Venting the floor. Proven methods

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Airing up of the underfloor heating system is a normal situation that occurs during its operation. When the heating system is aerated, the heating capacity of the entire system is reduced.

What are the symptoms of a leaking heating system?

The main symptoms of an aerated heating system are:

  • a decrease in heating efficiency,
  • noises and other audible symptoms.

Causes of a vented underfloor heating system are:

  • incorrect or too fast filling of the heating system;
  • inaccurate initial bleeding of the system; it occurs right after the installation is made;
  • air may be sucked into the system through micro leaks e.g. on connecting elements;
  • air can penetrate from outside if the pipes in the system were made of plastic without an anti-diffusion liner;
  • air can precipitate out of water under the influence of temperature;
  • hemp bundles that have been left in the system rot and produce methane gas.
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Photo by volodymyr_vorona from: Freepik.com

How to vent floor heating?

An underfloor heating system is usually made with a manifold that serves several loops of underfloor heating. When deaerating underfloor heating, it is important that the manifold is located in relation to the heating system, i.e. the manifold is situated

  • on the same or higher floor as the underfloor heating system – most modern installations;
  • below the underfloor heating system.

Bleeding the system when the manifold is located on the same or higher floor

To bleed the system, use the pump and vents installed at the manifold:

  1. Turn on the floor heating pump to the highest possible operating gear.
  2. Turn off all the valves on the return loops, leaving only the valve to be bled open.
  3. Open the water valve and wait 10 – 15 minutes until water flows through the vented loop. During this operation you may hear a swishing sound, which disappears.
  4. This should be repeated for all underfloor heating loops.
  5. The more air is removed, the more the water pressure in the system will decrease. If necessary, water should be added to the heating system after venting.
  6. In the case of a mixed system (underfloor heating + radiators), radiators must be bled after the bleeding of the underfloor heating.
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Photo by volodymyr_vorona from: Freepik.com

Venting the system when the manifold is located below the floor with underfloor heating

Venting such a system is a bit more difficult and requires more work.

  1. The floor heating pump should be switched off.
  2. It is necessary to unscrew:
    1. valves to cut off the pump,
    2. valves at the manifold,
    3. valves on heating loops,
    4. all air vents.
  3. Flexible pipes previously connected to the sewerage system should be connected to drain valves at the return bar on manifolds. On the other hand, flexible hoses should be connected to the drain valves at the supply beam to the water system. You must be able to see water flowing through each flexible line.
  4. Open the first heating circuit and run water through it until there are no visible air bubbles.
  5. This is how you should proceed with the bleeding of all underfloor heating loops.
  6. If all heating loops have been bled, close the drain valves at the joists on the manifolds and disconnect the hoses.
  7. Open the valves at the manifolds on the beams and at the pump so that water can flow freely.
  8. Open the air vents in the manifold and remove any air left in it.
  9. Open the heating loop and turn on the pump.

Venting the underfloor heating system is a very labor intensive activity, but is necessary for the proper operation of the system.

Peter Bowers

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