When talking heat there are three ways heat or cold moves through space. Knowing these ways is important because it determines what kind of insulation you use or on the opposite end what kind of heating to use.
Convective heat transfer is what most of us are familiar with. This is how our forced air heating system or our baseboard system transfers energy (heat) to a space. Air moves over a heating element, becomes warmer and expands into the space. In a forced air environment, most of the hot air is at the ceiling, much the same way the hot air balloon rises, so will the warm air in a room heated with forced air. Convective heat transfer is the least efficient means to transfer energy.
In terms of insulation convection happens when thee is a crack in the window or a hole in the insulation. Hot and cold air passed through the space via convection. Stop convection by sealing all holes in the house, aka seal the envelope.
Conductive heat transfer refers to two surfaces touching each other. Imagine a metal pan on the stove. If your hand is positioned an inch above the hot handle, you really won’t feel much from the handle, and you can keep your hand there as long as you wish. But, when the handle is touched, your hand instantly begins to feel hot. This is conductive heat transfer. The pot is giving off the energy (heat) in the handle to your hand in a very fast, efficient manner.
Conduction is one of the more efficient modes of heat transfer. In home insulation you reduce it by putting bad conductors between good ones. Wood conducts heat well so you would put a material like foam that conducts poorly over the wood studs to reduce heat loss.
Radiant heat transfer is the best because it isn’t slowed down by air. Radiant energy is only felt when the energy wave strikes another surface. This means the surrounding surfaces all reach set temperature. By enclosing your body by warm surfaces, we can better control how our bodies lose heat. Radiant floor heat means better comfort with higher efficiency.
To reduce radiant heat loss the best materials are ones that literally reflect the heat. These are foil covered insulation and types of silica that also reflects heat.