Joule cylinders and heat pumps

Joule is an Irish-founded heating and hot water manufacturer, established in 2008, that now sells stainless steel hot water cylinders and air to water heat pumps into the UK from a base in Pontefract, West Yorkshire¹. For a household, the practical question is usually narrower: whether a Joule cylinder can be paired with a heat pump, and what the company's own heat pump record looks like. On the first, Joule states that its stainless steel cylinders are compatible with its Samsung heat pump, solar thermal, underfloor heating and aluminium radiators². On the second, the record includes a live product safety recall.

That recall is the first thing to know. A product safety report published on GOV.UK on 9 July 2024 identified a risk of fire from the Joule Hot Water Systems ModulAir Heat Pump, and states that the product does not meet the requirements of the Electrical Equipment (Safety) Regulations 2016³. Affected units were manufactured since May 2023, and Joule Hot Water Systems UK Ltd has contacted owners to arrange an upgrade to the ModulAir All E Heat Pump⁴. Any household with a ModulAir unit installed since May 2023 should treat the recall notice, not the sales literature, as the governing document.

The rest of the range is cylinders first. Joule began as a small manufacturer of domestic copper hot water cylinders in Ireland in 2008, introduced the Cyclone unvented cylinder in 2009, and has developed its stainless steel cylinder range over the last 10 years¹. It entered the air source heat pump market in 2012, partnered with manufacturers including Samsung, and launched the Kodiak Heatpump in 2022¹.

Joule: the company behind the cylinders and heat pumps

Joule describes itself as a leading manufacturer and supplier of high-quality heating, hot water and ventilation systems, with a dedicated in-house design team and a nationwide network of highly trained customer support engineers¹. The company was established in 2008 and carries CRO number 482712 and EEE producer registration number WEE/MM8931AA¹. Its UK operation is at Unit 3, Leftfield Park, Park Road, Pontefract, West Yorkshire, WF8 4PS, and the main UK contact number is 0330 808 8488, with email at info@joule.ie¹.

The corporate history explains the shape of the range. Joule began in 2008 making domestic copper hot water cylinders in Ireland, expanded to a larger Dublin facility and introduced the Cyclone unvented cylinder in 2009, and launched solar thermal solutions in 2010¹. It established a manufacturing and distribution centre in Liverpool in 2011 to serve UK customers, entered the air source heat pump market in 2012, and added Smart Plumb pre-plumbed systems and the InvaHeat underfloor heating brand in 2013¹. Aluminium radiators followed in 2014 under the Riva name, and the InvaVent ventilation range in 2017¹.

The UK footprint has moved several times. Joule acquired RM Cylinders Ltd and opened a Technical Sales and Design facility in Galway in 2018, then moved its facilities out of the Wirral and into the RM factory at Castleford in 2019¹. It moved to a permanent location in Pontefract in 2022, the same year it launched the Kodiak Heatpump, and in 2024 invested in robotic welding lines, reconfigured its production facility and introduced the Modulair EAHP¹. For a household, that matters less as history than as an indicator of where spares, service and design capacity sit: the cylinder side of the business is long established and UK-distributed, while the heat pump side is newer and has already produced one recall.

From copper cylinders to heat pumps: how the range developed

The cylinder business is the older and broader half of Joule. The company states that it has developed its range of stainless steel hot water cylinders over the last 10 years, and that because it has one of the widest ranges of models available, it is able to present a solution for any hot water application². Its stainless cylinders are constructed with Duplex stainless steel⁵. The Cyclone range is listed as single phase⁶.

The heat pump side arrived in 2012, when Joule entered the air source heat pump market and partnered with manufacturers including Samsung¹. That partnership model, rather than wholly in-house development, is visible in the product listing: Joule sells a Joule-Samsung monobloc air source heat pump with a 7 year warranty, and its air source heat pump range is listed with a 7 year warranty and an operation range down to -20°C⁶. The Kodiak Heatpump followed in 2022 and the Modulair EAHP in 2024¹.

