Heating a house is a lot larger task than heating an insulated cylinder of water.

‘Hydronic’ space heating is possible, but not very viable unless integrated with another technology – the problem being, that space heating is mostly required in Winter and at night, precisely at the wrong times of year and day!

These factors mean that an enormous volume of hot water storage (several thousand litres) would be necessary for space heating purposes, and this puts space heating out of the question.

In practice you can provide a significant amount of supplementary heat in the spring and autumn (and some people have implemented such systems). You would also need to fit many more solar tubes to your roof.

By contrast, solar water heating is effective even in Winter, as the amount of heat required is considerably less than that required to heat a house and it can be effectively stored throughout the night for use the next day.