Heat Pump Defrost Cycles in Winter: Solar Impact

Last updated: November 2026

A January evening can expose a gap that an annual solar estimate misses: the house needs heat after the array has stopped generating. A defrost event, electric backup heater or other household load can change the electrical demand again. The design needs to explain how the battery, grid and heating controls respond together.

Defrost is normal operation for an air-source heat pump. Its electrical effect depends on the equipment and installation, so a universal power multiplier is a poor basis for buying an inverter. Separate electrical input from thermal output, and distinguish ordinary grid-connected operation from backup operation during an outage.

This guide covers the defrost process, winter generation, battery power and energy, tariffs, refrigerants and connection checks. It uses manufacturer and public-agency documentation alongside explicitly illustrative calculations. It does not present a monitored customer installation or measured savings result.

How Defrost Cycles Work

Reverse-cycle defrost sends heat to the outdoor coil to melt accumulated frost. A reversing valve changes the refrigerant flow; the compressor does not physically run backward. The normal delivery of heat to the building is interrupted or reduced while the system clears the coil and returns to heating.

Natural Resources Canada’s heat-pump guide explains the reversing-valve sequence and the distinction between demand-based and time-temperature defrost. It also notes that supplementary heating may be required during defrost. That distinction matters when the supplementary heat is electric resistance heating on a separate circuit.

The coefficient of performance (COP) is useful heat output divided by electrical input over the stated measurement boundary. A heating COP is not an electrical demand rating. A temporary reduction in useful heat delivery can worsen efficiency even when electrical input does not rise sharply.

Vaillant’s explanation of automatic defrost describes temperature and pressure sensing, warming the outdoor coil and draining the melted frost. It does not publish a universal defrost power multiplier for every model. Request the actual unit’s operating data before assigning one.

When Defrost Happens: Temperature and Moisture Together

Frost formation depends on the outdoor coil conditions and the moisture available in the air. Outdoor air temperature alone cannot tell a designer exactly when the next event will happen. The coil can be colder than the surrounding air, and the controller uses its own logic to decide when clearing is needed.

Do not turn a weather forecast into a fixed schedule of defrost events. Use the following planning table to choose what evidence to collect, rather than assigning unsupported durations to broad climate bands.

Natural Resources Canada describes time-temperature controls that can initiate at 30, 60 or 90 minutes, depending on the design and climate. These are examples of a control method, not a measured interval promised for a modern variable-speed unit or every winter day.

How Often: Use the Controller Record

The useful question is how often the selected system defrosts under the site’s operating conditions. Ask for the controller’s event marker, start and end times, recovery behavior and backup-heater state. An electricity trace by itself may confuse defrost with hot-water heating, a thermostat change or another appliance.

For an existing system, collect observations across contrasting weather conditions before drawing conclusions. Include ordinary heating periods as well as events. Otherwise, a chart that contains only unusual peaks will make those peaks look more representative than they are.

For a proposed system, record which values come from the manufacturer and which remain assumptions. Obtain the applicable hydraulic and electrical requirements. Leave an explicit sensitivity in the design if event data is unavailable; do not fill the gap with an unrelated brand’s measurements.

The Energy Cost of Defrost: Annual vs Peak

Defrost affects heat delivery, electricity use and timing in different ways. Annual energy analysis asks how much electricity the system uses to provide the required heat. Power analysis asks whether circuits, the grid supply and any backup inverter can serve simultaneous loads at the relevant moment.

Annual Energy Penalty: Avoid a Universal Percentage

There is no single defrost percentage established here for all heat pumps and climates. A blanket annual allowance would obscure differences in equipment, weather, water temperature, auxiliary heating and measurement boundaries. Use a documented seasonal method or a measured seasonal performance factor appropriate to the project.

The seasonal coefficient of performance (SCOP) describes performance under a stated rating method and climate. Before using it, check the standard and the manufacturer’s declaration for what is included. Do not add a generic defrost allowance to a model that already accounts for it, and do not assume the rating predicts the exact installed system.

A designer should write down whether the estimate includes circulation pumps, crankcase or tray heating, electric backup, hot-water cycles and standby consumption. These items can sit inside or outside different quoted efficiency figures. Keeping the boundary visible is more useful than applying an unexplained percentage to every annual total.

When comparing an estimate with a bill, use matching periods and account for weather and changes in occupancy. Total household electricity includes many loads unrelated to heating. A higher winter bill alone cannot identify how much energy was attributable to defrost.

