Yes - they are just a basic heat exchanger at about 60% efficient - you can demonstrate that from basic physics
They can recover heat from the waste - it's not that easy to get that heat anywhere useful, but putting it into the cold feed for an electric shower works OK (you get a slightly better flow rate) as does putting it into the cold feed to a mixer shower (you can use "warmer" cold to replace some of the "hot")
Given that showers are not particularly long affairs (unless you're a teenage girl) then their recovery potential is "low" and they would take a considerable amount of time to recoup the capital and installation cost and the carbon used in manufacture.
For those that are pretending to be "deep green" really - better to spend the money on more wall or roof insulation or some draught proofing - more effective return on the investment (in every sense)
Yes - they are just a basic heat exchanger at about 60% efficient - you can demonstrate that from basic physics
They can recover heat from the waste - it's not that easy to get that heat anywhere useful, but putting it into the cold feed for an electric shower works OK (you get a slightly better flow rate) as does putting it into the cold feed to a mixer shower (you can use "warmer" cold to replace some of the "hot")
Given that showers are not particularly long affairs (unless you're a teenage girl) then their recovery potential is "low" and they would take a considerable amount of time to recoup the capital and installation cost and the carbon used in manufacture.
For those that are pretending to be "deep green" really - better to spend the money on more wall or roof insulation or some draught proofing - more effective return on the investment (in every sense)
