Dedicated Hot Water Return Line - Concrete Foundation

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Greenthumb77

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My California home sits on a concrete slab. The water system has no dedicated hot wrer return line. My handyman friend said he could install a dedicated return line by teeing from the hot water line that comes up from the slab in my bathroom at the furtherest point from the water heater. He said he the would then install a recirculation pump at the water heater. He said that doing this would keep the cold water cold and solve my slow hot water to my kitchen island

Is this approach a sound idea? Can a dedicated return line be done like this where the system is looped uner the slab. If so, should I use pex or copper for the return line. Also, should the pipe size be 1/2 or 3/4 inch.

Please let me know what you think.


Thank-you

Jim
 

Gary Swart

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Not totally wrong, but I would advise a pump in the return line. I use a Laing system, and Grundfos has a good one as well. Google them and take your pick. These require some simple but necessary things besides just the piping. I found mine on that well know auction site several years ago and it has worked perfectly. Their websites have videos and installation instruction.
 

Smooky

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I would think if the problem was at the kitchen sink then that is where he would tee into the line. If all the hot water is branched off one main line, his plan should work. The reason he may not be teeing in under the island is that he plans to go overhead and not under the slab. Running under the slab will be difficult if it is not a suspended slab. The return line does not have to be very big to get the job done, so ½ inch should be fine.
 

hj

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The "concept" is fine, but it depends on the execution. IF the kitchen is NOT part of the run from the heater to the bathroom the circulation line will have no effect on how fast the water gets hot. I cannot imagine why, or how, he would think a circulation line would "keep the cold water cold", however.
 

Reach4

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I cannot imagine why, or how, he would think a circulation line would "keep the cold water cold", however.
I presume the OP had considered one of the systems that recirculates the water into the cold line. So compared to that, a separate return line keeps the cold colder.
 

JerryR

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Has anyone calculated the cost to continually heat the water that losses heat as hot water circulates in the insulated pipes under the slab?

I probobly have almost a 100 foot run from my HW heater to the master bath. It takes over 2 minutes at full hot, before hot water gets to that shower. Thats 5 gallons of wasted water down the drain before hot water reaches the shower.

Monitoring hourly ekectric usage it costs us about 40 cents for 2 consecutive showers.

If I take a shower 10 minutes after my wife does, the water is already no longer hot and takes another 2 minutes to stabilize hot again.
 
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Jadnashua

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One company did run some numbers...assuming that you have a system that has an aquastat that only actually flows water when needed and, you put the system on a timer such that it normally only runs when you are likely to use hot water, it ends up saving money when you also include the water and sewer costs. Most systems do not circulate and get the maximum water temp (typically 120F), they shut off the flow when things are warm at the sensor. It matters where you are sensing it, but many of them seem to shut off at about 105F. This usually means you have at least warm, and depending on where in the loop you're sensing, probably hot very close by. I'm using a RedyTemp unit, and I have it at the furthest point in my supply line, set to shut off when it gets warm (uses the cold line for return), and my shower is closer to the WH. I find that if I flush the toilet, by the time it has refilled, I have only a few seconds of warm water at the bathroom vanity tap before the cold runs cold. Otherwise, it may be warm (not hot, because I have the aquastat adjusted fairly cool) for up to about 30-seconds as it purges the cold line. Since everything else is closer to the source, with the setup I have, the cold stays cold since it doesn't need to pump all that much back. Every layout will differ, and where and how well insulated the lines are all make a difference. In the system I have, the pump tends to only run about maybe 5 to 8-minutes per hour in the winter. Many of them, the pump runs constantly, and the valves open and close to adjust the flow...this one I have, turns the pump on and off. Been going strong for over 10-years now. The check valves are rated at over 1M operations, but the pump may or may not last as long with the on/off cycles...but, it's still going! One that ran constantly would probably be dead by now after 10-years.
 

Jadziedzic

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A recent issue of Fine Homebuilding had some information on cost to operate, energy savings, etc. for recirculation systems - the current crop of electrically commutated motors cost surprisingly little to operate, and there's significant savings (hundreds of dollars per year) to be had due to less water down the drain.
 

Greenthumb77

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I would think if the problem was at the kitchen sink then that is where he would tee into the line. If all the hot water is branched off one main line, his plan should work. The reason he may not be teeing in under the island is that he plans to go overhead and not under the slab. Running under the slab will be difficult if it is not a suspended slab. The return line does not have to be very big to get the job done, so ½ inch should be fine.