Peak Power: Read Electrical Data, Not the Heating Label

A heat pump’s advertised heating capacity is not its electrical input. Manufacturer operating points and maximum-input figures serve different purposes. None should be silently relabeled as a measured defrost peak.

The following example uses one exact model from Vaillant’s aroTHERM plus technical table, accessed November 2026: VWL 75/8.1 A 230V. The published data distinguish operating conditions from maximum electrical consumption.

Here, A identifies outdoor air temperature and W identifies water temperature in the manufacturer’s operating-point labels. The points differ in both conditions and heat output. They are not a controlled defrost comparison or a complete house load schedule.

For procurement, match the full model suffix, supply configuration and installation manual. A similar product name is insufficient. Ask whether an indoor electric heater, circulation pump or other accessory has its own supply and whether it can operate concurrently with the outdoor unit.

Why Winter Solar PV Sizing Must Account for Defrost

Winter design requires a time-based comparison between generation and heating demand. Annual photovoltaic (PV) generation can equal annual heating electricity while leaving substantial winter imports. Defrost belongs within that load assessment, but it is not the only reason demand and generation differ.

1. Demand Can Exceed Available PV Output

Use a site-specific generation model with the roof orientation, tilt, horizon and shading. Examine the winter profile and individual low-generation periods. Do not transfer a generic Birmingham monthly estimate to a different roof, location or year.

At night there is no direct PV contribution. During cloudy daylight, available output may be well below the array’s nameplate rating. The system must then use stored energy, grid electricity or an approved alternative heating source, according to its design.

There are different success criteria. A grid-connected project may accept occasional imports to avoid buying more battery capacity than it can economically use. A backup project must define the loads and duration it promises to support during an outage. Those are separate requirements and should appear separately in the proposal.

2. Battery Power and State of Charge Both Matter

A battery needs enough usable energy and sufficient output power at the time of the event. State of charge (SOC) describes how much charge remains. Nameplate capacity is not a guarantee that the same energy or power is available at every SOC and temperature.

Check manufacturer limits for the installed battery configuration, usable capacity, minimum reserve, continuous output and any temporary overload. Then check the inverter’s limits and the way those limits interact. A larger energy capacity does not automatically increase output power if another component remains the constraint.

Avoid predicting battery damage from one arbitrary winter SOC range. Warranty conditions, operating temperature, throughput, control limits and chemistry affect battery life. Model the approved operating range and cycling assumptions, then compare them with the selected product’s documentation.

3. Grid-Connected and Backup Operation Behave Differently

A grid-connected house can normally import the portion of demand that PV and storage do not supply, within the electrical installation and connection limits. A load above the battery inverter’s output rating does not by itself mean that the heat pump trips or that the inverter clips the household load.

An islanded backup circuit has a different boundary. Its inverter must supply the connected loads without grid support, subject to continuous and transient limits. If demand exceeds those limits, the system may shed loads or shut down according to its controls. Check the backup-output rating separately from any grid pass-through rating.

Draw the actual topology before making a sizing claim. Mark the heat-pump circuits, indoor heater, essential-load board, PV inverter, battery inverter, grid connection and any load-control device. This reveals whether the heat pump is even connected to the backup supply being discussed.

For a wider planning sequence, use the solar and heat-pump integration guide. Keep its project assumptions aligned with the equipment selected here.

Battery Sizing for Defrost: Power, Not Just Energy

Specify a battery around an explicit service requirement: lower import cost, higher solar self-consumption, a defined backup load, or a combination. Each purpose needs a different dispatch model. A blanket multiplier on heat-pump input cannot replace that model.

The Power-Energy Mismatch

Power is the rate of electricity use, measured in kilowatts. Energy is accumulated consumption, measured in kilowatt-hours. A short event can require little energy but exceed a power limit; a modest load can exhaust a battery if it runs for long enough.

Consider this illustrative electrical-load example, not a measured heat pump or a product recommendation. During a chosen ten-minute interval, assume the outdoor unit uses 3.5 kW, circulation uses 0.1 kW, other household loads use 0.6 kW and an enabled electric heater uses 3.0 kW.

The energy calculation is power multiplied by ten divided by sixty. The difference between the cases comes entirely from the assumed heater state. It is not evidence that defrost always adds 3.0 kW or that every unit enables resistance heat during the event.

