Choosing to install a hot water recirculation pump

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Mulligan Stew

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I'm choosing whether or not to install a recirculation pump for a standard 50 gallon tank type electric water heater in a one story building, residential. I'd like to start working with 1/2" home runs to fixtures using a distribution block. I'm wondering if this will eliminate the need for a pump since there's more velocity to each fixture than if I was branching off of larger tubing directly from the water heater. Water pressure at the building will be approx 50PSI. Is there a rule of thumb max length for each run before the hot water response is too slow?
 

James Henry

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a circulating pump is for a looped system. a home-run system is not a looped system. It could be done, but if the distances aren't to far you can do without it. less to worry about.
 
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Tuttles Revenge

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From personal experience with them running 3/8ths lines located directly at the water heater and fairly central to most plumbing.. I would never do it again. Each home run has to be evacuated to get hot water.. I think its a terrible system.

I would run a small recirc loop over homeruns any day of the week.
 

Reach4

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I'd like to start working with 1/2" home runs to fixtures using a distribution block. I'm wondering if this will eliminate the need for a pump since there's more velocity to each fixture than if I was branching off of larger tubing directly from the water heater.
For 3/4 inch pex, there are 1.83 gallons contained in each 100 ft. For 1/2 pex, 0.92 gallons per 100 ft. For 3/8, 0.50 gallons per 100 ft.
 

Jadnashua

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You have to first purge the room temp (or colder if it is in an outside wall) water, then warm the pipe up, so it's a bit more than just evacuating the water in the line. With copper, the Copper Institute recommends NGT 5-fps flow rate. That can be an issue by itself, but mostly on longer runs in larger buildings. Pex allows slightly faster flow velocities. Note, when most people open the tap, it's adjusted for warm versus all hot, so it will take longer to purge the lines. Most tub valves can't get to all hot if they're adjusted properly to limit the max temperature to a safe level.

If the lines are well insulated and you use a timer, using a recirculation system can save energy when you take into account the water costs (it costs to pump it, whether in your well or the utility), to heat it (that also decreases the amount of hot water you have when you run some down the drain to get it there), and what you may pay for sewer charges. That doesn't take into account the wasted water when you want hot dumped down the drain.

That all ignores the convenience factor of having hot water there when you open the tap.
 

Mulligan Stew

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From personal experience with them running 3/8ths lines located directly at the water heater and fairly central to most plumbing.. I would never do it again. Each home run has to be evacuated to get hot water.. I think its a terrible system.

I would run a small recirc loop over homeruns any day of the week.
Hey thanks for the hard earned advice. Best kind...
 

Mulligan Stew

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You have to first purge the room temp (or colder if it is in an outside wall) water, then warm the pipe up, so it's a bit more than just evacuating the water in the line. With copper, the Copper Institute recommends NGT 5-fps flow rate. That can be an issue by itself, but mostly on longer runs in larger buildings. Pex allows slightly faster flow velocities. Note, when most people open the tap, it's adjusted for warm versus all hot, so it will take longer to purge the lines. Most tub valves can't get to all hot if they're adjusted properly to limit the max temperature to a safe level.

If the lines are well insulated and you use a timer, using a recirculation system can save energy when you take into account the water costs (it costs to pump it, whether in your well or the utility), to heat it (that also decreases the amount of hot water you have when you run some down the drain to get it there), and what you may pay for sewer charges. That doesn't take into account the wasted water when you want hot dumped down the drain.

That all ignores the convenience factor of having hot water there when you open the tap.
Yep, the factors you list are the ones I'm concerned about but never got a straight answer on it. I'll do the recirc. Safer is better.
 
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