Best Under Sink Water Heater on The Market in 2021
Your search for the best under sink water heater ends here. Today, we present the top-rated instant hot water heaters for your kitchen, bathroom, or cloakroom. We made our selections according to the niche they serve, their performance and features, and ultimately value for money.
Later in the article, you’ll also find a buyer’s guide that will help you make your own decisions about which under sink boiler best fits your needs and budget. Ready to banish tepid water from your faucet forever? This article is for you!
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Best value under sink water heater for the money
Not all water heaters are created equal, and the market is positively flooded with subpar undersink boilers. Such an overwhelming selection could lead to a hasty, and ultimately regretful purchase. That’s why we compiled this shortlist of the best under sink water heaters for your money. Each serves a different need and price point, so be sure to consider them all carefully.
The Eltron DHC-E12 from Stiebel is hardly a budget pick, but you get what you pay for. This German-made under sink water heater is renowned in the plumbing industry for its ease of installation and maintenance. It is also incredibly durable with a solid copper heating system and robust plastic housing.
Users regularly report decades-long life spans, which is par for the course from Stiebel.
There are two models on offer, rated at 9600W and 12000W. Even the larger of the two is nicely compact, at just 10.4 x 20.1 x 36.1cm. Due to the exceptional array of safety features, the Eltron DHC-E12 finds plenty of deployment in commercial spaces. Though we’re confident you’ll also appreciate the thermal cut-out to prevent scalding, IP24 waterproofing, and exceptional hydroelectric insulation.
Both you and your plumber will be well pleased, as Stiebel has designed this unit to be as easy to install as possible. There’s no need for safety valves, non-return valves, nor tundish valves, offering truly fuss-free installation and maintenance. The DHC-E12 features thermostatic stabilisation, so you can reliably predict the temperatures coming out of the tap every time.
We particularly like how this unit seems to work just as well under low water pressure. The DHC-E12 is an unvented water heater, and thus doesn’t require a separate cold water tank and provides superior flow. Stiebel has created a masterpiece of instantaneous hot water production in the DHC-E12.
They clearly stand by their produce, with a 7-year warranty against leakage and 3-year guarantee vs. workmanship and material defects.
This unassuming range of under sink water heaters from ATC is one of the industry’s best-selling, and for good reason.
There are three models on offer: Z-5U, Z-10U, and Z-15U; with 5, 10, and 15L tank capacities, respectively. Each model is rated at 2000W of power, and can produce piping hot water in just a few seconds. The largest of these (the Z-15U) is a manageable 275 x 290 x 460cm, and they all can be deployed free-standing or mounted on the wall under your sink.
Under the hood of the ATC Z-Series, you’ll find high-density polyurethane foam for superior thermal insulation. What’s more, there’s a dry powder coating of industrial porcelain enamel that forms a lining twice as resistant to corrosion than traditional glass lining.
Still worried about tank rust? Don’t be; there’s also a sizeable sacrificial magnesium anode rod to further stymie oxidation. There’s also a hardy expansion relief valve, pressurised to 6bar.
Taken together, and you have a highly durable water heater that will last years and years. Of course, ATC is worth more than its robust design; the Z-Series is highly useable, with an external thermostat, exceptional flow rates, and easy installation. You’ll still likely need a plumber, but you won’t need to buy a tundish valve.
While the Z-Series gets quite hot, you won’t have to worry about scalding. There’s a limiter which prevents against overheating, though the thermostat is sensitive enough to prevent false lockouts at higher temperatures, as well.
Overall, you’ll be hard-pressed to find better performance for the price than with ATC’s Z-Series, and they guarantee your purchase with a generous 2-year warranty.
Hyco has faithfully serviced the UK market for over 30 years, and their Speedflow SF15K under-sink water heater is an exemplar of their product line. With a 15L thank capacity, the Speedflow can reliably supply up to three basins with near-instantaneous hot water.
By default, the SF15K comes equipped with a 2000W heating element. However, you can request a 1200W element instead when you need to limit heat production for economic or safety reasons.
The Speedflow is highly attractive, and it’s almost a shame it’ll mostly be hiding under your sink. But they say beauty should be more than skin-deep, and that’s what we have from Hyco. There’s high-density poly foam for increased thermal efficiency; IPX4 waterproofing for your peace of mind; plus, the one-two punch of a glass-lined steel tank and sacrificial grey magnesium anode for rust-resistance.
