very different levels of access; none should be assumed from a marketing badge.
- Monitoring: compare measured energy into and out of the heating system. A room-temperature graph alone cannot prove heat pump COP, boiler efficiency or monetary savings.
- Best buying approach: commission a room-by-room heat-loss and emitter assessment, insist on a documented controller/gateway and agree what happens when the internet or Home Assistant fails.
An existing gas boiler may remain the sensible short-term choice where the building or electrical installation is not ready for conversion. An air-to-water heat pump is an attractive long-term upgrade when emitters, hot water, hydraulics and controls are properly designed. The quality of the heating design matters more than the number of smart-home integrations listed on a product page.
Air-to-water heat pump vs gas boiler: the real difference
Both appliances can feed water-based radiators or underfloor heating, and both can be integrated into a modern smart home. They produce heat in very different ways. A condensing gas boiler burns fuel and transfers the combustion heat into circulating water. An air-to-water heat pump uses electricity to move environmental heat from outside air into that water. Its efficiency depends strongly on how far the refrigerant system must lift the temperature.
This changes the control strategy. A boiler can usually supply relatively hot water and respond quickly to a morning schedule. A heat pump is often more efficient when it distributes lower-temperature water over longer periods, using a heating curve to match heat output to the building’s demand. A heat pump does not require underfloor heating in every house, but its radiators must deliver enough heat at the selected design flow temperature.
| Decision factor | Air-to-water heat pump | Modern condensing gas boiler |
|---|---|---|
| Energy source | Electricity; moves heat from outside air | Natural gas; converts fuel to heat |
| Typical control philosophy | Weather-compensated, steady output, low flow temperature | On/off or modulating, time scheduling, compensation where supported |
| Space heating emitters | Existing radiators may work if sized adequately; larger emitters can help | Often works with existing high-temperature radiators |
| Domestic hot water | Usually a compatible cylinder, controls and periodic hygiene programme | Combi boiler on demand or system boiler with cylinder |
| Data access | Vendor cloud, supported gateways, Modbus or limited local integrations—model dependent | Thermostat demand, OpenTherm, proprietary bus, vendor cloud—model dependent |
| Efficiency metric | Seasonal performance factor (SPF/SCOP), measured boundary matters | Seasonal fuel-use efficiency, affected by return water temperature |
| When internet fails | Native controller must continue independently; optional remote data may vanish | Native controls must continue independently; optional remote data may vanish |
| Installation complexity | Outdoor siting, heat loss, emitters, electrics, hydraulics, noise, hot water | Gas regulations, flue, ventilation, hydraulic checks, hot water |
Heating curves and weather compensation: why the controls differ
A heating curve maps outdoor temperature to target water-flow temperature. As the weather becomes milder, the controller asks for cooler water. For an air-to-water heat pump this can improve coefficient of performance (COP), reduce unnecessary compressor stops and make indoor temperatures steadier. The Energy Saving Trust’s installer guidance describes the reason: lower flow temperature reduces the temperature lift the heat pump must achieve. Energy Saving Trust: weather compensation and other controls.
A boiler benefits too. Lower central-heating flow temperature generally helps produce cooler return water, increasing the chance of condensing operation. The engineering objective is not to select the lowest number on the display; it is to deliver the required room heat at the lowest practical water temperature. With a separate domestic hot-water cylinder, the boiler and cylinder-temperature requirements must be evaluated together rather than blindly turning down one common setting.
| Control mode | What it changes | Potential benefit | Key limitation |
|---|---|---|---|
| Room thermostat, on/off | Enables or disables heat demand | Simple, widely understood, inexpensive | No direct control of burner/compressor output or flow temperature |
| Weather compensation | Flow-temperature target as outdoor temperature changes | Adapts to building heat load; helps lower temperatures | Needs correctly commissioned heating curve and sensor |
| Load compensation / room influence | Water target in response to indoor conditions | Can reduce overshoot and improve comfort | Vendor-specific implementation and sensor placement |
| Modulating bus control | Communicates variable demand/setpoints over supported protocol | Often better matched output and reduced cycling | Protocol support must be verified on both endpoints |
| Smart schedule or setback | Alters comfort target over time | Can reduce energy demand during long unoccupied periods | Aggressive setbacks can trigger slow recovery or inefficient boosts |
For a heat pump, use the original controller’s weather compensation and a modest comfort setback unless its installer specifically recommends a different operating mode. Some thermostats make efficient heat pumps behave like large on/off boilers by demanding frequent stops and restarts. A heating-system designer must confirm minimum water volume, circulation flow and zones before substituting controls.