Independent certification work in the wider market gives a sense of how heat pump ranges are typically assessed. Heat pump KEYMARK certification operates on what its own documentation calls a robust model range approach, and Joule holds KEYMARK certificates covering air source heat pump models⁷. That is a testing and certification point rather than a performance claim: it establishes that specific models have been assessed under a recognised scheme, not how any one installation will perform.

Cylinders: unvented, indirect, horizontal and stainless steel

Joule's stainless steel hot water cylinders are available in Indirect, Direct, Horizontal, Vented, Unvented, Solar, Twin Coil, Triple Coil, High Gain and Slimline types². That list covers the main domestic configurations: indirect cylinders heated by an external source such as a heat pump or boiler, direct cylinders with their own immersion element, horizontal models for low spaces, vented and unvented arrangements, and solar and multi-coil variants for systems with more than one heat source.

The copper side of the range is separate and includes Combination tanks, Eco Solar tanks and Part L cylinders⁵. Copper and stainless steel behave differently in service, and Joule has published its own comparison of the two⁵. The choice between them is a specification decision for the installer rather than a headline performance difference, but it affects weight, cost and the coil surface available for heat transfer.

For a heat pump specifically, the cylinder is not a passive tank. Independent guidance notes that in many heat pump models the hot water cylinder is built into the case of the heat pump as a fully integrated system, while in others it is separate¹⁰. A Joule cylinder paired with a Joule or Samsung heat pump sits in the second category: a separate store, sized and coiled to suit the heat pump's output and flow temperature. That is the arrangement most UK retrofits use, and it is why cylinder selection and heat pump selection are usually made together rather than independently.

Joule heat pumps: air to water, R290 and the Samsung partnership

Joule's heat pump line is air to water, and the refrigerant in the current models is R290. KEYMARK certification documents list an Air Source Heat Pump, R290, under models JMU150HC and JMU150HC3N, described as an outdoor air to water heat pump⁷. A separate certificate covers an air source heat pump, R290, model VAHM-V8N5M-A, also listed as an outdoor air to water heat pump⁸.

R290 is propane, and it carries a specific safety dimension that households should understand. The Heat Pump Association has published a statement on the R290 safety zone, and the guidance for manufacturers is that they have a key responsibility to ensure their products meet all relevant safety legislation as well as health and environmental protection requirements¹¹. That is a general obligation on all makers, not a finding about Joule.

The Samsung partnership is the other half of the heat pump story. Joule entered the air source heat pump market in 2012 and partnered with manufacturers including Samsung¹, and it lists a Joule-Samsung monobloc air source heat pump with a 7 year warranty⁶. Monobloc means the refrigerant circuit stays inside the outdoor unit, with water pipework running into the house, which is the arrangement most commonly fitted in UK homes.

Compatibility: pairing a Joule cylinder with a heat pump, solar or underfloor heating

Joule states that its stainless steel cylinders are compatible with its Samsung heat pump, solar thermal, underfloor heating and aluminium radiators². That is the maker's own compatibility claim for its own products, and it is the clearest statement available on what the cylinder range is designed to sit alongside.

The wider system context is well established independently. Heat pumps can work with radiators or underfloor heating, though some types can work without either¹². Underfloor heating is often installed in combination with a heat pump and works with all types of heating systems¹³, and heat pump systems are described as ideal for underfloor heating systems because of the low flow temperatures involved¹⁴. None of that is specific to Joule, but it explains why a cylinder and an emitter strategy are chosen together: the lower the flow temperature the heat pump runs at, the more the cylinder coil and the emitters both need to be sized for it.

Solar thermal is the third input. Joule launched a range of solar thermal solutions in 2010 and lists Solar and Twin Coil cylinder types¹. A twin coil cylinder allows a solar thermal circuit and a heat pump to heat the same store, with the solar coil typically sitting below the heat pump coil. That arrangement reduces the volume of water the heat pump has to raise, though it depends on roof orientation and collector area rather than on the cylinder alone.

