Radiant heat is like the sun’s heat. It travels through the air until it finds an object (did you ever notice how hot the pavement gets in mid-summer?).
Typical heating systems rely on “convection”. Convention simply means that the heated air will rise, and the cooler air will fall (unless it’s forced warm air, which is driven by a blower).
Have you ever put on clothes that seemed to be cold?
How about crawled into a bed that seemed rather chilly under the covers?
That’s what happens with convective heating- the air is warm, not the surrounding objects in your home. With “warm air”, your skin is tricked into thinking that the living environment is comfortable until your skin has to give up its heat to another object!
This subject becomes physiological as well: Have you ever stood next to a glass window or door and felt the cool air against your skin?
Next time this happens, find a thermometer and go back to that window.
Unless you have a literal draft of air coming in through the jams, you won’t see the thermometer go down! That’s because your body is giving its heat over to the glass, and therefore cooling off our skin!
Remember, our skin is a breathing organism. That’s why it’s possible to feel comfortable with radiant heat at 68 F, yet feel cold and clammy with a convective heat source at the same room temperature.