Hot water recirculation pump orientation

[Terry]

When the water expands and then retracts with a gas water heater, the tube going down through the tank to the fire chamber flexes back and forth.
The welds break. Someone buys a new water heater. Pretty cool.

Or..........the expansion tank with the rubber bladder and air behind it compresses and expands as needed.

 

[Reach4]

guess that means those plumbing systems risk damaging pressure levels if the local public utilities have installed check valves or when they eventually do.

You can buy a garden hose thread pressure gauge pretty cheap. After taking a hot shower, and stopping all water use, see how high the pressure rises.

 

[Sponsor]

 

[Niccolo]

You can buy a garden hose thread pressure gauge pretty cheap. After taking a hot shower, and stopping all water use, see how high the pressure rises.

I'm guessing I'd attach it to an outside faucet, open the valve, take a shower, and then approximately how many minutes after the shower would I expect the pressure to peak?

 

[Reach4]

I'm guessing I'd attach it to an outside faucet, open the valve, take a shower, and then approximately how many minutes after the shower would I expect the pressure to peak?

I don't know. About the time the water heater turns off. Maybe 5 or 10 minutes.

Some gauges have a lazy/tattletale hand to remember the peak. Vibrations can make that hand jump, so it is not totally sure.

You could also take a movie of the gauge as you shower and finish.

 

[Niccolo]

I don't know. About the time the water heater turns off. Maybe 5 or 10 minutes.

Some gauges have a lazy/tattletale hand to remember the peak. Vibrations can make that hand jump, so it is not totally sure.

You could also take a movie of the gauge as you shower and finish.

Sounds good.

By the way, I'm correct that expansion tanks aren't usually required under existing codes, right? Just curious.

 

[Reach4]

Sounds good.

By the way, I'm correct that expansion tanks aren't usually required under existing codes, right? Just curious.

California uses UPC. I think localities and the state can modify parts.

http://forms.iapmo.org/email_marketing/codespotlight/2018/aug16.htm says

From the 2018 UPC Illustrated Training Manual

608.3 Expansion Tanks, and Combination Temperature and Pressure-Relief Valves.
A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized and installed in accordance with the manufacturer's installation instructions.
​

If your pressure rises after a shower, you have a check valve. You should then want a thermal expansion tank, even if there is no code requirement.

 

[Niccolo]

California uses UPC. I think localities and the state can modify parts.

http://forms.iapmo.org/email_marketing/codespotlight/2018/aug16.htm says

From the 2018 UPC Illustrated Training Manual

608.3 Expansion Tanks, and Combination Temperature and Pressure-Relief Valves.
A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized and installed in accordance with the manufacturer's installation instructions.
​

If your pressure rises after a shower, you have a check valve. You should then want a thermal expansion tank, even if there is no code requirement.

So the key question is whether the utility has installed some kind of a one-way valve. The houses in my development were all built in 2004-05 and none appear to have expansion tanks (or pressure-relief valves, as best I can tell). I infer from this that our water isn't delivered through a one-way valve, or at least wasn't when the houses were built. As Terry has noted, these kinds of one-way valves are increasingly widespread, so it's always possible they could be added at some point (but if the utility did such a thing, I would think there'd be some kind of notification).

I'll be checking my pressure, curious to see the results.

 

[Jadnashua]

Plumbing fixtures are designed for a maximum of 80-psi. A water heater is tested to 300-psi, and the safety valve opens at 150-psi, and it will without an expansion tank if you have a closed system. The hoses that feed your faucets, toilet, and washing machine and maybe refrigerator's icemaker don't expect more than 80-psi. The seals on your toilet may leak or wear out sooner if your pressure gets too high. You're more prone to having water hammer when shutting off the water when the pressure is higher (it causes it to flow faster in the pipes, so stopping it quickly is the issue just like hitting something in your car at a higher speed).

A constant high pressure may be less problematic than one that gets higher, then is released, as that can stretch things, then they MAY recover...depends on whether that stretch exceeds the elastic limit of the item. Ever taken a steel coat hanger and bent it? It doesn't break the first time you bend it, but bend it back and forth for awhile, and it does. Water will bend things when the pressure gets higher. If you have a closed system, the thing that bends is the bladder in the tank (usually, a synthetic rubber), and it will last MUCH longer than other things, and it significantly limits the pressure change with expansion. It's important to precharge and size the ET, if you have one, properly, or you'll be exceeding its limits and prematurely wear it out.

With the likelihood that the utility company will (if they haven't already) install a check valve on your supply, IMHO, adding an ET won't hurt, and may solve a lot of issues either now, or down the road. They're not expensive, or hard to install properly. My city began requiring an ET to pass an inspection way back in the 80's, as the recommendation to install check valves had come out from the feds. This is not a new situation, but some are slower to implement than others.

