Renovation of cast iron radiators step by step

The cast iron radiator restored by Terma. In the background the same product in the condition in which it was delivered to our factory. 

Longevity and timeless design 

Cast iron radiators are unique products, due to both the material from which they are made and their decorative properties. Terma offers brand new cast iron radiators as well as renovation services, which allow older models to be renovated and brought back to their original beauty. 

For radiators renovated in our factory, we give a 5-year warranty for tightness and coating.

Cast iron radiators are suitable not only for classic and stylized interiors, but also for modern spaces, giving them character and timeless elegance. Cast iron is perfectly combined with other natural materials, such as wood, stone or high-quality natural textiles, such as wool. In addition, cast iron is a long-lived material that can be renovated. After renovation it will serve you for the next several dozen years. By choosing a cast iron radiator, you can also be sure that the changing fashions and design trends will not affect its timeless character. 

     The radiator after the renovation. 


Cast iron radiators often have sentimental or even historical value. Terma receives richly decorated items from the turn of the 19th and 20th centuries, as well as simple sections from the socialist era, whose owners who value eclecticism want to preserve the original elements of the interior of that period in their homes. A very wide range of finishes for cast iron radiators that we offer allows you to play with colours and allow you to emphasize decorative elements. 

Renovation of cast iron radiators is an artisanal process that requires experience and a sensitive eye to notice and bring out the beauty hidden under a layer of old coating. We treat all radiators entrusted to us with due respect, as they are often items that remember the youth of our grandparents and great-grandparents. During the renovation process, we do not take shortcuts, we devote as much time to every section and every detail to get the desired effect. Our employees are masters of their profession, devoting themselves to daily creative work, the result of which are unique products, one of a kind, radiators "with a soul". The team works under the supervision of an artist sculptor Krzysztof Michalak, the creator of the original Kaszub radiator, who supports, the renovation of historical radiators with his knowledge, and his hands. By entrusting us with renovation of your radiators, you can be sure that they reach the hands of enthusiasts with the experience and knowledge necessary to properly carry out the renovation process.

In the further part of the text, we present the consecutive stages of the renovation process, so that you know exactly what actions will be taken during renovation. 

What happens when your radiators arrive at our premises. 


If you are interested in renovating cast iron radiators, please submit an inquiry using the contact form. Our team will make an initial quote and contact you to present an offer. Submitting an inquiry does not oblige you to accept the offer, you do not incur any costs before delivering the radiators to us. 

If you decide to accept the offer, we will assist you in delivering the radiators for renovation. We work with experienced carriers; we will also provide you with information on how to prepare the radiators for shipment. 

Upon arrival, the condition of the radiators will be visually inspected and photographic documentation will be prepared. If damage beyond repair is identified at this stage, we will contact you to agree on the net steps. 

After determining the final price for the service, the renovation service order will be processed in our system. It is the basis for generating a pro forma invoice, which you will receive by e-mail. 

I want to ask about the renovation of my cast iron radiator



After completing the inspection stage and making formal arrangements, first, we get rid of the old, damaged paint coating from the radiator. This process occurs as a result of pyrolysis, which consists of the thermal decomposition of successive layers by exposing them to high temperature. The pyrolysis takes place in a special furnace, and during the process, limescale deposits inside the sections are also cleaned. After completing the operation, the radiator is set aside to cool down, and the result of this process is a pure cast, with no coatings or sediments. The pyrolysis service is provided by an experienced external supplier and usually takes no more than one week. 

The radiator after the pyrolisis. 

 Radiator after pyrolysis and disassembly. 


Using a specialized set of keys, our employee disassembles the radiator into its components: ribs, nipples, reduction plugs, screw connections. Each of these elements is carefully checked for possible damage and surface defects. 

The most common cast imperfections are socket damage, deep pits, and overgrowths on the outer surface. As a rule, they are the result of the low technical quality of the casting itself. 

In the event of detecting elements that cannot be repaired, defective sections or nipples are excluded from further processing. The information is shared with the customer. 



Each section is cleaned by blowing out compressed air. In addition, if necessary, sediment is removed with a scraper. Then, the sections are tested for tightness by filling them with water, which provides additional flushing of any dust and sediment residues. If a leak is detected, we will repair it or, if it is not possible, we will exclude a section from further processing. The damaged ribs are repaired after shot blasting (stage 6). If an item is excluded from the process, you will be notified immediately. 

    Threading process. 


Each thread is renovated using appropriate tools (taps). The regeneration of the threads results in a thorough cleaning of the sockets and the sharpening of the threads, thanks to which the sections adhere to each other as closely and evenly as possible during the screwing process. 



The surface of the sections is cleared of corrosion and other contaminants with a strong stream of steel shot. This process takes place in a special cabin, to which the sections are delivered suspended on special hooks. 

The result of this process is to obtain elements whose surface is pure raw cast iron. 



The sections while prepared for the painting are carefully examined for minor damage, which only become visible at this stage. Damage and defects are repaired with specialized repair compounds for cast iron from reputable manufacturers, which effectively and permanently adhere to the surface. 

The repair of cavities is a very important stage, requiring the employee skill and knowledge to take special care. In the case of very large deformations caused by the poor quality of the casting, our employee will consult you to discuss the scope of the repair. You can choose to smooth the surface or leave the section in their original condition to preserve the authenticity of the radiator.  

 Painted sections and cast-iron radiator elements. 


Prepared sections are first covered with a layer of primer. After drying and hardening of the coating, the sections are returned to the paint shop, where they are painted in a selected colour/finish.  

We offer a wide range of RAL, special colours and decorative finishes to choose from. All paints and varnishes used in the painting process are properly selected for use on cast iron surfaces. 

Check out our finishes for cast iron radiators

    Radiator water tightness test after assembly, the last stage before the packaging process. 


When the painted sections are dry, they are reassembled. The configuration is agreed with you in advance, it is possible, for example, to assemble two five-section radiators from the ten-section radiator. The sections are reassembled using the original nipples. If the original nipples are damaged, we will replace them with standard ones. Each joint is fitted with a new fibre gasket, this also applies to reduction plug joints. 


The assembled radiator is tested for water tightness. The radiator is placed on a special stand, where it is filled with water. After filling, the liquid pressure increases twice, successively to 5 bar and 13 bar. Each increase in the radiator pressure is completed with a thorough inspection, the purpose of which is to detect any leaks. An employee uses a paper towel to check the surface of each rib and each joint. If a leak is detected, the leak points are marked, and the radiator is returned to the assembly station, where the necessary corrections are made. 


Ready and tested radiators are appropriately prepared for transport. The transport takes place on a pallet, which guarantees safe journey for the radiator. After the renovation process, the radiator is ready to be connected to the central heating system, or it can be filled with oil and work as an electric radiator. We provide our clients with advice on the selection of any accessories.

We will be happy to answer your questions and prepare an individual offer for you. Please do not hesitate to contact us. 

Click to go to the contact form.