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Water Heater – just a need or a convenience?

Buying a water heater becomes a necessity when the old one breaks down, we have decided to do renovations in the bathroom or kitchen, we have a new home to furnish. In all three cases, we face the same problem – thinking about something that is not familiar enough to us, and in this case we feel insecure.

The approaches are usually:

  1. We see what brand the old water heater is and search for the same one. The logic is elementary – if it has worked for so many years, then it is good. However, there remains the unformed anxiety that something better may have appeared over the years.

  2. We turn for advice to the neighbor or friend who enjoys the reputation of a technical genius. However, we secretly doubt his competence, at least partly.

  3. We go to nearby white goods stores or hypermarkets and do our own research. Should we leave ourselves in the hands of the sales consultants? How do we know what exactly we need when we don’t know the exact selection standards? Except, of course, to compare the prices of the offered water heaters. This is not satisfactory enough – if one item is cheap and another is expensive, there must be a reason why!


Another option – whatever the sellers offer us, we buy it.

4.   We browse different websites and forums until we are exhausted and our heads are in turmoil because everyone is anonymous and the companies always butter up their goods. And there are always controversial opinions and one must intuitively or with didactic methods seek the truth. This is too tiring and engaging.

5.   Some of the more impulsive ones trust the latest advertising hype they have seen the most recently, go and boldly buy that brand that’s stuck in their heads.

6.  There are also those who do their own research, thoroughly study all the sources mentioned above, read between the lines, make their own judgments and conclusions based on their own logic, which they only trust because “everyone is a rotter”, and find the object of purchase.

These are basically the six ways determining the action of the customer when buying a water heater. We will try to help you with your choice with practical advices.


First, let us specify the selection standards without fixing their place of importance:

A.      Commercial Terms.

1.       Price.

2.       Product warranty.

3.       Possibility of installation and cost of installation.

4.       Product service assurance.

5.       Delivery method.

6.       The possibility of a wide range of choices to suit our specific needs.

7.       Innovative and economical alternatives.

B.      Performance

1.    Economy of the water heater – the standard here is heat losses per 24 hours. We should not forget that the main purpose of the water heater is to heat the water and therefore to keep it warm for a long time. This depends on the type and thickness of the heat insulation layer.

The main purpose of the heat insulation is to save energy. What would be the benefit of alternative energy sources, high efficiency boilers, gas boilers, solar collectors and expensive electricity, when we lose them through the water heater insulation?

Just for the sake of the topic, we will give an example: to heat the water in an 80 liter water heater to 75 degrees accumulates about 6 kWh of energy. The recommended heat loss rate for an 80l. according to the EU SAVE programme is approximately 1,2 kWh for 24 hours. This means that the loss through the insulation overnight is 20%! What is the situation with the “Eldom” water heaters with 4 cm insulation - the losses for 24 hours are 0,85 kWh or 14%, and for those with 3 cm insulation – 1,1 kWh – 18%. For reference, for mss water heaters of other manufacturers with insulation up to 2 cm, the losses are 1,50 kWh or 25%. We are talking about a difference between 7 and 13% of the energy consumed by the water heater!


1.1 The basic parameter of any heat insulation is its conductivity coefficient LAMBDA – λ. This parameter is measured in W/m. K°(watt per meter per degree Kalvin). Obviously, the most important parameter of insulation depends not only on its quality but also on its sizes. Polyurethane foam is the best insulation for water heaters. There are different types of polyurethane foam with λ = 0. 02 - 0. 035 W/m . The system we use atEldominvest” has one of the best λ - 0. 023! Furthermore, it does not change its parameters significantly over time. There are insulations that can worsen up to 30% in 3 years of use!

- The amount of insulation is essential. Through practical tests we have proven that the difference between 3 cm and 2 cm insulation is 7%, and between 4 cm and 2 cm insulation - 13% heat losses. This difference becomes insignificant at thicknesses of 6 cm and more, making the use of such insulation unprofitable.

