Should I install a recirculating system?

DawalliAugust 14, 2014

My question is twofold and please bear with me. I am new to all this and so I may not have the terminology right.

1) I have a house that is being gutted and new plumbing put in. Should I put in a recirculating system? I have been looking at the ACT D'Mand Kontrol System.

2) Since I am putting in a new plumbing system, is it worth it to put in a dedicated return line? Or since the D'Mand Kontrol System can be used with or without a return line, would it just be an unnecessary expense?

Some additional info: I have a standard water heater tank and I'm not looking to replace it since it's 3 years old. I'm not sure if it's gas or electric. The house is a 2 story with 3 bathrooms, but only 2 will be used regularly. The water heater is in the attic. We don't have a basement. A bath is run for the kids every night but we keep that water quite shallow.

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jakethewonderdog

A recirc system will reduce the amount of time you wait for hot water. The question of "should you install one" is entirely up to you.

The positives are that they can reduce your wait for hot water and may reduce your water usage if you run a lot of water waiting for it to get hot. The negatives are the cost of the system and that it will increase your energy usage somewhat through the loss of heat to the surrounding area.

If you do put one in, put in a dedicated return line since you are redoing the plumbing. Otherwise your cold water will be warm.

Also - very important -- insulate all of the hot water lines including the dedicated return.

The D'Mand Kontrol System seems pricy for a residential system.

    Bookmark   August 14, 2014 at 3:01PM
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Dawalli

Would you please elaborate on your comment about heat loss to the surrounding area? Why is there more heat loss with a recirculation system versus a standard plumbing setup?

    Bookmark   August 14, 2014 at 5:40PM
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saltidawg

If you use the cold water supply at the remote location to simply recirc the water FROM the hot water heater back TO the hot water heater, there is no measurable loss of heat. You only operate the recirc pump when you intend to use hot water heater.

    Bookmark   August 14, 2014 at 7:07PM
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jakethewonderdog

What Saltidog said is not correct.

The reason that you have a water circulation system is because the hot water in the pipes lose their heat through the pipes to the surrounding air and become room temperature instead of warm. This can happen quickly (about 10 minutes) if the pipes aren't insulated.If the pipes are insulated, it will take about an hour.

With a standard system, this happens once (or every time the hot water is used).

When you have a circulating system, regardless of if it uses the cold water line or a dedicated return line, the pump keeps the water in the lines hot by moving the cooled water back to the water heater. The heat loss through the entire loop is continuous.

If those pipes are not insulated, that heat loss can be significant. If they are insulated, it will be much less, but still an issue (pipe insulation is only about 1//2" thick over a significant surface area). If you are heating the space anyway, there's no problem. If you are cooling the space, you are paying to add heat to a space that you are paying to cool.

Many circulating systems have a timer on them, to reduce this heat loss when people aren't likely to be using the plumbing ( I can't imagine that being effective since my schedule isn't that predictable). Others use a thermostat on the pipe. The most efficient use a demand system (you press a button before you want hot water).

The reason to use a dedicated return is so that you don't put hot water back through the cold water line. Otherwise when you go to get a cold glass of water, it's warm and you end up running the cold water to get it cold.

This post was edited by jakethewonderdog on Sat, Aug 16, 14 at 14:31

    Bookmark   August 16, 2014 at 9:02AM
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saltidawg

And again jakedog is mistaken.

The recirc pump only runs when you walk up to the sink intending to draw hot water.

You can run the hot water down the drain until it is hot enough...

OR

You can start the pump and recirc water back via the cold water line until it is hot enough.

In either case, if you want a drink of water you might get that first... however, I've never actually noticed the water heating up enough to be noticeable after running just a couple of glass fulls down the drain.

Assume that when you get to the sink or shower that there are two gallons of warm water in the hot water supply line coming from the hot water heater. There is very likely about the same amount - two gallons - in the cold water supply line. By using the recirc pump you'll replace the cold water line water with the hot water line water - essentially no effect. And you'll have hot water available at the sink/shower with nothing wasted down the drain. (Because there will some mixing of the hot water leaving the tank with the water in the line, there is indeed going to be some small amount of water that will make it into the cold water supply - but as I said, in my experience it is not noticeable.)

Jakedog has seemingly been going around posting in different forums information that has been at odds with a helpful approach. I'm not sure what is going on there.

This post was edited by saltidawg on Sat, Aug 16, 14 at 16:47

    Bookmark   August 16, 2014 at 2:55PM
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jakethewonderdog

Excuse me? I am neither mistaken nor being less than helpful. What I wrote was quite factual and accurate.

"The recirc pump only runs when you walk up to the sink intending to draw hot water." - Really?!? and how does it magically know you have walked up to the sink and intend to run hot water?

The overwhelming majority of recirculating systems are controlled by 1. a timer and/or 2. thermostat on the pipe -- The pump / controller that the OP was considering uses a thermostat only so it's keeping hot water in the lines at all times. Please note the timer on the link provided to one of the most popular retrofit circulating pump kits.

Timers tend to be disabled in practice, because you want hot water when you get up in the middle of the night to use the bathroom. Schedules aren't that predictable.

I have advocated on here for pumps triggered by motion sensing or on demand (push a button) but they are very rare.

Because circulating systems keep hot water in the pipes virtually all the time, they result in significantly more heat loss to the surrounding space. That can be reduced with pipe insulation, but the loss is still significant.

If you are installing plumbing - install the circulating return line. The systems that feed back through the cold water line are intended as retrofits. They work, but are less than ideal.

As water becomes more expensive, a recirculating system can reduce water usage. Insulating the hot water and return loop will reduce some of the energy wasted as a result. Pipe insulation can also greatly reduce the need for a circulating system in the first place. Running the circulating pump "on demand" will eliminate the energy waste factor completely.

Here is a link that might be useful: Pump with timer

    Bookmark   August 17, 2014 at 1:18PM
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david_cary

Agree with Jake. But I do use the timer, I can honestly say that I don't wash my hands if I go to the bathroom in the middle of the night.

There I said it. I wash my hands every other time but not in the middle of the night.

OP - you absolutely should have a dedicated return line. You absolutely should insulate. There are varying amounts but I would go with the largest (highest R value) available. It will pay off very quickly vs not using insulation. Even if you do heat the house all the time, usually the hot water heater is not as efficient as the furnace and it isn't putting the heat were you want it.

    Bookmark   August 17, 2014 at 4:11PM
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