Hot water recirculation pump orientation

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Niccolo

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I have a house built in 2004 with a traditional hot water recirculation setup with hot water return. I recently had to replace a defective tank-based gas water heater. The original water heater was installed with the Grundfos recirculation pump pulling hot water out of the return location near the bottom of the water heater and pushing it from there into the hot water return line.

A plumber who installed the new water heater insisted that's how it needed to be installed and there was no downside to pulling hot water out of the lower part of the hot water heater rather than from the top of the water heater. The plumber said flipping the recirculation pump so that it pulled water back toward the water heater would pressurize the water heater in a way that was problematic.

A general contractor (with plumbing license) told me he thought it should be flipped, so that the recirculation pump would pull hot water out of the return pipe and push it back into the water heater.

From looking online, I can see that recirculation pumps are often installed above hot water heaters, so they can pull out of the heater there and push into the house. Assuming my recirculation pump continues to be located where it currently is, near the bottom of the unit, which way should it be oriented, i.e. who is right here, the plumber or the general contractor? And what are the consequences of doing it the other way, i.e. whatever "backwards" is?

Thanks!
 

Terry

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Every install I've seen returns the recirc to either the cold incoming or to the bottom of the tank. The incoming dip tube puts it in the bottom of the tank too. I use a spring check to prevent the recirc from going the wrong direction. I've never heard of returning the recirc to the hot side.
 

Niccolo

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Every install I've seen returns the recirc to either the cold incoming or to the bottom of the tank. The incoming dip tube puts it in the bottom of the tank too. I use a spring check to prevent the recirc from going the wrong direction. I've never heard of returning the recirc to the hot side.

I want to make sure I understand you.

The top of my water heater has a cold water inlet (call it A) and a hot water outlet (B). On the lower side of my water heater is a drain valve which has a secondary attachment point (C), and that's where the hot water return comes back into the water heater. The recirculation pump is connected near C, where it pulls hot water out of the tank and pushes it toward the house through the hot water return piping. The question is, is that correct, or if the recirculation pump is in that location, should it be pulling returned hot (warm) water out of the pipes and pushing it into the water heater (to be reheated).

Have I described it well? And does what I described make sense, i.e. does it seem set up properly?

It's important to emphasize that this is a full or traditional hot water recirculating system with a dedicated hot water return line, not a so-called comfort system that uses the cold water pipes to return hot water. Having said that, I am not a plumber, so my knowledge is basically what I can find by googling.
 

Niccolo

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I want to make sure I understand you.

The top of my water heater has a cold water inlet (call it A) and a hot water outlet (B). On the lower side of my water heater is a drain valve which has a secondary attachment point (C), and that's where the hot water return comes back into the water heater. The recirculation pump is connected near C, where it pulls hot water out of the tank and pushes it toward the house through the hot water return piping. The question is, is that correct, or if the recirculation pump is in that location, should it be pulling returned hot (warm) water out of the pipes and pushing it into the water heater (to be reheated).

Have I described it well? And does what I described make sense, i.e. does it seem set up properly?

It's important to emphasize that this is a full or traditional hot water recirculating system with a dedicated hot water return line, not a so-called comfort system that uses the cold water pipes to return hot water. Having said that, I am not a plumber, so my knowledge is basically what I can find by googling.

I found a schematic that seems to represent our setup well, except that as currently set up, the recirculation pump is pushing hot water the other way into the house, rather than pulling warm (formerly hot) water back toward the water heater.

And here is a video associated that that schematic, which shows a setup like mine, *except* that the recirculation pump is pulling warm (formerly hot) water from the house back to the water heater.


recirculating-systems-for-hot-water-heating-heater-recirculation-pump-design-13.png
 
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Niccolo

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The video and drawing you have is how we do it.

So you have the recirculation pump pulling warm (formerly hot) water from the house and pushing it into the hot water heater, as the general contractor suggested. The plumber installed my recirculation pump the other way around. Do you have any sense of whether that might have consequences and what those might be?

I tried to find an installation manual on the Grundfos website, because I was curious whether they would have any instructions about this situation, but I was unable to find it. I have a Grundfos UP 15-29 SU recirculation pump, for what it's worth.
 

Niccolo

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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.
 

Terry

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The water is cleaner at the top of the tank.
The sediment is all at the bottom.

Incoming water is at the bottom with the dip tub, so normally you would bring the cooler water from the recirc and let it run it's cycle of starting where the tank water is cooler and and supplying fixtures with water from the top, which is where the hot water is.
It's a loop. It doesn't matter which direction it's going as long as the check valves are with the flow. You should have an expansion tank for the water heater regardless.
 

Jadnashua

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As you use hot water from the tank, cold gets introduced into the bottom of it. So, after some use, if you were sourcing the water from the bottom, you'd be pushing cooler water into the pipes. You really want to be pulling (or pushing) water out of the top of the tank where it is the hottest into the lines. Whether you return it to the cold inlet of your tank, or the drain valve doesn't really matter.

Pulling it out of the bottom of the tank is just wrong, and, if you have heat traps on your WH, wouldn't work as they would close off the flow since they're a one-way valve out of the hot side...you can't 'push' water back into the tank from the hot outlet.
 

Niccolo

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The water is cleaner at the top of the tank.
The sediment is all at the bottom.

Incoming water is at the bottom with the dip tub, so normally you would bring the cooler water from the recirc and let it run it's cycle of starting where the tank water is cooler and and supplying fixtures with water from the top, which is where the hot water is.
It's a loop. It doesn't matter which direction it's going as long as the check valves are with the flow. You should have an expansion tank for the water heater regardless.

