frequently asked questions about water treatment for heating
Why water conditioning is the key to the longevity of your heating system
Most homeowners and operators of commercial buildings think that when installing a new boiler or replacing radiators, they have taken care of everything necessary. They have bought a quality device, had it installed by a professional, and are looking forward to the first heating season. What is often overlooked, however, is the fact that the boiler itself is only the "engine" of a system that runs on water. And this water is not distilled laboratory water, but a complex mixture of minerals, gases, and impurities.
From my experience, I know that as much as 70% of boiler malfunctions that end up in service do not come from the manufacturer of the device, but from neglected water quality in the system. Corrosion, deposits, and bacteria are silent killers that gradually destroy heat exchangers, clog valves, and increase fuel consumption. Water conditioning is not a luxury, nor just an "additional service," but a fundamental part of maintenance that pays back in the form of a longer investment lifespan and lower energy costs. In this section, we will take a detailed look at why filtration is critical, how it works, and what you need to know before installation.
What happens in your system without water conditioning?
When we talk about "unconditioned water" in heating, we are not referring only to visible dirt. It is about chemical and physical processes that are constantly taking place. The first and biggest threat is corrosion. Water contains dissolved oxygen, which reacts with metals (especially iron in pipes and cast iron in older boilers). This reaction creates iron oxides—rust particles that float in the water like micro-dust.
These particles, along with limescale (calcium carbonate) and organic substances, settle on surfaces with the highest temperatures. This means that layers form on the walls of the heat exchanger in the boiler. The formation of such a layer, even a few millimeters thick, is enough to reduce heat transfer efficiency by tens of percent. The boiler has to work longer and at a higher flame to achieve the desired temperature, which leads to excessive wear and increased gas or pellet consumption.
The second threat is sludge formation. If impurities are not removed, they gradually settle in the narrowest parts of the system—in valves, in thermostatic heads, and in individual radiator branches. The result is that the radiator is cold at the top, warm at the bottom, or does not work at all. In the hot summer months, when the system is idle, these impurities can settle permanently and become difficult to remove.
Physical principle of separation: How a filter works in practice
Many people think that a filter is just a mesh that "catches big stones." In the real practice of professional heating, however, it is a much more complex matter. A filter in heating serves to mechanically separate solid particles suspended in the liquid. These particles vary in size, shape, and density.
The key parameter is the micron rating (μm). One micron line is one thousandth of a millimeter. If you have particles of 50 μm in your system, a filter with a pore size of 100 μm will let them pass. On the other hand, if you have a 20 μm filter, it will catch these particles. The problem arises if you use a too fine filter (for example, 5 μm) on a system that is not yet cleaned. It will quickly become completely clogged, and the pressure loss will be so high that the pump will stop circulating water.
As you can see in the diagram above, the filter works like a sieve. Large particles (red circles) are stopped on the surface of the mesh, while smaller particles (orange circles) pass further. It is important to realize, however, that in heating we want to catch precisely those particles that are harmful to the heat exchanger. These often have a size between 10 and 50 microns. Therefore, the choice of the right insert is critical.
Another aspect is hydraulic resistance. When impurities get into the filter, a "sludge cake" begins to form. This cake blocks the pipe cross-section. If the cross-section is blocked, the pressure before the filter rises and the pressure after the filter drops. This is called pressure loss. In a properly dimensioned system, the pressure loss through a clean filter should be minimal (about 0.05 - 0.1 bar), but when the filter is clogged, it can rise to levels that cause the pump to no longer have the power to move water to the upper floors.
Types of filters and their application in the system
In the category of water filtration and conditioning, you will find two main groups of solutions: manual filters with replaceable inserts and automatic filters with backwash. Both have their place, but it depends on the type of building and the quality of the water.
Manual filters with insert (Strainer)
This is the most common solution for family homes and smaller buildings. It is a simple construction, where a mesh (insert) with a defined pore size is placed in the body of the filter. The most commonly used inserts have a pore size of 20 μm. Why exactly 20? Because they are able to catch most corrosion particles and sand, but at the same time have sufficient cross-section to not clog too quickly.
The advantage of these filters is the price and ease of operation. It is enough to open the cover once per season (ideally in the fall before the start of heating), remove the insert, clean it or replace it with a new one, and put it back. On the market you can find various variants, for example Filter 5" - 1"F; without insert, which is ideal for larger pipe diameters, or Filter 5" - 3/4"F; without insert for standard installations.