- The quality of the insulation material is also of great importance. It is important that the quality of the product is maintained throughout the warranty period in line with the quality at the time of purchase. For this purpose, insulation should only be used from leading manufacturers who have proven their quality.
The data from the examples above are indicative, but accurate enough to make appropriate conclusions. It should never be forgotten that the consumer value of an appliance depends on its performance, not just its functional characteristics. All water heaters heat the water, but "ELDOM" water heaters have been proven to keep the water warm, not heat the surrounding area.


- The even distribution of the polyurethane foam around the water tank is by no means an unimportant factor. Thanks to our many years of manufacturing experience, we atEldominvest” have perfected the method of properly injection molding CFC Free components.


You can discover the differences between different brands of water heaters without such complicated calculations. If your friends have a water heater like yours, pop the jacket on when the water is hot. If you feel a pleasant warming - it's not exactly your water heater :)


1. 2. The use of electronic control provides the opportunity to provide additional energy savings of up to 15%. Modern microprocessor-controlled water heater models feature intelligent "self-learning" software with temperature hysteresis optimization, programming to turn on only in low-cost time zones, etc.


2. Safety - we have hardly thought about the fact that a water heater is an electrical appliance that works under high pressure. This requires a more responsible attitude when choosing a water heater and its operation. A safe water heater must have all kinds of protection: against overpressure, against overheating, against freezing, against corrosion, against limescale accumulation, against flow, against current flow, against voltage deviations of the electric current. Make sure all of this is available before you purchase your water heater. The "Exploded" water heaters of the newsreels are the result of "skimped" manufacturer protections or incompetent intervention by self-appointed workmen.


3. Reliability and long service life - the water heater should work trouble-free for a long time. Of course, it does not have to work flawlessly only within the warranty period. On what depends the long life of a water heater:

3. 1. The quality of the enamel coating. Years ago the water heater tanks were galvanized. It was some protection against corrosion, but not effective enough. In addition, the water contacting the galvanized surface of the water tank is harmful to people’s health. The enamel / or as some call it glass ceramic / coating of the water tank is essential for resistance against stubborn corrosion processes. The enamel in the form of a liquid or powder substance is applied mechanically to the inner surface of the water container. After firing in enamel furnaces, this substance sticks tightly to the water contact surface of the water container. This process is called adhesion. Thus the black steel of which the water tank is made is insulated from the aggressive effects of water.

The enamel frits and clays used in enameling practice worldwide are almost identical. However, the addition of certain components to the enamel formula increases its resistance to high temperatures. For example, zirconium, which we use in the Eldom water heaters.


3. 2. Availability of cathodic protection and its efficacy. Cathodic protection is used for additional prevention against corrosion processes in the water tank. It is something as simple as a construction, as difficult to explain as a physic-chemical process.


For effective cathodic protection is important to know just the basics: the active elements of the protection are one or two anode protectors. They are most often made of a special magnesium alloy. All other alloys do not provide effective enough protection! Located at opposite ends of the water tank, the anodes inconspicuously but securely protect its entire volume. How does this happen?
No matter how perfect the glass ceramic coating (enamel) is, there is always a risk of micro pores as well as defects at the weld seams where water has access to the base metal. Then corrosion processes start to take place in the water tank.

The cause of corrosion always lies in the difference between the potential of the metal (in this case the black steel of the water tank), and its environment(copper electric heater, stainless pipe, brass sockets, etc.). Corrosion is an electrochemical process in which a withdrawal of material occurs on the surface of the metal. As a result, breakthroughs appear in the water tank that cause leaks in the water heater.

Cathodic corrosion protection is an active method of protection and, unlike passive methods, attacks the cause of the problem directly. The method is based on the interdependence between the potential and the speed of corrosion development. Anodes also create potential. Between them and the defective surface flow very weak currents, opposite to the corrosion currents. Thus, the cathodic protection leads to delay and, under certain conditions, to prevention of corrosion.

The electrical conductivity of water is also very important for the effective operation of the cathodic protection. For values above 200 µS, such as hard waters, the protection works perfectly. In soft waters with electrical conductivity below 100 µS, such as the water in the areas around Sofia, the effect of the cathodic protection is significantly reduced. That is why we recommend water heaters with stainless water tank for such areas.