Suppose the illustrative battery can supply 5.0 kW continuously at that moment. With the grid available, the 7.2 kW case leaves a 2.2 kW import requirement before other changes in supply. Without the grid, the same load would require an approved reduction in demand or a suitably rated backup system. Energy remaining in the battery would not remove the power shortfall.

Sizing Rules for Heat Pump and Battery Systems

Start with the actual maximum-input data and approved simultaneous-load assumptions. Check the electrician’s circuit and supply assessment separately from the energy consultant’s annual model. Both matter, but they answer different questions.

For power, record continuous input, auxiliary heaters, startup behavior where relevant, inverter output and permitted overload duration. A demand figure averaged over a long interval can hide a shorter event that matters to equipment protection. Use adequate time resolution for the intended assessment.

For energy, integrate the load over the required support period and account for conversion losses, reserve and the allowed operating range. Do not promise overnight autonomy from a label that only states nominal battery capacity. State whether grid charging is allowed and whether the reserve is available for routine bill savings.

For control, identify which loads may be deferred and which must remain available. Heat-pump protection, freeze prevention and required heating operation should remain within the manufacturer’s control strategy. An external energy manager should use supported interfaces and approved settings.

Buffer Tanks: Thermal Support Is Not Electrical Supply

A buffer or volumiser can provide required water volume and support the hydraulic design. Its role depends on how it is connected and on the manufacturer’s minimum flow and volume requirements. It is not automatically an economical thermal store, and making it larger is not a universal solution.

Stored water heat can support the thermal side of a defrost sequence in an appropriate design. It cannot power the compressor, pumps or control electronics. A claim that a warm tank removes all battery or grid demand during defrost confuses thermal energy with electricity.

Ask the heating designer to document minimum active water volume, flow, zone-valve behavior and the source of heat used during defrost. Check what happens when emitters close and whether the proposed vessel remains hydraulically available. Tank nameplate volume alone does not answer those questions.

If thermal storage is intended for tariff shifting, calculate usable heat over the permitted temperature range and include standing losses. Raising the storage temperature can affect heat-pump efficiency and comfort control. Compare the complete system result instead of selecting an arbitrary percentage above the minimum tank size.

Dynamic Tariffs and Defrost Timing

Tariffs change the cost of electricity at a given time; they do not change the heat pump’s need to protect and clear its coil. Use supported scheduling to manage flexible heating and battery charging. Do not disable or delay protective defrost through an improvised external control.

The Tariff-Defrost Collision

Octopus describes Agile as a tariff with prices changing every half hour and identifies the usual evening rush period as 4 pm to 7 pm. That is a tariff description, not a guarantee of tomorrow’s price or a universal expensive period for every supplier.

Use the customer’s actual tariff version and interval rates. Keep import and export prices separate. A battery charged from PV has an export opportunity cost, while a battery charged from the grid has a purchase cost and losses. Neither source should be treated as free in an operating-cost comparison.

As a simple illustrative calculation, an electrical event using 0.50 kWh costs 17.5 pence at an assumed 35 p/kWh and 4 pence at an assumed 8 p/kWh. The difference is 13.5 pence before storage losses or other effects. Those assumed prices are not a live tariff quotation and do not predict a monthly saving.

Smart Control Strategies

Pre-heating may shift some heating demand into a preferred period if the building, emitters and occupants allow it. Ask the heating designer to set limits for room temperature, water temperature and recovery. Maximum heat-pump output is not automatically the most efficient way to achieve the shift.

Battery dispatch can reduce imports during a selected interval if enough charge and power remain available. Compare the extra charging cost, losses, throughput and any missed export revenue. A high price difference does not guarantee a benefit if the battery would otherwise be reserved for backup.

A supported smart-grid interface can request an operating mode, but its label alone does not prove control over defrost. Ask what signals are supported, what the controller does when a signal disappears and which protections take precedence. Keep the manufacturer’s safety and equipment-protection functions authoritative.

Commission the sequence with the customer present where practical. Show the difference between a normal defrost event, a price-driven schedule and a fault. Clear operating explanations can prevent a homeowner from repeatedly overriding controls that are working as intended.

Monobloc vs Split: How Configuration Changes Defrost

Monobloc and split describe the arrangement of the refrigerant circuit. They do not establish a universal ranking for defrost speed, noise or electricity use. Compare the actual models, hydraulic arrangements and controls.

Monobloc Units

A monobloc generally contains the refrigerant circuit in one unit. In a common outdoor air-to-water installation, water connections carry heat into the building. Vaillant’s monobloc and split explanation describes this arrangement and contrasts it with a split refrigerant circuit.