For safety’s sake, there’s also overheat production, which is easily reset with a switch at the heater’s base.
There’s plenty for your plumber to love as well, including a pre-wired 1.5m copper cable to save time on installation. The SF15K ships with a pressure relief valve, and you have the option to add on a thermostatic mixing valve for more constant water temperatures. So long as the power is on, the Speedflow’s anti-frost system will ensure no damage is done to the unit during cold snaps and periods of disuse.
So, whether you select Speeflow for commercial or residential applications, you’ll be glad to know it drops easily into any conventional sink system. You won’t need a special tap to enjoy the SF15K’s full thermostatic range up to 75°C. We’re further confident in our recommendation of the Speedflow thanks to Hyco’s amazing 10-year warranty.
Looking for something a bit smaller for use in cloakrooms, shops, or home extensions apart from the combi-boiler system? This Mini Water Heater from HEEPDD deserves a second look, in that case. Despite its small size, the boiler within roars with a mighty 5500W of power, making good on its promise of instantaneous hot water.
The thermostat can be set between 30-55°, and delivery is consistent in both high and low-water pressure systems.
HEEPDD has outfitted its Mini with multiple layers of safety protections, as well. These include an anti-dry sensor, which shuts down the electricity when there’s no water; double-layered leak protection; exceptional triple-layer hydroelectric insulation; waterproofed motherboard; and overheat protection.
Left alone for long periods of time, the HEEPDD’s auto-off function will politely shut down the power to save on your monthly bill.
We appreciate the LCD digital display, which makes the thermostat setting easy to read in the darkness under your sink. There’s a universal ½” water pipe outlet, so you can deploy the Mini anywhere in the house. And at just 1.5kg with 22x14cm dimensions, you truly can fit it anywhere!
Just make sure to hire a plumber–and let them know HEEPDD does not include the 2.5mm2 copper wire this heater needs to operate safely.
Once installed under your sink, you’ll enjoy piping hot water on demand, reaching full temperature within just 5 seconds. Not bad for such a small water heater!
The BuoQua 12L-LPG is sufficiently robust a unit to justify using anywhere–not just under the sink. Nevertheless, at 72 x 41 x 20 cm, it is indeed compact enough for most kitchens or larger bathroom sinks. Unlike the other entries on this list, the BuoQua is a propane-heater, which only accepts LPG as fuel.
If you’ve already got a gas hookup or use a mini tank in your camper, the 12L-LPG offers several important benefits over electric.
Because the BuoQua is tankless, it can continually heat water on demand.
However, gas heating is more robust and less costly than electric, and thus you’ll rarely feel you’ve run out of hot water with the 12L-LPG. Indeed, the 12L-LPG boasts greater than 80% thermal efficiency, so a bit of gas goes a long way. Not that there’s a dearth of power; with a heat output power rating of 24000W, the BuoQua easily accommodates a hot water flow of 12L/min.
This heater has no problem starting up with low water pressure, and has built-in protection vs. excessively high pressure systems. Rest easier knowing that there’s overheat protection on board, which locks out in excess of 75°C. Constructed of stainless steel in and out, the BuoQua is a highly durable under-sink water heater.
Further bolstering its longevity is anti-freeze functionality, which flushes any water out automatically during extended periods of disuse before it turns into ice and damages the unit.
Installation is certainly more complex than other heaters on our list, and requires a Gas Safe engineer’s expertise to achieve safely. Be aware that the BuoQua requires two 1.5V batteries, which are not included. While you won’t use it when deployed undersink, the 12L-LPG comes with a shower kit in case you decide to repurpose your trusty water heater for bathing down the line.
Rounding out our list is the aptly named Compact Plus CPU 10 from British manufacturer Crown. Deployable over or under the sink, the CPU 10 comes pre-wired for enhanced ease of installation (your plumber will thank you with a lower bill!)
Just be aware you’ll need a non-return valve and mini expansion vessel, as these do not come included in the box. (There is a safety valve, however.)
Maintenance is similarly simple; the nickel-plated, corrosion-resistant immersion heating element features a flange for easy removal and cleaning. The glass-lined stainless steel tank is also highly resilient against rust, with a huge, easily replaceable sacrificial anode. Everything is also protected by a generous 2-year warranty, so you can buy and use your CPU 10 in confidence.
