When you're choosing water heaters, start with the job, not the label: mains pressure or stored, electric or gas, and how much room you've actually got for the unit. Point of use models suit short runs and small draw-off points. Larger vented or unvented options make more sense where demand is steadier. The usual mistake is buying on output alone, then finding the footprint or supply arrangement doesn't suit the site.
Redring MS6 Undersink 6L Unvented Water Heater - 6L 1.5kW
6 litre undersink water heater with 1.5kW element and 15-minute heat-up
Heatrae Sadia OEM Lower Immersion Heater
Lower immersion heater for water cylinders, includes seal
Ariston Andris Lux Under Sink Unvented Water Heater - 2.0kW 10L
Ariston Andris Lux under sink water heater, 2kW 10L
Tesla Copper Immersion Heater & Resettable Thermostat - 11"
Copper immersion heater with resettable thermostat, 11 inch (279.4mm)
Tesla Copper Immersion Heater & Resettable Thermostat - 27"
Copper immersion heater with resettable thermostat, 27 inch (685.8mm)
Ariston Andris Lux Over Sink Unvented Water Heater - 3.0kW 10L
10L over-sink unvented water heater, 3kW, ErP A
Tesla Dual Safety Rod Thermostat - 7"
7-inch rod thermostat with safety cut-out for immersion heaters
Tesla Incoloy Immersion Heater with Rod Thermostat
355mm Incoloy immersion heater with rod thermostat for copper & stainless steel …
Copper Immersion Heater & Reset Button - 2 1/4" BSP 3kW 14"
Copper immersion heater 3kW, 14-inch element with thermostat and reset button, 2…
Heatrae Sadia Megaflo HE Upper or Top Straight Immersion Heater
Immersion heater for Heatrae Sadia Megaflo HE systems, includes O-ring and fixin…
Start with the space you’ve actually got and how the unit will be used, because that usually rules out half the options before you get into finishes or extras. If the layout is tight, a compact unit saves grief on the install. If demand is steady, look at output and recovery rather than just the cheapest box on the shelf. Electric water heaters suit jobs where the supply is straightforward. Gas water heaters make more sense where you’ve already got the fuel and the spec calls for it. Commercial water heaters are a different conversation again. It’s more about duty and demand than footprint.
You’re usually choosing water heaters by how the job is fed and how fast the hot water needs to be there. Electric water heaters are the straightforward pick where the supply is simple and you want less to sort on the fuel side. Gas water heaters make more sense where gas is already in place and the demand justifies it.
Instant water heaters and instantaneous water heaters suit jobs that need hot water on demand without waiting on stored volume. The trade-off is less buffer if several outlets are drawing at once.
Point of use water heaters work best when you want the heater right at the draw-off. That keeps the run direct and avoids overspecifying the whole Central Heating setup.
If space is tight, compact water heaters are the first place to look. You get a smaller footprint, but you give up stored capacity. That matters when the outlet needs to run for longer than expected.
For straightforward replacements, check what is already there before you commit. If the rest of the kit needs changing, sort that at the same time. If you are picking up the extras as well, Central Heating Accessories usually covers the bits that get missed. Where the installation needs the right termination and fittings, Flues & Boiler Accessories is the other one to line up before you start.
Once you’ve picked the water heaters, the next call is what sits around them and what the room still needs to finish properly. That covers the surrounding finishes, any storage or screening the job needs, and the details that stop you going back later to tidy up.
A lot of call-backs come from the last 10% - awkward access, a finish that doesn’t match, or no allowance for maintenance. Keep the main unit choice in mind, then look at the adjacent plumbing and finishing items from the same central heating range so you’re not mixing parts that don’t suit the rest of the install.












