Breeze blocks

What is the best brick for energy efficiency?

I have planning permission for a new bungalow in Bucksinghamshire. I have a building advisor who has helped me on various parts of the construction and also completed the building specification and build regs drawings. I am at the stage of selecting a builder. I am keen that the new house is as energy efficient as possible, and have decided on an air source heat pump solution.

My building adviser has specified standard ‘Celcon’ blocks for the inner walls. Outer walls to be standard brick. I understand that these blocks are made of ‘aircrete’ and have a very low thermal conductivity.

The builder has indicated that this type of block is unsatisfactory, as they are prone to cracking as they dry out. He would wish to use more traditional ‘fibre light blocks’ from Plasmor. These blocks have a higher thermal conductivity, but are not prone to crack. If I use them, the house will require more energy to keep it  warm, such that I will need an external air source heat pump, rather that the internal Nibe unit currently planned.
Which blocks should I use?

I prefer dense concrete blocks. They are stronger, better for sound insulation, and have a much higher thermal mass. If you have insulation in the cavities, which I presume you will, then the house will not require more energy to heat. The higher thermal mass of the concrete blocks will help smooth-out temperature fluctuations.

I disagree that heat pumps are “energy efficient”. They use electricity as a fuel, which is three to four times more expensive than gas or oil. As discussed here:

air heat pumps article