For the installer, document external water-pipe protection, the approved hydraulic arrangement and electrical supplies. Do not assume all power enters through a single outdoor circuit. Indoor controls, circulation or supplementary heating can require separate consideration.

Outdoor compressor placement also does not mean no noise or vibration can be perceived inside. Siting, supports, pipework and the building affect transmission. Use the equipment’s acoustic data and the relevant installation assessment instead of promising silence during defrost.

Split Units

A split system divides the refrigerant circuit between indoor and outdoor units. In the common air-to-water arrangement described by Vaillant, the compressor is outdoors. The claim that split heat pumps inherently place the compressor indoors is incorrect.

Pipe routing, installation requirements and servicing differ from a monobloc, but refrigerant-line length alone does not supply a defrost-duration comparison. Request performance and installation evidence for the selected model. Likewise, do not assign a universal crankcase-heater wattage or assume that only split systems have auxiliary consumption.

The first two rows describe the usual arrangements discussed in the linked manufacturer guide. The remaining rows are project checks. None of them ranks one arrangement as inherently more solar-compatible.

Refrigerant Comparison: R290 vs R32 vs R410A

The refrigerant matters for equipment design, environmental characteristics, installation requirements and service planning. It does not, by itself, determine event frequency or electrical energy per defrost. Compare complete systems under equivalent operating conditions.

R410A: Assess the Installed Equipment

For an existing R410A system, start with the exact nameplate, service record and manufacturer’s operating data. Do not assume a fixed penalty relative to every newer system. A replacement decision should include condition, expected remaining service, performance, installation work and applicable rules.

A refrigerant change is not a casual drop-in modification. The contractor should establish what service or replacement options the manufacturer permits. A solar designer should not recommend changing refrigerant as a shortcut to reducing electrical demand.

R32: Check the Model and Application

For an R32 proposal, check equipment classification, permitted siting and handling requirements against the current product documents and local rules. Ask for the same electrical and heating data requested for competing systems. A lower refrigerant climate impact than another substance would not prove a lower household bill.

Keep environmental comparisons separate from operating comparisons. The global warming potential (GWP) metric describes a refrigerant’s climate effect on a defined basis. It is not a COP, a defrost-efficiency score or a percentage saving in purchased electricity.

R290 Propane: Verify the Actual Product

Vaillant’s linked aroTHERM plus product page identifies R290 as its refrigerant. Verify refrigerant identity from the exact product documents instead of assuming it from the manufacturer’s broader range. The illustrative example below uses no branded heat pump or claimed field performance.

R290 equipment still needs the manufacturer’s siting, handling and safety requirements. Do not infer permitted locations or clearances from a general article. Equally, do not infer a universal reduction in defrost energy from the refrigerant name or from a seasonal efficiency figure quoted for a different model.

For context, the European Commission’s air-conditioning and heat-pump guidance separates equipment categories, refrigerants and restrictions. Use that classification when checking future procurement, with the exact product and jurisdiction identified.

Illustrative Winter Design Example: Birmingham

This is a fictional planning example, not monitored data from a Birmingham installation. It demonstrates the records a designer needs before promising winter coverage. No customer, equipment manufacturer, measured defrost event count or bill saving is represented.

System Configuration

Assume a project is considering a 6 kWp PV array and a battery described as 10 kWh with a 5 kW continuous output limit. These are example labels, not a complete specification. The heating unit, usable battery energy, winter output and backup topology still require evidence.

The first question is what the customer wants the battery to do. If the objective is bill reduction with the grid available, imports may be an acceptable part of the design. If the objective is heating during an outage, the customer and installer must agree on connected loads, duration, reserve and load shedding.

The second question is whether the 5 kW limit applies to the battery, the inverter or the backup output. These can differ. Record the installed configuration and identify the most restrictive applicable limit rather than selecting the largest number on a brochure.

A Winter Monitoring Plan

Replace invented weekly readings with a plan that can produce useful observations. Collect a common timeline for the heat-pump status, electrical circuits, PV, battery and grid. Make the measurement boundary clear enough that another engineer can reproduce the calculation.

Agree the logging resolution with the engineer responsible for the assessment. Short events and starting behavior may require more detail than tariff-meter intervals provide. Confirm timestamps, meter direction and units before calculating results.

