Best 24kW instantaneous water heater for the gas you already have
Updated: 21 October 2026
You want the best 24kW instantaneous water heater you can order from amazon.co.uk, and the useful answer is which of three kept listings matches the supply in the building. There is no UK laboratory ranking of these ASINs. Stars are the listing stars, and many of the review texts are not British house installs. In this set the GASLAND GS318NG is the top pick only when you already have natural gas at about 20 mbar. On that same condition it is the lower shelf price, about £151.99 against about £239.99 for the LPG unit. It is not a tested winner, and a UK review says the flue was missing. The full cards are in the [24kW instantaneous water heater comparison](/hub/hot-water/24kw-instantaneous-water-heater). Peter F. read those listings on 19 October 2026. There was no lab test. A qualifying purchase can earn a commission at no extra cost to you.
You want the best 24kW instantaneous water heater you can order from amazon.co.uk, and the useful answer is which of three kept listings matches the supply in the building.
You want the best 24kW instantaneous water heater you can order from amazon.co.uk, and the useful answer is which of three kept listings matches the supply in the building. There is no UK laboratory ranking of these ASINs. Stars are the listing stars, and many of the review texts are not British house installs. In this set the GASLAND GS318NG is the top pick only when you already have natural gas at about 20 mbar. On that same condition it is the lower shelf price, about £151.99 against about £239.99 for the LPG unit. It is not a tested winner, and a UK review says the flue was missing. The full cards are in the 24kW instantaneous water heater comparison. Peter F. read those listings on 19 October 2026. There was no lab test. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Fuel | Meant for | Listing stars | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  GASLAND GASLAND GS318NG | Natural gas, 20 mbar | Indoor, as claimed | 4.2 from 947 | 8.4 | about £151.99 | View offer |
| Best value |  CAMPLUX CAMPLUX GX318LP | LPG, 28–50 mbar | Indoor LPG home | 4.2 from 129 | 8.4 | about £239.99 | View offer |
 GEESEN GEESEN RV05 | Liquid propane | RV and camper | 3.8 from 19 | 7.6 | about £219.00 | View offer |
On this page
What best can mean on this shelf
Best here means the listing whose gas family, pressure and stated job match what you already have, with the review file read for what it actually contains. It does not mean a Which?-style trial, a room-sealed certificate, or the cheapest unit that happens to print 24 kW. The GS318NG and the CAMPLUX GX318LP both show 4.2 stars. The GASLAND file has 947 reviews and the Camplux file has 129, of which two stored texts are from the United Kingdom. The GEESEN RV05 shows 3.8 from 19. A higher count is a larger sample, not proof that every reviewer installed the heater in a UK bathroom. Trade heaters such as a Rinnai 11i sit outside the table. They are price context, not extra winners. If you only have a 13 A socket and no gas, skip all three. Whether 24 kW is the right class at all is on the buying guide.
Natural gas already in the house
If the house has a natural-gas meter, the listing that states the matching fuel is the GASLAND GS318NG, model Gasmart C 12L, ASIN B0DHBYSJ8C. The page says methane at 20 mbar, 24 kW and 12 L/min, wall hung, 12.6 kg. The efficiency field reads Wysoki, which is not a UK A–G label with a load profile. A UK mobile-home review describes stable temperature and pressure and a hot shower. A UK gas engineer who viewed one in an outdoor building called the build sound. The same UK sample includes an exhaust flue that was not in the box, ignition that only fired after the batteries were disconnected and reconnected while water ran, and a leaking gas valve with no support reply. Reviews from Italy and Spain dispute the indoor sealed claim. Skip this listing if you are on LPG, if you need the flue in the carton, or if you wanted a certified bathroom install rather than a title that says sealed.
LPG already on site
If you already have LPG cylinders or a bulk tank, the listing that states that fuel is the CAMPLUX GX318LP, Climatech 4, ASIN B0F7KN3J8H, at about £239.99. The bullets say LPG at 28–50 mbar, up to 24 kW and 12 L/min, a 60°C maximum, control claimed within ±1°C, and a balanced flue of 60/100 mm for coaxial or twin pipe. Class A is printed without a load profile. Two UK reviews describe a professional install: a holiday let that heated quickly and ran quietly, and a one-bed chalet where the installer connected a kitchen, a bathroom and three radiators and called the product fine. Most of the other stored texts are from the United States or Canada and may belong to another Camplux model. The specification table says Floor while the sales copy describes a compact indoor unit, and the voltage field prints 3 volts. Skip it if you have a natural-gas meter. Feeding a 20 mbar methane heater from a cylinder, or this LPG heater from the meter, is not a setting on either page. That split is on the natural gas versus LPG page.