What this means for independence is mixed. A Joule cylinder paired with an air to water heat pump moves space heating and hot water off gas and onto electricity, which is the main shift. It does not remove dependence on a supplier: the heat pump runs on grid electricity, and the household remains exposed to electricity prices and to the network. Adding solar thermal or photovoltaics reduces the imported share but does not eliminate it, and the cylinder itself adds no independence of its own beyond storing heat for use later.

System design service: sending plans for a complete proposal

Joule has a dedicated in-house design team¹, and the company has published guidance on sending plans in for a complete system proposal. The design service is aimed at producing a specification that covers the heat pump, the cylinder and the associated components as one system rather than as separate purchases.

Commissioning is where design meets installation. Official guidance for Wales states that heat pumps and any dedicated ancillary products, for example integrated hot water cylinders, should be commissioned in accordance with both the manufacturer's instructions and the appropriate system design parameters¹⁵. That dual requirement is the reason a design proposal matters: a cylinder commissioned to the maker's instructions but not to the system's design parameters can underperform even when both components are correct in isolation.

Joule also runs training for the trade. Its installer heat pump course is designed for heating engineers to give them the additional knowledge required to install and commission Joule heat pump systems, and it is completely free and takes place online⁶. For a household, the practical implication is that the quality of the installation depends on the installer having completed that kind of training, and on the design having been done before the equipment was ordered.

Noise assessment is part of the design process in England and Wales. The MCS 020 calculator requires the heat pump make and model and the heat pump installation location for a single heat pump assessment, with project details optional¹⁶. MCS has also consulted on the inclusion of air-to-air heat pumps for the Heat Pump Design Standard¹⁷. Those are the standards a design proposal has to satisfy, and they sit alongside the manufacturer's own instructions rather than replacing them.

Cost: what a Joule system sits within

Joule does not publish a list price for its cylinders or heat pumps in the material available, so prices are installer-quoted. What can be said is what the wider market costs, which is the context a Joule quote will sit in.

Independent figures put air source heat pump installation at £8,000 to £12,000¹⁸, and a separate estimate puts total costs at £6,800 to £17,700 with an average of £13,000¹⁹. The Energy Saving Trust looked at typical heat pump costs of around £11,700 on average²⁰. Running costs are a different figure: heat pumps cost around £800 to £1,050 a year to run, making them one of the cheapest electric heating options²¹.

Cylinder insulation is the cheap end of the same picture. A hot water cylinder jacket costs about £30²², and jackets at around £15 each pay for themselves in a year or less¹⁵. Those are retrofit measures for an existing cylinder rather than a reason to choose one brand over another, but they are the lowest-cost way to reduce standing losses from any store.

UK manufacturing, availability and support network

Joule's UK base is Pontefract, West Yorkshire, and the company supplies stainless steel hot water cylinders across the UK¹. Its support arrangements are a nationwide network of highly trained customer support engineers and an in-house design team¹. The UK contact number is 0330 808 8488 and the email address is info@joule.ie¹.

The recalled ModulAir product has its own contact route. Joule Hot Water Systems UK Ltd can be reached on 020 3744 4200 or at modulairuk@jouleuk.co.uk, and the company has contacted owners to arrange an upgrade to the ModulAir All E Heat Pump³. That is the number and address to use for anything relating to the recall rather than general sales.

On the wider supply chain, official guidance notes that support is also available for installers and manufacturers to expand supply chains in the UK²³. That is a policy context rather than a Joule-specific commitment, but it bears on availability: cylinder and heat pump supply in the UK has been a constraint across the market, and Joule's own history of moving and expanding its production facilities reflects that pressure¹.

For a household weighing energy independence, the position is this. A Joule cylinder paired with an air to water heat pump moves hot water and space heating onto electricity, which reduces direct gas dependence but leaves the home on the grid and on an electricity supplier. The cylinder stores heat rather than generating it, so it adds flexibility rather than independence. The heat pump side of the business is newer than the cylinder side, and the ModulAir recall means that for any unit manufactured since May 2023 the recall notice, not the product page, is the document that governs. Households comparing options across the market can read the wider picture in heat pumps, hot water cylinders for heat pumps and heat pumps and household energy independence.