Heat pump, hot water & battery FAQs.

HISA Engineering is an independent Scottish heating and energy technology company based in Glasgow. It develops and supplies products for heating and home energy, including R290 air source heat pumps, hot-water cylinders and battery storage. HISA works with installers and technical partners to support product selection and aftersales enquiries. For advice about an installation, contact HISA or use the Find an Installer service to discuss the next step.

Start with an assessment of your home rather than choosing a heat pump from its model number. Your installer should assess heat loss, radiators or underfloor heating, hot-water demand and the installation space. That information helps establish the right equipment and operating temperatures.

It helps to explain what you want to achieve, the type of property or building, your existing heating system and whether you need heating, hot water, battery storage or a combination. For a commercial enquiry, include any heat-loss calculations, design temperatures and electrical-supply information already available. You do not need to guess technical figures you do not have.

HISA offers separate product ranges for heating, hot water and energy storage. The right combination depends on your property and what you want the system to do. Do not assume every product can be connected in every arrangement: your installer should confirm the equipment, controls and installation requirements for your design.

Not reliably from a product headline alone. Any meaningful comparison needs to account for your building, heating demand, operating temperatures, current heating system and energy tariff. The published performance data helps your installer assess the equipment at relevant operating conditions; it is not a guarantee of a particular household bill or saving.

An air source heat pump takes heat from the outside air and transfers it into your home's heating system. Unlike a gas boiler, which burns fuel, it uses electricity to move heat. It can deliver several units of heat for each unit of electricity used, depending on operating conditions. HISA's R290 air-to-water heat pumps provide central heating and can heat domestic hot water through a suitable cylinder.

Yes. HISA's published domestic Gen 2 heating operating range extends down to −25°C, subject to the selected model's limits. This does not mean the unit delivers the same heating output or efficiency at every temperature. A correctly designed installation needs enough capacity at the outdoor temperature expected for the property. Your installer should check room-by-room heat loss and the model's performance at the proposed heating-water temperature.

Yes, in many homes existing radiators can be retained. The installer must check whether each radiator can provide enough heat at the proposed water temperature. Some may need upgrading, particularly in rooms with greater heat loss. HISA's R290 heat pumps can supply water up to 75°C within their operating conditions, but lower heating-water temperatures generally support better efficiency. A survey should identify any radiator or pipework changes before installation.

Yes. Older homes, including traditional stone-built houses, can be suitable for an air source heat pump when the system is designed for the property. Heat loss, insulation, radiator output and the required water temperatures matter more than the building's age alone. A room-by-room heat-loss assessment helps establish the appropriate equipment and any improvements needed. It should also identify radiator or pipework changes rather than assuming every older home needs a complete heating-system replacement.

Indicative HISA installation prices are £11,500–£13,500 for systems up to 12 kW and £13,500–£14,500 for an 18 kW installation. The standard package includes a suitable hot-water cylinder, standard installation materials, labour and commissioning. These figures exclude VAT and are before government funding; 0% VAT applies only where the installation qualifies. Radiator upgrades, associated heating-distribution pipework changes and other non-standard works are quoted separately. A property survey and agreed scope are needed for an accurate quotation.

They can be, but lower running costs are not guaranteed. The comparison depends on your electricity and gas prices, heating demand, seasonal heat-pump efficiency and the existing boiler's efficiency. A heat pump can deliver several units of heat per unit of electricity, but electricity usually costs more per unit than gas. Suitable radiators, lower flow temperatures, weather compensation and correct commissioning can help. A headline COP figure alone cannot predict your household's annual savings.

The right size depends on your property's calculated heat loss, not just its bedrooms or floor area. HISA's domestic R290 range has 4, 6, 8, 12 and 18 kW model designations. An installer should carry out a room-by-room heat-loss calculation and check the selected model's output at the proposed outdoor and water temperatures. Model names are not guaranteed outputs at every operating condition. Oversizing or undersizing can affect comfort, efficiency and running costs.

COP measures efficiency at one stated operating condition; SCOP describes performance across a defined heating season. For example, a COP of 5 means about 5 kWh of heat is delivered per 1 kWh of electricity at that test point, not throughout the year. Compare COP values at matching air and water temperatures. Compare seasonal SCOP only on the same climate and water-temperature basis, with the relevant model, test standard and system configuration identified.

