# Hot water recirc question



## Michaelcookplum (May 1, 2011)

I know there have been threads about this before, but here I have an exact example. The 1" ball valve you see in the picture is the cold feed coming down serving two 50 gal power vents. To the right of that is a 1/2 hot water recirc line with a pump and a check valve after. It then ties back into the cold feed, goes through what looks like a heat trap (maybe) and then feeds both cold sides of the water heaters. I have always tied my hot water recirc line into the bottom of the heater. My question is how does this actually work without another check valve on the cold water feed above the tee that goes to the heaters? How does this untimered constantly moving hot water not mix with the cold water system in the house? It clearly doesn't because HO said everything has worked fine for years. I'm just looking to understand how this works. Here's a few pics. The 3/4 FIP adapter had an expansion tank screwed in(yes horizontally) and the 1/4" line feeds the humidifier(which is hot water?? Or cold??) I replaced both heaters today and reconnected all the water lines as they were. I appreciate all the insight you can share! Btw, for all the new members who have joined here lately, don't tear me apart for this, it's not my work I'm posting. Check out my previous 4000 posts if you don't think I know my ****. This is a perfect example of of why us professionals use this forum, to learn from others a different and correct way of plumbing. 

I'll be waiting for your professional responses...tick tock


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## Plumber patt (Jan 26, 2011)

Michaelcookplum said:


> I know there have been threads about this before, but here I have an exact example. The 1" ball valve you see in the picture is the cold feed coming down serving two 50 gal power vents. To the right of that is a 1/2 hot water recirc line with a pump and a check valve after. It then ties back into the cold feed, goes through what looks like a heat trap (maybe) and then feeds both cold sides of the water heaters. I have always tied my hot water recirc line into the bottom of the heater. My question is how does this actually work without another check valve on the cold water feed above the tee that goes to the heaters? How does this untimered constantly moving hot water not mix with the cold water system in the house? It clearly doesn't because HO said everything has worked fine for years. I'm just looking to understand how this works. Here's a few pics. The 3/4 FIP adapter had an expansion tank screwed in(yes horizontally) and the 1/4" line feeds the humidifier(which is hot water?? Or cold??) I replaced both heaters today and reconnected all the water lines as they were. I appreciate all the insight you can share! Btw, for all the new members who have joined here lately, don't tear me apart for this, it's not my work I'm posting. Check out my previous 4000 posts if you don't think I know my ****. This is a perfect example of of why us professionals use this forum, to learn from others a different and correct way of plumbing.
> 
> I'll be waiting for your professional responses...tick tock
> 
> ...


The hot water is going to go in the path of least resistance. The pump is pumping it into the tank through the cold, and its gunna exit the hot side which is connected to the re circ piping on the other side of the hot system. When the system is not running, the cold water is at a stand still but the hot water will keep circulating.


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## wyrickmech (Mar 16, 2013)

Michaelcookplum said:


> I know there have been threads about this before, but here I have an exact example. The 1" ball valve you see in the picture is the cold feed coming down serving two 50 gal power vents. To the right of that is a 1/2 hot water recirc line with a pump and a check valve after. It then ties back into the cold feed, goes through what looks like a heat trap (maybe) and then feeds both cold sides of the water heaters. I have always tied my hot water recirc line into the bottom of the heater. My question is how does this actually work without another check valve on the cold water feed above the tee that goes to the heaters? How does this untimered constantly moving hot water not mix with the cold water system in the house? It clearly doesn't because HO said everything has worked fine for years. I'm just looking to understand how this works. Here's a few pics. The 3/4 FIP adapter had an expansion tank screwed in(yes horizontally) and the 1/4" line feeds the humidifier(which is hot water?? Or cold??) I replaced both heaters today and reconnected all the water lines as they were. I appreciate all the insight you can share! Btw, for all the new members who have joined here lately, don't tear me apart for this, it's not my work I'm posting. Check out my previous 4000 posts if you don't think I know my ****. This is a perfect example of of why us professionals use this forum, to learn from others a different and correct way of plumbing. I'll be waiting for your professional responses...tick tock


 basically the pump is pulling water off the end of the hot water line and pumping it back in to the tank on the cold side. It really needs a check to keep migration from happening. I would suggest cutting it all out and re piping.