What the Example Can and Cannot Show

The earlier illustrative 7.2 kW simultaneous-load case would exceed an available 5 kW battery output by 2.2 kW. With suitable grid support, that difference can be imported. In backup mode, the accepted load schedule or equipment rating must address it. This conclusion comes from the stated arithmetic, not from a claimed Birmingham monitoring campaign.

The example cannot predict January generation, a monthly bill or upgrade payback. Those require a generation profile, actual load records, tariff assumptions, battery behavior and a quoted investment. It also cannot show that a larger buffer would maintain a particular room temperature without a building and heating-system model.

Use the example to frame a commissioning test. Observe an approved operating sequence, record available battery output and confirm expected grid or backup behavior. If commissioning occurs outside frost conditions, state that limitation and arrange a seasonal follow-up instead of marking defrost performance verified.

Demand Peaks and DNO Considerations

A Distribution Network Operator (DNO) assesses connection requirements for the local electricity network. The installation must follow the applicable connection or notification route. Heat-pump thermal capacity alone is not enough information for the electrical assessment.

National Grid Electricity Distribution’s guidance points installers to the Energy Networks Association heat-pump database and combined process, which distinguish connect-and-notify equipment from cases requiring an application. Check the applicable route for the selected model and site.

The Diversity Question

Diversity is an assessment of which loads may operate together. It must be justified for the actual installation and connection process. Do not assume that every heat pump on a street defrosts simultaneously, and do not assert that defrost eliminates diversity without measured or network-model evidence.

For a single property, identify the heat pump, electric backup, hot-water immersion, cooking, vehicle charging and other major loads. If a control scheme limits demand, document its operating limits and failure behavior. The network operator and electrical designer should assess whether that scheme is acceptable.

Connection Documentation

Provide the model, manufacturer electrical data, supply arrangement, expected auxiliary loads and site maximum-demand assessment required by the applicable process. PV and battery generation or export requirements may involve additional information; the heating application alone does not settle them.

Retain correspondence, accepted settings and any connection conditions with the project. If the installer changes the heat-pump model, backup heater or load-management arrangement, review the assessment again. A substitution can change demand even when the advertised heating capacity appears similar.

This article does not assign new defrost-specific thresholds to individual DNOs. Obtain their published requirements or written project response rather than relying on an unsupported generic threshold.

Design Recommendations for Installers

A defensible design ties generation, heating, electrical supply and controls to the same assumptions. Use the following sequence to turn the analysis into a reviewable proposal and commissioning plan.

1. Size the Electrical System from Supported Loads

Separate the grid-connected supply assessment from backup-inverter sizing. List the circuits that are actually connected to each boundary. Use manufacturer electrical limits and approved simultaneous-load assumptions, with qualified review of protection and supply capacity.

Where measurements are available, keep their conditions and uncertainty visible. A measured event can inform operation, but it does not automatically replace the equipment maximum or required design rules. Use the right evidence for each decision.

2. Design the Hydraulic Circuit Before Enlarging a Tank

Meet the heat pump’s required flow and available water volume through the selected hydraulic arrangement. Assess buffer, volumiser or direct-circuit options with the heating designer. An oversized vessel can add cost, space requirements and losses without solving the actual issue.

Record which valves can close, which pumps continue running and where heat comes from during defrost. The scheme should remain valid across the control states that occur in service, not only when every emitter happens to be open.

3. Model Contrasting Weather and Operating Conditions

Review a mild heating period, a cold damp period and a low-generation winter period. Use site data or explicit assumptions for each. Do not attach universal solar fractions or event intervals to these labels.

Also examine an outage if backup is part of the sale. State what happens at the reserve limit and which loads remain supported. A winter-energy assessment and an outage test should not be merged into one unexplained autonomy figure.

4. Use Supported Smart Controls

Document the permitted operating requests, temperature limits, fallback behavior and customer override. Explain which priorities apply when tariff savings conflict with comfort, hot-water requirements or equipment protection.

Use the guide to time-varying electricity prices to structure the financial comparison. Match the rate period to the model interval and keep any forecast prices visibly separate from observed prices.

5. Examine Demand-Based Defrost Without Inventing Savings

Demand-based controls can avoid unnecessary cycles when compared with an unsuitable fixed schedule. The benefit depends on the equipment and conditions. Ask the supplier to explain its method and provide relevant evidence rather than assigning a generic percentage reduction.

Do not modify factory control logic simply to create a smoother battery trace. If normal operation causes a problem, resolve the equipment, hydraulic or electrical design with the responsible installer and manufacturer.