Note also that as more houses are built, it is not unusual for the utility to add booster pumps or new water towers to accommodate the increased demands. They're required to provide a minimum pressure, but the maximum isn't as restricting. IF you live on say the bottom of a hill, you're pressure will likely be higher than a neighbor higher up. Just static pressure changes from elevation differences amounts to about 0.43#/foot change. So, your pressure may have been below 80-psi when the houses were built, but now could be different. IT also will likely change overnight when the utility may be replenishing water in the water towers and the usage is lower.

 

[Niccolo]

Plumbing fixtures are designed for a maximum of 80-psi. A water heater is tested to 300-psi, and the safety valve opens at 150-psi, and it will without an expansion tank if you have a closed system. The hoses that feed your faucets, toilet, and washing machine and maybe refrigerator's icemaker don't expect more than 80-psi. The seals on your toilet may leak or wear out sooner if your pressure gets too high. You're more prone to having water hammer when shutting off the water when the pressure is higher (it causes it to flow faster in the pipes, so stopping it quickly is the issue just like hitting something in your car at a higher speed).

A constant high pressure may be less problematic than one that gets higher, then is released, as that can stretch things, then they MAY recover...depends on whether that stretch exceeds the elastic limit of the item. Ever taken a steel coat hanger and bent it? It doesn't break the first time you bend it, but bend it back and forth for awhile, and it does. Water will bend things when the pressure gets higher. If you have a closed system, the thing that bends is the bladder in the tank (usually, a synthetic rubber), and it will last MUCH longer than other things, and it significantly limits the pressure change with expansion. It's important to precharge and size the ET, if you have one, properly, or you'll be exceeding its limits and prematurely wear it out.

With the likelihood that the utility company will (if they haven't already) install a check valve on your supply, IMHO, adding an ET won't hurt, and may solve a lot of issues either now, or down the road. They're not expensive, or hard to install properly. My city began requiring an ET to pass an inspection way back in the 80's, as the recommendation to install check valves had come out from the feds. This is not a new situation, but some are slower to implement than others.

Note also that as more houses are built, it is not unusual for the utility to add booster pumps or new water towers to accommodate the increased demands. They're required to provide a minimum pressure, but the maximum isn't as restricting. IF you live on say the bottom of a hill, you're pressure will likely be higher than a neighbor higher up. Just static pressure changes from elevation differences amounts to about 0.43#/foot change. So, your pressure may have been below 80-psi when the houses were built, but now could be different. IT also will likely change overnight when the utility may be replenishing water in the water towers and the usage is lower.

Fascinating, thanks!

 

[Niccolo]

Here's where I currently stand:

Bradford White and many licensed plumbers: A recirculation pump feeding a house with dedicated hot water return lines can either A) pull water from the hot water outlet of the water heater and push it into the house or B) can pull water from the house through the hot water return line and push it into the water heater, using a secondary attachment point at the drain valve.

Another licensed plumber: While option B above is often done, forcing the pump to push water into the bottom of a full water heater will stress it, and will also lead to corrosion of the inlet at the drain valve.

Licensed plumber who installed warranty replacement water heater: Pump should pull water from water heater and push it into house even if it is located at the hot water return to water heater location. Running it the other way is dangerous because the pump would be pressurizing the water heater. (Bradford White says this is simply wrong and that circulating hot water backwards like this will cause a "mess," though they didn't specify what they meant by that.)

Grundfos: We can't answer your question or provide relevant literature, please talk to your supplier.

I've got this figured out at this point.

But I was just thinking about "Another licensed plumber" who said that forcing the pump to push water into the bottom of a full water heater will stress the pump, and will also lead to corrosion of the inlet at the drain valve.

I'm not sure this makes any sense. Assuming no taps are open or appliances drawing hot water, the dedicated hot water line with return is a closed loop. So a pump located at the hot water output of the hot water heater, pumping water out, and a pump located at the hot water return to the hot water heater, pushing water back into the water heater, should see the same pressure, assuming my logic is right.

And since the lines are fixed, the water should move at the same speed whether the pump is located at the hot water output or the return, and I don't see why locating it at the return would cause any more corrosion there.

 

[Jadnashua]

It shouldn't hurt pushing it into the tank. One problem some get themselves into is using a much larger pump than needed. On copper pipe using hot water, the copper institute calls for a maximum velocity of 5-fps. ANd, in reality, you don't need anywhere near that velocity. My first recirc system lasted about 15-years. The pump was still good, but some internal parts were no longer available. It was a 1/28th HP motor, about 26W. My new one is all of about 13W. It works fine.

 

[Niccolo]

I got a cheap pressure gauge and screwed it onto an exterior hose spigot. Assuming it's accurate, the steady state pressure is 53 PSI, and it rises a maximum of a few PSI above that, including after a hot shower (when I'm assuming the water heater kicks in). I'll keep watching it, though.