Flow temperature and radiator compatibility matter more than a clever app
Before replacing a gas boiler, the installer should calculate each room’s design heat loss and compare it with the output of the installed radiators at the intended heating water temperatures. Conventional radiator catalogues may quote output at a higher temperature difference than a modern heat-pump design; a radiator with a headline rating of 2 kW does not necessarily deliver 2 kW at 40–45°C flow. That does not mean every radiator needs changing—only that the assessment must use the correct design temperatures.
Underfloor heating generally provides a large emitter area and can work particularly well at low water temperatures, provided manifold and mixing arrangements are correctly designed. Existing radiators may be upsized or supplemented with suitable fan convectors. Small-diameter pipework is not automatically disqualifying, but pipe pressure loss, velocity and the required circuit flow must be checked. Energy Saving Trust: microbore pipework design.
| Site finding | Likely implication for a heat pump | What to request |
|---|---|---|
| Large, well-sized radiators | May retain existing emitters at lower temperature | Output schedule showing each room at design flow/return temperatures |
| Small radiators requiring very hot water | Higher running cost or inadequate comfort | Replacement/emitter calculation, not guesswork |
| Mixed radiators and underfloor heating | Potentially different circuit temperatures/flow rates | Hydraulic schematic and approved zone-control approach |
| Many smart TRVs shut together | Possible minimum-flow and short-cycling problems | Hydraulic balancing and manufacturer-approved minimum flow strategy |
| Microbore or restricted pipework | Flow/pressure loss may become critical | Pipework survey and flow calculation |
| No suitable hot-water cylinder | Additional space and installation cost | DHW design, reheat times and hygiene strategy |
Energy Saving Trust explains why some existing radiators may be adequate with a boiler yet too small for a heat pump operating at lower flow temperatures. See its May 2026 efficiency guidance. The thermal design of the building remains the first decision—not the integration brand.
Smart thermostat compatibility: on/off, OpenTherm, eBUS and manufacturer controls
The term “smart thermostat compatible” is dangerously broad. In one system it means a wall thermostat can close a demand contact. In another it means a modulating bus controller requests variable flow temperatures. In a third it means a manufacturer gateway mirrors settings to a cloud app. The comfort experience and data available in Home Assistant can be completely different.
Simple switched demand
A dry-contact or switched-demand input can tell a compatible controller that a zone needs heat. It does not automatically provide compressor power, burner modulation, flow temperature, diagnostic codes or energy readings. Whether an external room demand is supported, and how it interacts with weather compensation, depends on the system wiring and control design. Never connect arbitrary relays or supply voltage to an input without manufacturer documentation and a qualified installer.
OpenTherm for compatible boilers
OpenTherm is a heating-control communications protocol used by certain boilers and thermostats. A compatible OpenTherm thermostat may exchange temperature setpoints and other information with a compatible boiler, allowing modulation rather than simple on/off demand. But a boiler may use a proprietary bus instead, and even two OpenTherm-branded devices can expose different supported functions. Heat-pump compatibility cannot be inferred from boiler OpenTherm support.
Home Assistant has a documented OpenTherm Gateway integration. It exposes thermostat and boiler entities through suitable gateway hardware; many entities are disabled by default, and some advanced overrides can affect safe or efficient operation. For the hands-on ESP32AliExpress price angle, see our existing OpenTherm Gateway with ESP32 and Home Assistant guide. It is not a generic wiring recipe for every boiler.
