Underfloor heating

I overheard someone moaning about the running costs of underfloor heating and I couldn’t resist chipping in. “Underfloor heating is generally cheaper to run than radiators because it uses lower temperatures so, if you set it up correctly, the boiler will stay in the condensing mode and deliver efficiencies in excess of 90%.” I said or words to that effect.
“Well I have switched mine off after I got an electricity bill for over one thousand pounds. My central heating never cost me anything like that.” replied the man.

That word ‘electric’ changed everything. In the UK electric underfloor heating is usually a tile warm up system that is used in kitchens and bathrooms. It is not the same as warm water underfloor heating but is sometimes miss sold as a total heating system. It works in kitchens and bathrooms because it responds quickly to warm the tiles so you set the timer for an hour or two in the morning and the same in the evening. It turned out that his builder had installed electric underfloor heating under the entire ground floor. This was not a new build or an extension so I wondered what sort of insulation they had used. After a little bit of questioning it turned out that the builders had simply stuck the underfloor heating mesh down on the existing screed. No wonder they didn’t go for warm water. To make matters worse this house was thirty years old so was very unlikely to have any insulation on the ground floor. The heating was simply warming up that great mass of concrete and disspaeraing into the ground. A very small part of it was coming up through the tiles and wooden flooring.

I asked him whether he or they had ever mentioned insulation and he told me that he had but they told him “Heat rises”. They were obviously paying attention during their school physics class but may have dozed off during the bit where the teacher said heat will always move from hot to cold and never the other way. In other words until the slab of concrete reaches the same temperature as the tiles the tendency will be for the heat to travel at a faster rate down into that concrete than up into the tiles.

“So that means I need to hack up the entire ground floor to out down insulation?” said the man.

I gathered it was more of a statement than a question.

"The other alternative is to not have under floor heating" I said which is effectively what he has now decided.

“That can’t be right” He said.
“What can’t be right?”
“Me not being able to have underfloor heating, it is wrong, there should be a way.”
“There is” I replied
“What is it?” he asked
“Insulation”