Yes. HISA's domestic R290 range has a published maximum flow temperature of 75°C, within the specified model and operating conditions. This is a capability limit, not a promise of maximum output or efficiency at every outdoor temperature. Higher temperatures can be useful for some existing heating systems and hot-water duties, but usually reduce efficiency. Your installer should aim for the lowest practical heating-water temperature that maintains comfort and meets the system's requirements.

HISA heat pumps produce sound from their fan and compressor, as other air source heat pumps do. What you hear depends on the model, operating state, position and nearby walls or other surfaces. Your installer should assess the correct model's acoustic data and the applicable planning or assessment requirements before choosing a location. Sound power and sound pressure are different measurements, so a number without its measurement conditions is not a reliable guide to what neighbours will hear.

Yes. The current HISA heat-pump warranty terms require servicing at least once every 12 months by a suitably competent person. A service should follow the relevant model's maintenance instructions and can include checks on water flow, pressure, filters, electrical connections, controls and the outdoor unit's condition. Keep the service records with your commissioning and registration documents. Routine servicing is not itself included in the manufacturer warranty; the full terms explain how maintenance can affect a claim.

A 10-year parts-and-labour warranty is available for qualifying HISA heat pumps, subject to the applicable terms, including registration, servicing and eligibility requirements. Ask HISA or your installer to confirm the warranty supplied with your installation and check your warranty documents. Inclusion can depend on the purchasing package: do not assume every heat pump automatically includes ten years of cover or that every customer must buy an extension. Cover does not automatically extend to every component of the wider installation.

Yes. HISA provides lifetime remote monitoring for qualifying compatible heat-pump systems, subject to the relevant connectivity and system requirements. Remote access can help HISA and authorised support personnel investigate operating information and faults where available. The information accessible and the support arrangements depend on the model, controller and connection. Check the applicable documentation for your system rather than assuming all installations offer identical monitoring or diagnostic functions. Remote monitoring does not itself establish which homeowner app controls are available.

Yes, the HISA smartphone app supports compatible heat-pump systems. The available functions and connectivity requirements must be checked against the documentation for the relevant heat pump, controller and app. Ask HISA or your installer to confirm compatibility and explain the supported controls before relying on a particular function. They should also explain which settings homeowners may adjust and which should remain under installer control. Do not assume that every HISA system or app version has identical features.

Not necessarily. Heat pumps often work well by maintaining a steady indoor temperature rather than repeatedly heating a cold home at a high water temperature. This can mean longer periods of operation at lower output, not continuous operation at full power. The right schedule depends on the property, occupancy, controls and tariff. Your installer should explain the recommended settings and any suitable temperature setbacks. Weather compensation can help match the heating-water temperature to changing outdoor conditions.

Weather compensation adjusts the heating-water temperature in response to the temperature outside. In milder weather it can supply cooler water; when it becomes colder, it raises the temperature according to the configured heating curve. This helps avoid unnecessarily high flow temperatures while maintaining comfort. HISA heat pumps support weather compensation, but the installer needs to set it for your property's heat loss and radiators or underfloor heating. It is not a substitute for correct system design.

Yes. HISA heat pumps can serve wet underfloor heating as well as suitable radiator systems. Wet underfloor heating circulates warm water through pipes in the floor and often operates at relatively low temperatures, which can support heat-pump efficiency. The installer still needs to check heat output, flow rates, controls and the hydraulic arrangement. A property combining radiators and underfloor heating may need separate temperature zones; it should not be treated as a standard arrangement without assessment.

Not every heat-pump installation needs a separate buffer tank. The decision depends on water volume, minimum flow, zoning, defrost requirements and the hydraulic design. HISA heat pumps incorporate hydraulic components intended to simplify installation, but the precise equipment must be checked for the model and generation. Integrated components do not remove the need for system design. Your installer should follow the applicable requirements and determine whether a buffer, volumiser or another approved arrangement is needed.

R290 is propane, a refrigerant with a low global warming potential compared with many conventional synthetic refrigerants. It also supports the high-temperature capability of HISA's domestic monobloc heat-pump range. R290 is flammable, so the outdoor unit must be positioned and installed in accordance with its model-specific safety requirements and any applicable clearance or protection-zone rules. These are matters for a competent installer; refrigerant work or changes to the unit are not homeowner maintenance tasks.

