I first learned about immersion water heaters last winter. My combi boiler had just broken down and the entire household was freezing in frigid weather. The plumber who came to fix the broken unit advised me that I should consider installing an immersion heater as a backup.

The things he told me about immersion heaters surprised me to say the least.

I was astonished to find out that immersion heaters aren’t connected to your boiler. So if your boiler breaks down, as mine did, the heater will still generate hot water for your household.

You won’t be left freezing in cold weather.

That’s not the only piece of information I picked up that day. In that article I’ll share what else I learned in the process.

Don’t Have Much Time? Here’s Our Top Three Picks

Why Choose Immersion Water Heaters?

Immersion water heaters provide multiple benefits, including serving as an excellent backup option to your existing boiler, letting you control your energy use, and eliminating the need for gas supply. These heaters also cost less up front and are relatively easy to install, too.

Here are the major benefits of immersion water heaters:

1)   Backup your home’s hot water supply

One of the most sought-after benefits of immersion water heaters is as a backup supply of hot water. Immersion water heaters don’t rely on boilers to work because they have their own electricity supply. This means that you’ll have access to water even if your boiler breaks down.

2)   Help lower your heating bill

An immersion water heater with thermostatic control will help lower your heating bills. The water heater thermostat will turn the heater off when the water attains your desired temperature. It will then turn it back on if the water cools off too much.

3)   Don’t need gas supply to run

Some homes and flats, particularly in remote locations, might not be connected to the gas supply. Provided you live in one of these areas, the best source for hot supply for you are immersion heaters. That’s because they only require electricity, and every home has it.

4)   Relatively easy to install

In contrast with gas heaters that need ventilation equipment and additional piping, immersion water heaters require no house infrastructure adjustments. This makes their installation process fast, effortless and, more importantly, less expensive.

5)   Extremely simple operation

Immersion water heaters are incredibly easy to use. Just submerge them in water, plug their wire in a grounded wall outlet, and they will start heating your water. Their small and lightweight construction means you can use them in hot tubs, inflatable pools bathtubs, etc.

Top 5 Best Immersion Water Heaters

We selected all the immersion heaters based on the following criteria:

• One-year warranty: Three out of five models you see below are backed with a 1-year warranty. This should give you the peace of mind that in case they don’t work as advertised, you can always return the heater and get a new one.

• Auto-shutoff: When you use a water heater of any type, there’s always the risk of fire. The auto-shutoff feature minimizes this risk by turning off the heater when their body temperature exceeds a safe limit. So you can continue to use the model safely.

• Built-in thermostat: Four out of five heaters you’d see below come equipped with a built-in thermostat. One which would turn them off when the water reaches your desired temperature, ensuring savings on your heating bills.

• UL-listed: Underwriters Laboratories (UL) is a globally renowned company that tests and verifies various equipment against standards set by Occupational Safety and Health Administration (OSHA) and American National Safety Institute (ANSI).

Gesail Electric Immersion Heater

Why is the Gesail Electric Immersion Heater our top pick? Start with its stainless steel guard that keeps its heating element from coming into direct contact with persons or animals. The porous guard (that’s right; it’s full of holes) also brings down heating time by releasing heat to the water.

This model will also keep your heating bills in check. It comes equipped with a built-in thermostat that turns off the heater when water reached your desired temperature. That’s not all. The thermostat will also turn the heater back on if it water cools off, ensuring effortless operation.

We were also impressed with this heater’s auto shutoff switch. It will shut down the heater the moment its body temperature exceeds a manufacturer-determined setpoint. The shutoff switch also keeps the heater from turning on if it’s empty, preventing dry burning.

On top of everything else, this immersion water heater is one of the very few that are UL-listed. This means it meets the criteria set in place by main consumer safety organizations, such as the American National Standards Institute (ANSI). So you won’t have to worry about your safety while using it

Things We Like   

• It’s UL-listed
• Backed by 12-month warranty
• Has auto shutoff and built-in thermostat

Things We Don’t Like      

• Not a small tank water heater – needs at least 8’’ of water to work properly

How It Compares With Our Criteria

1. UL-listed: Yes
2. Auto-shutoff: Yes
3. Built-in thermostat: Yes
4. Warranty: 1-year

Kingwork Immersion Heater

There are many similarities between Kingwork immersion heater and our top pick. Both are UL-listed, come equipped with a stainless steel guard, and also have an auto shutoff feature. Both claim of being able to heat up to five gallons of water in a matter of minutes. And both are backed by 1-year warranties.

