A lot has been said and written about the choice of water heating appliances for private houses and apartments. This information is often contradictory or simply sucked out of the finger by advertisers seeking to market their product. There are especially many insinuations about which radiators are better - bimetallic or aluminum. We will try to clarify this issue and explain to ordinary homeowners how things are in real life.
About the design of heating appliances
Understanding the design of modern batteries will help to thoroughly understand the question of which radiators are better - aluminum or bimetal. Here, one should immediately clarify - in this context, aluminum refers to its alloy with silicon - silumin, since this metal is not used in its pure form. The proportion of silicon in the alloy reaches 14%, less than 1% of its composition is occupied by impurities - iron, copper, manganese and zinc. Bimetal is a product of two different metals, in our case, steel and silumin. But first things first.
Aluminum heater consists of sections made of silumin by casting or extrusion. Each section of complex shape consists of the following elements:
- silumin body (radiator body);
- two longitudinal channels with a diameter of 25 mm with right and left-hand threads at the edges for twisting sections;
- a vertical channel of circular or oval cross section 25–45 mm in size, connecting horizontal ones;
- vertical convection ribs on the sides and front of the housing for better heat exchange with air.
Note. The sections are twisted together by steel nipples with a cylindrical thread with a diameter of 1 inch. The fact of using steel fasteners is useful to us later, when comparing batteries.
Bimetal heating devices are also made of aluminum alloy, inside of which there is a welded frame made of steel pipes. The goal is to eliminate the contact of silumin with the coolant and increase the structural strength and reliability of the product.
Partially bimetallic batteries are also on sale, where steel pipes are embedded only in horizontal channels. Neither discuss, nor even buy such a product does not make sense.
Comparative analysis of radiators
What is the first concern for the buyer of heating batteries? Three things:
- To heaters well warmed and served for a long time.
- The price of products.
- Their appearance.
Comparison in appearance can be immediately excluded, since the design of modern sectional radiators is almost the same, and the vast majority of products are coated with a durable white polymer coating. It remains only to choose a heater according to the height corresponding to the place of its installation.
It remains the first 2 points, by which it is worth judging which radiators are better - aluminum or bimetal. In technical language, the comparison criteria are as follows:
- good heating provides heat dissipation of the heater;
- the duration of operation depends on the magnitude of the working pressure and the ability to withstand the effects of poor-quality coolant (corrosion resistance);
- The concept of price refers to 1 section of the device.
Reference. The need for bimetallic batteries arose due to the high pressure in the central heating systems of apartments and private houses, as well as due to the low quality of the coolant. Therefore, it is better to compare them with aluminum from this point of view.
Compare heat dissipation
Aluminum and its alloys are characterized by excellent thermal conductivity of 220 W / m * K. For radiator silumin, this indicator is 150-180 W / m * K.In terms of heat transfer, only copper is better than them (λ = 380 W / m * K), but batteries are not made from it. In bimetallic radiators, a steel mediator appears between the heat carrier and the aluminum case with much lower thermal conductivity - 70 W / m * K.
If we assume that the speed of water and its temperature are the same in devices made of silumin and bimetal, then the heat transfer of the second will be less. Steel does not have time to take as much heat as silumin from the coolant. This is in theory.
In practice, the heat transfer indicators declared by the manufacturers are almost the same for silumin and bimetal sections. To verify this, just look at the table, which shows the data for products from two well-known manufacturers - Global (Italy) and Rifar (Russia):
Note. The heat transfer values are indicated for certain conditions: the temperature difference between the heat carrier and the air in the room should be 70 ° С (90 and 20 ° С, respectively). This means that in reality the batteries will give off heat about 1.5 times less.
If we compare the sizes of the sections of the presented models, it becomes noticeable that they are able to transfer approximately the same heat flux into the room. Hence the conclusion: both types of radiators heat equally efficiently and according to this criterion there is no difference between them.
Which batteries are more reliable
The service life of heaters operating in a central heating network depends on the corrosion resistance of the material and the pressure for which the radiator is designed. As for the pressure on the Internet, many horror stories roam, their content boils down to one thing: aluminum sectional batteries can not be placed in apartments with central heating, because they will be torn apart by water hammer and high water pressure.