Proprietary heating buses and heat-pump controllers
Manufacturers may use proprietary networks for coordinating the outdoor unit, hydrobox, cylinder, mixing valve, auxiliary heater and room controller. Vaillant, for example, documents sensoCOMFORT as a weather-compensated system controller intended to coordinate multiple heating circuits and associated equipment: Vaillant sensoCOMFORT. A third-party thermostat that can request heat is not necessarily capable of replacing this hydraulic and safety logic.
| Interface | Typical availability | Useful data/control | What to verify before buying |
|---|---|---|---|
| On/off heat demand | Many boilers; some heat-pump configurations | Call for heat, coarse schedule | Electrical compatibility, controller permission, anti-cycling and fallback |
| OpenTherm | Compatible boilers/controllers; not universal | Variable demand/setpoints and some diagnostics | Both endpoints, supported functions, existing thermostat architecture |
| Proprietary bus (e.g. vendor controller) | Vendor-specific boiler/heat-pump systems | Potentially rich modulation and multi-zone state | Supported gateway, licence, documented entities, warranty |
| Modbus RTU/TCP | Selected heat pumps and gateways | Registers may include state, temperatures, alarms and setpoints | Exact model, address map, permissions and firmware |
| Vendor cloud API | Some boilers and heat pumps | App controls, status, schedules, sometimes energy reports | Connectivity, polling, subscriptions, region and outages |
| External meter / isolated sensors | Independent of manufacturer heating protocol | Actual electrical energy or temperatures at measured locations | Meter boundary, accuracy, electrical certification; no automatic safety control |
Home Assistant integration: which information can you really access?
For a Home Assistant buyer, the key question is not “does the product have Wi-Fi?” It is: “Which exact sensor and control entities does this model and gateway expose, how are they updated, and what functions remain available offline?” A climate entity showing target room temperature is useful, but cannot tell you whether an immersion heater ran for two hours or whether the heat pump spent all night cycling.
Integration technologies vary substantially between brands and even generations within the same brand. Home Assistant documents local NIBE connections for relevant models, including a built-in Modbus TCP server on supported S-series systems. By contrast, Mitsubishi MELCloud Home and Viessmann ViCare are documented cloud integrations, with account/API limitations. A product can have a native local controller and yet expose its consumer smart-home data only through the cloud.
| Example integration path | Where Home Assistant data comes from | Offline from internet? | Buyer caveat |
|---|---|---|---|
| NIBE Heat Pump with supported Modbus TCP | Local unit registers via LAN | Often yes for supported local connection | Requires correct S-series model, enabled Modbus and appropriate read/write mapping |
| NIBE/myUplink | Vendor cloud API | No, for cloud features | Capabilities and remote control may require a subscription |
| Mitsubishi MELCloud / MELCloud Home | Vendor cloud | No, for integration data | MELCloud and MELCloud Home are distinct integrations; model support varies |
| Viessmann ViCare | Vendor REST cloud API | No, for integration data | API rate limits, access tiers, exposed features and cloud availability matter |
| Compatible boiler with OpenTherm Gateway | Local physical protocol via gateway | Yes if locally installed | Gateway compatibility and thermostat topology must be checked |
| External electricity meterAliExpress price | Local meter via Modbus, CT system or other supported interface | Often yes, if local meter path | Measures consumption only; cannot replace the appliance controller |
References: NIBE Heat Pump, myUplink, MELCloud Home, and Viessmann ViCare. Confirm the exact hardware, gateway and installed firmware before ordering anything for automation.
Which entities should a good heating integration expose?
A properly designed heating dashboard needs temperatures, operating state, energy data and alerts. Do not assume the manufacturer will expose every item through its consumer integration: some values are available only at the service console or require a paid API tier. Separate measured values from inferred estimates in your dashboard labels.
