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How does a manifold work?

  • 23 November 2017

    Underfloor heating systems require a huge amount of small bore pipe. After all, the heating pipe needs to completely cover your floor area.

    Water needs to flow through all these pipes evenly so that you don’t get hot and cold spots around the house. That means we need to be able to control the temperature and flow rate of the water as it moves through these pipes.

    To do that we use an underfloor heating manifold. This is essentially two large-bore distribution tubes, each with a set of sockets to connect the smaller heating pipe circuits into.

    The hot water from the boiler (or heat pump) comes into the “flow” tube, and is distributed to each of the underfloor heating zones. The water transfers heat to the floor slab (which goes into heating your house) and then returns to the manifold and joins into the “return” tube, before going back to the boiler to be heated again.

    The manifold itself is fitted with a range of controls and valves. Each nozzle connecting to the zone circuits will have a balancing valve and a flow meter. The designer should specify to flow rate required through each circuit, based on the amount of heat required for the zone.

    During the commissioning phase, your installer will adjust the balancing valves to ensure the correct flow for each circuit. A typical flow rate is 2 Litres per minute for each floor loop.

    The flow and return tubes are also usually fitted with thermometers to you can read the temperature being supplied to, and returning from the floor. This allows the installer to ensure the correct amount of heat is being transferred to the floor slab.

    Depending on the type of boiler supplying your heat, your manifold might also be fitted with a mixing pump. Underfloor heating requires low temperature water (usually around 40°C – 45°C). A diesel boiler, for example, can’t produce water at such a low temperature.

    To provide the correct temperature, a mixing circuit needs to be installed and will be joined into the manifold. Sometimes this will include a pump.

    You also might have a set of actuating valves that can open and close the flow to each zone circuit. These are controlled by thermostats in the rooms and it means that you can individually control the temperature in each room.

    The good news is that the manifold, if properly installed, will take care of itself. As the homeowner, you don’t need to touch it! But like everything, it’s good to have a basic understand of all the different components, what they do and why they’re there.