Why, then, is the one and not the other our top pick? Mainly because this floating immersion water heater doesn’t come with a built-in thermostat, even though its description claims otherwise. You’d thus have to buy the thermostat (sold separately) if you want to keep a lid on your heating bills.

Fortunately, the absence of a thermostat is this heater’s only major shortcoming. It’s UL-listed like our top pick and is equipped with a fully-submersible stainless steel guard. One that won’t only protect your fingers from touching naked wires but would also transfer heat to the surrounding water.

Some of the users have also commended its performance in their hot tub. Others, meanwhile, have praised its ability to remain safe-to-the-touch even when it’s working. You can thus use this electric immersion water heater for coffee, bathtubs, tea, pool, among various other applications.

Things We Like

• Porous stainless steel guard
• US Standard Ground Plug
• UL-listing and 1-year warranty

Things We Don’t Like      

• Doesn’t come equipped with a built-in thermostat

How It Compares With Our Criteria

• UL-listed: Yes
• Auto-shutoff: Yes
• Built-in thermostat: No
• Warranty: 1-year

KD Immersion Bucket Water Heater

The KD Immersion Bucket Water Heater beats our top two picks on two counts. Firstly, while both of them can heat water up to 180 Fahrenheit, the maximum range of this model’s thermostat is 210 Fahrenheit. This expands the list of applications of this immersion heater.

Secondly, this model comes with a water level indicator, a feature both our top two picks don’t have. A gauge on top of its handle shows the water level once you dip the heating rod into the water container. Anyone who wants to monitor their daily water use can benefit a lot from this feature.

This model also shares many similarities with the two we reviewed before it. It can also heat five gallons of water within minutes and has an auto shutoff sensor to prevent overheating. And, unlike the Kingwork Immersion heater, this unit does come equipped with a built-in thermostat.

Why, you might ask, then this model is 3^rd and not 2^nd in our review? Mainly because it costs three times as much as each of our top two picks. But also because it isn’t UL-listed and there’s no mention of any warranty on this product’s Amazon page. 

Things We Like   

• Adjustable thermostat up to 248*F
• Auto-shutoff prevents water from overheating
• Auto water level sensor

Things We Don’t Like      

• Astronomically expensive

How It Compares With Our Criteria

• UL-listed: No
• Auto-shutoff: Yes
• Built-in thermostat: No
• Warranty: N/A

Gesail 1500W Immersion Heater

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The Gesail 1500W Immersion Heater is the most powerful model in this review. And for good reason too. Its massive wattage enables this unit to heat 10 gallons of water to over 180*F in less than 10 minutes. The stainless steel heater is also compact enough to fit into sinks, pails or tight buckets.

This model is safe to use, though you shouldn’t touch water with the heater running inside. It’s UL-listed and has an auto-shutoff feature whose benefits are clear as day. This feature turns off the model automatically once it detects overheating, extending this model’s shelf life.

The heating element is protected by an external stainless steel guard, so you can expect rust and corrosion to stay away from it. An insulated handle minimizes the risk of burn injury while handling, which means you can safely carry it around while it’s in operation.

Another notable feature of this model is that it comes with a built-in thermostat. A 12-month warranty is provided on this model and a well-coated wire – using which you can plug it into the mains – does well to minimize the risk of any electric shock. Still, we suggest you don’t hold the wire with wet hands.

Things We Like   

• UL-listed
• Built-in thermostat
• Auto-shutoff

Things We Don’t Like      

• Not a small tank heater

How It Compares With Our Criteria

1. UL-listed: Yes
2. Auto-shutoff: Yes
3. Built-in thermostat: No
4. Warranty: 12-months

Fully Submersible Portable Electric Immersion Water Heater

Most immersion water heaters you saw above only work with fresh water. This portable electric immersion water heater is different. It is also fully submersible in salt-water solutions, too, making itself an excellent choice for those of you who live in areas where the underground water is hard.

