Recirc strategy for tankless

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Nukedaddy

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I have a gas fired instantaneous heater. On a 25 year old slab house with un-insulated underground piping, all copper. Takes way too long to get Hot to the master bath.
Couple of ways I thought about. Laing small circulator from hot to cold under cabinet on adjacent lavatory faucet in master bath. On a timer to not run all night and with a thermostat so as to not fill cold water lines with hot water (at least not real hot water).
The deal is though, that seems to mean that the 200KBtu waterheater would be firing almost continually at minimum fire (while the pump is running) to simply make up for heat loss to the ground during the day.

Would a better deal be to get a small electric tank point of use type waterheater, put it in the line in series with the tankless, set it's thermostat at 105 F and let it cycle just for the purpose of keeping the line to the far end of the house hot? I would set the flow rate of the Laing circulating pump low enough that the tankless would not turn on unless someone actually opened a faucet for using hot water at a reasonable rate.....something over 1/2 gallon a minute or so. If the circulation rate was only a 1/4 gallon a minute, the tankless stays off and the electric handles the heatloss with its thermostat regardless of flow.

Opinions?
 

phishfood

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A circulating pump under said lavatory, with either a sensor eye that picks up movement, or a push button, that will activate it. Then a thermostatic switch to turn it off when it senses a temperature rise. This whole system is available as a package, no need to piece it together. The biggest problem will be getting power to it.
 
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