Help with a recirculating system

[hotwire73]

I got a 36kw endless hot water system, and put a 6 gallon Rheem 120v behind it to cut out the delays in hot water, and use the 6 gallon to take care of the recirculating system. Now what I am having an issue understanding is how a recirculating system ties the hot and cold water supply lines together at the farthest point and not interfere with the cold water supply. If the water pressure is 75 psi on both sides, while I can grasp the concept of using the pump to push the water back around, how does this not interfere with the cold side when only cold is used? My other concern is Im using expansion pex, and a hub to route the cold water to each area, is this a risk to that? Sorry to sound like such a noob, Im just not grasping the concept without losing somewhere. From experience to push the cool water back down the cold side, would mean the psi would have to be greater coming in the hot side to push it back down the cold side, thus 75 psi on hot side would have to be at least 80-100 or something to actually push that cold water back. Any direct explanation would be greatly appreciated, or suggestions.

 

[frodo]

the circ line ties into the hot line not the cold line

 

[hotwire73]

Your drawing is showing a blue line. I know there is an option of adding a line, but most of these units show just using the 2 lines, thus pump on heater, and a connector at the farthest point that ties the cold and hot lines together.
For reference Im looking at the WATTS Series 500800.
This install is on a 2nd floor where its not easy to run a 3rd line without ripping some walls back out of the first floor, why Im looking at these systems that just tie the cold and hot water supply together at the farthest point. I just dont get how they work without causing other issues.

 

[hotwire73]

Their systems show similar to these installs. I just dont get how it is doing enough pressure to force the cold back on a connected line without some issues.

 

[havasu]

I have a Grundos recirc system installed at my house and the only drawback is the cold water to the farthest (connection line as shown above) faucet has tepid cold water for the first few seconds out of the cold water side of the faucet. It is not hot, but you know the water has been warmed somewhat. The thermostat will shut off before you receive any hot water out of the cold water side of the faucet.

What are some of the other issues you see?

 

[hotwire73]

One how is it forcing the warm water down the cold side, and what risk is it on hubs. That is one of the issues, technically you would have luke warm for cold as well. 1 do you lose any volume of cold water due to this setup? 2 can expansion pex take the forced back water pressure though a 6 way hub without any issues?

 

[havasu]

Since the end faucet connection is thermostatically controlled, only about a quart of water is noticeably warmer (not hot, but warmer than pure cold water). The pump pushed the cold water from the hot side backwards into the cold water side at a very slow volume, so there is no radical pressure used. It is safe for all systems as far as I know. I will tell you that my farthest sink use to take at least 5 minutes to get warm, which was all water down the drain. Now, depending on if I have my timer set properly, I flip the faucet on hot, and the hot is immediate.

I will add that I am not a professional plumber myself. I am just an old, retired guy who does lots of work around the house, and knows what works and what does not work. My "other half" is very happy at the instant hot water, and I know my water consumption has been greatly reduced, which is very important since I live in Southern California.

 

[Caduceus]

The manufacturers literature should explain that the hot water is recirculated drawing the hot water through the cold piping in a loop and when you turn on the cold water there may be a brief moment of warm water before the cold comes through. There is an integral check valve that is supposed to keep the hot and cold water from crossing over and mixing during times when cold water is only in use.
This is not a typical recirculation system and is for home owners who do not want the added expense of piping and remodeling to install a full recirculating system.
There are no additional pressures added to the system it is just recirculating what pressure is already there.

 

[hotwire73]

Thanks, just curious if anyone has done this on a expansion pex system using a 6 way hub. I have just redid the pipe from the meter to house and added a pressure regulator and will be redoing all the plumping on the first floor to expansion pex. But I had spent about 60 bucks for 2 hubs to route the water to each area from one centralized area. I just want to have a full understanding of what Im dealing with since Im installing a new endless system so I can do everything right the first time. My new addition to home is only 3 years old and is cpvc, but Im debating ripping out part of the ceiling and a wall to run a return line for this system.
Hasavu, Im retired to at a young age being a disabled vet, so I have to do all the work myself and just learn as I go. Nothing is really that difficult to do; the hard part is getting facts and the truth.
If there any pros on here that has installed this both ways, extra line versus cold line return; and have done this for years; please list the pros and cons of long term use. Im currently looking at a watts, but would rather have something that can be controlled in home or timer set, my artifical knees cant keep going in the crawl space every time I need to adjust the timer. If you know any units have stood up to the test of time, please post.
Tks caduceus, was curious since I seen alot of units using different size motors to pump, yet I seen people posting you dont even need a pump. Thanks for clarifying. Please list any units you know that are best for the price.

 

[frodo]

my opinion, you cant buy a cup of coffee with it, but i give it out any way.

is a 3rd line that runs from the farthest fixture back to the water heater.

for control, different options.

if you want to circ 1 bathroom, run a romex with the 3rd pipe from the water heater to the light switch in the bathroom
when you turn on the light, the pump comes on, circ's the water.

if you have 2 bathrooms and you want to control the pump from both bathrooms

run a traveler wire from bathroom to bathroom and use 2 , 3 way switch's

hope this made since,,


i do not like the under sink circ pumps..no reason, just dont like em

 

[Mr_David]

A more reliable recirc system is one that uses a 3rd line like FRODO described.
If you have the ability to run a third line do it. Those systems like you are showing are typically for using with an existing hot and cold system that wasn't built with a third line.
The comfort systems I have used, have the pump at the heater and a thermostatic block valve at the furthest fixture.
When the warm water reaches the block valve it closes thermostatically allowing only small amount of warm water to pass into the cold.
The same thing with the system you have.