Beyond its durability, the Crown CPU 10 offers exceptional performance, with its 2200W rating. With a huge 10L tank, you won’t quickly run out of warm water, even with heavy usage. While there’s no fancy digital display, you’ve got two broad manual dials for turning it on/off, and adjusting the thermostat.
The thermostat is particularly sensitive, and won’t trip false lockouts via the overheat protection system even at high heat.
Overall, the Crown CPU 10 offers robust functionality in a small frame, just 45.5 x 38.5 x 28.5 cm. It weighs 7.2kg, and mounts easily under your sink with the included hardware. We also appreciate the inclusion of twin neon indicators for on/off and heating up for piercing the darkness underneath your sink.
There’s nothing fancy about the Crown Compact Plus, but it’s a system which just works like it should–and that’s worth its weight in gold.
How to Shop for the Right Under Sink Hot Water Heater
The selection of under sink boilers isn’t quite as vast as other types of water heaters, but there’s still a wealth of choice. Sadly, there seems to be a higher concentration of duds out there, so you need to be careful before making a purchase.
It helps tremendously to educate yourself on what makes a good water heater, and which features you need for your specific purposes. Here below, we present a short buyer’s guide on under sink water heaters, so you can shop smarter.
Tank Storage vs Tankless Heaters
When pressed for an answer on the main difference between the two major types of water heaters, most people could probably point to the tank, or absence thereof. But what exactly does it mean to have a tank, and why would anyone spend more for a tankless heater?
Essentially, tank storage heaters retain a large volume of water in a copper or stainless steel tank. There is a heating element of some kind inside this receptacle, which slowly heats the water up to the point specified on your thermostat. When you need hot water, it is ready to go, and dispenses fully hot until the tank is empty. The temperature tends to stay nice and even throughout, and the hot water comes right when you call it.
But the limitations of a tank storage heater become quite apparent when that tank runs out. If you’ve ever showered for too long only for the water to go cold, you’ve experienced the shortcomings of a tank storage boiler. It’s this problem that tankless heaters are primarily meant to solve.
Since there’s no place to reserve pre-heated water, your tankless heater will draw its flow directly from your mains. Of course, this is typically cold water, and will need to be heated as dispensation occurs. Because there’s no tank to run out, you can enjoy warm water as long as you need in theory.
The problem with tankless heaters is that they’re considerably more expensive on average. What’s more, a poor-quality tankless has the capacity to frustrate you utterly, with always-insufficient hot water production. Hence, you’ll need to consider your tankless heater something of an investment; after all they are much more efficient than tank storage heaters, and can pay themselves back in savings within a few years.
Related reading: The best instant hot water dispensers
Unvented Water Heaters Explained
How many times have you seen listings for under sink water heaters vaguely claim “unvented” as a headline virtue? Honestly, online shops are rife with this label, but there’s relatively little explanation as to why it matters. Allow us to explain…
An unvented water heater simply refers to the fact that it draws water directly from the mains, rather than a separate tank. Don’t confuse this tank with boiler storage tanks; in traditional systems, there is a tank suspended above the boiler, which uses gravity to feed water down through a pipe (called a “vent”) into the heater for consistent pressure.
Drawing directly from the cold mains, as in an unvented system, offers decidedly superior pressure performance to traditional systems. However, it’s not without its drawbacks, either. Unvented systems are costlier upfront and to maintain. The main reason for this is that a special expansion vessel is required to compensate for the pressure spikes that come with the expansion of newly warmed water. This requires a specialist technician to install and maintain, and it does indeed require regular maintenance.
However, it isn’t unusual to find that product listings for unvented water heaters include this expansion vessel. That said, it’s certainly something you need to keep an eye out for. An apparently well-costed listing might take a virtual jump in price if you have to buy this separately.
Why You Will Always Need Professional Installation
Whether you select an all-electric or gas-powered water heater, you will need a plumber or Gas Safe engineer to handle installation. This is because the combination of hot water and high pressure can be a particularly volatile one, and a DIY miscalculation can lead to certain disaster.
What’s more, most manufacturer warranties actually require professional installation. If you do it yourself, you make void any guarantee on parts and labour for repairs down the line. This can be a dearly expensive mistake, and one best avoided.
So, when you’re shopping around for under sink water heaters, you’ll need to factor the cost of professional installation into the total investment.
Understanding Capacity Ratings
Confusingly, both tank storage and tankless water heaters will advertise capacity in a certain number in litres. With tank storage heaters, the meaning of this figure is straightforward, as it refers to how much water the heating tank can physically hold. Meanwhile, tankless heaters mention the number of litres per minute they are able to heat.
