Just wondering what your thoughts were on this.
Ah, I've never plumbed a recirculation loop, and my energy code would require the whole loop to be insulated and the pump only activated by a separate momentary switch, so I don't have any performance expectations.
20 seconds doesn't sound unreasonable, maybe it's at the edge of acceptability. But I think the calculation that gave us 20 seconds may have been a slight overestimate.
If the pump comes on with the light switch, does it stay on the whole time the light is on? That seems excessive, I would think there should be a mechanism for the pump to shut off when the water temperature at the fixture is adequate.
Personally, with the short distances involved, I don't see recirculation as worth it. If each of the runs from the water heater to a bathroom is 25' and done in 1/2" PEX, that's a volume of under 1/4 gallon that you'd have to wait to drain to get hot water. Of course, you'd be wasting 1/4 gallon of water each time.
Cheers, Wayne