Hot water circulation pump question

[Mark.S]

Hello
I recently had my hot water heater replaced and the plumber told me that this valve next to the heater (photo) is for the return feed of a hot water circulation line. He said the pump probably failed at some point in the past and the owner decided not to replace it.
We do have a long wait to get hot water to some of the remote faucets so I'd like to (re) install a circulation pump. However I have some questions/ concerns

1. He told me the pump should be installed between this valve and the drain valve on the tank. Is this correct? This valve is only 1/2" which seems too small for the pumps I've seen that are sold for this application?

2. Would it be better to install the pump on the 3/4" hot water line exiting the tank on the top and connect the 1/2" return to the drain valve via a check valve etc ?

I sketched the two options as I understand them A or B. Which is best ? Or maybe another setup is even better that I'm not aware of
Thanks

Mark

 

[Twowaxhack]

Either way you still have a 1/2” return.

The best method is to pipe the return to the top of the heater and connect to the cold side, installing a check valve upstream on the cold water supply to the water heater. Install an expansion tank downstream of the check valve. Install the pump in the return line.

I suggest a 3 speed pump and use the lowest setting that meets your systems needs.

 

[Mark.S]

Thank you. So if I understand right it would be per the diagram in this photo ?

 

[MicEd69]

First you need to verify the circulating piping. And if you install the return line to the cold-water inlet pipe, you need an expansion tank like Twowaxhack said.


You can install the return line to the drain. If you do that, and if you don't have a check valve in the cold-water line separately or integral with a PRV if you have one, then you don't need an expansion tank, unless the code your local jurisdiction uses requires it. I will say it's still good practice, however.

You also need to decide on how you want to control the circulating pump. Some are run 24-7, some are temperature controlled, some have a timer running the pump when the expected usage is going to be, and some have them manually turned on with a preset time of running. I personally like the manual turn on. If I'm going to take a shower, I turn my pump on while I brush my teeth, then I turn on the shower and have instant hot water. When my wife, or I as is often the case, do the dishes, the pump gets turned on while the dishes are being collected and when the hot water is needed, it's there.

 

[Twowaxhack]

The problem with running to the drain is if your return water cools off too much it’ll trigger the heater to short cycle. This can cause overheating, an effect called “ stacking “ . Stacking can cause thermostat overvshoot and even trip the high limit on electric tanks. It could also burn someone with the higher than expected temps.

Water heater manufacturers shortened the dip tubes in water heaters at some point, I think it was the early 90’s. The reason ? Because of stacking. Short draws of hot water that conveys cold water to be fed by the dip tube and discharged into the heater near the thermostat.

The circulator piped to the bottom can recreate this if the return temp is too low. To stop this you can speed the pump up but that causes other problems, like erosion of the piping system.

So you will see some manufacturers recommended a top fed return through the dip tube.

 

[MicEd69]

The problem with running to the drain is if your return water cools off too much it’ll trigger the heater to short cycle. This can cause overheating, an effect called “ stacking “ . Stacking can cause thermostat overvshoot and even trip the high limit on electric tanks. It could also burn someone with the higher than expected temps.

Water heater manufacturers shortened the dip tubes in water heaters at some point, I think it was the early 90’s. The reason ? Because of stacking. Short draws of hot water that conveys cold water to be fed by the dip tube and discharged into the heater near the thermostat.

The circulator piped to the bottom can recreate this if the return temp is too low. To stop this you can speed the pump up but that causes other problems, like erosion of the piping system.

So you will see some manufacturers recommended a top fed return through the dip tube.

A couple question.

1. If the water heater is gas, is there still a stacking issue?
2. If the pump is only run in a manual mode for a period of say 2 minutes, does that eliminate those concerns?

Just wanting to better understand the issues.

 

[Twowaxhack]

Gas can do it but it’s not as likely to overheat because it has a thermostat that gets wet, it reads the temp quicker. Electric uses convection through the wall of the tank so you get lag, over-shoot.

I think it would be a pink unicorn to happen with manual mode for 2 minutes but if that two minutes cycle was repeated many times, then yes.

 

[Twowaxhack]

I use to make my water heater stack on purpose just to do it. Turn on a hot faucet for a minute or so then cut it off and listen for the lower element to fire. Wait for it to cut off then repeat. And repeat and repeat.

I replaced my diptube with a longer one to squeeze more hot water out of the tank. The lower the dip tube extends into the tank the more hot water you’ll get out of the tank.

 

[Mark.S]

Thanks to you both.
This is on a 50 gallon conventional vertical gas fired water heater.
I like the idea of feeding the return water back into the heater via the cold line rather than the drain for various reasons. Stacking was new information for me which adds to the list of good reasons to do it via the cold supply connection.
Thanks for the suggestion about the 3 speed pump. I certainly want to avoid any chance of eroding the piping.....that was part of my concern about putting a 3/4 sized pump on a 1/2" line ....could it cause a too high velocity in the 1/2" line and/or cause cavitation in the pump due to pressure drop on the suction line ? I've spent 25 years in an industrial pump company and seen too many bad pump installations causing premature failures .... mainly due to bad sizing and/or poor suction conditions ...

 

[Twowaxhack]

I use the Armstrong stainless three speed circulators and run it on the slowest speed that works, piping be damned because usually the piping is already in place. Ideally you want the entire run insulated with closed cell rubber insulation. I usually set my customers up on a morning and evening schedule. 5am-9am and 5pm-9pm. That’s 8 hrs a day.

There are many ways to set the on/off. Motion detectors, timers, push buttons, Alexa voice control and thermostat control. One guy has a pump that activates under flow conditions to speed up the delivery by about 1/2 the wait time without the pump, it only runs when he opens the lavatory it’s mounted under. It’s a 1/2 bath over his garage he uses as an office.
Most of the time I see 1/2” copper return lines.

 

[Twowaxhack]

 

[Mark.S]

Sounds good. Thanks for the info !

 

[Mark.S]

I have looked into the different options for pump control and it seems like the 'smart' controllers that learn demand patterns are not so smart. Also the timer option probably won't suit our usage patterns. So overall I think I may set up a smart switch on our WiFi and control it via an app and/or remote switches in the kitchen and bathrooms as needed. I do also like the pressure activated switch that senses the demand and starts the pump. It can be triggered easily by just opening a faucet for a few seconds, closing it again and waiting for the pump to circulate for a minute or so. Removes the need for switches and apps.
Anyone have experience of the pressure activated system?