An important detail is the type of insert. You can choose between plastic (PP) and stainless steel mesh. Plastic inserts are cheaper and work well in clean systems where water conditioning has already taken place. Stainless steel inserts, on the other hand, are more resistant to high temperatures and chemical cleaning agents, which are sometimes used to flush the system.
Automatic filters with backwash
In areas with higher load, such as panel buildings, administrative buildings, or industrial halls, automatic filters are often used. These devices have an integrated electric motor and pressure sensor. When the pressure difference between the inlet and outlet exceeds a set limit (for example, 0.3 bar), the filter automatically starts and flushes the internal mesh using part of the water from the supply. Water with impurities is discharged into the sewer.
This type is ideal for systems where it is difficult to regularly access manual filters, or where the risk of rapid contamination is very high. However, they are not suitable for systems with low pressure, as they require a certain flow and water pressure to flush.
Dimensioning and Choosing the Correct Diameter
One of the most common mistakes during installation is choosing the wrong diameter of the filter. Many plumbers think that "bigger is better" or, on the contrary, that "it must fit exactly on the pipe." The reality, however, is that the filter should have the same diameter as the pipe, or one size larger if technically possible, in order to minimize pressure loss.
Our category offers a wide selection, including Filter 5" - 3/4"F; stainless steel insert - special offer and Filter 5" - 3/4"F; PP insert - special offer. These models are designed for standard pipes DN20 and DN25, which corresponds to 3/4 inch. For larger installations, for example for main house connections, there is a version Filter 5" - 1"F; without insert.
Always check whether you have an external or internal thread on the pipe when choosing. Most modern filters have an external thread (F), which means they are connected to an internal thread on the pipe or valve. If you have a pipe with an external thread, you will need reductions or adapters. Incorrect installation can lead to water leakage or the filter not sealing properly.
Practical Scenarios: When Filtration is Not Worth It and When It Is
There is a myth that if you have a new system and clean water, you don't need a filter. This is not true. Even in a new system, impurities arise during installation. Pipe cuts, sawdust, insulation tapes, gaskets, and even rust from new valves get into the water. Without a filter, these particles flow directly into the boiler's heat exchanger. In this case, a filter is essential.
Another scenario is the renovation of an old system. If you are replacing a boiler in a house that is more than 15 years old, there will definitely be deposits. In this case, it is necessary to first perform a chemical flushing of the system and then install a filter with a coarser insert (for example, 50 μm), which will catch larger pieces of scale and rust. Only after a few weeks of normal operation can you switch to a finer insert of 20 μm. If you were to install a 20 μm insert in a heavily clogged system immediately, the filter would clog within two hours, and you would have to clean it all day.
Another common problem is "hard water." If your house has a high calcium content, deposits form faster. In such a case, it is advisable to consider not only mechanical filtration, but also the installation of a water softener, which removes calcium and magnesium ions. The mechanical filter will then serve only to catch deposits caused by other factors.
Maintenance and Problem Diagnosis
Installing a filter is only half the job. Regular inspection is more important. We recommend checking the filter at least once a year, ideally in the fall before the heating season starts. If you have a system with a complex geometry or high load, check it twice a year.
What should you pay attention to? Look at the pressure gauge before and after the filter. If the pressure difference is greater than 0.2 bar, the filter is clogged and needs to be cleaned. Another sign is a drop in heating performance. If the radiators are not heating as they should, or if the boiler frequently stops operation due to overheating, it may be due to restricted flow caused by a clogged filter.
Regular replacement of the insert is a cheap investment. The price of inserts is in single-digit euros, while the repair of a damaged heat exchanger in the boiler is counted in thousands. Therefore, it is worth having spare inserts at home. If you use Filter 5" - 3/4"F; stainless steel insert, you can clean the insert with a brush and reuse it, which is more economical. Plastic inserts, however, are recommended to be replaced, as they can deform at high temperatures.
A common mistake is also incorrect installation orientation. The filter must be installed with the arrow on the body pointing towards the boiler. If you were to install it backwards, the water would push against the mesh and could damage it or cause the filter to work inefficiently. In addition, if you have a pump in the system, the filter should be installed before the pump to prevent cavitation (formation of bubbles), which could damage the pump.
