LG Therma V heat pumps

The LG Therma V is LG's air-to-water heat pump range for UK homes, and the current R290 monobloc family covers 9 to 16 kW across four sizes, sold in both 1-phase and 3-phase variants¹. It is a monobloc design, meaning the whole refrigerant circuit sits in one outdoor unit and water, not refrigerant, runs into the house⁴. The range uses R290, a natural refrigerant with a global warming potential of 3, and it carries ErP energy labels of A+++ for space heating at a 35°C water outlet on the 12 kW and larger models⁵.

For a household, the appeal is straightforward: a Therma V replaces a gas or oil boiler with a unit that extracts heat from outside air and moves it indoors using electricity, removing the gas supply and the gas bill from the heating system. What remains is a dependence on electricity, on the installer and manufacturer for service, and on MCS certification if grant funding is part of the plan. This page sets out the range, its efficiency, refrigerant, operating limits, warranty position and UK availability, so a householder can weigh it against the alternatives on air source heat pumps generally.

Monobloc Therma V units with outputs from 9 to 16 kW

The R290 monobloc family is described as a next-generation model of LG air source heat pump, with a capacity range of four sizes from 9 to 16 kW aimed at both renovation projects and large new builds¹. The individual listings break down as follows: a 9 kW 1-phase model, 12 kW models in 1-phase and 3-phase form, 14 kW models in 1-phase and 3-phase form, and 16 kW models in 1-phase and 3-phase form². The 9 kW model is listed as suitable for new build, with the wider range covering renovation and large new build².

The monobloc concept matters for the household: because the refrigerant is sealed inside the outdoor unit, the indoor side is a water circuit, and the range is connectable with three types of indoor unit to suit different homes⁴. The distinction between monobloc and split systems, and which suits which installation, is covered on monobloc and split heat pumps. Sizing itself should never come from the range listing: it comes from a heat loss calculation on the actual house.

How a Therma V is powered: air alone

A Therma V is an air source heat pump: it takes low-grade heat from the outside air, raises its temperature through a refrigerant cycle, and delivers it to water that circulates through radiators or underfloor heating¹. The energy input is electricity for the compressor and fans; the heat itself comes from the air, which is free and unlimited. That is the whole independence argument for the technology: the household stops buying a fuel to burn and starts buying a smaller quantity of electricity to move heat.

This is also the dependence that remains. A Therma V home is off the gas supply but firmly on the electricity grid, and the running cost depends on the electricity tariff, not on the unit. The running costs question is therefore about tariff and efficiency together, not about the heat pump alone. For homes not ready to leave gas entirely, hybrid arrangements exist: guidance from the heating industry notes that systems running on electricity alongside natural gas, LPG or oil are an effective interim solution that could be seen as a boiler-plus measure, helping accelerate the transition to low-carbon heating⁹. Those arrangements are covered on hybrid heat pumps.

The A+++ rating explained

The efficiency headline for the range is the ErP energy label. The 12 kW and larger models carry A+++ / A+++ for space heating, measured at an average climate at 35°C and 55°C water outlet respectively⁵. The 9 kW model is rated A+++ / A++, the lower second figure reflecting its performance at the higher 55°C flow temperature⁴.

Two things follow from that. First, the label is temperature-dependent: the same unit scores its best rating when it delivers water at 35°C, which suits underfloor heating or generously sized radiators, and scores lower when it has to push 55°C water for conventional radiators. The gap between A+++ and A++ on the 9 kW model is the label's way of showing that. Second, the label is a laboratory comparison, not a bill forecast: what a household actually gets depends on the flow temperature the system is set to run at, the insulation of the house, and the emitters the heat feeds. The measures that matter, explained on heat pump efficiency: COP, SCOP and SPF, are the ones measured across a whole heating season in a real house.

Why R290's reduced GWP is significant

The R290 monobloc range uses R290, a natural refrigerant, with a low global warming potential of 3¹. That figure is the range's main environmental credential. For comparison, the heat pump industry's own technology collaboration describes the shift toward short-term synthetic refrigerants such as R32 in Europe, chosen for their low GWP values relative to older refrigerants¹⁰. R290's GWP of 3 sits far below even those synthetic options, which is why propane has become the refrigerant of choice for the newest monobloc ranges.