You are correct. However the sink is plumbed into a kitchen island. My wife does remember getting hot water to the sink when the back bathroon hot was turned on or the adjacent utility room washing machine was running.

Thank you guys for all the help. May it be returned to you many times over.

Now to find best price for the Grundfos Comfory PM
 

Greenthumb77

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I called the distributor of the Grundfros and he said that running a dedicated return line up through the attic would requie an air vent on the suction side of the pump

What is an air vent
Do i install it near the hot water heater or up in the attic


Please advise

Jim
 

Jadnashua

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An air vent will let trapped air out of the closed system piping, but once water reaches that point, it closes. Because the pipe run would be going up, and the air in the dry lines will want to stay trapped up there when you turn the water on, and, because the pumps used for recirculation are really quite small, it will not have enough head to push all of that air out and through...the pump would just run, not pumping any water, and burn itself up. Those pumps get both lubricated and cooled because of the water flowing...no water flow, no cooling or lubrication. Most of those I've seen are not designed for potable water - they are very common in closed system hot water heating systems with a boiler. Those designed for potable water cannot be made of steel or iron, and must either be made of stainless steel, brass, or bronze. Those typically used on heating systems are steel/iron, because they are a lot cheaper. Something like this: http://www.supplyhouse.com/Watts-05...CsIp5A2GeCH1YBEoNbpDbF9LEuq9PoxfkYaAgpz8P8HAQ, but one rated for potable water (this one MIGHT be okay, but you should check).
 

Greenthumb77

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An air vent will let trapped air out of the closed system piping, but once water reaches that point, it closes. Because the pipe run would be going up, and the air in the dry lines will want to stay trapped up there when you turn the water on, and, because the pumps used for recirculation are really quite small, it will not have enough head to push all of that air out and through...the pump would just run, not pumping any water, and burn itself up. Those pumps get both lubricated and cooled because of the water flowing...no water flow, no cooling or lubrication. Most of those I've seen are not designed for potable water - they are very common in closed system hot water heating systems with a boiler. Those designed for potable water cannot be made of steel or iron, and must either be made of stainless steel, brass, or bronze. Those typically used on heating systems are steel/iron, because they are a lot cheaper. Something like this: http://www.supplyhouse.com/Watts-05...CsIp5A2GeCH1YBEoNbpDbF9LEuq9PoxfkYaAgpz8P8HAQ, but one rated for potable water (this one MIGHT be okay, but you should check).


Are yiu saying to have the air vent at the highest point on the pex line?

Also should the pex be insulated?
Should the pex be run on the attic floor or hung on the rafters?
 

Jadnashua

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You typically need a check valve to prevent water from running both directions in the recirculation line. As a result, if the air can get out of that loop, the water pressure when you first turn things on should purge the air if you have an air valve in there. Otherwise, it will be trapped, and you'll not get proper recirculation. If there is air on the suction side of the pump, it can't pump any water. Extracting it there would probably work...see what one of the pros thinks, but that seems to correlate with what the company said.

As to insulating the lines - it's always a good idea to insulate the lines, and on pex, depending on how your roof is constructed, it's possible you might get some UV in there and pex is not supposed to have extended exposure to UV sources. If there's any chance of freezing, I'd want the water pipe to be on the ceiling side of the insulation to protect it. That also would keep any UV off of it. Otherwise, put it where it would be out of the way and not damaged by stepping on it or storing things on it.
 

Greenthumb77

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An air vent will let trapped air out of the closed system piping, but once water reaches that point, it closes. Because the pipe run would be going up, and the air in the dry lines will want to stay trapped up there when you turn the water on, and, because the pumps used for recirculation are really quite small, it will not have enough head to push all of that air out and through...the pump would just run, not pumping any water, and burn itself up. Those pumps get both lubricated and cooled because of the water flowing...no water flow, no cooling or lubrication. Most of those I've seen are not designed for potable water - they are very common in closed system hot water heating systems with a boiler. Those designed for potable water cannot be made of steel or iron, and must either be made of stainless steel, brass, or bronze. Those typically used on heating systems are steel/iron, because they are a lot cheaper. Something like this: http://www.supplyhouse.com/Watts-05...CsIp5A2GeCH1YBEoNbpDbF9LEuq9PoxfkYaAgpz8P8HAQ, but one rated for potable water (this one MIGHT be okay, but you should check).

Does anyone know where i can a potable air vent ? I have done a lot of internet searching with no connection.

Big thx

Jim
 
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