Comparison Table: PP Insert vs. Stainless Steel Insert
| Property | PP Insert (Polypropylene) | Stainless Steel Insert (Stainless Steel) |
|---|---|---|
| Price | Low (disposable) | Higher (long-term) |
| Estimated Lifespan | 1 season (recommended to replace) | Several seasons (with proper maintenance) |
| Heat Resistance | Limited (up to approx. 80°C) | High (up to 200°C+) |
| Chemical Resistance | Good (to common cleaning agents) | Very good (to aggressive substances) |
| Application | Standard family homes, new systems | Old systems, industry, high temperatures |
Hydraulic System: Difference Between Parallel and Series Connection
The diagram shows how the water flow changes depending on whether the filter is connected directly into the main pipe (in series), or whether it has its own circulation loop with a pump (in parallel). Series connection is standard for family homes, where the entire system flow must pass through the mesh. Parallel solutions are used in large industrial buildings, where it is possible to let part of the water circulate outside the filter to limit pressure loss.
Impact of temperature and pressure on filter material selection
The filter material is not just an aesthetic choice, but a technical parameter that affects operational safety at extreme temperatures. For standard systems with a maximum temperature up to 90 °C, high-quality plastic PP or stainless steel is sufficient. However, in heat pump or solar systems, where temperatures can reach 100 °C to 120 °C, special heat-resistant components must be used. If you were to use a standard plastic filter in a system with a solar collector, it could deform and cause a water leak.
Separation principle based on density and particle size
The diagram illustrates how impurities behave in relation to the filter mesh depending on their size and density. Larger and heavier particles (red) are trapped on the surface, while smaller particles pass through, highlighting the importance of selecting the correct micronic permeability.
Critical installation orientation and hydraulic pressure
This diagram highlights incorrect installation that can lead to immediate destruction of the mesh or inefficient filtration. The flow direction must always go from the center of the mesh outward, so that water pushes against the mesh and does not push it out of the holder.
FAQ: Frequently asked questions about water treatment for heating
Why do my filters keep clogging, even though I have a new boiler?
This is a classic case of a "new system." During installation, a lot of dirt (sawdust, insulation tape, sealant) got into the pipes. These particles are now circulating and being trapped in your filter. That is actually good news – the filter is doing its job. We recommend replacing the insert more frequently (for example, every two weeks) during the first two months of operation, until the system is "cleaned."
Can I use a 10-micron insert instead of 20?
Technically yes, but in practice it may not be advantageous. Filtration at 10 μm is extremely fine and in a standard heating system it can clog very quickly, causing high pressure loss. If you have a very clean system and want maximum protection, you can try it, but be prepared for more frequent maintenance. For most cases, 20 μm is the optimal compromise.
Is it necessary to remove the filter in summer?
No, the filter should remain in the system all year round. In summer, when the boiler is not operating, the water in the system can still warm up and deposits can form even when the system is idle. Moreover, if you remove the filter, you risk letting impurities into the boiler at the start of the heating season. The only exception is if you are planning a full system flush, in which case the filter is temporarily removed.
What should I do if I forgot to insert the filter media?
Never operate the system without the filter media! Without it, the filter becomes just a passive object that captures nothing. Impurities will go directly into the boiler. Immediately stop the system, drain some water, insert the media, and restart the system. If the system has been running without the media for a longer period, we recommend checking the condition of the heat exchanger in the boiler and having it cleaned if necessary.
Can I use a heating filter for drinking water?
No, filters designed for heating are not certified for drinking water. They are made from materials that may release substances unsuitable for consumption. For drinking water, use special filters with the appropriate certifications (NSF, WQA).
How often should I replace the 20-micron replacement media?
The standard frequency is once a year, in autumn before the heating season starts. However, if you have an older system or hard water, we recommend checking twice a year. If the media is completely black or difficult to flush, replace it immediately.
Conclusion: An investment in cleanliness is an investment in safety
Water treatment in heating is not just about having a clean filter. It is about protecting your investment. Every euro you spend on a quality filter and regular maintenance will be returned to you in the form of a longer boiler lifespan, lower energy costs, and less stress from unexpected breakdowns. Don't wait until the boiler breaks down. Installing a filter is a simple step that can change the rules of the game in favor of your home.
Remember, choosing the right product is half the success. Choose a filter with the appropriate diameter and type of media according to your needs. If you have any doubts, do not hesitate to contact our experts, who will help you choose the best solution for your specific system. Your heating system deserves the best possible protection.
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Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.