It also comes equipped with a user-intuitive controller. The dial on the controller’s base lets you increase or decrease the water temperature with 10*F jumps. A red LED light on top of the dial keeps blinking until you turn off the heater or the auto-shutoff comes into action.

You read that right. This model comes with an auto-shutoff that keeps it safe against overheating. A built-in thermostat is also on offer. You can count on it to turn this electric immersion water heater off once the water attains your desired temperature.

Not everything about this model is great, though. It doesn’t work as well as the other models you see above in vertical position. Perhaps that’s why its manufacturer suggests to install it in horizontal position. And despite being the most expensive unit on this review, it isn’t UL-listed.

Things We Like   

• Overheating prevention
• 100% waterproof construction
• Extended temperature range

Things We Don’t Like      

• Not UL-listed

How It Compares With Our Criteria

1. UL-listed: No
2. Auto-shutoff: Yes
3. Built-in thermostat: No
4. Warranty: N/A

What are Immersion Water Heaters?

Immersion water heaters work by submerging their heating element in water. The heating element, a coil, receives alternating current (AC) via a cable. The passage of electricity through the element generates heat, which it then transmits to the surrounding water, raising its temperature.

Unlike natural gas heaters, which require ventilation, immersion water heaters can safely operate in a closed environment. And while they have higher running costs than their natural gas counterparts, you can bring down these heaters’ operating costs by attaching a timer.

The timer will switch off the heater once the water surrounding it reaches a specific temperature, ensuring substantial energy savings. Some people also refer to the timer as a thermostat. You might want to attach it with your immersion heater if you intend to keep your electricity bills manageable.

Types of Immersion Water Heaters

Immersion water heaters are available in three major types. These include screw plug, over the side, and circulation water heaters. All three types have different applications because they are designed to work in different environment.

Here are the three main types of immersion water heaters:

Screw Plug Heaters

Screw plug immersion heaters consist of tubular heating elements. These heating elements are welded or brazed to a screw plug and into the wall of the equipment, such as water tanks, vessels or chemical containers. These heaters can adequately heat both oil and water.

Screw plug immersion heaters provide fast and efficient heating and are simple to use. They are ideal for small-scale applications, too, and are also easy to replace. Their only drawback is that these units are sometimes too small to meet the heating requirements of a large household.

Pros

• Simple to use
• Fast and efficient heating
• Ideal for smaller applications

Cons

• Might not be up for large scale

Over-the-Side Heaters

Over-the-side immersion heaters immerse their heating element along the side or at the bottom of the tank, though the rest of their housing is installed in the top of the tank. These heaters take up little space, can be easily removed for service, and are ideal for heating water.

What’s more, when you feel the need to clean your tank, you can easily remove these heaters without emptying your tank or container first. But they also suffer from one drawback. The installation of the heater through an opening exposes water to ambient conditions, leading to heat loss.

Pros

• Are budget-friendly
• Extremely easy to clean
• Take up little space

Cons

• Suffer from heat loss

Circulation Water Heaters

Also known as flanged immersion heaters, they have hairpin-bent tubular elements brazed or welded into a flange. The element-flange combo is then provided with an electrical enclosure. These heaters are bolted to the wall of the container or tank requiring heating.

Little wonder, then, that they provide their users with various benefits. Circulation water heaters offer fast and efficient heating, are easy to install and much easier to clean and maintain. However, they are prone to scaling and coking, so you must schedule periodic cleanings to prevent the risk of failure.

Pros

• Easy to install
• Easy to clean and maintain
• Are the best for heavy-duty jobs

Cons

• Require periodic cleaning to prevent scaling and coking

How to Choose Immersion Water Heater

Whether you’re buying an immersion water heater for the first time, or replacing an existing model, there are a few things you’d do well to keep in mind. Doing so might help you pick up the model that meets your home’s hot water requirements.

Size

How do I know what size immersion heater? To do this, you need to calculate your water tank’s capacity and the temperature increase needed. Once you have both these pieces of information at hand, perform this quick calculation:

Power (kW) needed = (Tank Volume x Temperature Rise x 4)/3412

Say you have a 160-liter water tank holding cold water at 20*C, and you want to heat the water to 60*C. Put all these numbers in the calculation: 160 x 40 x 4/3412 = 6.4KW. That means you need a 6kW water heater to heat the entire tank in one hour. A 12kW heater, on the other hand, will heat it in half an hour.

