Minimum Floor Temperatures

Worried that your underfloor heating system will be too hot to walk on?

In fact, it’s a pretty simple matter to make sure that the floor doesn’t get too hot. The system will have a thermostat with a sensor embedded in the floor, and it can be programmed to switch off the heating system if the floor temperature gets above 29°C.

A less well understood issue is maintaining the minimum floor temperature. Here’s the problem:

Imagine that your heating system keep your home warm all night. In the morning, the sun comes up and shines through the living room windows, heating up your house. Because the room is now warm, the thermostat turns off your heating system. While the room is warm all day, the floor isn’t being heated so it slowly cools down.

When the sun goes down at the end of the day, the air temperature drops quickly so the house suddenly gets cold. The thermostat senses this and switches on the heating system.

The heat pump starts up, but because the outdoor temperature has dropped, the heat pump has to work much harder to get the floor back up to temperature. It takes too long to heat up the floor slab, so while you’re having dinner and watching the evening news the floor isn’t warm enough to heat your house.

So how do we get around this problem?

We have to set a minimum floor temperature to stop the slab from getting too cold. That way, when the sun goes down the heat pump can get the concrete floor slab up to temperature quickly enough so that it can warm your room.

You might be asking: If the floor slab has to stay warm during the day, won’t that overheat my house?

The answer is, yes, it’s possible! That’s why it’s important to have your heating system properly designed by an expert. It’s not enough to have an installer rely on rules of thumb to size the equipment.

If you’re getting a heat pump system installed, ask to see the heat load calculations which show how much heat is required and how the pipework has been designed to match. Once the underfloor pipework has been installed and your concrete floor slab poured, it can’t be fixed so you only have one chance to get it right!