Hi sirs
There are many bathroom(as business) in our place. Most are using coal boiler. the waste water can reclaim heat by heat pump. And 1kwh can produce hot water as 2 kg coal does which is a good deal for money and environmental protection. I'm not sure if there are heat pump product for this application. I know there's no in my country. it's maybe a business chance.
welcome any input

regards
LC