The sun produces massive amounts of energy from nuclear reactions and disperses the resulting energy into our solar system by radiation. A tiny proportion of this energy hits the surface of the earth, barely diffused by its journey through 90 million miles of vacuum, and onto our grateful faces, where the radiation is converted instantly to heat. A wood-burning stove works the same way.
The difference to appreciate here is with convected and conducted heat, which both rely on the movement of molecules. Central heating runs at relatively low temperatures, and while it still radiates some energy, its main effect is to warm the air and disperse heat slowly around the room through convection. If you touch the radiator, heat will be conducted into your fingers, but the main premise of central heating is that it will warm the air, which then heats your home through convection. Gradually, you, the animal, will come to no longer feel cold as the air temperature rises to roughly half the temperature of your body, which is itself, helped by the insulating effect of clothing, simultaneously generating enough heat to compensate for heat loss.
The intense heat from a radiant surface is different. Because there is no molecular exchange, energy is transferred directly through the air by infrared electromagnetic waves. Only when it hits a surface is it, like sunshine on your skin, converted into heat. Most objects emit radiation, but we experience no sensation of heat from them because our bodies are emitting radiation in equal or greater proportions: there is either a shortfall or they cancel each other out, so yield no sensory impact.
However, in proximity to the high surface temperature and the emissivity of a cast-iron or steel stove (they have roughly the same conductivity), we absorb much more radiation than we emit, thus receiving a net energy gain. For illustration, the sedentary human body produces about 500 British thermal units per hour, and a Clearview Pioneer stove, burning a kilo of wood over the course of an hour at around 70% efficiency (it’s actually a little higher!), will produce roughly thirteen and a half thousand Btu, most of which will be transferred by radiation from all the surfaces of the stove. However, the insulating effects of the firebricks at the back and sides, the ashes below and the baffle plate above means that a disproportionate amount of that energy is projected from the front of the stove. The closer you sit or stand to the stove, the more surface area you present to it and the greater the amount of radiated energy will hit your body, resulting in the maximum transfer of energy and satisfyingly high localised temperature. If we estimate that a third of the radiation is projected from the front of the stove, and half of it hits your body, the ratio of energy received to emitted by your body is 4.5.
The increase in skin temperature is intensely satisfying, in the same way as turning your face to the sun, and engenders an incomparably greater sensation of warmth than that provided by air temperature. A radiator pales by comparison; as fire guru Vince Thurkettle so lucidly puts it, “I’ve never known someone to get the same feeling by snuggling up to their radiator.” Thus, in the same way that you can sunbathe in the Alps, when the air temperature is hovering slightly above freezing, or when Bear Grylls emerges sodden from a freezing lake and strips in front of a blazing fire to regenerate body heat, you can feel intensely warm by your stove even if the air temperature is well below notional ambient room temperature.
While this is the fundamental difference in the quality of the heat from a stove or central heating, a stove, will, of course, also increase the air temperature in a room over time, through radiation, convection and conduction, but it lacks the facility of central heating to disperse the heat through separate rooms (at least without additional infrastructure; in cold countries where wet heating systems are a liability, there is significant expertise in distributing dry heat around houses).
Nonetheless, it is a simple fact that most life, from trees to lizards to hominids, prefers to experience heat through radiation, and in domestic situations, for people, dogs and cats, a wood burning stove is the best possible mimic for the natural heat of sunshine. Another reason why it’s “warmth for the wise”.