A van or a motorhome
If the job is a camper rather than a house, the listing that says so is the GEESEN RV05, ASIN B0D1VJ633X, at about £219.00. The item type is an RV water heater. It is 12 V propane with a remote, a stated 10 L/min, and a top forced exhaust fan. UK reviews describe a van conversion, a replacement for a leaking heater, an RV swap with a steady temperature, and a first start that needed about 15 minutes of water flow before it fired. The title also says 3.0 gallon, 24 kW and 55,000 BTU. The wattage field says 55,000 watts and the heat-output field says 25,000 BTU. Those are not the same duty, so you should not quote one output. A Canadian review reports a burner with no hot water at the tap, and another reports failure inside a month. The remote was wired, not wireless, in a US review. Skip it for a mains-gas house. Depth is not stated, and the temperature lines disagree: 124°F on the table, 35–51°C in a bullet.
What a wider UK search also shows
A search for a best indoor gas water heater in the UK also returns trade multipoints that are not these ASINs. Rinnai’s 11i is a room-sealed internal heater with natural gas, LPG or BioLPG versions. The manufacturer’s page gives gas consumption from 4.53 to 23.7 kW, a maximum flow of 11 L/min, 37–65°C and a weight of 14 kg. Some merchant pages print a heat output around 35 kW for the same 11i. That clash is left as a clash. This page uses the manufacturer’s consumption range and the 11 L/min line. One retailer, gasproducts.co.uk, showed the 11i with a flue at about £428.30, reduced from £513.96, in searches on 19 October 2026. Those are shelf prices for a different product, not an amazon.co.uk price and not an installed price. They explain why a listing at about £151.99 can look cheap beside a trade heater sold with a flue. If the amazon unit’s gas family is wrong for your meter or your cylinders, the dearer trade heater is still the one to ask a Gas Safe engineer about.
Common questions
Which listing is for mains gas?
The GASLAND GS318NG, B0DHBYSJ8C, states methane at 20 mbar. That is the natural-gas listing in this set, at about £151.99 with 4.2 from 947 reviews. It is the conditional top pick, and the lower shelf price, only when that gas is what you have. The efficiency word Wysoki is not treated as a UK energy class. A UK review says the flue was not in the box, so the price is the heater, not a finished flue run.
Which listing is for cylinders?
The CAMPLUX GX318LP, B0F7KN3J8H, states LPG at 28–50 mbar, at about £239.99 with 4.2 from 129 reviews. It names a 60/100 mm balanced flue. Only two stored reviews are from the United Kingdom, so the star line is a thin British sample beside a larger North American file. Do not buy it for a natural-gas meter.
Is the cheaper one missing a flue?
The GS318NG included-items line lists one item and does not name a flue. A UK buyer reported that the exhaust flue was not supplied and was not easy to find as a separate part. The GX318LP includes installation kits and a manual, and it does not list a separate flue length either. Budget the flue as its own line until the engineer confirms what arrived.
Is the RV unit a house heater?
No. The GEESEN RV05 item type is an RV water heater on 12 V propane. UK reviews use a conversion van and an RV. The title’s 24 kW line conflicts with 55,000 watts and with 25,000 BTU elsewhere on the same page. It is not a substitute for the GS318NG or the GX318LP in a house.
Why is a Rinnai dearer if these are also called 24 kW?
The Rinnai 11i is a different product, with a manufacturer flow of 11 L/min and gas consumption up to 23.7 kW, often sold with a flue. One UK merchant showed about £428.30 with a flue on 19 October 2026. The amazon prices are the three ASINs above, without an installed flue. A similar kilowatt class does not make the cartons equivalent.
Can I trust 947 stars?
The 4.2 from 947 is the amazon.co.uk line for the GS318NG. The first 50 reviews in the saved listing include many that are not from the United Kingdom, and some describe camping or propane use the GS318NG bullets do not state. Use the count as a large sample with that limit. It is not a UK house trial of 947 bathrooms.
What should I skip if I only have a 13 A socket?
Skip every listing on this page. None of them is a 13 A electric water heater. The indoor pair are gas appliances with a low-voltage or 220–240 V lead for controls, not a 24 kW heating load from a plug. A true 24 kW electric unit is three-phase. Sizing that supply is on the buying guide, not a fourth amazon winner.
Related pages
Sources
Public UK sources named below. amazon.co.uk prices, stars and review counts on these three listings were read on 19 October 2026. Page updated 21 October 2026.
- Approved Document G, with 2024 amendments (retrieved 19 October 2026)
- Gas Safety (Installation and Use) Regulations 1998, regulation 30 (retrieved 19 October 2026)
- HSE: gas safety in rented homes (retrieved 19 October 2026)
- Approved Document J (2022) (retrieved 19 October 2026)
- BS EN 26:2023, gas-fired instantaneous water heaters (retrieved 19 October 2026)
- GOV.UK: energy labelling of products (retrieved 19 October 2026)
- Water Supply (Water Fittings) Regulations 1999, regulation 5 (retrieved 19 October 2026)
- Instant water heaters: electric and gas flow notes (retrieved 19 October 2026)
- HSE: who may carry out a landlord gas check (retrieved 19 October 2026)
- BS EN 26:2023 CEN summary (retrieved 19 October 2026)
- Flexiheat instant gas water heaters (retrieved 19 October 2026)