Australian Passive Solar Home

You may be tempted to place a hand on an interior house surface to see if it cold or hot. For example, is the thermal mass of the concrete floor cool or warm? However, using your hand is not an effective way of judging temperature.

Imagine two objects at room temperature. They are both empty mugs – but one is metal and the other, ceramic. The metal one will always feel cooler to touch than the ceramic one! That’s because metal is a better conductor than ceramic and so when you touch the metal mug, heat flows from your hand to the mug. You perceive that as the mug being cooler – even though it is not.

Therefore, the temperature you feel when you place a hand on a surface is much influenced by the conductivity of the material, not just its temperature.

Using your hand can also result in misconceptions. For example, someone once commented that the water tank (thermal mass) in our lounge room would be like a block of ice in winter, sucking heat out of the room. His rationale? When you put your hand on the tank, it always feels cold. But of course it will feel cool to touch, even if its temperature is a little above room air temperature, so it is actually heating the room.

Use a thermometer with a remote probe, not your hand!