The trade-off is flammability: R290 is propane, a flammable gas. In a monobloc design the refrigerant is entirely contained in the outdoor unit, so none of it runs through the house, which is one reason the monobloc layout suits this refrigerant. The broader picture on refrigerants, including the F-Gas rules pushing the change, is on heat pump refrigerants, and the head-to-head comparison is on R290 vs R32 heat pumps.

Operating limits and hot water storage

No published operating-range figure for the Therma V monobloc appears in the material here, so the low-temperature limit and the maximum flow temperature should be asked for in writing with any quote. What holds for air source heat pumps generally is that output and efficiency fall as the outside air gets colder, without the unit stopping, and that behaviour, and how it compares with ground source systems, is explained on heat pumps in cold weather and ground source vs air source in cold weather.

On hot water, the general guidance for heat pumps is that a sterilisation cycle guards against legionella¹¹. Hot water is stored, not made on demand as a combi boiler does, so the household needs a cylinder. Storage sizes vary: thermal stores range from around 120 litres to 500 litres or more¹², while other guidance puts the typical size between 250 and 500 litres¹³; the two figures differ, and the right volume depends on the household, not the heat pump.

Three years of cover included

The warranty position needs care, because LG's published terms for the Therma V have not been stated consistently: figures of 3 years as standard and up to 7 years have both appeared on the maker's own product pages, and the two differ. The term that actually applies is the one written on the warranty documents issued at installation, and that should be confirmed in writing before signing anything.

What is well established is the registration process. Warranty registration for heating appliances normally runs through the manufacturer's website or a phone call to their service team, and in practice the installer usually completes it as part of handover¹⁴. Registration matters because an unregistered warranty can be reduced or invalidated, a point consumer guidance makes about heating warranties generally¹⁴. Ongoing servicing also affects the position, and the interaction is covered on does servicing a heat pump affect the warranty.

UK listed models and where to buy them

The R290 monobloc models are listed as available for the UK market, with the caveat that the products may only be available in specific regions⁸. LG sells the range in the UK through its own air-to-water heat pump pages, and the listings link through to LG's UK site for purchase³. In practice, a householder does not buy a Therma V from a shelf: it is specified and installed by an installer, and availability is really a question of which models and indoor units that installer can supply in your region.

The practical steps are the standard ones for any heat pump: confirm the exact model in the quote, confirm the installer holds MCS certification, and get several quotes, as covered on how many heat pump quotes to get. MCS product certification is what ensures compliance with UK regulations, and it is also the route through which grant funding flows¹⁵, so the certificate for the specific model matters as much as the brand name.

LG's standing among UK heat pump suppliers

LG is a significant but not dominant supplier. An analysis of MCS-certified installed heat pumps from January 2010 to September 2021 put LG at approximately 6% of installations⁷. For context, heat pumps held a 5.6% share of the UK space heating market in 2024¹⁶, so the technology itself is still early in its UK growth, and the government's ambition is large: an investment roadmap points to up to 1.9 million heat pump installations a year by 2035¹⁷, and Parliament's briefing on the technology cites a target of 600,000 installations a year by 2028¹⁸.

The wider industry structure is worth knowing when reading any brand claim. The Heat Pump Association's members represent around 90% of the volume of heat pumps sold in the UK market¹⁹, so most units sold, whatever the badge, come through a fairly concentrated industry. LG's roughly 6% installer share⁷ means a householder considering a Therma V is choosing a mainstream product with an established UK service presence, not an exotic import, but also not the largest player in the market.

Suitable applications and what stays the same

A Therma V suits a household that wants to leave gas or oil behind and has, or can achieve, a home that can be heated at moderate flow temperatures. The range's A+++ ratings at 35°C flow⁵ reward low-temperature systems: underfloor heating or well-sized radiators. Existing radiators can often stay, and thermostatic radiator valves are encouraged on existing radiators²⁰, but each emitter needs checking against the heat loss calculation, as covered on do I need to upgrade my radiators for a heat pump. One compatibility trap sits on the controls side: most smart radiator valves will not work with another manufacturer's smart thermostat and connecting device, so the control chain should be chosen as one system²¹, a point developed on heat pump controls.

What a Therma V does not change is the household's dependence on electricity, on an installer for servicing and repair, and on MCS paperwork for grants. It removes the gas bill and the gas supply, and the R290 refrigerant removes most of the climate cost of the refrigerant itself⁶. Whether the overall package beats the alternatives depends on the house, the tariff and the installation quality, which is why the cost and grant pages, and the pillar guide at heat pumps, are the right next stops.