Hot but no hotter.

It's very likely that the classroom where you are working just now is heated by part of a very large central heating system. Somewhere in the school, there wiII be a big boiler where water is heated by burners which use oil or gas. The hot water is piped to radiators in the classroom. There it gives out the heat to keep you warm.

Like every workplace, a school has to be run at a comfortable temperature. In fact, the law sets a minimum classroom temperature. Architects have to do some careful calculations when they are designing a school. They have to make sure that the boiler can supply Enough heat to keep aII the classrooms at the correct temperature even in the coldest weather. Heat energy is measured in kilojoules’:

• 4.2.kilojoules is the amount of heat energy needed to heat up 1 kilogram of water by 1 'C.

A small school will need a smaller boiler than a large school.

You may wonder why different sizes of boiler have to be used. After all, ail schools have to be heated to the same temperature. The answer is that, in a large school, there are more rooms, more radiators and so more water to heat. If the boiler isn't big enough it won't be able to heat the water quickly enough and the rooms will be cold.

But as you well know, the room can get too hot. If the radiator keeps pumping out heat energy, the room temperature will keep going up, and so will yours. That wastes heat (and money) and makes the room uncomfortable. That's why thermostats are used. Their job is to keep the temperature of the room steady. They contain sensors which detect whether the room is hotter or colder than it should be. When the temperature is too high, thermostats shut off the flow of hot water, turning it on again when the temperature gets Too low.