Planning a Domestic Hot Water Recirculation Loop

Question

My coper piping has lots of pinhole leaks and I am planning to replace everything with CPVC. I have a one-story ranch house with an unfinished basement, so I can access almost everything very easily. The water heater and washing machine are in the basement, everything else in on the main floor (two bathrooms - one with tub, one with shower, two sinks are both in the kitchen). There is a cinderblock wall down the middle (black line):

I have issues right now with hot water taking an extraordinarily long time to get to my fixtures, so I was looking into adding a recirculation loop, but it isn't clear how I should run the loop since one of the bathrooms is so far away from everything else. The house isn't so big overall, so it seems like a waste to have more than one pump. I also don't want to have to make too many holes.

How can I make this work?

Answer 1

If "good" or "better" are not sacraficed to perfect, this would get hot to both bathrooms, and near the other fixtures.

The "complicated join" is intended to make the pipe lengths roughly equal so flow would be roughly equal with one pump - it will not be perfectly equal. "Good enough" is probably achievable. That may not be the best route to do that, actually. if the shower run is more straight, bringing the join over to the tub side would balance better, perhaps.

Use lots of pipe insulation on both sides of the loop. Hot water loops without excellent insulation are very expensive to operate.

Perhaps better balance - also playing with a different pump location.

Answer 2

An extraordinarily long time to get warm/hot water to one or more faucets in standard one family homes is often caused by failing back flow preventers in old thermostatic shower valves.

Very easily to be checked if those valves do have internal shut off valves - sometimes only to be seen and accessible after removing the trim or casing. Another possibility would be to close the cold water line downstream of the connection/branching to the warm water line (boiler etc.), if possible.

A similar test option is to open many cold water valves and to see if the waiting time is decreased at the concerned sink where only the warm water valve is open. The open cold water valves would reduce the (dynamic) pressure of the cold water net which would reduce or even stop the cold water flooding/invading the warm water net.

If a back flow preventer fails, cold water will be pressed into the warm water net, since the (dynamic) cold water net pressure is bigger than the (dynamic) pressure of the warm water net, since warm water tubes do collect more limestone coatings which reduces the effective tube diameter.

With the cold water line closed, the warm water can't be mixed any more with cold water before leaving the faucets.

A recirculation line would not much help in that case, unless that one story ranch house was made for a huge family.

F.e., 15meter distance from boiler to faucet should take less then 10-20 seconds to get warm water, if the (uninsulated?) line is not used for many hours and if no micro or tube-in-tube circulation is present. With micro circulation (which is sometimes intended as simple alternative to a recirculation system), that time will be even shorter.

Those back flow preventers are prone to fail in thermostatic shower valves. Sometimes dirt, metal rust parts or limestone keep the back flow preventer open, sometimes the thin diaphragma is torn or has holes.

Anyway, recirculation lines should be avoided where possible.

The energy losses of a recirculation system could be reduced by using timers for the recirculation pump, but still are often underestimated.

A second reason is the hygienic aspect - legionellas and other bacterias are more likely to settle in systems with recirculation, especially in "plastic" pipes. Copper is antibacterial to some extent.

A 3rd reason to avoid recirculation is the problem of corrosion in metal pipes, which can be increased by the recirculating tiny metal bits/ions.

Are the warm lines insulated? Warm water pipes/tubes should be insulated with a thickness of at least 3 times the diameter.