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## tim666 (Mar 11, 2014)

The recirc line is constantly circulating back down the dip tube and out the hot side. If you open a cold faucet the circulation continues, there is positive pressure at the inlet of the water heater but negative at the outlet to keep circulating. If the pump fails or is put on a timer then you will get crossed lines


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## bct p&h (Jan 19, 2013)

I've seen that same setup before. The only time it doesn't seem to be a problem is when there isn't a cold line pulled off close to the heater. I'm sure if you touched the cold water piping above the heater the pipe would be at least warm. If I was replacing those heaters I would have either moved the recirc to the bottom of the heater or cut in a couple checks on the cold above the heater.


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## singingplumber (Sep 10, 2014)

I'm not sure I'd trust the HO unless you have a good history with him/her. That said, is that a Taco 0014 circulator?


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## plumberkc (Jun 23, 2011)

Michaelcookplum said:


> This is a perfect example of of why us professionals use this forum, to learn from others a different and correct way of plumbing. I'll be waiting for your professional responses...tick tock


The professionals aren't the only ones learning here.


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## KoleckeINC (Oct 22, 2011)

What's silly is the warm water that's going to come out of the nearest cold fixture for the first 30 seconds. Heat trap nipples won't do anything. Should have tied it into the drain with a new check and valve both sides of the circ.


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## wyrickmech (Mar 16, 2013)

KoleckeINC said:


> What's silly is the warm water that's going to come out of the nearest cold fixture for the first 30 seconds. Heat trap nipples won't do anything. Should have tied it into the drain with a new check and valve both sides of the circ.


 check valve will solve the problem.


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## Michaelcookplum (May 1, 2011)

Thanks for the insight, I understand now how doing it this way works and how to make it even better if someone else did it this way. I think I will still continue to take my line down to bottom of heater as I always have.


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## Plumber patt (Jan 26, 2011)

Tieing it into the cold works just fine. You dont need any additional check valves. The way its piped in that picture will work no problem.


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## jeffreyplumber (Dec 7, 2009)

Works fine as pictured. Ive run them to the bottom probebly 20 times more than to the top. Mostly because I was told to by a boss. Probebly cheaper to run it high though (no Brass tee or nipple less pipe etc). Also when changing the heater later its easier.


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## singingplumber (Sep 10, 2014)

Michaelcookplum said:


> Thanks for the insight, I understand now how doing it this way works and how to make it even better if someone else did it this way. I think I will still continue to take my line down to bottom of heater as I always have.


Most manufacturers recommend using the dip tube to introduce recirc water unless you already have a bottom fed heater. It is more efficent and causes fewer issues with thermostats and tempering valves. I asked about the pump (comment #6) because the Taco 0014 is a high velosity medium head pump and not a good choice for the application. Hot water recirc pumps should be sized just strong enough to circulate while there is no call for hot water. Anything stronger wastes energy & creates other issues: pressure, pitting of pipe, high temps through mixing valves.


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## wyrickmech (Mar 16, 2013)

singingplumber said:


> Most manufacturers recommend using the dip tube to introduce recirc water unless you already have a bottom fed heater. It is more efficent and causes fewer issues with thermostats and tempering valves. I asked about the pump (comment #6) because the Taco 0014 is a high velosity medium head pump and not a good choice for the application. Hot water recirc pumps should be sized just strong enough to circulate while there is no call for hot water. Anything stronger wastes energy & creates other issues: pressure, pitting of pipe, high temps through mixing valves.


 5 feet per Minuit is what we size them to. You don't need to move much water just enough to keep it hot. Most of the time in a house if it works out you can use a gravity system with no pump.


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## plumbdrum (Nov 30, 2013)

wyrickmech said:


> 5 feet per Minuit is what we size them to. You don't need to move much water just enough to keep it hot. Most of the time in a house if it works out you can use a gravity system with no pump.


 Your sounding a bit like RJ, lol. I miss his freakin humor.


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## BOBBYTUCSON (Feb 8, 2013)

Well , whats in the pictures should work. But i always install according to what the manufacturers specify. That being said , most of em are calling for install around the hight of the cold inlet. Anothet point , stay the hell away from liang. They are gking down hill. Grundfos is my go to now


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## wyrickmech (Mar 16, 2013)

plumbdrum said:


> Your sounding a bit like RJ, lol. I miss his freakin humor.


 dam I did say that didn't I. Lol


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## JimmyMac (Nov 4, 2015)

Yes it should have a check on the cold side, then will also need to install an expansion tank to keep from stressing out tanks. 