| Entity / measurement | Heat pump value | Gas boiler value | Practical use |
|---|---|---|---|
| Room and outdoor temperatures | Essential to weather compensation analysis | Useful to evaluate scheduling and compensation | Check comfort and outdoor conditions |
| Flow and return temperatures | Shows emitter water conditions | Helps evaluate boiler return conditions | Identify unnecessarily high water targets |
| Operating state and cycles | Compressor / defrost / auxiliary heat if exposed | Burner firing and fault states if exposed | Identify short cycling and abnormal boosts |
| Electrical kWh | Compressor, pumps, immersion and controls depending on boundary | Boiler electrical auxiliary use only | Actual purchased electrical use |
| Gas kWh or volume | Usually not applicable unless hybrid | Utility gas meterAliExpress price or rated controller estimate | Fuel cost; distinguish meter reading from calculated use |
| Heat delivered (thermal kWh) | Only if integrated heat-meter data is reliable | Useful with proper heat metering | Compute seasonal performance / thermal balance |
| DHW target / programme | Cylinder mode, hygiene programme, reheat | Cylinder or combi mode | Avoid accidentally overriding safe DHW controls |
| Fault code and last update | Manufacturer-dependent | Manufacturer-dependent | Detect maintenance problems and stale cloud data |
For a dependable record of heating electricity, an appropriately selected external meter can be valuable even when rich native telemetry exists. For a gas boiler, accurate gas-fuel consumption may come from a utility smart-meter integration or approved meter rather than the thermostat. For whole-home data quality, compare readings using our guide to verifying Home Assistant energy against a utility bill.
Monitoring reality: COP, gas efficiency and the measurement boundary
A heat pump’s instantaneous coefficient of performance (COP) is useful heat delivered divided by electrical energy consumed across a defined boundary. A seasonal performance factor (SPF) applies the same principle over a longer, representative period. If the denominator excludes defrost, backup immersion, circulation pumps or ancillary controls, reported performance may look better than whole-system performance. A flow and return temperature pair alone is insufficient to measure delivered heat: the water flow rate and fluid properties are also required.
A boiler’s nameplate efficiency is likewise not the same as measured seasonal gas use. The result depends on load, weather, return water temperature, cycling, hot-water consumption and heat distribution. To compare systems fairly, use the same annual useful heat requirement, define whether hot-water energy is included and make all tariff assumptions explicit.
| Metric | Valid interpretation | Common error |
|---|---|---|
| Heat pump electrical kWh | Energy drawn by the included electrical loads | Assuming inverter report always includes immersion and pumps |
| Heat pump thermal kWh | Measured delivered heat with a qualified flow/temperature method | Computing delivered heat from temperature difference with no measured flow |
| SPF = useful thermal kWh / electrical kWh | Seasonal ratio for the stated system boundary | Comparing SPF at one boundary with advertised equipment COP at another |
| Gas consumption in kWh | Purchased fuel energy as billed | Comparing gas kWh directly with heat delivered to rooms |
| Boiler efficiency | Useful heat output divided by gas energy input for a stated test/boundary | Treating 90% as an exact real-world efficiency for every installation |
Home Assistant can trend all of these when suitable sensors are present; it cannot manufacture missing physical measurements. Our Energy Dashboard entity guide explains why correct meter boundaries and cumulative kWh entities matter for useful reports.
Worked running-cost example: why tariff ratios beat marketing claims
Consider a home requiring 12,000 kWh of useful space heat per year. These are deliberately illustrative assumptions, not a prediction for a real property: a condensing gas boiler averages 90% seasonal efficiency; an air-to-water heat pump achieves SPF 3.2 on an equivalent whole-system boundary; imported gas costs 7 p/kWh; electricity costs 25 p/kWh. Standing charges, service contracts, grants, export revenues and fixed costs are excluded.
| Calculation | Gas boiler | Air-to-water heat pump |
|---|---|---|
| Useful annual heat needed | 12,000 kWh | 12,000 kWh |
| Assumed seasonal efficiency | 90% | SPF 3.2 |
| Purchased energy | 12,000 ÷ 0.90 = 13,333 kWh gas | 12,000 ÷ 3.2 = 3,750 kWh electricity |
| Illustrative energy tariff | £0.07/kWh | £0.25/kWh |
| Illustrative annual variable energy bill | About £933 | About £938 |
At those particular assumptions the variable heating bills are almost identical. If the heat pump achieves SPF 3.8 instead, its electricity falls to about 3,158 kWh and the example electricity bill to roughly £789. If it performs at SPF 2.6, use rises to about 4,615 kWh and the example bill to approximately £1,154. Heat-pump design and how the home uses hot water can therefore outweigh the appearance of a clever schedule.