In fact, silumin products of all well-known manufacturers are designed for a working pressure of at least 16 Bar, and are tested at 24 Bar. This despite the fact that the pressure in the heat supply networks rarely reaches 14 Bar, taking into account tests and other operating conditions. As an example, the table shows the performance characteristics of products from several popular brands:
And in order to dispel the myth of bursting aluminum batteries, we suggest watching the video of our expert Vladimir Sukhorukov, where he conducts a tensile test of a steel radiator. Note that steel devices, unlike aluminum ones, are designed for a pressure of only 6 bar.
The sections of the Global bimetal models withstand up to 35 Bar during operation and are tested at 50 Bar. Characteristics from other brands are shown in the next table:
Such pressure indicators simply do not exist in any heating network, except for steam systems of industrial enterprises. Hence the logical question: why put a more expensive bimetal, if aluminum is enough? Perhaps due to the corrosive effects of the coolant, which we will discuss further.
To make sure that the reasoning is correct, visit your heat supply company and ask them to show the data of the system pressure tests (usually pressure testing is performed with a pressure of 12 bar). And then compare them with the technical characteristics of various types of radiators.
Poor heat transfer in central heating systems is a problem of all countries of the post-Soviet space, resulting from the extreme deterioration of underground pipelines. Therefore, only cast-iron batteries are “friends” with such water, the rest is facing such a fate:
- Silumin remains resistant to corrosion if the pH of the coolant does not go out of the range of 7-8.5 units. A more acidic environment damages the alloy.
- Abrasive particles moving together with water through the channels of the heater, relentlessly bombard the surface of the aluminum alloy. True, a fistula from such an impact may appear after many years.
- Steel pipes of bimetallic radiators also corrode and “overgrow”, although here it will take quite a long time to disable the product.
Leading manufacturers of silumin batteries practice applying a protective layer consisting of three or hexavalent chromium to the inner walls of the channels. The method of application is electrochemical (passivation). Such events practically equalize the chances of bimetallic and aluminum heating radiators in the fight against corrosion.
Which is cheaper?
According to general price statistics, bimetal is on average 20-25% more expensive than aluminum. In this case, batteries with a steel frame have a restriction on the size of the passage section of the channels due to the additional element - the pipe. The remaining advantages and disadvantages of sectional alloy radiators are almost the same, as we had the opportunity to see.
The difference in price is well reflected in the table with products of the same well-known brands:
Note: the cost of products of different companies is taken for the most popular size - 500 mm.
Which radiators to choose - recommendations
At various forums devoted to heating private houses and apartments, disputes on this topic do not subside. An ordinary landlord or tenant who has gone there in search of information may not find the truth. The situation is exacerbated by artificially created myths that have one goal: to sell some products.
The main myth about the insufficient working pressure of aluminum radiators is debunked by us, but there are others:
- when working in centralized networks, silumin quickly corrodes corrosion, so only bimetal is needed;
- aluminum forms a galvanic pair with some other metal in contact with the coolant, and therefore quickly collapses;
- as a result of chemical reactions of an aluminum alloy with dirty water, a lot of oxygen is released into the system;
- steel inserts of bimetallic batteries rust and rot through, which is why the section has to be thrown away;
- other incredible stories.
The processes described in myths take place, but to a very insignificant degree. For any serious consequences to occur, it takes decades, not decades. Provided that you did not buy a cheap fake and put the batteries correctly. And steel parts are also in aluminum heating devices (connecting nipples).
Finally, we give a number of recommendations that contribute to the best choice of radiators for your home:
- The best solution for autonomous heating systems operating from your own boiler is aluminum batteries.
- They are perfect for work in apartment buildings. Just buy quality products from trusted manufacturers and do not forget to compare the amount of working pressure.
- In multi-apartment high-rise buildings (16 floors or more) it is better to install bimetal radiators.
- If the heating system of the "high-rise" is not riser, but with horizontal branches entering each apartment, then aluminum batteries can be supplied.
- Advice to users who are not convinced by any arguments: buy and install bimetal heating appliances in your home and feel relaxed.
Any radiators connected to the central heating will last longer and heat more efficiently if they are periodically washed. Ideally - annually, in extreme cases - once every 3 years. Also, many valuable tips on choosing suitable batteries can be found in our expert’s video: