Waiting for hot water at the sink or shower can waste thousands of gallons of that precious resource every year. The wealthy have long been able to overcome this problem through the use of highly expensive hot water recirculation systems that were built into their hot water heater. These systems are different than our own. Where we have a hot and a cold line recirculation installations have two hot lines and one cold. Three lines instead of two plus a recirculation pump at the water heater. With this elaborate system, hot water is almost instantaneous at every fixture in their home. The thermostatically controlled pump shuts off when water in the line is hot end to end. As soon as the water cools, the pump starts again. Short of adding an additional water heater, this technique has, for years, been the most cost-effective method of getting instant hot water to all plumbing locations in the home – helping to cut down on wasted water by eliminating the wait for warmth. By the way, there is a caveat. It sure is nice not having to deal with 38-degree water at 5 A.M. on a chilly winter morning. Instant hot is very cool – if you get the pun.

Over the last two decades Hot Water on Demand systems have flourished. Everyone has gotten into the act. These systems have become simplified beyond belief and cost really has come down while installation has become something that most modestly skilled DIY’ers can do themselves in an hour or two.

Auxiliary Water Tanks:
When hot water on demand is mentioned some think of a small auxiliary water heater placed beneath the sink that provides hot water at all times. A secondary water heater if you will. These work well to solve the problem at a given sink. However, shower water – where most waste occurs – cannot be so easily retrofitted with such a unit. Another drawback to auxiliary heating tanks is that electrical is required for each unit – usually a dedicated circuit because of the great amount of current required to heat the water. Important to keep in mind that these units usually only handle one sink per. If you have 3 or 4 sinks you’ll be looking at a cost of at least $2,000 in heating units and electrical installations – not practical in our estimation.

Pump Systems:
Our idea of hot water on demand is a bit different than adding tanks. Why not – we’re guys – we like adding motors instead. Also, our choice of new technology utilizes that once used by only the wealthy, but with a couple of really cool twists that what’s new so inexpensive to purchase and so easy to install. And all without hot water pipe number two we might add. The theory is a brain twister because it is so very simple. There are two types that we like.

Grundfos Comfort System
Our first choice is one that involves the installation of a motor at the water heater and a small plastic pipe under the sink known as a crossover:

• First, a very small high speed, low volume (extremely quiet pump) is added to the outgoing hot water line at your water heater. We took about 20 minutes to install ours. The pump is regulated by a simple timer that causes it to run during those times of the day or night when you feel you will want hot water on demand. We had to use an extension cord to provide 110v power to our unit. The pump can be set up to run for as little as15 minutes once a day or 24/7 – you choose when you will need or want the convenience of automatic hot water when you turn on the faucet.

• In these systems there is no need for a secondary hot water line. Instead there is a 6 inch long plastic “crossover” pipe that connects to the faucet which lies farthest from the water heater – and thus impacting all fixtures in between. The crossover connects the hot and cold water lines together and contains a check valve so that the cold water won’t back up into the hot water line. The crossover is also thermostatically controlled and when it senses cold water in the hot water line it opens and lets the water silently run into the cold water line (and back into the water heater). This simple process continues until the hot water arrives at the faucet. Instant hot water at every location in your home with 2 simple additions – a pump and a crossover. When the crossover senses the heat it shuts off. The process repeats when the water cools (as long as the timer is set in the on position). What could be simpler?

The Metlund D’Mand System
Another on demand system the Metlund D’Mand system works especially well with thankless and hybrid water heaters. In fact it is the only one we know of that does. This system differs from the Grundfos in that it requires the pump to be installed under the sink (rather than at the water heater). Interestingly, the pump, thermostat and the crossover in the Metlund unit come in a single package (as a combined unit) making installation quicker and by far the least complicated. As with the Grundfos the Metlund needs a 110v power source. Unfortunately, with the Metlund you will probably have to add one since we don’t usually find outlets under sinks.

A manual switch is provided with the standard unit so that the pump can be turned on only when needed or wanted. An optional remote relay allows the use of a wireless control that turns the unit on from anywhere in the home. For example: you get up in the morning and before hitting the potty (or during) simply hit a remote relay and the system starts and runs only as long as it takes to heat the water all throughout the home – showers sinks – everywhere. Water gets hot and the Metlund system shuts off. Now that’s cost effective hot water management. And not one drop of water spilled with either of the tow types of recirculation units. User management or not this system is truly the most “on demand” of them all. Metlund’s mid-priced unit, the S-70 runs about $400 bucks with one remote control and one manual switch.

The Grundfos kit with a pump and a crossover retails for about $450.

It should be kept in mind that both of the systems that we have mentioned recommend a single installation. However, in our home we have two crossovers, because the water heater lies in the middle of our plumbing system rather than at one end. So here’s how the prices play out when two units are needed:

Metlund
$400..................First Unit
$400..................Second Unit
$200 each.........Electrical
$1,000...............Total Cost

Grundfos*
$450...................First Unit
$50.....................Second Unit
$0.......................Electrical
$500...................Total Cost
*System does not work well with on demand or hybrid water heaters.

Although the Metlund come out more expensive in the short haul the Grundfos will cost more money over the years because it runs by timer rather than on price demand.