The recirc pump is not a true pump. it only cups the water and moves it in a closed system. It does not increase the pressure of the hot system.

The system you are looking basically stops /slow the recirc flow as the temp passes through the thermostatic. the cold system near the thermostat valve will always be a little warmer than normal.

with a third line you can have it on a timer or even a switch. turn on the switch a couple minutes before you need to use it.
In a third line system the water temp is going to be more consistent.

 

[hotwire73]

Thanks Frodo, what Im having issues finding is the regular recirculation pumps with the 3rd line standard, with the remote sensors etc. But anyway if I do this, I planned on running from the hot water heater to kitchen 10 ft away, that is sink dishwasher and pot filler, back to lower bathroom (15 ft) that will branch off to faucet and tub, then back to the new addition up to the 2nd floor to the 2 man whirlpool, 2 sinks, and shower (30 ft from the lower bathroom). The idea I think will work best is the shower since its the furthest point and if Im willing to add 6 ft to the run total I can bring that return line down beside the staircase back to basement to the unit. So hard to do holes in those engineered truss's over 1 foot between floors with insulation in them. If you have a supplier that does these systems let me know, all I can find is lowes, home depot, and amazon, that all sell the standard cold/hot line tie in units.
Just seen your post Mr David, same thing if you know a supplier. I have completed the 2.5 story addition and it will be difficult but not impossible for me to add a 3rd line using pex. Again all the units I find are the hot/cold tricks. I would like a good quality recirc with dedicated return line, with the ability to be changed in a room remotely.
As for 3rd line being more consistent, I see that thus why Im willing to tear out sheetrock. No matter what if you jump in shower, it will have a mix of warm water in the cold line with the hot water side, after a few minutes the cold will catch up, thus you may get a shock lol. No matter what it will be a matter of fighting the hot/cold mix to get comfortable every time you take a shower using cold line for return.

 

[hotwire73]

36kw endless hot water heater, runs into 10 gallon 2kw standard rheem, then recirculator connected to it and looping back to it. Would I need to add an expansion tank or check valve for this anywhere, this is something Im not sure on.

 

[KULTULZ]

This type of hot water circulation (Passive Flow Control) makes me uneasy as hot water is introduced into the cold water supply (drinking).

What is/may be contained in a tank water heater system is undrinkable.

Read this- http://www.redytemp.com/hotwatercirculatorproblems.htm

 

[frodo]

Thanks Frodo, what Im having issues finding is the regular recirculation pumps with the 3rd line standard, with the remote sensors etc. But anyway if I do this, I planned on running from the hot water heater to kitchen 10 ft away, that is sink dishwasher and pot filler, back to lower bathroom (15 ft) that will branch off to faucet and tub, then back to the new addition up to the 2nd floor to the 2 man whirlpool, 2 sinks, and shower (30 ft from the lower bathroom). The idea I think will work best is the shower since its the furthest point and if Im willing to add 6 ft to the run total I can bring that return line down beside the staircase back to basement to the unit. So hard to do holes in those engineered truss's over 1 foot between floors with insulation in them. If you have a supplier that does these systems let me know, all I can find is lowes, home depot, and amazon, that all sell the standard cold/hot line tie in units.
Just seen your post Mr David, same thing if you know a supplier. I have completed the 2.5 story addition and it will be difficult but not impossible for me to add a 3rd line using pex. Again all the units I find are the hot/cold tricks. I would like a good quality recirc with dedicated return line, with the ability to be changed in a room remotely.
As for 3rd line being more consistent, I see that thus why Im willing to tear out sheetrock. No matter what if you jump in shower, it will have a mix of warm water in the cold line with the hot water side, after a few minutes the cold will catch up, thus you may get a shock lol. No matter what it will be a matter of fighting the hot/cold mix to get comfortable every time you take a shower using cold line for return.

if you can provide a simple one line iso drawing of your system
we can help.

something like this,,,simple,

 

[hotwire73]

Frodo I can try to work on a diagram somehow with paint, but all I need is a recirculation pump with a return line. I need or want the pump to a minimum 4 gpm flow. 3/4 of course. I want a timer on it or possible a remote system to kick it in. I just cant find one that is reasonably priced like 300 or so. Virtually every one Ive seen for sell is linking the cold and hot system, thus why Im asking if you have units you know the model to that you have purchased in past.

 

[hotwire73]

 

[hotwire73]

The endless and hot water heaters will be on top of each other in crawl space. All the Red is where its connecting to first floor, the green is connections to 2nd floor, and blue I can put in the wall and run back down to units. What Im having a hard time is finding a unit that does not want to just tie cold and hot together, and has a timer or a way to control it, plus does at least 4 gph or more. I do not want the small units that dont allow high flow. I already have issues with volume that I dont like and having to consider going from a 3/4 inch meter to a 1 inch sometime in future,

 

[hotwire73]

Havent seen any replies, for the pros that install these, what units are you using for a dedicated return recirc system?

 

[hotwire73]

Is there no professionals here that have installed a large enough recirc system to handle two appliances ( 2 showers at once)? If so please list the model and supplier of such, thanks..... What few systems I see are very expensive when it comes to higher flows.
Also if anyone has used a crawl space dehumidifier 208-240v for around 1200 sq ft that has stood the test of time with good results (low maintenance, hopefully some type that can self clean on filter) advise accordingly, thanks