Heat the Air, or the People?

Most modern heating systems are designed to make the air inside a building warm. If the heating is on often enough this will also warm the materials that make up the building too. The idea is that warm air plus warm building surfaces makes for warm people.

Heating the air is often called space heating.

Heating the air works great in a modern building that is well-insulated, draughtproofed, and either used most of the time or made of modern materials that warm up quickly. It’s less good in buildings where cold air can find its way in easily, because the heat is lost quickly and the air movement causes draughts that make people feel even colder. Heating the air can work in stone buildings, but stone is very slow to warm up, making it very hard to warm the people this way unless the building is in high use. If the walls stay cold, that makes the people inside feel colder. Building users will often try to compensate for this by turning the heating up, but if this makes the draughts worse, it doesn’t help. It’s also expensive.

There are other ways to heat a building that don’t attempt to heat the air, although they will heat it some as a side effect.

The first way is to use radiant heating to raise the perceived surface temperatures around the people, making them warm that way. It is a bit like having a bunch of mini-suns in the space. This works if it is well-designed - the radiant heaters need to throw the heat the right distance for the size of the space, cover the space well, and not be blocked by large pieces of furniture. They are often mounted high up or on ceilings for this reason. Radiant heaters and infrared heaters are the same thing.

The second way is to place people right up against something that’s warm, but not so hot that’s unsafe or uncomfortable. Hot water bottles, heated car seats, and cats are all common ways of achieving this effect. There isn’t a common name for this, but we think of it as contact heating.

Of course, all heating methods do a bit of everything - heating the air will eventually heat even stone, and radiant and contact heating will heat the air some.

It’s good to understand what your current heating system is designed to do, especially if you have an older building, because it might work very differently than at home.