- The size of the anode is essential. It is considered that 200g. anode mass at statistically average water parameters can successfully protect for 3 years 1 square meter of enameled surface with no more than 7 square cm. defects. From this point of view, 350g. The anode mass in the ELDOM water heaters provides truly reliable protection. In the case of water heaters with capacity of 50 to 750 liters and coil water heaters, where the coil acts like a kind of screen, we have, after multiple tests, come to the effective solution of using protection with 2 anodes. We have equipped all coil water heaters from 50 to 750l. capacity with 2 anodic protectors. The 1000l. water heater is equipped with 3, 5 kg anode, running along the entire height of the container. Unfortunately, such solutions are not practiced by many manufacturers.

As previously mentioned, any bare metal parts located inside the water tank, such as stainless tubes, brass sockets, heater, etc. interfere with the operation of the cathodic protection. The anode perceives these parts as defective and concentrates its protection on them, leaving it with no “power” to protect the water heater and the real defects. This is the moment to raise the issue of the plastic pipe we install in the water tank – in our opinion this is an excellent technical solution regarding the interaction with the cathodic protection and very good in terms of reliability and durability. The question we can answer for ourselves is who nowadays is running their plumbing installation for hot and cold water with anything other than plastic pipes and why is that?

- Verification of corrosion protection performance by anode tester.

In the operation process of the cathodic protection, part of the magnesium anode mass is lost – it gradually melts. This is why specialists call it a “sacrificial anode”. When we install protective anodes in the water heater and customers pay for it, there should be a way to rate or measure their performance. Only the ELDOM water heaters provide this capability due to the insulated anode installation as well as the robust galvanic connection to the body by a cable instead of direct contact. The rating of the cathodic protection performance can be done by a service technician.

There is another, much more convenient solution, by means of an anode tester built into the water heater. This is a simple and inexpensive milliammeter that displays the state of the anode protectors at the push of a button. If the indicator is in the green area, it means that anticorrosive currents are running. If the indicator is in the red zone, you should call your technician. This increases the life of your water heater by at least another 3 years.


The interesting part is that with almost all other water heaters brands, the possibility of checking by anode tester is not available. This is why their customers cannot rate the work of cathodic protection even if they want to. One possible answer is that most manufacturers are reluctant to do so, since they are not certain in their design solutions.


3.3. Quality of electric heating element

The electric tube heater is the “heart” of an electric water heater. That is why we pay special attention to it. In order to guarantee and control the quality of the heaters we put into our appliances, we have put into operation since the end of 2009 a latest generation line covering the whole production process of both copper and stainless heaters of different power, operating voltage, purpose, shape and length (up to 3 meters).

The modern technology we use enables maximum automated process control. In the production process, 100% control of nodal operating points is taking place:

- Check the quality of pipe welds by eddy currents (Eddy Carrant test);

- Check the weld of the spiral to the solid terminal by automatic parameter control;

- Dielectric strength test after filling before tube diameter reduction;

- Check in water environment – for the hermetic sealing of the heater;

-  Leakage current check;

- A complete check of the final control stands, including: repeated test for dielectric strength, leakage current check, heater power test;

- All the materials we use are of guaranteed quality, supplied by leading companies;

- The resistance wire is made of special chromium-nickel alloy of Kanthal. The Kanthal D we use allows heating temperatures up to 1300°C. For the temperature mode our heaters operate it is reinsured by a 40% range;

- We rely on flawless magnesium oxide (MgO) insulation, which is significantly better insulator than the quartz sand used in the mass heating elements. We use MgO class H with 99,97% purity, which allows the dielectric characteristics of the heater to be maintained even at temperatures of 1300°C;

- We use a hard pin made of special nickel plated steel.