The simple parity test is electricity price ÷ gas price < heat-pump SPF ÷ boiler efficiency. With 25 p electricity, 7 p gas and 90% boiler efficiency, a heat-pump SPF above about 3.21 makes the heat pump cheaper on variable energy alone. This ignores the changing standing-charge position if the home disconnects gas entirely. Actual decisions should use your region’s current tariffs and an installer’s defensible seasonal-performance estimate.
Installation economics and ownership: assess the whole system
Installed prices vary so much that comparing a heat-pump unit price with the sticker price of a gas boiler is misleading. A heat-pump quote may include upgraded radiators, hot-water cylinder, pump and valves, new electrics, outdoor-unit location and controls. A boiler quote may require flue changes, gas work, flushing, controls and compliance upgrades. Neither technology is properly assessed without a written scope of works.
| Cost or effort line | Heat pump quote should state | Gas boiler quote should state |
|---|---|---|
| System design | Room heat loss, design outdoor temperature, required flow temperatures | Boiler heat input/output, hot-water needs, existing radiator suitability |
| Hydraulics / emitters | Radiators/UFH, pipework, pump, volume, expansion and frost strategy | System flush, pump/valves, pressure and radiators |
| Hot water | Cylinder type/capacity, immersion, reheating and hygiene programme | Combi performance or existing/replacement cylinder |
| Power / fuel | Electrical supply assessment, protections and outdoor location | Gas supply adequacy, flue and ventilation |
| Controls | Native weather compensation, room influence, gateway, zones | Compatible on/off or modulating controller, compensation |
| Commissioning | Heating curve, hydraulic balancing, COP/energy telemetry and handover | Combustion checks, flow temperature, boiler modulation, controls and handover |
| Ownership | Servicing, firmware, gateway/API continuity, parts and warranties | Gas servicing, flue safety, smart controls, warranties |
For UK buyers, the Government’s installer guidance recommends an appropriately qualified professional and, for government-backed heat-pump support, an MCS installer where required. Confirm current scheme rules on the day you obtain the quote; grant availability and amounts are subject to policy changes. GOV.UK: find a heat pump installer. For other countries, check local accreditation, permits and utility requirements.
Automation architecture: make Home Assistant the supervisor, not the safety controller
The safe hierarchy is: appliance manufacturer controls and certified safety systems first; site hydraulics and primary room demand second; monitoring and low-frequency supervisory changes third. A Home Assistant host, cloud integration or Wi-Fi connection must not become the sole line of defence against frozen pipework, unsafe hot-water temperatures, failed circulation or loss of minimum system flow.
A useful supervisory automation might alter an approved holiday setpoint, notify when room temperature is unexpectedly low, or request a supported lower-cost domestic hot-water schedule. It should not rapidly rewrite heating-curve parameters every time a cloud-sourced temperature changes or disable legionella/hygiene cycles. When an application goes offline, native heating controls should continue at their commissioned defaults.
| Automation idea | Usually appropriate approach | Avoid |
|---|---|---|
| Away or holiday mode | Use the supported native holiday preset with a reasonable minimum comfort/frost setting | Cutting all power to save standby electricity |
| Time-of-use tariff | Shift discretionary cylinder heating only within manufacturer limits and comfort needs | Forcing huge heat-storage temperatures for small tariff differences |
| Solar self-consumption | Use manufacturer-approved PV/SG Ready/EEBUS or supported energy-management interface | DIY commands that override safety or anti-cycle rules |
| Room temperature monitoring | Alert on sustained under-temperature with stale-data checks | Assuming last cloud reading is always live |
| Zone demand | Use installer-designed zone controls maintaining minimum flow | Closing every radiator valve on a running heat pump |
| Internet outage | Keep independent manufacturer controller and basic local operation | Cloud-only thermostat with no adequate fallback |
If the project requires Home Assistant to alter the heating target, ask for the supported command list and fallback response. A well-defined fail-safe is part of the purchase specification, not an advanced feature to consider later. For those prioritising internet independence, see whole-home monitoring without cloud dependence.
