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24kW instantaneous water heater: what to settle first

Updated: 21 October 2026

You have seen a 24kW instantaneous water heater described as enough for a shower and a kitchen, and you still need to know whether that appliance matches the fuel already in the house, the flue, and a cold British mains. It heats water only while the water is moving, so there is no stored cylinder to cover a second tap. Settle those limits before you compare models. The [24kW instantaneous water heater comparison](/hub/hot-water/24kw-instantaneous-water-heater) lists the three amazon.co.uk units kept for this set. Peter F. read the shelf prices on 19 October 2026. There was no laboratory test. A purchase through our links can earn a commission at no extra cost to you.

You have seen a 24kW instantaneous water heater described as enough for a shower and a kitchen, and you still need to know whether that appliance matches the fuel already in the house, the flue, and a cold British mains.

Our top picks

GASLAND GASLAND GS318NG

Best overall

GASLAND GASLAND GS318NG
8.4/10about £151.99
View offer
CAMPLUX CAMPLUX GX318LP

Best value

CAMPLUX CAMPLUX GX318LP
8.4/10about £239.99
View offer
GEESEN GEESEN RV05

Rank 3

GEESEN GEESEN RV05
7.6/10about £219.00
View offer
On this page
  1. 1.What 24 kW can deliver in a British winter
  2. 2.Gas, LPG or three-phase electric
  3. 3.Flue, bathroom and who installs
  4. 4.What to ignore in the search results

What 24 kW can deliver in a British winter

A 24 kW instantaneous heater does not deliver a fixed shower. The outlet falls as the flow rises or as the incoming mains gets colder. Flexiheat puts winter mains near 10°C in much of the country and nearer 5°C in parts of Scotland. AIZO Quality Heating’s table puts 24 kW at about 11.5 litres a minute for a 30°C rise and about 9.1 litres a minute for a 38°C rise, with real flow often 5–10% lower after losses. The same article’s 14–16 litres for a 24–30 kW band is not the figure to size from. The worked example is on the shower flow page.

Gas, LPG or three-phase electric

On amazon.co.uk in this batch, the appliances that claim about 24 kW and stay in the set are gas units. The GASLAND GS318NG (B0DHBYSJ8C, about £151.99) is methane at 20 mbar. The CAMPLUX GX318LP (B0F7KN3J8H, about £239.99) is LPG at 28–50 mbar. The GEESEN RV05 (B0D1VJ633X, about £219.00) is a 12 V propane heater for a van or motorhome, and its title, wattage and heat-output fields do not agree, so you cannot size it as a 24 kW house multipoint. A trade electric unit at this duty is three-phase, and it is not in this set. At 230 V, 24 kW is about 104 A as a rule of thumb, a new circuit and Part P work, not a 13 A plug. With only a single-phase consumer unit and no gas, this shelf is the wrong one.
GASLAND GASLAND GS318NG

Testsieger

GASLAND GASLAND GS318NG
8.4/10about £151.99
View offer

Flue, bathroom and who installs

A gas water heater in a bathroom has to be room-sealed. The Gas Safety (Installation and Use) Regulations 1998 say the same for a gas water heater over 14 kW in a sleeping room. Sealed on a title is the seller’s wording, not a certificate. The GS318NG calls the unit sealed and does not list a flue in the box. A UK review says the exhaust flue was not included. The GX318LP names a balanced flue at 60/100 mm, coaxial or twin pipe, without a separate flue length. Approved Document J covers flues and combustion air for domestic gas up to 70 kW net. Connecting the gas, fitting the flue and commissioning are Gas Safe work. Day-to-day firing, once commissioned, is on the how to use page.

What to ignore in the search results

A stored cylinder is not instantaneous: you are buying a tank, not a 24 kW flow. A 5.5–12 kW electric unit, or a 6 kW camping gas heater, cannot do the winter shower this heading implies. A Navien model with 24 in the name was about 42 kW and sat near £1,290–£1,548, outside this shelf. The amazon figures are the unit, VAT as shown on 19 October 2026, not an installed price. Water fittings follow the Water Supply (Water Fittings) Regulations 1999. A regulation 5 notice applies to listed jobs, including a booster over 12 L/min, not to every like-for-like heater swap.

Common questions

Will 24 kW run two showers at once in January?
That table is one shower. The same supplier puts two bathrooms on a 27–30 kW row. A second outlet can still be a basin or a kitchen tap used after the shower. A listing slogan of 12 L/min does not state the temperature rise, so it is not evidence of two winter showers.
What has to be in the house already?
You need the fuel the appliance is built for. A natural-gas meter at about 20 mbar matches the GS318NG claim. LPG in the 28–50 mbar band matches the GX318LP claim. These listings do not offer three-phase power. The RV05 title describes a 12 V propane camper, and its kilowatt lines do not agree. No conversion kit is in these files.
Can I fit a 24 kW gas heater in a bathroom?
Only if the finished appliance is room-sealed, including a gas water heater over 14 kW in a sleeping room. A title that says sealed is not a certificate that your bathroom will be lawful. A Gas Safe engineer has to confirm the room, the flue route and the appliance together.
Who is allowed to connect the gas?
A Gas Safe registered engineer. Someone who is not registered must not do the work and must not have it signed off later. Landlords need an annual check, a record kept for two years, and a copy for the tenants. Reading the display after commissioning is ordinary use. Opening the gas pipe is not.
Why do some heaters with 24 in the name claim about 40 kW?
The digits in a model name are not the plate. A Rinnai 11i is sold as a 24 kW-class internal heater while the manufacturer’s gas-consumption range runs to 23.7 kW and the stated maximum flow is 11 L/min. Some merchant pages print a higher heat-output figure for that same 11i. Use the plate and the manufacturer’s consumption figures.
What should I budget beyond the unit?
The shelf price does not include a flue if the box omits one, pipework, a Gas Safe visit, or making good. The GS318NG included-items line does not name a flue. Trade indoor heaters in a similar class, sold with a flue kit, have been listed well above these amazon prices.

Related pages

Natural gas or LPG

24kW instantaneous water heater

Best 24kW instantaneous water heater for the gas you have

How to use a 24kW instantaneous water heater daily

24kW water heater shower flow rate in a British winter

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.

  1. Approved Document G, with 2024 amendments (retrieved 19 October 2026)
  2. Gas Safety (Installation and Use) Regulations 1998, regulation 30 (retrieved 19 October 2026)
  3. HSE: gas safety in rented homes (retrieved 19 October 2026)
  4. Approved Document J (2022) (retrieved 19 October 2026)
  5. BS EN 26:2023, gas-fired instantaneous water heaters (retrieved 19 October 2026)
  6. GOV.UK: energy labelling of products (retrieved 19 October 2026)
  7. Water Supply (Water Fittings) Regulations 1999, regulation 5 (retrieved 19 October 2026)
  8. Instant water heaters: electric and gas flow notes (retrieved 19 October 2026)
  9. HSE: who may carry out a landlord gas check (retrieved 19 October 2026)
  10. BS EN 26:2023 CEN summary (retrieved 19 October 2026)
  11. Flexiheat instant gas water heaters (retrieved 19 October 2026)