- To seal the heaters, we at Eldominvest use a special brand of epoxy resin. It is a better solution than the widely used silicone, whose characteristics worsens over time, and this leads to dangerous unsealing of the heater;

- We use ceramic insulation sleeves rather than the common used plastic ones;

- The copper tubes for our heaters are calibrated to a very high degree of accuracy and are supplied by a German company;

- The stainless steel pipes are made at Eldominvest. We use brand 321S with high alloying additives (NiCr and Mo), extremely resistant for operation in water and air environments;

- Our heaters are designed with longer length and larger cold zone. Despite the higher cost of expensive materials, this provides the customer with:

- Greater resource (longer life) and longer life of the heater due to the lower load, respectively less stress, on the tube and the spiral;

- High resistance even in case of improper use of the appliance in which they are installed;

- Resistance against calcareous water. The remoteness of the heating zone also protects rubbers, bushings, etc. flange sealing elements from scale build-up.

- The heaters in the ELDOM appliances are manufactured according to BDS EN60335 Part 1 and have been tested in SGS certified laboratory.


Perhaps this is the place to bring clarity to the matter of heater power and the electricity costs.

The water heating time depends on this. It is a misconception that the lower the power of the electric heater is, the more economical the water heater is. The heat energy that is given by a heater is equal to consumed electrical energy. A 2kW heater takes longer to heat 80 liters of water than a 3kW heater. However, the electricity consumption is the same.

4. Easy installation – ELDOM water heaters can be easily installed in the place of the old ones, on the same hooks because the wheelbase between the carrier sockets is 240 mm, as it is on traditional water heaters. They are easy to hook up, easy to connect to plumbing and electrical installation can be assembled to any wall, including plasterboard. For customer convenience, we have printed a template on how to hang it on the shipping package of each water heater.


5. What the water heater should be – enameled or stainless?

The price difference between enameled and stainless water heaters is tangible – stainless models are twice as expensive. This is not a whim of the producers but objectively determined by the international steel prices. In the last years, the production and use of corrosion resistant steels has been constantly increasing. Popularly, we call them stainless steels. In the practice, all around the world, for the production of water tanks for quality water heaters is used exactly the stainless steel, brand 316L. This is austenitic chromium-nickel steel containing molybdenum. It is non-magnetic, high strength and corrosion resistant. This type of steel has an approximate composition of 16-18% Cr (chromium) and 11-14% Ni (nickel) and 2-2, 5% Mo (molybdenum) added to increase corrosion resistance.

Stainless steel, class 316L is also known as medical steel. The surface of its products remains clean and shiny throughout their operational life and does not have harmful effect on the human health. That is why it is also used in the manufacture of appliances that have direct contact with food products or table water, as well as goods that have contact with the human body.

At Eldominvest we use AISI 316L steel in the production of stainless water tanks. In addition to the long life of the unit, this ensures impeccable hygiene and preserves the drinking qualities of the water.

Where do we recommend the use of stainless water heaters?

As we already mentioned, there are regions in Bulgaria with very soft waters where the cathodic protection of enameled water heaters does not work effectively. In order to rely on hot water in these areas, we recommend buying water heaters with stainless steel tanks. Otherwise, no matter what brand of water heater you choose, the risk of corrosion is huge.


6. How do we ensure the long life of the water heaters in areas with aggressive waters?

For the regions with highly calcareous and soft waters (which cover half of the country) we have specially developed ELDOM Eureka with dry tube heaters.

Dry tube heaters are referred to the heating elements of the water heater that are not in direct contact with the water, but are placed in optimally designed tubes through they radiate heat. They provide direct heat transfer without significant heat loss. Their energy performance and heating efficiency are similar to those of standard submerged tube heaters, but because they do not come into direct contact with aggressive waters, their lifetime is significantly longer.

The new Eldom Eureka water heater with dry tube heater is a universal solution even when:

- The water from the water mains has high lime content and assumes the release of a large amount of calculus;

- The water is very soft and due to its aggressive action a corrosive effect on the heater itself is observed.


Here are some of the main advantages of the new Eldom Eureka water heaters in solving            similar problems:

- The heating element has no direct contact with the water – the water is heated through a steel enameled pipe where the heater is installed. Due to the optimally selected power of the heaters of 2 kW, a much smaller amount of limestone is deposited on the new enamel coating of the Eldom water heaters. It does not accumulate, but separates and settles to the bottom of the water tank. The absence of limestone on the pipe preserves the heating efficiency of the water and the amount of hot water for the entire operating period.