Retrofit scenarios: which would I choose?
Scenario 1: an insulated house with underfloor heating and an electrical upgrade planned
An air-to-water heat pump is a natural candidate. The emitter area is large, design water temperature can often be low, and the home may benefit from future solar or battery scheduling. Ask the installer for an actual heat-loss schedule, supply design, hydraulic diagram, control compatibility and expected SPF. Prefer a manufacturer-supported local gateway when control independence is a priority, but do not reject a sound hydraulic solution only because a cloud dashboard is less attractive.
Scenario 2: an older house with small radiators and limited retrofit budget
Retaining or replacing a safe, adequately maintained gas boiler with well-matched modulation and weather compensation might be the more practical near-term decision. That does not prove a heat pump would be ineffective: an emitter-by-emitter survey may identify a manageable upgrade list. Compare the whole-system quotes before ruling either option out. Insulation and draught proofing can reduce the demand for both technologies.
Scenario 3: Home Assistant is the priority but hardware choice is still open
Start by specifying the data you actually want: electricity kWh, gas consumption, flow and return temperatures, compressor/burner status, DHW state, errors, room comfort and local control. Check a real installer demonstration or documented register list. A supported external meter may solve energy monitoring independently of the heating brand, while a manufacturer-approved gateway handles supervisory actions.
Scenario 4: multiple heating zones and smart TRVs
This is not merely a thermostat-shopping decision. A boiler can often respond to zoned demand, but minimum burner output and cycling still matter. A heat pump may need open flow paths, water volume and a coordinated control algorithm across zones. Allow the hydraulic designer to determine how zone valves, actuators and thermostat requests work before buying dozens of valves based on app compatibility alone.
Commissioning checklist: questions to ask before signing
- What is the calculated design heat loss per room, and what design outdoor temperature is used?
- At which supply and return water temperatures do the proposed radiators or underfloor loops meet that heat loss?
- Which controller performs weather compensation, and who sets the curve, room influence and anti-cycling parameters?
- Will every proposed smart thermostat work with the exact appliance, controller and firmware without losing modulation?
- How are minimum flow, system water volume, defrost and auxiliary heaters managed?
- How will the hot-water cylinder reach required temperatures, and how are periodic hygiene cycles preserved?
- Which exact Home Assistant entities are supported, which are cloud-only, and what needs a subscription?
- Can a manufacturer-approved local Modbus, OpenTherm or other gateway be supplied without affecting warranty?
- Which electricity, gas and thermal energy measurements are included in a quoted efficiency estimate?
- What is the intended behaviour during Home Assistant, network or cloud failure?
- What documentation, training and commissioning records are included at handover?
- Who maintains control compatibility after firmware or service changes?
Important safety note: gas appliances, mains wiring, refrigerant systems and pressurised hot-water heating require appropriately qualified tradespeople. Do not bypass a boiler or heat pump’s built-in protections or attempt to modify gas, electrical or refrigerant connections based on a smart-home tutorial.
Common mistakes and troubleshooting
“My new thermostat can switch the heat pump, so integration is complete.” It may only provide on/off demand. Check whether it preserves the manufacturer’s heating curve and room influence and whether the hydraulic circuit remains within operating limits. Repeated short runs often need system-level diagnosis, not more scheduling rules.
“The outdoor sensor says 10°C, but the heating water is 50°C.” That may be appropriate during domestic hot-water production, an auxiliary cycle or a service mode. Check the operating state before changing the space-heating curve. Compare steady-state heating data over several mild and cold days with the manufacturer’s intended behaviour.
“Home Assistant says the heat pump is using 1 kW, but the meter shows 3 kW.” Confirm which loads each source measures. An immersion heater, backup element, circulation pumps or stale inverter telemetry could explain a mismatch. Cross-check time windows, physical boundaries and units; do not invent a correction factor from one snapshot.
