Seven degrees. And I am not talking about outside

Just woke up. And it is cold. Seven degrees. And I am not talking about outside. I am talking about my living room. Ok, outside it is -4, and even colder.
But where did all the warmth go. In the evening, with the help of radiator on full blast, coal and wood in the open fire place I brought the heat up to 18. But all the efforts vanished.