Baumgrenze
Member
I have a recirculating hot water system with a return line driven by a Grundfos UP10 (96433899) pump. This pump can be set to turn on or off every 20 minutes. The house is a single-story, flat-roofed house on a concrete slab in Palo Alto, CA (read, a mild climate) and the water delivery lines are copper in the slab. The master bath is approximately 90’ from the water heater! Energy was cheap in 1955. The return line is on the roof under 3†of urethane foam insulation. Instant hot water is wonderful.
I am thinking about changing from a duty cycle of 5 AM to 9 AM and 5 PM to 10 PM to 20 minutes on and 20 minutes off from 5 AM to 10 or 11 PM. I believe we will find that the water temperature will not drop significantly in 20 minutes once the encasing slab is warmed and that gas usage to keep the water hot will be about the same. I am concerned that cycling the pump on and off every 20 minutes might trigger a more rapid failure of the pump and/or switch components. The number of on/off cycles each day would be about 24. If this works, we would have access to hot water from dawn to bed time and not need to use our water heater to warm up the slab twice a day.
Thanks
baumgrenze
I am thinking about changing from a duty cycle of 5 AM to 9 AM and 5 PM to 10 PM to 20 minutes on and 20 minutes off from 5 AM to 10 or 11 PM. I believe we will find that the water temperature will not drop significantly in 20 minutes once the encasing slab is warmed and that gas usage to keep the water hot will be about the same. I am concerned that cycling the pump on and off every 20 minutes might trigger a more rapid failure of the pump and/or switch components. The number of on/off cycles each day would be about 24. If this works, we would have access to hot water from dawn to bed time and not need to use our water heater to warm up the slab twice a day.
Thanks
baumgrenze