Our master shower is located roughly 60 feet from our hot water heater. Knowing this may be an issue, I added a hot water recirculating loop when we built our house in 2003. It works fine, but with our varying schedule the pump runs 4-5 hours in the morning, and another 4-5 hours in the evening. That wastes a lot of energy, as well as pump noise and maintenance issues. We are also considering a heat pump water heater in the future, which I've heard don't work well with recirculating systems.

I currently have a CPVC 3/4" main trunk line, with 1/2" CPVC stubs to each fixture. The return line is 1/2" from the furthest shower. Without the pump running, it can take well over a minute for hot water to reach the master shower (low flow shower heads). With the pump running that is reduced to 5-10 seconds or so (I assume this is the water in the 1/2" stub up from the recirculation loop).

I've tried a number of "on demand" triggers for the pump, but it still takes about a minute for the hot water to circulate through the loop before it's hot at the shower. No significant difference from not using the pump at all.

I'm curious if running a dedicated 1/2" PEX "home run" directly from the water heater to the shower would allow reasonable wait times without needing the recirculating system? What about a 3/8" home run line? We have two showers in the master bath. Would one 1/2" line serve both, or would two 3/8" lines be better?

Would love to hear other's experience with home run systems.

Thanks!

How long it takes hot water to get to the shower is strictly a function of how far away from the HW heater it is. If the shower is 60' of pipe away from the HW heater and a pex home run can take a short cut and get there with 30' of pipe, you will get hot water in half the time. If the pex has to follow the same 60' path back to the HW heater it's not going to get you HW any faster.

I would consider a wall switch for the recirc pump, simply turn the switch on a minute before you shower and hot water will be ready. Turn off when you're done showering. Typically you're doing other stuff for a minute or two before you get in the shower anyway. Possibly wire it to the light switch so recirc pump comes on when you turn on the light in the bathroom. Or if your schedules are regular, use a timer with multiple on/off settings so the pump comes on for each shower then shuts off.

Another solution would be to ditch the recirc system and put a point-of-use HW heater closer to the shower, but that install is more complex.

Quote

... How long it takes hot water to get to the shower is strictly a function of how far away from the HW heater it is. ...

Not entirely correct: the size of the pipe DEFINATELY affects the 'time frame' as the volume of (now cooled) water must be expelled before the hot arrives.


Soooo, if the bath group is fed by 3/4 and you can run a new SEPARATE 3/8 only for the shower the time would be reduced.


HOWEVER

Replacing the light switch with a double pole single throw so it also controls the recirc pump is an option, albeit requiring the 'running' of new electric cable.

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