So, how many litres do you need? The answer is actually a complex product of how much water you intend to use; how cold your region’s average water temperature is; and how high you wish for your heater to raise the temperature. We’re not here to explain the advanced maths behind this calculation, but we will give you a few rules of thumb.
For tank storage heaters, consider how many basins your heater will serve. 5L heaters are more than adequate for a single basin in your average kitchen, cloakroom, or bathroom. For two or three basins, you’ll want to upgrade to 10L, and for anything more 15L is the minimum. You can easily estimate how quickly these tanks will fill and heat: assuming you’ve got a 2000W heating element, it takes about 10 minutes to heat 5 litres of water.
For tankless heaters, pay attention to the litres per minute rating in conjunction with the maximum stated thermostat setting. Most kitchen sinks want around 50° heat available, and drink up about 6 litres per minute. The majority of under sink hot water heaters procure at least 12L/min. at 50° or more, but do keep an eye on this metric.
Remember, if your tankless heater lacks adequate heating capacity, you will be disappointed with its performance every time you reach for the tap. It’ll also waste energy constantly trying to achieve its paltry maximum temperature, wholly defeating the purpose.
Under Sink Water Heater FAQs
How does an under sink water heater work?
An under sink water heater is an electric device that takes in water from the mains and heats it. Tankless heaters do this instantly, producing hot water on demand for your tap. These devices rely on a powerful heating element that’s capable of heating cold water as it passes through. Those with tanks, like this Speedflow SF15K heater from our list, heat and store water for future use.
Note that since it can (generally) only serve a single fixture, an under sink water heater cannot replace your boiler — i.e. it won’t meet your entire home’s hot water needs. That said, it’s a great, efficient way to deliver instant hot water to any tap that’s not hooked up to your boiler.
What size under sink water heater do I need?
It depends on the type of heater you want to get, and where you want to use it.
As we’ve explained above, if you’re getting a heater with a tank, 5L capacity should suffice for a single basin. For 3+ basins, you’ll need at least 15L.
Instant water heaters aren’t limited by the tank’s capacity; however, they do have a limited flow rate. Still, most models out there are capable of supplying your regular kitchen or bathroom tap. Take this BuoQua 12L-LPG Tankless Instant Boiler — it gets you 12 litres per minute, which is about double the demand of a standard kitchen tap.
Does an under sink water heater need an expansion vessel?
If you have an under sink instantaneous water heater, you will not need an expansion vessel. That’s because these devices heat water on demand, so the hot water always flows from your tap instead of sitting in a tank where it could expand due to heat. Same goes for vented heaters — the venting feature allows water to expand without damaging the appliance.
On the other hand, if you’ve got an unvented system with a mains pressure of above 4.1 bar, you will need an expansion vessel. Most come with expansion vessels included in the purchase, but some don’t — so read the product description thoroughly before you buy your heater.
How to install an under sink water heater?
Long story short — better leave under sink water heater installation to a licensed plumber. Here’s why.
Installing an under sink water heater may sound simple, but there are quite a few things to plan, so depending on the circumstances, the job can quickly overwhelm any DIY plumber.
For instance, depending on the type of heater and existing piping, you may have to worry about:
- Securing the heater in place (the ones with the tank can get heavy when full)
- Connecting to existing piping or running new pipes
- Assembling the heater’s critical safety components — pressure relief valve, expansion vessel, etc.
- Connecting the device to electricity
Keep in mind that you’ll working with high-pressure water, heat, and electricity, so you’ve also got some inherent safety risks to consider. And, be aware that most manufacturer’s warranties will become void if you don’t use a licensed professional for the installation.
Last but not least, don’t forget that installing a heater under your sink involves, well, spending a fair amount of time sardined under the said sink. And the more of a novice plumber you are, the more time you’ll spend there.
In light of all these implications, it’s always best to hire a plumber to fit your new under sink water heater.
At this point, you should have a fair idea of which features the best under sink water heaters have. We’ve presented an array of popular products which boast excellent consumer satisfaction ratings. Whether you need tank storage or tankless; gas or electric; vented or unvented heating, there’s exceptional value for money on the market–if you know how to look for it.
Do you have anything to add to our buyer’s guide? Have you ever used any of our recommended under sink water heaters? Sound off in a comment below!