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NIBE S2125 vs LG Therma V: Which Air Source Heat Pump Is Better? (2026)

Quick Verdict

LG Therma V is the more efficient choice on its MCS-certified figures, with lower estimated running costs.

Side-by-Side Comparison

FeatureNIBE S2125LG Therma V
Installed price (before grant)Price on quotePrice on quote
After £7,500 grant (illustrative, England and Wales)Price on quotePrice on quote
SCOP at 35°C (MCS)4.85.33Higher
SCOP at 55°C (MCS)3.713.86Higher
Largest size12kW12kW
Standard warranty2 years3 yearsLonger
Longest warranty (conditions apply)7 years7 years
Sound power (declared)49 dB(A)49 dB(A)
Annual running cost (est., 45°C flow)~£620/yr~£575/yrLower
Refrigerant and max flowR290, up to 75°C flowR290, up to 75°C flow
CountrySwedenSouth Korea
UK brandNoNo
Best forBuyers who put quiet running and a long warranty first, and will use a NIBE Pro installerHomeowners who want a quiet R290 monobloc with strong cold-weather output from a major electronics brand

Specifications and pricing are indicative for the UK market as at June 2026. Post-grant figures illustrate the £7,500 Boiler Upgrade Scheme in England and Wales (Scotland uses the Home Energy Scotland grant and loan; Northern Ireland has no equivalent). Running costs assume ~10,000 kWh of heat a year at 26.32p/kWh (Ofgem cap average, October to December 2026; changes quarterly). Confirm current models and exact pricing with your MCS-certified installer.

Price Comparison

NIBE S2125 does not publish an installed price and no credible third-party figure exists, so we show none. For scale, the median Boiler Upgrade Scheme install cost £12,908 before the grant (DESNZ Boiler Upgrade Scheme median, April to June 2026). LG Therma V does not publish an installed price and no credible third-party figure exists, so we show none. For scale, the median Boiler Upgrade Scheme install cost £12,908 before the grant (DESNZ Boiler Upgrade Scheme median, April to June 2026). So this pair cannot be ranked on price. In England and Wales the £7,500 Boiler Upgrade Scheme grant comes off either quote equally, with 0% VAT until 31 March 2027; your MCS-certified installer claims the grant for you. Compare written quotes on the same basis: unit size, cylinder, radiator changes and warranty.

Efficiency Comparison

SCOP (seasonal coefficient of performance) is the key efficiency measure for a heating heat pump: the kilowatt-hours of heat you get per kilowatt-hour of electricity across a whole heating season. The figures here are MCS-certified, at 35°C flow (underfloor heating or large radiators) and 55°C (hotter radiators). NIBE S2125 is certified at 4.8 at 35°C and 3.71 at 55°C, while LG Therma V is certified at 5.33 and 3.86. On our estimates at a 45°C design flow temperature, the LG Therma V costs about £45 a year less to run at Ofgem cap electricity prices, or approximately £450 over ten years. Real-world efficiency depends heavily on system design and flow temperature, which is what the MCS heat loss survey is for.

Warranty Comparison

NIBE S2125: 2 years parts and labour as standard; 5 years through a NIBE Pro installer; 7 years through a NIBE Pro Partner or Pro Exclusive installer. All terms need registration within 28 days, commissioning by a NIBE-trained installer, servicing every year and completed Benchmark paperwork; mainland Great Britain only; units within 1 km of the coast need a Blygold coating. LG Therma V: LG UK's consumer warranty page lists Therma V at 3 years basic and 7 years extended, with the unit serviced 'biannually'. LG UK's business page lists 5 years extended but directs private homes to the consumer page. Neither page states what qualifies a home for the extended term. On standard terms, the LG Therma V has the longer cover; the longer terms on either side depend on registration, servicing and the installer. Workmanship cover for the installation itself comes separately from your installer and should be in writing.

Noise Comparison

Noise matters in UK homes because the outdoor unit often sits close to a neighbour's boundary or a bedroom window. The like-for-like figure is the maker's declared sound power: the noise the unit itself emits. NIBE S2125: 49 dB(A). LG Therma V: 49 dB(A). What a neighbour hears is much lower and falls with distance, and permitted development rules require the installation to meet the MCS noise standard at their window, so siting matters as much as the unit.

Cold-Weather and Retrofit Suitability

Two things decide how well a unit suits an older UK home: cold-weather output and flow temperature. NIBE S2125 uses R290 refrigerant (up to 75°C flow), while LG Therma V uses R290 (up to 75°C flow). Both reach 70°C or more, so both can work with existing radiators; the decision comes down to price, warranty and installer availability. Modern units hold useful output well below freezing. In the colder parts of the UK (Scotland and northern England in particular), frosty mornings trigger short defrost cycles that trim efficiency, so ask each installer for low-temperature output figures and take the MCS heat loss survey seriously; radiator upsizing is more commonly recommended there so the system can run at efficient flow temperatures.

Pros and Cons

NIBE S2125

Pros

  • R290 refrigerant
  • Quiet Mark certified (S2125-8 and S2125-12) with 49 dB(A) declared sound power
  • Up to 75°C flow, and up to 65°C at -25°C outdoor
  • Up to 7-year parts and labour warranty through NIBE Pro Partner installers
  • British Gas became an approved NIBE service partner in March 2025

Cons

  • Standard warranty is 2 years unless a NIBE Pro installer registers the extended cover
  • Heavy and deep: 163 kg and 831 mm deep for both the 8 and 12
  • Size labels overstate output: the S2125-12 is rated 6.8 kW at 35°C, 8.34 kW maximum at -7°C
  • Annual servicing is a condition of every NIBE warranty
  • No published installed price

LG Therma V

Pros

  • R290 refrigerant, rated A+++ at both 35°C and 55°C flow
  • Quiet Mark listed (9 kW and 12 kW), with 49 to 50 dB(A) declared sound power
  • Strong cold-weather output: 9.0 kW (9 kW model) and 11.8 kW (12 kW model) at -7°C
  • Up to 75°C flow and operation down to -28°C outdoor
  • Up to 7-year warranty for homes per LG UK's consumer warranty page, with servicing

Cons

  • Large and heavy: the 12 kW unit is 1,560 mm wide and weighs 181 kg
  • LG UK's warranty pages do not say what qualifies for the extended term
  • Standard warranty is 3 years, and LG requires servicing 'biannually'
  • No published installed price

Which Should You Choose?

Choose NIBE S2125 if...

  • Buyers who put quiet running and a long warranty first, and will use a NIBE Pro installer

Choose LG Therma V if...

  • You want the higher certified efficiency (SCOP 5.33 vs 4.8 at 35°C, MCS)
  • You want a longer standard warranty (3 yr (up to 7) vs 2 yr (up to 7))
  • You want lower estimated annual running costs (~£575/yr vs ~£620/yr)

The grant is the same, whichever brand you pick

Every air-to-water unit on this page qualifies for the £7,500 Boiler Upgrade Scheme grant in England and Wales (£9,000 for oil and LPG heated homes until March 2027) when fitted by an MCS-certified installer, who claims it on your behalf so it comes straight off the quote. Scotland uses the Home Energy Scotland grant of up to £7,500 (£9,000 rural and island) plus an optional interest-free loan; Northern Ireland currently has no equivalent scheme. 0% VAT on residential installations applies UK-wide until 31 March 2027. Accurate as at July 2026.

Boiler Upgrade Scheme guide →Gas boiler vs heat pump calculator →

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