“My cloud thermostat is unavailable, so the heating stopped.” A correctly designed primary system should have a documented fallback. Test internet disconnection with the installer during commissioning and verify that the native controller, domestic hot water and frost protection remain functional.
“I switched every room to smart TRVs and now the heat pump cycles.” The heat pump may have lost minimum water flow or usable thermal volume. Return control to the approved hydraulic strategy and ask the heating designer to assess valves, pump and zoning logic. This is not something to fix by disabling fault protection.
Frequently asked questions
Can I use the same smart thermostat for a gas boiler and a heat pump?
Sometimes, but compatibility with both products must be documented. A contact-only thermostat might signal demand to either system yet provide no modulation or weather compensation. A heat pump may require its native controller plus a separately compatible room sensor. Check the actual model and hydraulic architecture, not only thermostat branding.
Is OpenTherm better than a simple on/off thermostat?
For a boiler supporting OpenTherm, properly implemented modulation can be more capable than basic on/off control, but it is not a guarantee of savings. The exact boiler, thermostat and their implemented commands matter. Many heat pumps use different native control architectures, so OpenTherm support for one boiler does not indicate support for a particular heat pump.
Will a heat pump work with ordinary radiators?
Often yes. The condition is that the radiators must deliver the necessary room heat at the designed lower water temperatures. Some may already be adequately sized, while others may require replacement. A room-by-room heat-loss and radiator-output calculation answers the question.
Is a heat pump always cheaper to run than gas?
No. Annual cost depends on heat demand, real seasonal efficiency, the electricity-to-gas price ratio, domestic hot-water use and standing charges. A badly designed high-temperature heat-pump system can be expensive to run; a well-designed one can be competitive, particularly under suitable tariffs.
Can Home Assistant control the heat pump completely?
Depending on the model, Home Assistant may expose extensive settings or only a subset of safe supervisory features. Full appliance control is neither always possible nor desirable. Use the certified native controller for compressor, defrost, pumps, frost and hot-water safety; Home Assistant can supervise documented supported setpoints.
Do I need an external electricity meter for a heat pump?
Not always. A manufacturer’s meter may provide useful and sufficiently complete consumption information, but you must check what is counted. An independent approved meter provides a separate reference and often better whole-circuit accounting. True measured COP also needs a suitable heat-output measurement.
Does the best Home Assistant integration mean the best heating system?
No. Integration quality affects convenience and monitoring, but heat loss, radiator sizing, flow temperatures, commissioning, spare parts, acoustic siting and warranty service will usually have more impact on comfort and ownership cost.
Verdict: buy a heating system, then an integration
For an efficient, low-temperature heating retrofit, a well-engineered air-to-water heat pump is an excellent option; for a constrained property or budget, a modern condensing gas boiler with properly supported modulation may still be the practical choice. Either can be made smarter, but neither should be designed around an automation dashboard first. Choose a clear control hierarchy, insist on compatible vendor documentation, verify energy measurement boundaries and keep protective controls independent of the cloud.
If you are comparing heat pumps by Home Assistant compatibility, start with the actual gateways, entity lists, failover requirements and installer support. If you are still at the system-selection stage, start with a heat-loss survey and radiator assessment. This order avoids paying twice: once for the heating appliance and again to repair an unsuitable control scheme.
References and further reading
- Energy Saving Trust installer toolkit — weather compensation and controls
- Energy Saving Trust — how to run a heat pump efficiently (May 2026)
- Energy Saving Trust — air source/air-to-water heat pumps
- Energy Saving Trust — boiler flow temperature (May 2026)
- GOV.UK — find a qualified heat pump installer
- Home Assistant — OpenTherm Gateway integration
- Home Assistant — NIBE Heat Pump integration
- Home Assistant — MELCloud Home and ViCare
- Vaillant — sensoCOMFORT weather-compensated control
Editorial note (October 2026): Operating temperatures, product compatibility, APIs, tariffs, local building rules and support schemes vary by installation and can change. This is independent buying guidance, not commissioning, electrical or gas-safety instruction. Calculations are worked examples and must be replaced with site-specific measurements and verified prices.