6. Document the Result for the Customer and Network

Deliver a load schedule, generation assumptions, storage limits, control description and the required connection records. Add a practical explanation of expected imports, backup exclusions and the signs that warrant a service call.

For the solar side, SurgePV supports roof layout, shading, energy-yield and financial modeling. Its generation and financial workflow can support review of those project assumptions. Heat-pump defrost simulation, hydraulic tank sizing and electrical approval require their own methods and responsible specialists.

The Tradeoff: Energy, Power and Comfort

Similar event energy can come with different power requirements, but that does not prove one defrost algorithm is preferable. Heat delivered, recovery time, control behavior and the equipment’s limits all belong in the comparison.

As a purely arithmetic example, 6 kW for five minutes uses 0.50 kWh, while 3.5 kW for nine minutes uses 0.525 kWh. They are close, but not equal. The lower-power example might fit within a particular output limit, yet this says nothing about whether it clears the same frost or provides the same heating service.

Ask for the operating trace and its context rather than attempting to tune the appliance around a battery limit. If the homeowner accepts grid support, occasional imports may be preferable to a costly upgrade. If backup heating is essential, define a viable load schedule and assess the full system accordingly.

The financial comparison should include the investment, expected use, tariff assumptions and uncertainty. A larger battery cannot earn back its price from events that rarely occur, and a thermal store cannot be credited with electricity savings without accounting for how it is charged.

2026 Outlook: What to Check Before Specifying Equipment

The practical changes to watch are product availability, refrigerant rules, tariffs and connection processes. Check each against the equipment category and jurisdiction rather than carrying forward broad predictions.

EU restrictions distinguish self-contained equipment, split air-to-water systems and split air-to-air systems, as well as capacity, refrigerant GWP and safety exceptions. The European Commission page linked above sets out those categories. There is no single blanket date in this article for every R32 system or every monobloc, and EU rules should not be assumed to govern a UK or US installation.

Tariff offerings and control integrations also change. Verify the customer’s actual contract and the supported controller interface at procurement. A half-hourly tariff does not itself prove that a heat pump can be commanded at every price boundary, or that doing so improves overall efficiency.

For connection work, use the operator’s active process and preserve the applicable version in the project file. Do not claim that all DNOs now require event-level defrost reporting unless the specific requirement is published for that project.

Bring the verified solar assumptions to a guided SurgePV project demonstration, and keep the heating designer’s electrical and hydraulic requirements beside them. The useful deliverable is a winter operating plan the customer can understand and the responsible specialists can check.

Frequently Asked Questions

What is a heat pump defrost cycle?

A reverse-cycle defrost sends heat to the outdoor coil to melt frost. A reversing valve changes refrigerant flow; the compressor does not physically run backward. Heating delivery is interrupted or reduced during the sequence, and supplementary heating may operate depending on the system.

How much electricity does heat pump defrost use?

Defrost electricity use depends on the model, operating conditions and auxiliary-heater behavior. There is no universal percentage or power multiplier established by the sources in this guide. Use manufacturer electrical data and appropriately logged events with a clear measurement boundary.

Does SCOP tell me the peak power during defrost?

No, SCOP is a seasonal performance metric rather than a peak electrical-input rating. Check the applicable rating method before adding any separate defrost allowance. Use model-specific electrical data, auxiliary loads and operating records for the power assessment.

Will defrost overload my solar battery inverter?

It depends on the simultaneous load and whether the system has grid support. A grid-connected installation can import a shortfall within its supply limits, while an islanded backup inverter must support or shed connected loads. Check both available battery power and usable energy.

Should I oversize a buffer tank to cover defrost?

Do not apply a blanket oversizing rule. The heating designer should meet the manufacturer’s water-volume, flow and hydraulic requirements, then assess any additional thermal-storage benefit. A warm tank can support the thermal circuit but cannot supply electricity to the compressor or pumps.

Are R290 heat pumps always better at defrost than R32?

The refrigerant alone cannot establish a defrost-performance ranking. Compare complete systems at equivalent operating conditions, including electrical input, heat delivery, auxiliaries and controls. Installation requirements and refrigerant rules also need checking for the exact equipment and jurisdiction.

Can smart tariffs delay heat pump defrost?

A tariff does not authorize delaying protective defrost. Use manufacturer-supported scheduling and control interfaces to shift flexible heating or battery charging within comfort and equipment limits. Leave defrost and other protective functions under the approved heat-pump controls.