Retrofit flue heat recovery?

[Gooman]

We have a warm air heating system (Johnson & Starley J50). Before anyone kicks off suggesting that we rip it out - we really like it and aim to keep it.

 

I'm curious though about the amount of potential heat recovery that could be gained from the flue. There's a big (200mm?) asbestos cement flue that runs vertically from the boiler, through the loft and to a ridge terminal. The asbestos cement flue has been inspected by a specialist surveyor and it's all safe as long as it's not cut or drilled.

 

The flue does put some noticeable warmth into the loft.

 

Is there any feasible way of retrofitting a heat recovery system that would fit around the flue, providing an additional heat source to our hot water cylinder? There is no in-flue system available from the manufacturer.

[SteamyTea]

One problem of cooling a flue is that it can affect the gasses being extracted.

Basically it makes them denser, so do not rise so fast.  This could cause CO to be released into the building.

 

I do wonder, as you already have large vents and pipework around the house, it some sort of ventilation heat recovery could be easily incorporated.

 

I lived in a house with forced air heating and did like it, except when my girlfriend was typing in her office/spare bedroom, the noise coming into the main bedroom was terrible.

Have heard that conversations can carry down the ducts quite nicely too.

[Gooman]

Having looked into it a little further, it looks like the best option would be to replace the existing warm air boiler with a more modern version. The existing J50 is reportedly around 80% efficient, whereas the more modern versions are up to 98% and include PFGHR and are a straight retrofit.

 

The only point where we've had sound carry is through the return air vents as the one on the landing connects directly to the boiler cupboard, which has vents into the hallway and the kitchen. But we've been told by a warm-air specialist that we don't need both of the hallway and landing ones, so we'll block the landing one which will solve the sound problem.