- Effective protection against corrosion – the enameled tube, in which the heater is placed tightly, becomes part of the fully enameled inner surface of the water tank, which is effectively protected by two anodes with increased mass in Eldom Eureka water heaters.

- Double electric switch – Eldom Eureka water heaters have double electric switch for gradual turning on the two heating elements, which optimizes the water heating mode.

- Energy efficiency – dry tube heaters in Eldom Eureka water heaters maintain the energy efficiency when heating the water, unlike ceramic dry heaters, because of the sealed installation of the heating element in the enameled tube.

- Extremely easy repair – when replacing the heater, draining the water heater is not required.


Water heaters with coils.

In the West, the use of combined /direct/ water heaters has decades of traditions. In condition of skyrocketing electricity prices, many Bulgarians are turning to water heaters using alternative energy sources – boiler, fireplace, solar collector, heat pump, etc.

A major advantage of this type of water heater is that little or no electricity is required in the process of operating the alternative energy source. Even models with two heat exchangers allow this effect to be year-round with a rational use of energy sources.


What type of combined water heater is suitable in your case?


- Application of water heaters with upper coil.

It is not widely known that coils connected to high power sources, such as boilers and fireplaces; make more efficient use of a coil located at the higher end of the water heater. This does not accumulate heat in the entire volume of the water heater, but the appliance enters into flow mode and practically provides unlimited amount of hot water. Our laboratory tested the following water heater: 80l. M2 T, connected to 12 kW gas-fired boiler, with heat carrier temperature of 75 degrees flow rate of the pump – 1 cubic meter/hour. Hot water was consumed for 3 hours at a temperature of 48 degrees and a flow rate of 5 L/min, after which the experiment was discontinued because there was no change in the result.


-water heaters with low positioned coil

On the other hand, in the case of low-powered heat sources, such as solar collectors, the coil needs to be located at the lower end of the water heater or to fill its entire volume to heat as much hot water as possible, using the accumulative effect and the good insulation of the water heater.


- Water heaters with parallel coils

This model has two parallel heat exchangers for combined use of two heat sources. The coils are positioned throughout the entire volume of the appliance for maximum efficiency in heating the water, regardless of the season.


In any case, there must be a difference in the temperatures to have heat exchange. If the temperature of the heat carrier is, for example, 50 degrees and the temperature of the water heater is also 50 degrees, there will be no heat exchange, no matter what the coil is. The main rule here is: the greater the ΔТ is – the greater the heat exchange will be. So, the power of the heat exchanger and the received hot water – these are integral values and these parameters should not be announced and compared momentarily and one-sidedly.

Water heaters with two coils obviously combine both options.


It is important to know that the coil water heaters obey to standards different than those relevant to electric water heaters!

The standards for electrical water heaters are:

- EN 60335-1:2003 + A1:2005+A11:2005, - safety, part of Directive 2006/95/EC
- EN 60335-2-21:2003+A1:2005 - applies to storage water heaters
- EN 55014-1:2002+A1:2002
- EN 55014-2:1999+A1:2002
- EN 61000-3-3:2000 - Group of standards relating to electromagnetic compatibility of products, part of Directive 2004/108/EC


Standards for water heaters with coils:

- EN 12897:2006 - "Water supply-Requirements for indirect heated unvented (closed) water tanks". They are tested under periodic loading at higher and dynamically changing pressure. The coil and the heat exchanger parameters are tested while at the same time standards are set, which should overlap with the water heaters construction.

- EN 60379:2005 - "Methods for measuring the parameters of water tanks with electric heaters for domestic purposes".

The second standard refers to heat losses and the methodology for their calculation, as well as other parameters such as mixing ratio. Here, for the first time, a clear standard is set for water heaters that must be covered. Naturally, if the water heaters are combined, they must reach both sets of standards.



Water Heater