HISA's domestic range combines R290 refrigerant and high-temperature capability with Scottish-based technical support. Lifetime remote monitoring is available for qualifying compatible systems, and a 10-year parts-and-labour warranty is available subject to the applicable package and terms. Confirm the cover supplied with your installation rather than assuming it is automatic. Check the model-specific hydraulic equipment and connectivity requirements too. A fair comparison should consider like-for-like performance, sound data, warranty conditions and the quality of system design and installation.

Yes. Installers can contact HISA for technical support with product selection, installation and commissioning enquiries. The relevant model, generation, controller and document revision should be identified before advice or reference diagrams are used. Remote diagnostic assistance may be available depending on the equipment and connection. Project-specific design or heat-loss support should be agreed with HISA rather than assumed to be included in every purchase. Use the current technical documents and contact the support team where a requirement is unclear.

Compatibility must be confirmed for the exact heat pump, controller and proposed thermostat. Do not assume that every third-party control or connection arrangement is suitable. Ask HISA for the applicable compatibility information and current model-specific control documentation before installation. A competent installer should check the intended control strategy and carry out any electrical work. Homeowners should not alter control wiring: an incorrect connection can damage equipment or stop the system operating correctly.

Most conventional air-to-water heat-pump systems use a cylinder to store domestic hot water for showers, baths and taps. Unlike a combi boiler, a typical installation does not provide large quantities of instantaneous hot water on demand. The cylinder is separate from the water circulating through your radiators or underfloor heating. Your installer should match its storage capacity and heat exchanger to household demand, the selected heat pump and the intended operating temperatures.

Cylinder size should be based on occupants, bathrooms, showers, baths and usage patterns, not bedroom count alone. Standard HISA HPT cylinders have nominal capacities of 150, 200 and 300 litres. The right choice also depends on recovery time, available space and the heat pump's hot-water performance. A bigger cylinder is not automatically better. Your installer should assess expected demand and check the selected model's dimensions and technical data before recommending a size.

Yes. HISA's HPT cylinders are designed for heat-pump systems, and the HPTB range adds an integrated buffer option. The cylinder's heat exchanger needs to transfer heat effectively at the intended operating temperatures. Your installer must still match the exact cylinder to the heat pump, hot-water demand, controls and hydraulic design. A heat-pump-compatible description does not mean every model or connection arrangement is interchangeable without checking the relevant technical information.

A standard HPT cylinder stores domestic hot water; an HPTB also includes a separate 50-litre heating-system buffer. The published HPTB options are 150 litres of hot water plus a 50-litre buffer, or 200 litres plus a 50-litre buffer. The buffer is not extra domestic hot-water capacity. Combining the vessels can reduce the need for a separate buffer where the design permits, but does not remove the need to check controls, hydraulic arrangements or other required components.

The main difference is storage volume: a 200-litre cylinder stores more water than a 150-litre model. That may help a household with greater demand, but it does not guarantee a particular number of showers or baths. Usable hot water also depends on storage temperature, cold-water temperature, mixing and recovery. The larger model's dimensions and heat-exchanger specification should be checked as well. Your installer should choose a cylinder around actual demand and the available installation space.

There is no single recovery time for every heat pump and cylinder. It depends on storage volume, starting and target water temperatures, available heat-pump output and heat-exchanger performance. Outdoor conditions and how the system prioritises hot water and space heating also matter. Larger temperature rises require more energy. Your installer should estimate recovery for the selected equipment and control strategy rather than using a generic time as a promise of performance.

Yes, when the heat pump, cylinder and control strategy are correctly matched to the household. Storage capacity, recovery time and the pattern of hot-water use matter more than a simple family-size label. Several showers or baths close together can create a different demand from the same usage spread across the day. Homes with multiple bathrooms or high simultaneous demand may need more storage. Your installer should assess those requirements before selecting the system.

The HISA HPT and HPTB specifications identify a Duplex 2205 stainless-steel inner water vessel. That does not mean the whole cylinder casing is stainless steel: the standard HPT outer shell is galvanised steel, while HPTB specifies painted galvanised steel. Correct installation, suitable water conditions and maintenance remain important. Check the exact model's documentation rather than assuming the vessel, outer casing and heat-exchanger coil all use the same material.