Question on why homeowner never saw it, what is the location of the water heater? My guess is basement, can see the block wall behind the insulation. If that is the case then answer is gravity, much harder to migrate water UP, than down or horizontally.


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## jeffreyplumber (Dec 7, 2009)

Good point on expansion tank. No proper installation of a water heater is don
e without it (at least where I come from upc in ca). 
Check valve Im going back and forth on that I have had fixtures very close to the water heater send warm water out the the cold side of faucet. piping to bottom of heater at the drain might help that not totaly sure. But I have run them high and worked on houses that way with no check and no undesired symtoms. I suppose installing the check valve would insure no ill afects. just not 100 percent sure its nedded


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## plumberkc (Jun 23, 2011)

jeffreyplumber said:


> Good point on expansion tank. No proper installation of a water heater is don e without it (at least where I come from upc in ca).


 That's not true. I bet you've never actually tested for thermal expansion. I do it almost everyday, with an isolated expansion tank you can actually test to see how much it helps regulate. Nowadays homes are being built with PRV's even when the pressure is under 75. This makes them a closed loop but unless there is a check,the pressure will almost never exceed the city pressure. Other meters around the country might be more restrictive but I doubt it. 

Thermal expansion doesn't happen on open loop systems. People argue the meter will have a check but that's not case around here, at least 95% of the time. 

I'm sure a lot of good plumbers disagree with me here but I would invite somebody to prove me wrong with a video. Setup the expansion tank with an iso valve and close it off. Show the meter, main shutoff, and water heater with a gauge showing the pressure rise. 

Everybody is jumping on the bandwagon blaming every burst pipe on thermal expansion. I've had several calls ranging from attorneys to people trying to sue their builder. I would almost go as far to say that thermal expansion tanks will end up causing more floods than they prevent.


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## justme (Jul 4, 2012)

plumberkc said:


> That's not true. I bet you've never actually tested for thermal expansion. I do it almost everyday, with an isolated expansion tank you can actually test to see how much it helps regulate. Nowadays homes are being built with PRV's even when the pressure is under 75. This makes them a closed loop but unless there is a check,the pressure will almost never exceed the city pressure. Other meters around the country might be more restrictive but I doubt it.
> 
> Thermal expansion doesn't happen on open loop systems. People argue the meter will have a check but that's not case around here, at least 95% of the time.
> 
> ...


Spot on.


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## smoldrn (Oct 4, 2010)

plumberkc said:


> . I would almost go as far to say that thermal expansion tanks will end up causing more floods than they prevent.


I've seen a lot of rusted expansion tanks. Some have split and caused a flood. I remove them and install a thermal expansion valve.


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## jeffreyplumber (Dec 7, 2009)

plumberkc said:


> That's not true. I bet you've never actually tested for thermal expansion. I do it almost everyday, with an isolated expansion tank you can actually test to see how much it helps regulate. Nowadays homes are being built with PRV's even when the pressure is under 75. This makes them a closed loop but unless there is a check,the pressure will almost never exceed the city pressure. Other meters around the country might be more restrictive but I doubt it.
> 
> Thermal expansion doesn't happen on open loop systems. People argue the meter will have a check but that's not case around here, at least 95% of the time.
> 
> ...


 
I was comenting on a check valve on the cold inlet . If your saying its not true an expansion tank should not be used in such case I disagree. True though that an "open " system will not cause excess presure from thermal expansion. As far as I know code requires them here but mayby its just because I havent plumbed a new house in Decades that didnt recieve a prv.
If I were messing around with a tand p over and over again I would at least look into the posibility that a thermal expansion could be involve. Your right Ive never tested for thermal expansion. How do you do your tests ?


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## plumberkc (Jun 23, 2011)

You definitely should have one when there is a check valve. Whenever I see a check in the meter I start asking the HO questions. They always tell me about all the issues they have had with crappy washing machines, faucets, toilets, and sometimes their dishwashers.

Testing for thermal expansion will require adding an isolation valve for your expansion tank. Let the tank fill up with the isolation valve open. As soon as the tank is full and the air is purged put a gauge on the boiler drain. Light the heater and go about your business for the next 5-10 minutes cleaning up after your install. Make sure nobody is using any water, after 10 minutes you should have an increased pressure of thermal expansion is taking place. If your pressure is rising, say to 85 psi go ahead and open up the expansion tank. You'll see the expansion tank doesn't regulate pressure the way you might assume. Usually has to be about 7-10 psi higher than the wp for it to take on any water.