Seems like an expansion tank might still be a good idea, but for now may not be necessary.

And I don't know whether my house has the ability to adjust pressure, and if it does, I'm not sure where to do that.

 

[Jadnashua]

If you had a PRV and did not have a functional ET, then your pressure would spike when you stopped using water and the WH was running. So, presumably, you don't have either. A PRV can reduce the pressure. TO get it higher, you'd need to add a booster pump, which isn't your issue. 53-psi is nominal, and should be fine.

 

[Niccolo]

If you had a PRV and did not have a functional ET, then your pressure would spike when you stopped using water and the WH was running. So, presumably, you don't have either. A PRV can reduce the pressure. TO get it higher, you'd need to add a booster pump, which isn't your issue. 53-psi is nominal, and should be fine.

As best I can tell, the water comes into my house via a pipe that emerges from the ground near my front door, with a valve to shut off water to the house, and a hose spigot above that, and above that the pipe runs into the house. That spigot is where I put the pressure gauge. I don't see any device to regulate pressure there, or anywhere else in the house. I don't know where my water meter is, but I presume it must be in a concrete box somewhere at the edge of my property near the street.

 

[Niccolo]

Hmm, as of this morning the tattletale hand reports a maximum pressure of 140 PSI, though current pressure is the same 53 PSI. Reset the tattletale hand and will watch it more carefully

 

[Terry]

It's the up and down pressure that flexes the chimney in the center of the tank.

 

[Niccolo]

Hmm, as of this morning the tattletale hand reports a maximum pressure of 140 PSI, though current pressure is the same 53 PSI. Reset the tattletale hand and will watch it more carefully

Just took a hot shower, confirmed that the water heater kicked on, and the PSI didn't budge afterwards at all, consistent at ~53 PSI. So it seems like either something else spiked the pressure to ~140 PSI overnight or maybe the water heater ratched the pressure up overnight while there was no pressure release happening from other hot water uses. Open to other suggestions for stuff I might do to try to diagnose what's going on.

 

[Jadnashua]

The utility may need to raise the pressure to force water into the towers. They tend to do that at night, and with fewer people drawing off water, the pressure can rise more then versus during the day.

So, unless vibrations are bumping the tattle tale hand up and not the actual pressure, you SHOULD have a PRV which also requires an ET since the PRV will create a closed system. The thermal expansion will happen, but it only will raise the pressure if you've not closed off all water uses while it's happening. ANy water use will relieve the pressure. A typical amount of expansion is only in the order of a cup or so, but that's easily enough to raise the pressure sky high unless it's leaking out somewhere. A common place is the T&P valve at the WH, but that may not be necessary if something else leaks at a lower pressure (some toilet valves are common places and you may never notice as it just goes down the drain).

 

[Niccolo]

The utility may need to raise the pressure to force water into the towers. They tend to do that at night, and with fewer people drawing off water, the pressure can rise more then versus during the day.

So, unless vibrations are bumping the tattle tale hand up and not the actual pressure, you SHOULD have a PRV which also requires an ET since the PRV will create a closed system. The thermal expansion will happen, but it only will raise the pressure if you've not closed off all water uses while it's happening. ANy water use will relieve the pressure. A typical amount of expansion is only in the order of a cup or so, but that's easily enough to raise the pressure sky high unless it's leaking out somewhere. A common place is the T&P valve at the WH, but that may not be necessary if something else leaks at a lower pressure (some toilet valves are common places and you may never notice as it just goes down the drain).

I want to make sure I understand you clearly.

It makes sense that utilities would pump water into towers overnight, and that would increase the pressure.

Are you suggesting I do or likely do have a pressure relief valve (PRV), or are you suggesting that based on what I reported I either don't or do and it's not set right?

Would a PRV cap the maximum water pressure? Or it would reduce the pressure across the board, i.e. both reduce the current ~53 PSI steady state and reduce the overnight surges?

 

[Jadnashua]

A working PRV should hold the outlet pressure essentially constant (well, prevent it from exceeding the set value because of a supply pressure rise). It also acts like a check valve, so any thermal expansion has nowhere to go. That's why you also need an expansion tank. Setup properly, even with thermal expansion, the pressure won't rise more than a couple of pounds, if that (the water expands into the tank). Otherwise, the pressure will easily exceed 150-psi, at which point, if there are no other leaks to prevent it from getting that high, the safety valve on the water heater will open. MOst supply lines are quite rigid, so expansion immediately creates a pressure rise.

If your pressure didn't rise after hot water use and you weren't using water otherwise, then there's no check valve (the water pushed back into the supply), and likely, no ET. IF, otherwise, the pressure did spike, it was probably because the utility raised the pressure. You could get a spike if there was a high rate of flow and a quick acting valve closed as it rebounds off the the valve (a water hammer situation).