I do not have an expansion tank, and I don't see them in other installations in area houses, either. I do regularly see them in apartment installations, though. Not sure what the difference is.

Question: Do all water heaters have a one-way valve at the hot water outlet? If so, and if I'm understanding correctly, it would seem that all water heaters should be installed with expansion tanks. If not, it seems like expansion tanks might only be essential if one-way valves were installed somewhere in the system.

Happy to be educated about expansion tanks...are they only required under certain circumstances, but always recommended? Or always required? Are they actually required by (some) building codes?
 

Niccolo

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As you use hot water from the tank, cold gets introduced into the bottom of it. So, after some use, if you were sourcing the water from the bottom, you'd be pushing cooler water into the pipes. You really want to be pulling (or pushing) water out of the top of the tank where it is the hottest into the lines. Whether you return it to the cold inlet of your tank, or the drain valve doesn't really matter.

Pulling it out of the bottom of the tank is just wrong, and, if you have heat traps on your WH, wouldn't work as they would close off the flow since they're a one-way valve out of the hot side...you can't 'push' water back into the tank from the hot outlet.

Very helpful posts from both you and Terry, I really appreciate you guys talking me through this!
 

Terry

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Expansion tanks are for a closed system. I always install them with a recirc.

Some water heaters come with ball checks on the nipples that only go one direction. Reversing the recirc would not work with those.
It's common with a recirc system to have a check valve on the incoming cold supply so that hot water isn't pushed back into the cold lines.
 

Reach4

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The top of my water heater has a cold water inlet (call it A) and a hot water outlet (B). On the lower side of my water heater is a drain valve which has a secondary attachment point (C), and that's where the hot water return comes back into the water heater. The recirculation pump is connected near C, where it pulls hot water out of the tank and pushes it toward the house through the hot water return piping. The question is, is that correct, or if the recirculation pump is in that location, should it be pulling returned hot (warm) water out of the pipes and pushing it into the water heater (to be reheated).
If you replaced your pump with a pipe, you would probably get passive recirculation by the hot water rising, and the cooler water sinking. Many systems have been done that way for years. The direction of flow would be the same as for a properly installed pump.

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.)
He did not want to rework this mistake under warranty.
 

Niccolo

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Expansion tanks are for a closed system. I always install them with a recirc.

Some water heaters come with ball checks on the nipples that only go one direction. Reversing the recirc would not work with those.
It's common with a recirc system to have a check valve on the incoming cold supply so that hot water isn't pushed back into the cold lines.

Glancing at the old Bradford White that was replaced yesterday, it did not appear to me that the nipples had one-way valves, unless hidden out of view farther inside. Of course, I don't really know what I'm looking for.

It sounds to me as though an expansion tank is likely not required by code, but probably desirable.

At this point, I'm focused on having the plumber correct the pump that was installed backwards. I'm open to feedback on how strongly I should consider also having an expansion tank installed, and if so, what guidance I should offer, i.e. in my tank water heater setup with dedicated hot water recirculation return loop, where should the expansion tank be located? Should additional one-way valves also be added?
 

Terry

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Not all water heaters have checks. If they do, I put something different in. It was more common some time ago, and I have't seen that in a while.
 

Niccolo

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Not all water heaters have checks. If they do, I put something different in. It was more common some time ago, and I have't seen that in a while.

Thanks. This is all super helpful.

I could use as much clarity as possible on how to think about an expansion tank. Am I correct that building codes don't require it, but it's probably desirable? And is there anything else I need to know to be able to have the conversation with a plumber, e.g. in my tank water heater setup with dedicated hot water recirculation return loop, where should the expansion tank be located? Should anything else (like one-way valves) possibly be added?
 

Terry

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On a closed system where there is a check valve on the incoming cold, there also needs to be an expansion tank, on the cold water side, not the hot. It is located within the closed system, between the incoming check and the tank.
 

Jadnashua

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The Feds have highly recommended all public water utilities to install a check valve on every customer's supply when doing any upgrades or maintenance. So, as a result, many codes now call for the installation of an expansion tank to prevent problems when that happens. Functionally, when water expands during heating, it will either raise the pressure quickly in a closed system (leaking wherever it can at the weakest point), or push back out into the supply. That's the issue...if, for some reason, you might have polluted the water in your home, pushing it back out could contaminate the supply, sickening your neighbors. That's also why handheld showers and sprayers on kitchen sinks are required to have a vacuum breaker on them, so if the head is sitting in the water and there's a hiccup in the supply (say a fire department opens up a hydrant and the pressure drops), it can't suck that dirty water back into the supply. On a larger scale, the same is or will become true for all public water supply systems, eventually, if it hasn't happened yet where you live.

So, while people may not have 'needed' an ET previously, it is highly likely it will become a necessity in the future. IMHO, it doesn't hurt to have one, and you may need one. Relying on a relief valve means every time the WH heats water, you'll dump a bit of water which is a precious resource in many places, especially in CA. Think of doing that in millions of homes every time their WH turns on...
 

Niccolo

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Thanks both, this is really helpful.

I get the impression there aren't many expansion tanks around here. I don't think there are relief valves, either, though I could certainly be wrong about that. I guess that means those plumbing systems risk damaging pressure levels if the local public utilities have installed check valves or when they eventually do. I'm not sure what the immediate consequences of damaging pressure levels are, maybe harm to water heaters or connected appliances?
 
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