Looking to replace a dirty old copper tank with rock wool lining with a small "undersink" style water heater to be mounted on the wall. It needs to provide hot water on demand for 1 hot tap in the bathroom, and 1 hot tap/mixer tap in the kitchen - both on the same floor.


Any help would be greatly appreciated!



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alot depends on how cold your incoming water is in the coldest days of winter. that type heater is rated by deg temperature rise in gallons per minute.
so if your incoming water on the coldest days is 50 deg F and you want to raise it to 125deg F that is a 75 deg increase. if you open both hot water faucets full blast you may be looking at 3 gallons per minute (or more) at a 75 deg F rise. this of course is the maximum demand. you need to decide if that will ever happen or will the maximum demand be somewhat less..

Packy thanks for that. It is a bit hard to say - the coldest of days in UK are about 32F or a bit less if that gives any indication of what the water temp would be.

Alternatively I was thinking this might cut out that concern as it appears to heat the water as and when you need it



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here in new england we bury our water pipes at least 3 feet below grade. this keeps them warmer than if they were 1 foot from the surface. not only that but they would freeze at that depth. so, how cold your pipes get in the winter depends on their proximity to the cold air.