I'm no plumber, but I've always been a mechanical type who likes to know how things work. I know I wanted to have instant hot water in my house, but when I set out to do my research on the 500800 hot water recirculating pump (and similar products), I was dismayed by the lack of information about how it works. Fortunately, I arrived at an understanding, which I hope to share with everyone here.
Recommend this product?
Here's the setup: you've got a large house, or a house with many floors. When you go to take your shower in the morning or do anything requiring hot water, the water heater is on the other side of the house and it therefore takes forever for the hot water to come up.
Why is this? When the hot water supply isn't in use, the hot water is trapped in the plumbing between your hot water heater and your faucet or shower head. Over time, this water cools down. So, when you turn the hot water faucet on after a long period of time, you first get the cold water (previously hot water) which has been trapped in the plumbing. Eventually, the hot water from the water heater follows behind it, but it takes some time for that to push through. In my home, it takes close to 2 minutes for the hot water to reach full temperature.
Most people accept this shortcoming because waiting for hot water isn't a big deal. But is there a solution? From what I've found, there are two basic solutions. The details vary, but here's the short version.
In most normal household installations, hot water originates at the water heater, flows through the pipes and terminates at the faucets. When the hot water faucet is off, the water remains trapped in the pipes and cools off. When the hot water faucet is turned on, the water comes out--first the cold water that's been trapped, and then eventually the hot water. According to this solution, a plumber installs a return line from the faucet back to the water heater. So instead of the hot water terminating at a dead-end, it instead circulates continuously: it goes out to the faucet via the usual plumbing and back to the water heater via the return line. A continuous circulation of hot water guarantees that hot water will always be available. The problem, of course, is that the return line is just another set of pipes and unless your house was built with this in mind, chances are the plumber is going to have to open up the wall to do the job.
Solution 2 is employed by the 500800 Hot Water Recirculating Pump with Timer. The novelty of this product is that it uses the same general approach as described above, but doesn't require a special return line. Instead, it uses your existing cold water line as the return line. I was scratching my head for days trying to figure out how this could possibly work because common sense says that the direction of flow should be going TO the faucet, not back to the water heater.
I finally came across an elegant explantion of the operation. To understand how it works, I first need to explain the two main components of this 500800 kit. First is a special connector pipe which is supposed to be installed on the faucet furthest from the water heater. Basically, it connects the hot water supply to the cold water supply, but restricts the flow so that the water can only flow in one direction: from the hot side to the cold side. Also, there's the pump, which is installed on the hot water outlet of the water heater. Its purpose is to create extra water pressure on the hot water line, over and above the pressure already provided by the water heater.
So how does this work? Under normal circumstances, with both hot and cold water faucets turned off and no pump turned on, there's equal pressure in the hot water line and cold water line running to the faucet. Since the pressures are equal, the water goes nowhere unless the faucet is on. What about when the pump is on? The pump essentially increases the water pressure leaving the water heater. This extra water pressure created by the pump travels all the way to the furthest faucet where the special connector pipe mentioned above is installed. At this pipe, assuming both faucets are still turned off, there is now a pressure differential: the hot water side is greater pressure than the cold water side. Consequently, the water begins to flow from high pressure to low pressure. That is, from the hot water supply to the cold water supply. That is, the cold water travels not TO the faucet, but rather FROM the faucet back to the water heater. So, the cold water supply acts like a return whenever the pump is operating.
The underlying assumption here is that the hot water line has cold water in it (previously hot water which cooled off), which is now being moved to the cold water supply. In actuality, it will move both the cold water and then whatever hot water is right behind it, leaving you with possibly hot or warm water on the "cold" side of your faucet. For this reason, operating the pump continuously is not a good idea, but should rather be set to periodically turn on.
The pump installation really requires a plumber. This is not a self-install item unless you know what you're doing. In some states or municipalities, a license and/or permit may be required. The pump must be connected directly to the hot water outlet of the water heater. Once installed, the pump has a straightforward timer mechanism. If you don't like the built-in timer, you can leave the pump in the continuous "on" position and plug the AC cord into another timer of your choosing, or leave the pump running continuously.
The special connector pipe, on the other hand, can be installed by a do-it-yourselfer. At most, you may need a trip down to the hardware store for a couple faucet hoses.
The pump timer is analog. You can program the pump to turn on or off in 15 minute increments by moving the switches on the timer face to the "on" or "off" position. The idea is that you should program it to be "on" whenever you require instant hot water, and program it to be "off" at all other times to save yourself the costs of electricity.
This unit was pretty cleverly designed, but it's not perfect. Whenever the pump is running, you are potentially pumping hot water into your cold water supply line, unless you've fine-tuned the timing of the pump. So what could happen when you turn on your cold water?
That depends on where you are. On the facuet where you installed the special connector pipe, expect warm or hot water to initially come out the cold water side, but then it will taper off to cold water. That is to say, you'll have the opposite problem you had before you installed this product, which is that instead of waiting for hot water, you'll now wait for cold water.
However, this is not the case everywhere. It seems that the further away in distance you get from that faucet with the special connector pipe, the less of an issue this is. All of the faucets may suffer from this problem to some degree, but it seems like the one with the special connector pipe will be the worst. This makes sense because that's point at which fresh hot water is being injected into the cold water line--the further you get from it, the less hot/warm water you'll find in the cold water line.
In my particular installation, this issue was unnoticable everywhere in the house except at the faucet with the special connector. Even then, it wasn't that bad.
Whether this product is right for you depends on how annoyed you would be about hot/warm water coming out of your cold water faucet momentarily whenever you turn the cold faucet on. If having hot water immediately available to you is more important to you than the annoyance of having to wait a few seconds for the cold water side to cool down, then this product may be right for you. I should emphasize that, in my experience, the wait for cold water is generally a few seconds, whereas I was waiting 2 minutes for the hot water before I installed this product. For my particular application, the benefit outweighed the risks.
If you have small children, you may need to evaluate whether having warm or hot water coming out of the cold water faucets is a good idea for you.
As for appliances: in my experience, this product generally doesn't cause a big issue for washing machines on the cold cycle because any warm water coming out the cold water side of the intake of these appliances will generally be very brief and will eventually be diluted by the remaining cold water. If you have other appliances that are sensitive to taking in strictly cold water only, you may need to evaluate whether this product is a good idea for your application.
If you do encounter any problems, one thing to keep in mind is that you can always turn the pump off for good and your faucets will return to their previous behavior, as if the product was never installed.
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