How do existing radiators and underfloor heating work together?

Underfloor heating and radiators are regularly used together. Underfloor heating systems that are retrofitted into rooms outsell new full installations by far. Many of our customers have retro-fitted underfloor heating on the ground floor and radiators on the upper floors, and vice versa.

Keeping your existing radiators in upstairs rooms is certainly a proven cost-efficient alternative. Your existing boiler (if suitable) should provide hot water for both your underfloor and conventional heating systems. It should also be able to provide enough hot water for showers and baths, dishwashers etc.

How does underfloor heating connect to radiators


The diagram above shows an outline of a four-circuit underfloor system that connects to your existing radiators and heating system.

The boiler shown feeds three water circuits, each has hot water going out and a circuit to return the cold water back to the boiler. The water flow in each circuit is controlled by a motorised valve.

Circuit 1. Is a hot water circuit from the boiler. It goes directly to the existing radiator system and then returns to the boiler.

Circuit 2. Is a second hot water circuit to an existing cylinder. This is fed directly and then returned back to the boiler.

Circuit 3. The underfloor heating system has a new water circuit from the boiler. This third circuit has a pump pack fitted. A pump pack usually consists of a pump and a set of valves that are controlled by the heating system management controls. (See Image below) This circuit feeds a manifold which splits into four zones or rooms. You can have a single circuit up to a maximum of twelve depending on the manifold.

Your hot water supply and radiators use a timer and temperature controller. The underfloor heating system uses a new set of programmable room thermostats. You can add wiring centres to your heating system, these can control the boiler and a set of motorised valves that allow hot water to enter the radiators and underfloor circuits.

Larger view of an underfloor heating pump pack and manifold
Outline of an assembled UFCH Pump Pack