Which type of wall is likely to retain heat longer?

The 12" Double Brick Wall is likely to retain heat longer due to its greater mass and thickness compared to the other wall types listed. Thicker walls have a larger volume of material, which allows them to absorb, store, and release heat energy more effectively. This property is known as thermal mass.

Brick is also a good thermal mass material, which means it can absorb heat during the day and gradually release it at night, helping to stabilize indoor temperatures. The double-brick configuration adds an additional layer, further enhancing the wall's ability to retain heat.

In contrast, the other wall types, while they may have their own benefits, do not have the same level of thermal mass as the 12" Double Brick Wall. The 9" Brick Wall and the 9" CHB Wall are both thinner, resulting in lower heat retention capabilities. The 7" Concrete Wall, although also offering some thermal mass, is not as effective in this context as the thicker double brick. Therefore, the 12" Double Brick Wall stands out as the most effective option for heat retention.