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Extending an existing underfloor heating system

As many householders take the decision to improve instead of move the issue of extending their underfloor heating arises and the installer must be aware what needs to be considered.

As with any extension to a heating system the first thing to discover is whether the current heat source is large enough and how to route any flow and return pipe work. Additionally, with underfloor heating consideration must be given to positioning of the manifolds and the route from there to the underfloor heating zones.

There are two basic methods of adding capacity to the system:

  • Using existing manifolds
  • Adding new manifolds

Using an existing manifold may remove the necessity of installing new flow and return pipe work. However, this may not be the case as the larger the manifold the bigger the feed pipe to it needs to be. Continental's advice is that 22mm diameter pipe should be used for manifolds up to eight zones and 28mm pipe for manifolds over eight zones. Routing the underfloor heating pipe to the new area may not be possible, or result in long feeds by comparison to the heating loops. Also, to ensure air is removed from the system the manifold must be located above the heating pipe work. A downstairs manifold should not be used for the upstairs underfloor heating.

Space can also be an issue when using an existing manifold. The smallest expansion section is two zones. Blanking plugs are available to shut off any unwanted manifold zones.

To add the manifold extension manifold couplers are required and can be put at either end of the manifold, although adding them at the mixer/pump end of the manifold will require modifications to the flow and return pipe work. Adding the new zones at the end set end of the manifold is more usual. To do this the manifold must be sealed off using the isolation valves at the pump end of the manifold. Pressure can then be reduced in the manifold, prior to dropping the water out of the manifold through the end set on the lower manifold rail. The water in the current underfloor heating zones will not leak out as the manifold is above the underfloor heating pipe.

Extending an existing underfloor heating system
Continental Underfloor company brochure