Hot Water Demand Systems & Tankless Water Heaters – Great Home Improvement Products!

If you are looking for home improvement products, here is a great combination. Tankless hot water is energy efficient but it wastes water. Adding a hot water demand system will make your tankless unit water efficient as well. It will make turn your plumbing system into a green hot water system.

Tankless water heaters are more energy efficient than standard tank type water heaters because they don’t have the standby losses of a big tank of hot water. By eliminating the standby losses associated with storage water heaters they can save about 20 percent of the energy consumed for heating water when compared with storage heaters.

However, the tankless units also take longer to deliver hot water to your fixtures. For the water to be heated to full temperature it must pass completely through the heat exchanger all the way from the inlet to the outlet. The water in the center of the heat exchanger doesn’t ever reach full temperature before it exits the heater.

Thus tankless waters take longer to get hot water to the fixture. A lot more water is being run down the drain while you are waiting. Tankless water heaters really need a hot water demand system to address this problem.

Hot water demand systems typically consist of a pump located at the furthest sink from the water heater and connected to the hot and cold water lines. When hot water is “demanded” at the fixture you activate the system. The demand system speeds the water from the water heater to the fixture at high velocity and shuts off when the hot water reaches the pump.

The cold hot water in the hot water pipes left over from the last use gets sent to the water heater inlet through the cold water pipes. Instant hot water when you turn on the hot water faucet, and no water was wastefully run down the drain.

Traditional hot water recirculation systems with their low powered pumps won’t produce enough water flow in the pipes to turn on a tankless heater. Most tankless water heaters won’t work with traditional circulating systems and can void the warranty of the tankless heaters.

Hot water demand systems are different. Since demand systems are activated only when hot water is used they do not cause the tankless heater to cycle on and off over and over as is the case with traditional recirculation pumps. Demand systems do not affect the warranties for the tankless units.

Not all demand systems are created equal and there are models that don’t have enough power to turn on a tankless water heater. Be sure to find a pump that has the power to you need to send at least the ½ to ¾ gallons per minute normally required to turn on the heater. Longer pipe runs require more horsepower from the pump to produce the required flow, so take that into account as well.

Add a hot water demand system to your water heater and you will conserve energy, water, and money. At the same time you are turning your plumbing system green, and you will be reducing your carbon footprint. You will feel good every time you use hot water.

Finally, water conservation without inconvenience!

Combine Tankless and Demand

Takagi - Noritz - Rinnai - Navien – Comparison of Tankless Water Heaters

Of the major brands of tankless hot water heaters Noritz, Navien, Takagi, & Rinnai, which brand is best? I recently asked a friend of mine this question. He installs and services tankless water heaters so I figured if anyone would know he would. Here is his reply.

All the major brands of tankless hot water heaters are very similar in construction, operation, and quality. Each brand has claims by the manufacturer that theirs is better, but nothing really stands out in my opinion, to differentiate between the brands.

Noritz advertises its "Dual Burner" technology as a big advantage. Is that a significant advantage over the others? I don’t think so. Since all of the brands modulate the flames I don’t think having two small burners is any better than one larger burner. In fact, if I had to choose I would take the single burner since it is simpler and I think simpler is better.

Rinnai, Noritz, and Takagi are all made in Japan and Noritz and Takagi both share some components, and they have similar warranties. Rinnai uses a different venting system than Noritz and Takagi. Do I think its better? Not really.

I do like the fact that Rinnai tankless water heaters have a built-in condensation trap. Sometimes installers forget or just don't bother to include the condensation trap when installing a tankless water heater because of the additional cost. This can result in a much shorter life expectancy for the heat exchanger. Unless the customer knows something about tankless heater installations he would have no idea that it was missing. Vent condensation is highly corrosive and should not be allowed to drip on parts of your water heater.

Navien tankless water heaters are made in South Korea. Navien is better established in Canada. The Navien units have unique and interesting features, like a built in small buffer tank that lets you obtain low flows of hot water and eliminates cold water sandwiches.

Navien heaters have 98% efficiency while the other major brands have about 94%. Is the 4% difference significant? It would not be enough for you to notice on your utility bill.
Navien, Noritz, Rinnai and Takagi are mechanically very similar. They all deliver roughly the same amount of hot water for the gas or electricity used. The warranties are all pretty much the same.

I personally like Takagi because of their excellent service. They even have a toll free number 24/7 that I can call when there is a problem. When your hot water heater stops working on Friday night, and you can’t get any help until Monday morning you can become quite frustrated.

I feel that the most important thing when buying a tankless water heater is to be sure that heater is installed correctly; it is not like your standard storage type water heater where you connect a couple of pipes up and you are done.

With a tankless hot water heater It is very important to purchase it and have it installed by a plumber that is experienced with tankless water heaters particularly with the brand you are purchasing. If you experience problems in the future, you will be glad you did.

Another tankless water heater comparison article: Compare Bosch, Takagi, Noritz & Rinnai

Motion Sensing for Residential Hot Water Demand Systems

Using a motion detector to start your hot water demand system can have unexpected results.

Demand systems are meant to be activated and then used quickly. Hot water in your piping cools off quite rapidly. Since a demand system shuts off the pump when hot water reaches it, if you don’t use the hot water quickly it will soon become “warm” water and to get hot you will still need to run more water out of the pipes and down the drain.

How the hot water demand system behaves a short while after being used depends mainly on how long since the system was last used. If the water hasn’t cooled to below 96 degrees the pump will be locked out and won’t start until the water in the pump cools to below 96 degrees F. You will be forced to purge the warm water from the pipes to obtain hot water and end up running that water down the drain.

If the water has cooled to just below 96 degrees… say about 90 degrees, then the pump will run again until it sees a sudden increase in temperature or if it senses water hotter than 96 degrees and then shut off again. Now however, there will be 90 degree water filling the cold water line.

If you begin using the hot water mixed with cold, after a short time the warm water will be purged from the cold water line and you may need to re-adjust the temperature to add more hot and less cold water. More details about how the hot water demand system behaves in different situations. It pretty much depends on the water temperatures in the piping.

Using a Motion Sensor

As you can see, any significant wait after you have tripped the motion sensor can cause an inconvenience and or end up wasting water.

Another thing to consider when using motion sensors to control your demand system is what happens when someone enters the bathroom while you are taking a shower? Depending on your plumbing layout and how long since the pump was last run, it could cause a fluctuation in water temperature like flushing a toilet sometimes does.

This is especially true when you have a tankless water heater. Since tankless water heaters take time to heat the water, typically 10 to 20 seconds, if the heater has been off for a few minutes you may experience a brief “cold water sandwich”.

Before you decide you want a motion sensor to activate your demand system you might consider how often you enter your bathroom when you don’t want hot water. Each time the pump runs and you don’t use hot water you are wasting energy and increasing your water heating bill. This is especially true with tankless water heaters. It doesn’t take many firings of the heater to use more energy than a standard tank type water heater loses in standby loss.

The same things hold true when using a timer based system. You can have the demand pump turn on automatically at say 7:30 a.m. every morning, but if you push the snooze button a time or two you are still going to need to run the pump again when you get to the bathroom.

Since the piping is warm you will get hot water faster but you pay the price in extra energy consumption.

For some people motion sensing to control the delivery of hot water is a welcome convenience, but for many others it would just be a wasteful nuisance.