Tankless Water Heaters – They Save Energy – Do They Save Water?

Tankless water heaters are all the rage now. Green is in and tankless heaters are considered greener than storage water heaters. They don't have standby losses and so they are typically more energy efficient than tank type units. Are they really green?

Tankless Water Heater Savings

The dollar amount of tankless water heater savings is relatively small, and makes the payback iffy over the lifetime of the heater. Tax rebates are substantial though, and with the rebates many more home owners can expect to save enough money to more than pay for the unit. That is if there are no breakdowns.

Tankless units are more complex than storage heaters, and thus are more likely to breakdown and more expensive to repair. A service call or two can wipe out any savings realized by reduced standby losses.

Water Conservation and Saving Water

Tankless water heaters are not water conservation friendly. It takes them up to 20 seconds longer to deliver hot water since they must first heat the water and then deliver it to the fixture. A study done by the Australian government found that tankless water heaters typically take 10 to 20 seconds longer to deliver hot water than a storage type heater.

While you purge the cooled off hot water from the hot water pipes, you are running water down the drain. The longer the wait, the more water gets run down the drain.

Since tankless units require a minimum flow rate the keep the heater turned on of typically 1/2 gallon per minute to 3/4 gallons per minute, you will have to run the hot water at a higher flow than you might normally run it, and mix it with additional cold water to get the temperature where you want it. A trickle of warm water will no longer be an option.

For those people who for one reason or another want to run a small stream of warm water will have to make do with a much larger stream of warm water, again, wasting water.

Tankless water heaters are marketed with slogans like "endless hot water". Does this sound like a water conservation product? You don't buy a tankless water heater for saving water.

If you have a tankless water heater, and you want to save water, get yourself a hot water demand system pump. Then you will have a green hot water system, one that saves energy and water.

Tankless Water Heaters Need More Love... or At Least More Attention

Because tankless heaters are limited in the gallons per minute that they can heat to a specified temperature, one must consider the inlet temperature when deciding on a size. Too small, and the heater will not be able to meat your peak load demands and the temperature at the fixture will decrease as the flow rate is turned up at the faucet.

Too large of a model, and it will be difficult to adjust the temperature without the heater shutting off. And if you live where the water temperature varies widely from summer to winter, then you may have to change the outlet temperature setting on the heater as the seasons change.

Most gas tankless water heaters need to be plugged into a 110v outlet to power the electronics need to control the unit. Some units use the flowing water to spin a tiny generator powering the controls. Bosch water heaters have such a feature. So most units won't be able to supply hot water during a power outage.

I have seen a lot of chatter in forums about the need to clean the Bosch units frequently due to that tiny generator...

If you live where temperatures go below freezing you will have a new worry... damaging the heat exchanger. With a storage water heater freezing isn't going to happen. With a tankless unit you have to protect it from freezing as freezing will destroy the heat exchanger.

Some units come with a little built in heater for freeze protection... so much for eliminating standby losses...

Recirc Pumps and Hot Water Demand Systems

Most tankless water heaters will not work with a traditional hot water recirc pump. Read the warranty. Even so, most circulating pumps won't pump enough water through the heater to turn it on anyway.

Hot water demand systems are on the other hand ideal for tankless applications. They don't circulate the hot water, they get your hot water to the fixture without running water down the drain, and they can often get your hot water to the fixture more quickly.

All brands including Rinnai, Takagi, Noritz, Bradford White, Bosch, and Rheem work better when you combine them with a hot water demand system.

Point of Use Water Heaters & Your Plumbing Layout

The most water and energy efficient plumbing layout is to have the heater a close as possible to the end use fixture. This can virtually eliminate the wasted water, and eliminates the need for a pump. Often it is an ideal application for a small electric tankless water heater.

Tankless water heaters can provide you with "endless hot water" and can save you money, but there are other considerations, so choose carefully...