Instant hot water has a lot to be said for it. Not having to stand around waiting is one. Saving tons of water is another. Instant hot water can save you time water and energy, and along with those savings are other less tangible benefits. Reduced green house gasses are released into the atmosphere when you use less water since it requires energy to pump and process water before it gets to your home, and then again as sewage. If you have a septic system it can extend the life of your system. If you are on a well, your pump won't have to run as much.
There are a variety of systems on the market today that are designed to get you faster hot water. There are different views on just what "instant hot water" is. Some people say that you have to be able to get hot water within a second or two after turning on a tap. With most of these systems there is definitely a waiting period, which usually occurs before you turn on the tap, so not all people view all of these systems as producing "instant hot water".
For our purposes we shall define "instant hot water" as that which arrives within a few seconds of turning on the tap even if you had to wait before turning on the tap.
One way to have instant hot water is to circulate the water in a big loop from the outlet of the water heater, past each fixture, and on back to the inlet of the water heater. In my opinion this is the only way to really have "instant" heated water. You walk up to the tap and turn it on, and within a second or two it's there.
At first this sounds like a great idea, but after closer scrutiny it becomes obvious that this system is not so great after all. It is an energy hog! What you end up with is a giant heat radiating system that keeps the water heater working harder and more often to keep this big piping radiator hot. Even if you insulate the heck out of the pipes, the surface area to volume ratio insures that you will consume a huge amount of energy. Energy to heat water is much more expensive than the water that is being heated.
These continuously circulating systems also suffer from breakdowns due to the fact that heated water tends to form sediment even while being circulated. This sediment gets deposited on the surfaces of the pump parts and pipes forming clogging deposits which cause breakdowns.
Continuous circulating systems won't work with tankless water heaters. This is unfortunate, since tankless water heaters take longer to get the heated water than normal plumbing systems. More wasted water is the result.
Grundfos and Taco are two manufacturers of continuous circulating pumps and systems.
An alternative to the continuous circulating systems are the temperature controlled circulating systems that use the cold water piping as the return line back to the water heater. Like the previously discussed system, the hot water gets circulated in a big loop from the water heater, past the fixtures, and back to the water heater. The pump is usually located at the fixture furthest from the water heater, and the inlet connects to the hot pipe and the outlet connects to the cold water pipe With some systems the pump can be located at the heater, and just a valve at the fixture.
Since you obviously don't want your cold water piping full of heated water, the pump has a temperature sensing circuit, and the circuit shuts the pump off when the water gets up to about 95 degrees at the pump. The pump turns back on when the water temperature cools down to about 85 degrees. This means that when you turn on the tap you don't have to wait as long for the hot water to reach you since the pipes aren't as cold and won't suck the heat out as much as cold pipes would and so you get hot water more quickly. It certainly isn't instant though.
These "luke warm" systems as I call them also waste a whole lot of energy since they keep the pipes full of partially heated water. They don't use as much energy as the standard circulating systems, but they still use much more energy than a normal plumbing system uses.
Again, as with the previous types of systems the luke warm systems will not work with a tankless water heater. They pump water much too slowly to activate the tankless water heater's flow switch, and so they would just circulate cold water around and around.
Manufacturer's of the luke warm systems include RedyTemp, Laing, Grundfos and Watts.
The good news is there is a type of system that gets you fast hot water, doesn't run water down the drain, doesn't use more energy, and even works with tankless water heaters. In addition it is inexpensive and easy to install. The type of system I am talking about is a "demand system". When you "demand" heated water, by pressing a button, the pump comes on and pumps the heated water to your fixture rapidly. As with the luke warm systems, the pump is located at the furthest fixture from the heater, and connects to the hot and cold lines.
Instead of being temperature controlled though, the pump only turns on when you turn it on. It has a temperature sensor built in, and when hot water reaches the fixture the pumps shuts off. At that point you have instant hot water when you turn on the tap. Since the heated water was not circulated, you did not use any more heat energy than if you had a normal plumbing system. Since the pump only runs for a few seconds each time, it only uses a dollar or two per year in electricity costs. If you have a system with a powerful pump like the Chilipepper CP6000 pump, you can get your water much faster than normal. The CP6000 pumps up to 3 gallons per minute, and many fixtures limit flow rates to less than one gallon per minute. So you can get your heated water up to three times as fast. And what you get is hot water, not luke warm water.
The demand type systems do not seem to have any drawbacks. They get you your hot water faster, saving you time. They don't use more energy than a standard system. They are inexpensive, or at least some of them are. And some of them work with tankless water heaters as well. As long as the pump is strong enough to turn on the heater, it will work.
The Chilipepper pump has the strongest pump on the market and will turn on any tankless water heater. Metlund makes several models, and not all will work with a tankless water heater so if you have a tankless water heater check with the manufacturer to make sure it will work with your model of heater.
Demand systems are typically inexpensive, the least expensive being the Chilipepper at about 0.00, and Metlund with several models under 0.00. Taco also manufactures a demand system very similar to the Metlund D'mand system. Often you can install them without even turning off the hot water to the house, just turn off the angle stops under the sink where you are installing it. You will need a 110 volt outlet to plug the pump into.
If you decide you are interested in a demand type system check with you local water company, as several water companies around the country offer their customers rebates of up to 0.00 for the installation of such a system to conserve water. So be green, help out the environment, and stop waiting for hot water.
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