Replace radiator

Radiator replacement - for home improvement

Radiators are often overlooked during renovations. The old radiators are often not only clumsy, but also a risk of possible, age-related leaks. Also, old radiators are not always mounted according to the criteria of a modern, energetically optimized design.

With our instructions below, not only old radiators can be replaced: The detailed article on radiator calculation also gives an orientation framework for radiator purchase.

Calculate heating: Radiators made to measure

Radiator calculation: The radiator should fit the room. This actually very simple insight is often neglected in the energetic renovation. With this manual, even do-it-yourselfers can easily calculate the required radiator size.

Calculate radiator

Radiators: types at a glance

Radiator types, which go beyond the standard construction, can be found, for example, in bathrooms or very tight spaces. Compact radiators, special bathroom radiators and much more we present in this article.

Radiators and radiators: Type overview

Thermostatic valves: Temperature controller in detail

Thermostatic valves regulate the room temperature directly at the radiator by mechanical means. Electronic thermostatic valves are an energy-saving solution of the 21st century. We introduce both types and explain advantages and disadvantages.

Radiator thermostatic valves at a glance

Installation of flat radiators and panel radiators

Replace radiator: replace

In old buildings you can often still find them: The large, cast-iron monsters from the past of heating technology. Cast iron radiators have the disadvantage over modern flat radiators that they do not efficiently utilize the space available for the radiator.

On the other hand, the old valves often no longer work reliably, the radiators are often calcified, leaks on the old flanges and seals are possible.

The replacement of old radiators should not be missing in an energetic renovation of a house or apartment. With this guide, savvy do-it-yourselfers can easily replace even old radiators with modern variants.

Buy radiators with a sense of proportion and expertise

Before buying new radiators you should first calculate the number and power of the required radiators. After these results, the new radiators will be bought.

Compared to cast iron radiators modern flat radiators have the advantage that they have arranged in several levels heating elements. A modern flat radiator with three levels measures only one third of an old cast iron radiator with conventional ribs.

In addition, modern panel radiators convection optimized, i. the flow and outflow of the room air has been improved by a special shape compared with cast iron radiators.

Replace heater: overview

Warning and safety information

Do-it-yourselfers should not dare too much: The connection of a heating system is not without reason part of the installer training!

In particular, the transitions, sleeves and flanges should be finally tested by a specialist. Consequential damage due to escaping water is often not covered by insurance in case of self-construction.

Therefore: In case of doubt always ask the specialist!

Replace radiator: replace

4-fold radiator.

Replace radiator: heating

6-fold radiator.

The somewhat misleading designation "quadruple" and "sixfold" does not refer to the heat output of radiators, but to the possibilities of connection to the heating system.

Quadruple radiators are the older version. Here are the connections at the four corners of the radiator, the valve is attached top right or top left. This type of radiator is particularly suitable for replacing existing radiators. Radiators of this type of connection have been installed since the 1960s, especially in old buildings.

Six-fold radiators are preferably mounted in new buildings. These can also be connected to the bottom, and the installation of concealed electronic heating valves is also possible. When replacing radiators in new buildings so 6-fold radiators should be used.

Occasionally, systems for 6-fold radiators are also used in fully renovated old buildings with new screeds. However, this is more the exception.

Materials and tools for the radiator connection

For quad radiators the following parts are required:

  • radiator
  • thermostatic valve
  • lockshield
  • Mounting (radiator rail or base and standpipe)

For six-fold radiators are additionally required:

  • valve core
  • thermostatic head
  • Hahn block

Generally needed:

  • Bleed keys or automatic bleed plugs
  • heater rosettes
  • Schnappfix (pipe lining)
  • possibly S-connections for inappropriate connection distances
  • Hemp and sealing paste


  • Fitting pliers (pipe wrench)
  • screwdriver
  • Cavity dowel (for fixing to plasterboard)
  • Concrete dowels (for fixing to walls or concrete walls)
  • spirit level
  • ruler
  • pencil

Mount radiator (both types)

First, the heating system is switched off, disconnected from the mains and drained the water from the heating system completely. Then the old radiators can be dismantled.

The new half-inch connections are now screwed to the connections in the wall. Depending on the system, these are either screwed down (six-fold radiator) or on the sides. If the new connection does not fit spatially, so-called S-pieces can be used. A connection with flexible hoses is possible, but should be avoided if possible in the interests of durability and heat loss.

Mount with sealing hemp

Heating connections must remain tight for decades. Therefore it is recommended to mount the threads with sealing hemp and sealing paste. Hemp is used for centuries for line sealing. First, some longer fibers are loosened from the tufts of hemp, these are wound tightly around the thread to be sealed. Then some sealing paste is applied. This keeps the hemp in place and additionally seals. Then the thread is screwed to the heating connection.

Secure radiator brackets

Depending on a suspended or fixed mounting, the mounting brackets are now attached. Usually this is a fixing instructions. It is important, above all, that the radiators be securely and firmly pegged to a durable wall.

Connect radiator

Then the radiator is hung on the attachment. Now the flow and return are screwed (always work with hemp and sealing paste!):

Depending on the design, the thermostatic valve is placed between the flow connection and the radiator (quadruple radiator) or the supply line is screwed directly to the radiator at the bottom (six-fold radiator). Then the thermostatic valve is screwed in and provided with the thermostatic head.

Finally, the return is screwed, here the water can flow back from the radiator in the heating circuit.

Replace radiator: radiators

Sixfold radiator: connections and valve.

Replace radiator: heating

Quadruple radiator: connections and valve.

Check heating system and start up

Once all radiators have been mounted, all screw connections should be checked again. If everything is tight and apparently tight (do not forget the dummy plugs!), The heating system can be filled with water.

Each heating system has a pressure gauge on the boiler: If no pressure builds up here when filling the water, normally the pressure for heating systems is at min. 1 to max. 3 bar, something is leaking!

Thereafter, all the thermostatic valves on the heaters are opened: Does the water rush into the empty radiators? Very important: is it in there? Everything tight? In the positive case, the pressure at the boiler can now be increased to the standard pressure (cold water) for the operation of the system.

Now the heating system is switched on, the breather key is used. Starting at the highest point of the heating system (in homes this is the highest above the floor mounted radiator or the end of the pipe section) the individual radiators are carefully vented until water shoots from the vent.

Regular pressure checks are now announced: If the pressure now remains constant over the following days, everything was done correctly!

Photo credit:

  1. Replace radiator: © Hornbach
  2. all other pictures: ©

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Video Board: How to Replace a Radiator (Complete Guide)