The Best Instant Water Heater in 2021

With enough capacity to provide hot water for up to two sinks, the 5 litre ATC under sink heater is a practical solution where a larger hot water tank is not practical. And as it is suitable for caravans can be used on your road trip travels too. Made with a durable outer casing, it also has high density polyurethane foam for internal insulation as well as a porcelain enamel lining. The inner tank is also fitted with a magnesium anode for extra protection against corrosion.

We like the fact that the ATC tankless water heater is easy to install and can be either wall or floor mounted. Once heated, the water will be sufficient for several sinks full of dishes and the fast-heating element means you won’t wait too long for a refill. The heating ability of this 2kw unit is impressive, it can get very hot, but you do have an adjustable thermostat and overheat protection. An excellent water on demand heater for your money. 

For those compact and bijou spaces, this electric instant heater from Stiebel Eltron is small but powerful enough for the job. And, as it needs unvented installation, so a case of plumb-in and plumb-out, it is both versatile and easy to fit. We think this instant tankless water heater is just the ticket for a home office, garden room or small kitchen as it is quickly provides you with the hot water you need without taking up much space. Reviewers say it is quiet as it heats up and the water, while not instant, is quick to heat up to supply hot water as you need it. The thermostat is easily controlled via the external dial and can be set between 30 and 60 degrees. The whole unit is splashproof rated to IP24 too.

Designed for both domestic and commercial use, the Ariston Aures Slim Multi tankless water heater is fast and efficient, giving you instant hot water on top. While you can’t just ‘plug in and go’, as you will need an electrician to install it, it is a compact design that should be easy to install. And as an instant water heater, it is able to supply multiple points with hot water. You get three settings – low, medium and high – which range from 4kw to 9.5kw so plenty of heating choice. And it includes a double safety thermostat to prevent the risk of scalding if the temperature is set too high. Wall mounted, the design is clean and simple without taking up too much wall space. The only down, as reported by users is that the higher the water flow rate, the lower the maximum temperature you can achieve so you may need to look at adding a flow restrictor to get more heat precision. 

While it a sizeable unit, you get a lot of quality usage out of the Camplux tankless water heater, which uses propane natural gas to produce its instant hot water on demand. And with its 0.3 bar pressure set up, it is a great choice for caravan or RV camper living. Capable of serving two outlets at once with its 16 litres per minute output, this means you can supply hot water to your shower and sink – and a little extra luxury on your road trip. The effective heating is due to the internal copper heat exchanger and it can also be installed outside as well as in, as long as the environment is well vented, and a flue pipe is installed. When it comes to safety, you have what you need, including flame failure protection, overheat protection and safety shut off and you also have a drain feature so you can fully drain the system if it is not going to be used for a while. Robust, versatile, portable and able to supply plenty of hot water, this is the ideal instant heater for the outdoor or adventurous life. 

With one of the highest flow rates in our review, the substantial Z Zelus instant water heater can provide an impressive 18 litres of water per minute, making it one of the best tankless water heaters you can buy. Using LPG, the heater is pretty energy efficient, and the whole design is slimline, so can be installed in most spaces. We like the fact that it only needs low water pressure to get started yet can still build up the temperature for a decent hot water flow. This makes it a good choice for low water pressure areas, such as apartments as well as holiday homes. And it can be used to supply several water points, however, it should not be installed in a bathroom, so for kitchen or other room use only. You also get two modes – summer and winter – to ensure your hot water supply is as energy efficient as possible. 

Designed to fit neatly under a sink, this robust heater has a good hot water flow rate and can provide 10 litres of hot water in one sitting. The 2kw heating capacity gets the water up to temperature really quickly and there is no need for an expansion vessel, meaning it can be quickly and easily installed. It is on the chunky size, so will take up most of the under-sink cupboard space but it’s stainless steel construction is built to withstand plenty of use, either as a main hot water tank or as a back-up. 

When it comes to heating your water, you have a choice of five modes, with a 7-75℃ temperature range as well as frost protection and thermal cut-off for added safety. Well-priced, this is a no-frills under-sink instant water heater that does what it says on the tin.  

Hyco’s Handyflow has the looks of a traditional over the sink heater and is both a good size and uncomplicated to install. Straightforward and reliable, this instant water heater would be a good choice for a workshop, garage or home office or a small holiday home when you need fuss-free hot water on tap. The water is heated via a decent 2kw element and the whole heater has a 5-litre capacity for instant hot water. However, as the tank replaces water with cold water as the tap is turned on, you do need to keep the temperature setting quite high, so the cold water doesn’t cool down the hot water it holds. The tap itself moves freely and the simple twist control knob is effective. You also get the expected safety functions such as thermal cut out, but overall, the features on the Handyflow are limited to a basic, but well-performing instant hot water heater. 

Our final instant water heater is designed for RV camping and the outdoor life and can be set up both indoors and out. And with an impressive 10 litres per minute flow rate, you get a lot of on-tap hot water for your money. It is at the upper end of our review budget, but this quality gas water heater is well-built and has plenty of features and functions. It is pretty simple to set up and includes a shower attachment for either human or pet (dog or horse) impromptu cleaning! You also get a weatherproof rain cap to keep it safe when outdoors, whatever the weather or conditions. The controls are easy to use, you have a clear LED display to read the temperatures and there is both overheat, and 20-minute shut off protection. All-in-all, this is the hot water heater to take with you when you have time to enjoy the great outdoors.