In winter we can remain comfortable in lower air temperatures by increasing the share of radiation or conduction in the total heat transfer of a space by using underfloor hydronic heating. Radiant heat can keep people comfortable at a lower air temperature.
The obvious example of radiant heating is direct sunlight. In spring or autumn, we can sit comfortably outside in the sun wearing only a T-shirt, even if the air temperature is relatively low. A metre away, in the shade, it can be cold enough to need a jacket, although the air temperature is more or less the same. In summer, we prefer the shade as it screens excessive radiant heat.
The difference is explained by the radiant energy of the sun, which heats the body directly when it is exposed to sunlight. The use of radiant underfloor heating creates a higher “radiant temperature”, allowing thermal comfort at a colder air temperature in winter, reducing the energy costs required for heating.
That’s why a radiant underfloor heating system can create very comfortable indoor air temperatures in winter with the wall thermostat set a couple of degrees lower 19C than an equivalent size forced air heating system 22C.