The brick works as a thermal battery - if it's cold, you're heating your house, and the intermittent exhaust is keeping the brick warm. If you're not heating, well it's not cold so the brick temperature doesn't matter much.
Increasing thermal inertia in our housing is a great idea. It saves energy.
But: we need to build low energy housing to manage climate change. That means there is very little waste energy available. Last house we built was 230m2, family of 5, had a total energy consumption, including everything from heating to water to home electricity, sitting at 8000kWh/y. That's in southern Sweden (N58deg).
There is no relevant amount of waste energy available.
This is the kind of housing we'll need to meet future energy targets.