Yes. The published HPT and HPTB specifications include an electric heater with a thermostat. It can provide supplementary or backup hot-water heating where the electrical installation and controls allow. This is direct electric resistance heating, not the same process as the heat pump moving heat from outside air. Your installer should explain its intended use and setup. Check the exact cylinder specification, as heater electrical details differ between the HPT and HPTB families.

Legionella risk needs a system-specific hot-water hygiene strategy, not an assumption that a heat pump's maximum flow temperature makes stored water safe. A periodic high-temperature cycle may form part of the control strategy, but the required approach depends on the cylinder, controls, temperatures throughout the system and applicable guidance. Your installer should follow the relevant manufacturer instructions and explain the settings you need to maintain. Do not disable hygiene controls or attempt a disinfection procedure from a general FAQ.

A thermostatic mixing valve may be required or recommended by the system design and applicable requirements. It mixes hot and cold water to control outlet temperature and help reduce scalding risk. Stored water and water delivered at a tap need not be at the same temperature. The installer should select a suitable valve and position it in accordance with the relevant instructions. A general FAQ cannot determine the valve arrangement for a particular cylinder installation.

A multiblock is a combined inlet-control assembly used with suitable unvented hot-water systems. Depending on the assembly, it can provide functions such as pressure reduction, check-valve protection and expansion relief. The correct assembly must match the cylinder, water supply and applicable installation requirements. It should not be selected or adjusted from generic advice. Your installer should use the relevant model's instructions and confirm which safety components are supplied and which must be provided separately.

The required expansion arrangement must be checked for the exact cylinder and installation. An unvented domestic hot-water system needs an appropriate means of accommodating the water's expansion as it heats, but a separate vessel should not be assumed either necessary or unnecessary from the product name alone. An integrated heating-system buffer is not a substitute for a potable-water expansion arrangement. Your installer must follow the model-specific instructions and applicable safety requirements.

Yes, if the cupboard and surrounding installation meet the selected cylinder's requirements. The installer needs to allow for its dimensions, pipework, safety components, electrical connections and access for inspection or maintenance. Floor loading, access into the property and any required safe discharge arrangement must also be considered. HPT and HPTB models have different dimensions, so do not approve a location from nominal litre capacity alone. Check the current model drawing before confirming the space.

Yes. The cylinder and associated safety components need maintenance in accordance with the relevant instructions. The current HISA cylinder warranty terms call for inspection or servicing at least every 12 months where required for the installation, by a suitably competent person. For an unvented system, servicing can include checks on the applicable safety valves, expansion arrangement and temperature controls. Keep installation, registration and service records. Homeowners should not alter or bypass safety devices; any fault or uncertainty should be referred to a competent engineer.

Potentially, yes, if the exact equipment and control arrangement are compatible. The installer needs to check heat-exchanger performance, available heating output, operating temperatures, controls and hydraulic connections for the proposed combination. A cylinder designed for heat pumps is not automatically suitable for every heat pump or installation. Ask for the compatibility assessment before purchase, and check the applicable warranty conditions rather than assuming a mixed-brand system has identical cover.

You may be able to use the cylinder's immersion heater if it is correctly installed, operational and supported by the electrical supply and controls. This is not guaranteed for every fault: a problem affecting power, controls or the cylinder itself may also prevent backup heating. Ask your installer to explain the permitted backup arrangement for your system. Do not change wiring or bypass safety controls. Arrange support for the heat-pump fault rather than relying indefinitely on resistance heating.

A heat-pump cylinder has a heat exchanger selected to transfer heat at the temperatures and output available from a heat pump. A conventional boiler cylinder may have been designed for a hotter heat source, and its heat exchanger may not suit efficient heat-pump operation. This is a compatibility question, not a rule that every existing cylinder must be replaced. Your installer should assess the actual cylinder specification, recovery requirements and proposed heating system before deciding.

No. The 25-year manufacturer warranty applies to the qualifying stainless-steel inner vessel against defects in materials or manufacture, subject to the warranty terms. It does not mean that every valve, immersion heater, sensor, control, expansion vessel or accessory has 25-year cover. Ask HISA to confirm the applicable cover for other components.

No assumptions should be made across the two ranges. HISA's current public WRAS statement applies to standard HPT-150L, HPT-200L and HPT-300L only; it does not establish approval for HPTB. Likewise, model-specific pressure ratings and installation information must be checked against the correct documentation. Contact HISA if a drawing and specification appear inconsistent.

