Domestic Waste Heat Recovery

In the winter I keep my walking boots on top of the gas boiler...mmmm toasty warm boots
Del

When I was first married, we lived in an older house that had a small cabinet adjacent to the stove flue for setting dough to rise. You could adjust the temperature by leaving the door ajar.

In the UK, many domestic heating systems operate on a balanced flue arrangement, whereby the outgoing exhaust is used to preheat the incoming cold air. The effect is that less fuel is consumed to supply the same building heating demand compared with earlier non-balanced arrangements.

The usual way of doing it is to run the two ducts concentrically, the wall between them acting as a waste heat exchanger surface. The exhaust gases are still quite hot, though not as hot as with a non-balanced flue.

A greater level of efficiency can be achieved in a condensing boiler arrangement, which is newer than the balanced flue arrangement. The temperature of the exhaust is lowered below the point where the water in it condenses, thereby keeping even more heat within the building.

For some reason, a pot of beans on the wood stove just tastes better.

Depending on the fuel used, taking too much heat out of the exhaust gas stream can prove a bit dangerous, because as the exhaust gas is cooled, one can get a build-up of deposits in the flue which can ultimately result in a chimney fire...Which is why chimney sweeps were a required workforce in days of old...