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## plumbdrum (Nov 30, 2013)

Water heater flue is wrong. Lol


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## jeffreyplumber (Dec 7, 2009)

Thanks KC sounds like a way to testbut like you said unless its a closed system wh y bother testing? also since your against expansion tanks if it passes the test you leave the valve shut off and remove the tank thats prone to causing floods? In the case where the expasion tank is needed our code requires that no valve be installed between the heater and the exp. tank. So that would have to go after the test. You do them this way almost every day?


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## jeffreyplumber (Dec 7, 2009)

btw. KC dont mean to pick but doesent your exp. tank tee off need to between the cold water shut off and the water heater? It sure looks wrong to me.


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## plumberkc (Jun 23, 2011)

I will usually leave them on even if there is no thermal expansion. I make sure to explain to the HO that the expansion tank will fail before the water heater. Once it fails they have the option to turn the valve off. The reading isn't always 100% accurate. A humidifier can prevent thermal expansion as well as a bad fill valve. 

I'm not sure of your point about the expansion of the tank being below the shutoff. I usually try to install them that way if I don't have a separate isolation valve. In this case I don't see the point.


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## jeffreyplumber (Dec 7, 2009)

your installation looks good but I dont think your allowed any valves between the water heater and the expansion tank because if the valve are closed there is no protection provided. yours has 2 valves that when closed will negate the expansion tank. In practicle terms its unimportant but I dont think it would pass inspection.


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## Workhorseplmg (Apr 10, 2013)

jeffreyplumber said:


> your installation looks good but I dont think your allowed any valves between the water heater and the expansion tank because if the valve are closed there is no protection provided. yours has 2 valves that when closed will negate the expansion tank. In practicle terms its unimportant but I dont think it would pass inspection.


I've bid jobs with approved plans that show a valve between the expansion tank and water heater. I don't think it's a good idea but that's the way they were drawn and approved.


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## MACPLUMB777 (Jun 18, 2008)

plumberkc said:


> I will usually leave them on even if there is no thermal expansion. I make sure to explain to the HO that the expansion tank will fail before the water heater. Once it fails they have the option to turn the valve off. The reading isn't always 100% accurate. A humidifier can prevent thermal expansion as well as a bad fill valve.
> 
> I'm not sure of your point about the expansion of the tank being below the shutoff. I usually try to install them that way if I don't have a separate isolation valve. In this case I don't see the point.


 Because when the cold valve is off the thermal expansion can rupture the tank!


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## tater6061 (Feb 25, 2013)

In Commercial applications, we always tempered the cold supply to ease the temperature split, the circ pump was piped between check valves to reduce the risk of cross flow.


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## tater6061 (Feb 25, 2013)

And I'm pretty sure it would be Full Port valve, check valve, expansion tank, , & dielectric connection to water heater.If you want a recirc pump in the mix put it in before the check valve, and have an isolation valve, and check in front of the pump.


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## tater6061 (Feb 25, 2013)

Dang it, the expansion tank should be between the heater and check valve... 
It looked good at midnight, but the way I wrote it up the first time didn't protect the waterheater. 
During thermal expansion event, the check is closed and there is nowhere for the excess pressure to go. 
None the less, In Ft. Worth, we have to build upsidedown p traps with the waterlines to create a heat trap. It just came out of the slab about 7 feet, another 6" is the answer??


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## sparky (Jan 8, 2014)

wyrickmech said:


> 5 feet per Minuit is what we size them to. You don't need to move much water just enough to keep it hot. Most of the time in a house if it works out you can use a gravity system with no pump.


Where would you tie the hot water return line back in at the heater???at top or bottom and wouldn’t you need a check valve on the hot water return also???can somebody draw up this system using no circulating pump???


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## sparky (Jan 8, 2014)

Anyone seen RJ around!?!??


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## GAN (Jul 10, 2012)

sparky said:


> Where would you tie the hot water return line back in at the heater???at top or bottom and wouldn’t you need a check valve on the hot water return also???can somebody draw up this system using no circulating pump???



Remove the drain valve, pipe in a tee connect the return there and replace the drain valve. on a residential top fill heater. Natural convection drives the system. Heat up, cold down.

When you do a gravity loop the return line is smaller 3/8" and ideally should be below the feed at the point it takes off to return. If done correctly natural convection takes over.


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