HBS-H is the hybrid route: it supports direct input from compatible solar panels and can also be used in an AC-coupled arrangement. HBS-AC connects storage on the AC side of a compatible existing PV inverter. The appropriate choice depends on your existing equipment and the installation design.

Potentially, yes. An AC-coupled design can add storage alongside a compatible existing PV inverter, and both HBS-H and HBS-AC support this approach. Your installer should check the existing inverter, electrical arrangement and control requirements before confirming compatibility.

Do not assume whole-home backup. Both HBS-H and HBS-AC can supply designated loads connected to the backup port, within the system's limits. Your installer must select and connect suitable essential circuits and assess their loads. Appliances elsewhere in the property are not automatically backed up simply because a battery is installed.

The currently published HBS-H configurations list usable energy from 3.68 kWh to 22.08 kWh. Use the stated usable-energy value when comparing capacity, not the model-name suffix. Your installer should also distinguish complete-unit parallel configurations from separate battery expansion packs: they are not interchangeable descriptions of the same arrangement.

HISA's battery systems support scheduling with compatible time-of-use or dynamic tariffs when correctly configured. The result depends on your tariff, solar generation, household consumption and system design. Tariff compatibility does not guarantee a particular bill saving.

The published HBS-H and HBS-AC base units have an IP65 ingress-protection rating, but this does not mean every outdoor location is suitable. A qualified installer must assess siting, temperature limits and local conditions in accordance with the applicable documentation.

Qualifying residential HISA battery systems have system-hardware and battery-performance warranty cover, subject to the full terms. The performance warranty includes an energy-retention threshold and expires at the earlier of the applicable ten-year period or warranted energy throughput being reached. It is not a promise of unchanged battery capacity for ten years. Check the terms for your product's registration, usage and operating requirements.

HISA's published commercial R290 range includes the HR290-050C-3PH and HR290-075C-3PH, with 50 and 75 kW model designations. These designations are not guaranteed outputs under all conditions. Selection should use confirmed performance at the project's required outdoor and water temperatures.

The published commercial range supports parallel operation of up to 16 units. A cascade is a project-specific plant design, not simply a matter of multiplying the model designation. Heat demand, load profile, sequencing, hydraulics, electrical supply and controls all need assessment.

The current commercial information lists MODBUS RS485 communication. The interface, accessories, equipment, configuration and integration scope must be confirmed for the project. A listed communication feature is not a guarantee that every BMS will connect without additional design or equipment.

The relevant product pages provide model-specific technical information and approved downloads. The domestic heat-pump page also includes hydraulic reference material. Confirm the exact model, generation and document revision before use. Where a published diagram is conceptual or reference-only, it must not be treated as a complete installation design.

HISA is verifying differences between the supplied catalogue and performance tables. The public page therefore shows the original catalogue curves for reference without estimating selectable numerical points. Obtain confirmed project performance data from HISA before equipment selection.

The published terms require qualifying installation and commissioning, completion of the required commissioning documentation and registration with HISA within 30 days of commissioning. The heat pump must also be serviced at least once every 12 months by a suitably competent person. Keep your purchase, commissioning, registration and service records. The full terms explain cover, exclusions and how claims are assessed.

No. Routine servicing and normal maintenance are not themselves covered by the manufacturer warranty. Servicing and maintenance still matter: failure to maintain the system may affect a claim where it caused or materially contributed to the fault or damage being claimed.

Include the model and serial number if available, a clear description of the issue, any displayed fault code and the installation or commissioning details you have. Relevant photographs can help explain the situation. Do not send passwords or unrelated personal information. HISA may request further documents when assessing a warranty claim; submitting an enquiry does not itself mean the claim has been accepted.

Use the warranty-registration link provided by HISA. If it does not open, contact HISA at enquiries@hisauk.com or 0141 530 2010 for help rather than assuming registration has been completed. Keep your commissioning details and any confirmation you receive. A general enquiry should not be treated as completed warranty registration unless HISA confirms it.

No. The current website enquiry notice states that HISA uses your details to respond to your enquiry and that submitting it does not sign you up for marketing. For Find an Installer requests, relevant contact and project details may be shared with a selected HISA installer partner so they can discuss your project. Read the Privacy Policy for the full explanation.