About Radiant Heat

In a resting position the human body will produce about 400 Btu's/hour. This is about 300 Btu's more than we need to survive.
In order to "feel" comfortable, we need to shed these extra Btu's. A heating system is a mechanism is which we control the rate excess heat is lost.
The slower we lose heat, the warmer we feel.

In order to heat a space, something within that space has to be warmer than the desired space temperature (hot to cold).
In a forced air environment, the air coming from the duct is between 120° and 140°, assuming a 72° desired room temperature.
In a radiant floor system the floor temperature is between 72° and 85°, assuming a desired 68° room temperature.

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Heat Transfer
All forms of heating work on three basic modes of heat transfer: Convection, Conduction, Radiant.
Convection Heat Transfer is the most familiar type of heat. All forced-air systems are convective heat transfer systems. This includes hydronic baseboards and fan coils.
Conductive Heat Transfer is energy moving through an object. Place a metal pot on the stove and in a few minutes the handle is hot.
Radiant Heat Transfer is the exchange of energy from a hot source to a cold source. The sun is typically used to illustrate this mode of transfer.
Regardless of the type of heating system used, all follow one basic rule. Hot always moves to cold. Place your hand under a lamp and your hand begins to get warm. This is because the lamp is hotter than your hand and is trying to lose energy to its cooler surroundings