Material

The purchase cost of an immersion water heater depends greatly on its material of construction. Copper immersion heaters are the most inexpensive but not suitable for hard water. Though, you can still go for copper heaters if you can’t find your area in this US hard water map.

Titanium and Incoloy immersion heaters can easily deal with hard water but cost more than their copper counterparts. These heaters usually cost less than $50. Keep in mind, though, that this doesn’t include the cost of the heater’s installation or hot water tank, which varies from installer to installer.

Built-in Thermostat

If you’re serious about lowering your heating bills, make sure your immersion heater comes with a built-in thermostat. A thermostat ensures energy savings by turning off the heater the moment its water attains your desired temperature, before turning it on if the water cools off too much.

Auto shut-off

The auto-shutoff sensor will turn off the heater if the water exceeds a safe limit. That’s not all. It will also prevent the heater from dry burning, which means it would switch off the heater if there’s no water to heat, ensuring your safety and the heater’s long life.

UL-certified (optional)

UL-certified immersion heaters might cost more than those without this certification. But they justify their initial asking price by reducing the risk of potential injuries to their users. The UL mark is a testament that the heater meets the standards set by top safety organizations across the US.

Immersion Water Heater Problems

By this point, you know everything you need to about immersion water heaters and how they work. However, if you’re considering purchasing this water heater, there’s something you must know: immersion water heater problems.

Here are the common immersion water heater problems and their solutions:

Damaged Immersion Component

• Signs of the problem: Heater taking ages to heat water; it’s turning off and off repeatedly without any rhyme or reason

This issue mostly starts arising when the immersion water heater has reached the end of its shelf life. Why? Because rust takes it time to build up and damage the immersion elements. That means that the longer you continue to use your immersion water, the more apparent this problem will become.

What’s the solution? Remove the existing heating part, clean the opening where it was installed, and install a new element. This solution might seem easy to read, but you need much experience in plumbing to apply what you’ve just read. So we suggest you hire an expert plumber.

Limescale Buildup

• Signs of the problem: Water not achieving your desired temperature or taking too long to attain temperature

This issue mostly crops up in heaters being used in hard water areas. Hard water contains large amounts of calcium and magnesium, besides other trace elements. You can test your water hardness by adding a few drops of liquid soap in a bottle 1/3^rd full. If there are no bubbles, your surface water is hard.

What’s the solution? Install a hard water filter at the opening of your immersion heater. This solution will come handy if the limescale build-up hasn’t picked up pace already. However, if the issue has already begun, disassemble your heater and remove the scale with a high-pressure water steam.

Tripped Circuit Breaker

• Signs of the problem: You won’t get hot water

Is your hot water cylinder not working? Is it failing to supply hot water? Then that might be the case that there is no electricity to power the heating element. In some cases, a tripped circuit breaker, potentially due to overloading, might be to blame for this issue.

What’s the solution? Go to the main breaker panel and check if the immersion water heater’s circuit breaker is on. If you see a tripped circuit breaker, switch it off. Wait for a few seconds before turning it on again. If it doesn’t trip again, you’re good to go. If it does, call a professional as the issue is serious.

Frequently Asked Questions

How do I reset my immersion water heater?

Most immersion water heaters come with a ‘Reset’ button that you can press to reset them to default factory settings. Depending on the model you have purchased, you may need to use a small pin to press that button.

What happens if you leave the immersion water heater on?

If you leave the immersion water heater on for an indefinite period, the water coming out of the cylinder will be boiling. In the ‘best’ case scenario, this might result in the heater breaking down. In the worst case scenario, you might end up scalding yourself.

How much electricity does my immersion water heater use?

You can calculate how much electricity your immersion water heater uses by multiplying its power rating with the time you’d be leaving the heater on. For instance, if you’re using a 3kW heater and the cost of electricity is 14p/kWH, running the heater for one hour would cost about 45p.

Conclusion

I hope your search for a water immersion heater ends here.

If you are on a budget but still want a heater with all the bells and whistles, the Gesail Electric Immersion Heater has got you covered. It’s UL-listed, comes equipped with auto-shutoff feature and thermostat, and is backed by a 1-year warranty. No matter how you look at it, this is a formidable combination of features.