Underfloor heating, turned on its head

It is well-known that warm air rises and cold air falls, so radiant cooling systems make sense to be installed at ceiling level. Jupiter have experience in installing radiant ceiling and wall cooling and can also advise on associated control systems.

Underfloor heating pipework can also be used for cooling, however your choice of floor finishes must be carefully considered. This is because there is a risk that condensation can form on cooled floors, resulting potentially in damage and possibly a slip risk. It is therefore important that the dew point and relative humidity are kept in check. Luckily there are some simple ways around this problem, such as dew point sensors.

Our experience from previous projects has demonstrated that chilled flooring systems can offer on average a 5°C reduction in temperature (compared to outside temperature) even without humidity control using our cooling system. Mechanical Ventilation with Heat Recovery (MVHR) controlled environments assist in keeping steady Relative Humidity (RH) levels which in turn prevents possible condensation problems.

Cooling source

Typically ground source or air source heat pumps are the perfect companion when it comes to providing chilled water for the underfloor heating circuits in the summer months. Modern thermostatic control systems such as Danfoss and Honeywell supply automatic switch systems that reverse solenoid operation so that floor circuit valves open when a cooling demand is called for (in the summer) or open when a heating demand is called for (in the winter). Compatible heat pumps should be able to send heating / cooling signals to thermostat wiring centres.

Condensation prevention

As our manifolds are manufactured from stainless steel they are the first part of the system where condensation would form. Dew point sensors can be fixed to manifolds and linked to a shut off valve to protect delicate floor finishes.


With an 18°C – 20°C flow temperature (21°C -23°C return), specific cooling capacity through a floor with a hard finish such as tile / stone is typically in the region of 30-40 W/m².

For wet rooms such as bathrooms, it is generally recommended, for comfort reasons, not to cool the floor, but to close this circuit during cooling. This can be done manually at the valve or automatically via a zone valve. Zone valves must be able to open for cooling operation. Therefore, check whether the heat pump can also switch this contact.

System Vertical cooling installed via the use of system vertical

Due to the natural limitation of cooling output, a floor system may not always be able to cool the room temperature to a fixed value. The flow temperature should therefore be regulated to avoid the risk of condensation. Some heat pumps have the ability to provide weather-compensated cool water as well as weather compensated warm water. Such a heat pump provides the optimum solution.

The graph below shows that in summer the moisture content of the air reaches just over 9g/kg air. This water vapour content results in a dew point of approx. 13° C (at a relative humidity of approx. 55%). It is recommended to set a flow temperature of approx. 20° C here. At an air temperature of 25° C and a relative humidity of 70%, the dew point is only reached at a temperature of 19° C. On average, the house has a relative humidity of 50 - 55%, so that a dew point undershoot does not occur. The upper humidity of 65% should not be exceeded according to EN 814 T1 - T3 and DIN 1946.

Moisture Content to Dew Point.png

The humidity in the building depends on the outside air humidity and the internal loads (i.e. additional humidity introduced by bathroom operations). For a few hours a year, the outside air humidity of 13 g / kg (18° C dew point) is exceeded. For pipes laid in the screed, it is possible to lower the flow temperature by approximately 1°C to 2°C by heating the water between the mixer and the distributor. With dry installed systems the flow temperature should not be lower than the dew point temperature.

If cooling it is also important to insulate primary pipework within risers as well as manifolds to avoid vapour diffusion and condensation water. Since the absolute humidity in a house is approximately the same in all rooms due to the air movement, it is sufficient to choose a common flow temperature for all rooms. With a ventilation system with heat recovery, the limit of humidity according to EN 814 and DIN 1946 can be maintained.