With winter upon us, a “homemade” method to improve the efficiency of our radiators consists in applying a layer of tin foil on the wall behind the radiatorcovering the radiator area. But does this trick really work? Short answer: yes, can offer a benefit to heat domestic environments more quickly and for longer and possibly save a little on the bill. So much so that ENEA itself – the national agency for new technologies, energy and sustainable development – includes this “trick” in its decalogue of advice for saving on heating: «It’s good (…) to insert reflective materials between the wall and the radiator: even a simple sheet of tinfoil helps to reduce dispersion towards the outside».
But why does tin foil help the radiator heat a room faster and for longer? It’s not a trivial question. In fact, it seems a bit like a paradox if we think that tinfoil sheets are made in aluminumwhich is a material that conducts heat well. Well, how does a good thermal conductor avoid heat loss? Usually to retain heat we want thermal insulators, not thermal conductors!
The answer lies in the fact that there are different ways in which heat travels through space. In fluids, such as air or water in a pan, the best known way is undoubtedly the convection. It works like this: the air that warms up expands, thus becoming slightly thinner. Consequently, it moves upwards and in its place colder air is introduced from the surrounding areas, ready to be heated and rise, while the air that has already risen cools, compresses and descends again, thus closing the cycle.
However, not all heat is transmitted this way. Another method is theirradiationwhich unlike convection does not need a fluid but works through the emission of electromagnetic waves. In our case, the hot radiator has a certain temperature and for this reason it emits infrared rayswhich we perceive on our skin as heat. What aluminum does is not hinder heat loss by convection, but rather hinder heat loss by radiation.
In fact, aluminum is highly reflective in the infrared band. In this case, reflects 93-94% of infrared emitted by a turned on radiator. In other words, aluminum creates a kind of small-scale greenhouse effect: it reflects heat into the room that would otherwise have gone to the wall and dispersed outside the room.
But be careful, we should not expect a dramatic increase in heating efficiency (realistic values could be a few percentage points): we are still talking about a do-it-yourself home method. However, the effect is there and the difference can be felt: the room warms up a little sooner, it stays warm a little longer and consequently the heating can be kept on for a slightly shorter time, with a possible economic savings.
To have a more significant effect on the efficiency of our heating (up to around 10%) we can use heat-reflective panels to be applied behind the radiators, which are composed of two layers of aluminum separated by airan excellent thermal insulator (it’s the reason why it’s hot in igloos) which prevents heat from being absorbed by the wall. For greater efficiency, more serious insulation methods will have to be used, such as windows with double or triple glazing or the “thermal coat”.
