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Old 10-26-2010, 12:33 AM   #1
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My hot water recirculation system is a disaster


I've now read a lot about the high expense of running a hot water recirculation system. With the benefit of hindsight, I would have not bothered with it. My system was installed by a professional plumbing firm but I am now questioning this. We use a standard 40 gallon natural gas hot water tank.

We first noticed that it was difficult to fill our bathtub with sufficient hot water. The water was instantly hot as expected but after a few minutes the temperature would drop to the point of being only warm. Suspecting that the recirc system was the cause, I disabled it (closed the valves to the loop and turned off the pump) and
allowed the tank to become fully reheated The tub now fills with plenty of hot water. I am now trying to understand why.

My theory is that when hot water starts to discharge from the tank (from the top) cold water is being put into the tank (at the bottom). Hot water rises and cold water sinks and so the two should remain relatively far apart so that only hot water is being discharged from the top until most of it has been used. However, with a recirc pump continually running the water in the tank is being stirred, mixing the hot and cold to produce warm water. Does this explain my situation?

With the pump running we have also noticed that the tank is being reheated many times during the day and night when no water is being used. During the building stage I made the suggestion to insulate the hot water lines but I was told that this was not needed. I also questioned placing both the hot and cold water lines too close together but was told this was also unnecessary. Our home is only 3400 feet on two levels and the tank is centrally located. Unfortunately, we now have warm water when we use the cold water (until enough water is used), we have high energy bills, and we have a warm bath. We do, however, have instant hot water!

I have since disabled the recirc system and have accepted waiting a few seconds for the hot water to arrive.

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Old 10-26-2010, 12:53 AM   #2
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My hot water recirculation system is a disaster


there should be 2 check valves on the hot water recirc system. One on the recirc pipe and one on the cold inlet before any tees to the recirc pipe. my first thought is that you have a bad check valve or are missing one. the pump can create negative pressure, sucking cold water into the recirc line and eventually to the fixture being used

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Old 10-26-2010, 12:59 AM   #3
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My hot water recirculation system is a disaster


Recirc systems do work when properly plumbed. I suspect that your heater is too small for a 3400 SF house
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Old 10-26-2010, 02:11 AM   #4
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My hot water recirculation system is a disaster


Quote:
Originally Posted by Michael Neill View Post
During the building stage I made the suggestion to insulate the hot water lines but I was told that this was not needed.
Seems to me that this is your problem. It's logical that in a hot water recirculation system both the hot lines to the fixtures and the return lines from the fixtures need to be insulated to prevent losing heat. In the perfect situation the water returning to the heater would be just as hot as when it left the heater. Of course this is not possible but insulating the to and from lines would work toward that goal.

I would insulate the entire hot water and return lines and then see what happens.

EDIT: To add to my reply, I think your uninsulated lines are working like a car's radiator. In an engine, heat is transferred to the water, then the hot water is sent to the radiator for cooling, then the return water to the engine is cooler. --- In your case, gas or electricity is heating the water in the water heater, then the hot water is sent to the long pipes (or tubing if PEX) which act as a car's radiator, and then the cooled water is returned to the heater. Your uninsulated system is working to cool the water in the heater.

Last edited by Homerepairguy; 10-26-2010 at 05:04 AM.
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Old 10-26-2010, 03:02 AM   #5
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My hot water recirculation system is a disaster


It sounds to me like the recirc system is incorrectly installed. Can you take some pics of what they installed and post them? Whats does the plumbing company say about this?
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Old 10-26-2010, 08:58 AM   #6
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My hot water recirculation system is a disaster


Your main issue is the insulation like others have mentioned, A hot water recric system is typically designed for a 10 degree temperature drop, so for example, the water leaves the heater at 120 degrees, flow through the supply and return piping and should return to the heater at 110 degrees. Without any insulation on the hot water piping, and depending on the length of the loop, your probably getting return temperatures around 80 degrees. You should also have an aquastat on the return leg which controls the pump, so when the return temp reaches a set temperature, it shuts off the pump. Your pump is probably running 24/7 because the return temp is not getting up to the set point because of the heat loss from no insulation. Also, you could consider getting a timer to control the pump during specific hours during the day, so the pump only runs in the morning and in the evenings while people are home to help limit energy loss. All this depends on the size of the loop and the gpm of the pump.

Also, you mention getting warm water out of the cold tap, that tells me you have hot water bleeding into the cold side somewhere close to the heater where the hot return and cold lines are piped back to the heater. There should be a check valve on the cold side before the hot return line ties in to prevent this, you should also have an expansion tank on the system because of the check valve.

If you could post a pic of the connections to the heater and the hot return/pump/valve configuration, that would help.
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Old 10-27-2010, 08:36 AM   #7
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My hot water recirculation system is a disaster


Stirring of the water in the tank is not (should not be) a problem because for those folks without a recirculation system the same stirring of water occurs when you turn on a faucet and cold water enters (hopefully) at the bottom of the tank to replace the hot water being drawn.

If only one person is using hot water at a time, the square footage of the house doe snot matter.

Getting lukewarm water from the hot faucet too soon, and/or getting warm water from the cold faucet with the recirculating system running and not with the recirculation system valved off means the system needs some mods (like check valves).

Getting a few minutes of hot water followed by lukewarm water is not a pipe insulation problem. But you should still insulate the full lengths of the pipes to minimize heat loss into the spaces inside the walls where the pipes run.
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Last edited by AllanJ; 10-27-2010 at 08:39 AM.
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Old 10-27-2010, 04:43 PM   #8
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My hot water recirculation system is a disaster


Here are some pics of what mine looks like for your comparison. It works like a champ, I have hot water at every faucet in under five seconds. Starting at the wall there is a ball valve, recirc pump, check valve, thermostat and then it tees off into the water heater and a drain spigot. That is also the flow of the water, from the house through the pump and back into the tank. I have no check valves on the top of the water heater only a ball valve on the inlet side. At this point insulating your pipes would probably pretty costly and labor intensive. I would make sure the system is plumbed right before anything else. Hope this helps and you get it all straightened out.
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Old 11-03-2010, 07:26 PM   #9
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My hot water recirculation system is a disaster


The need for a check valve seems clear. Is there a certain type, e.g., brass, or manufacturer that would be best? Are these valves OK with hot/warm water? My line is 3/4 in pex.
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Old 11-05-2010, 12:31 PM   #10
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My hot water recirculation system is a disaster


Just to tie up my question about the check valve for the hot water recirculation return line, I went to a plumbing supply store and was directed to a Campbell 3/4" check valve (CV-3T, $12).

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