How a Tankless Water Heater Works: an Overview of the Tankless Hot Water Heating System 

Most people in North America currently use a storage tank water heater to provide hot water in their homes without understanding the pros and cons of a tankless water heater. A storage tank water heater keeps water hot 24 hours a day, even while you’re at work or sleeping. A tankless hot water heating system, on the other hand, does not store hot water. It heats the water as you use it, providing endless hot water.  

Keep reading for the pros and cons of a tankless water heater system.

How a Tankless Water Heater Works (and How the Bosch Tankless Units Work)
In answer to our many visitors who ask how the Bosch tankless units work, when a hot water tap is opened, the cold water enters the heater and triggers the heating elements or burners to turn on. Your hot water tap acts as an ignition key for the energy used to heat the hot water you need. The water is then heated as it flows through the heating elements or heat exchanger. As you change the water flow, a water valve or thermostat controls the heating elements or burner flame to maintain a constant temperature and endless hot water.

The amount of energy used is always proportional to the volume of hot water being used. The water temperature can be adjusted to produce outlet temperatures ranging from 100° to 140° F.

Tankless Electric Water Heater
When a hot water tap is opened, heated water is drawn off the top of the tank. Cold water is fed into the bottom of the tank to replace the outgoing hot water. The incoming cold water triggers the tank's electric heating element, a gas burner or an electrical coil. The water is heated for as long as necessary to bring the entire tank back up to the preset temperature. If demand surpasses the tank's storage capacity, you must close the tap and wait until the tank reheats all the water. Stored hot water loses heat through the side walls and up the flue pipe (if it's a gas heater). As the water temperature drops, the heater kicks on to reheat the water again over and over. Overall, a very inefficient system.

How can a tankless water heater heat water instantly?
When you open a faucet, the flow of the water triggers the heater to turn on. Whether you use gas or electricity, the powerful gas burners or electrical elements will turn on, rapidly heating the water as it passes through the unit. The water is heated instantly, and the time it takes to obtain hot water is directly related to the distance the hot water has to travel from the water heater to where hot water is being used. The burners or elements then shut down when you shut off the hot water. The energy that is consumed is only for the hot water that is being used.

Advantages
Because a tankless water heater turns on when you open a hot water faucet and turns off when you close the faucet, the energy that is consumed is only for the hot water that is being used. Since there is no storage of water and thus no constant heating and re-heating of stored water, you’re not wasting energy heating water when you don’t need it, such as when you’re sleeping or not at home. This energy savings translates to dollar savings for you and reduced impact on our environment. Furthermore, since a tankless water heater heats the water as you use it, you can have an endless supply of hot water, provided you size the unit appropriately.

How much money can I save?
Depending on which model of tankless water heater you purchase, and what size storage tank you have now, and if it runs on gas or electricity, you could save anywhere from 11% to 69% off your hot water heating bill. How? Most homes use hot water for a cumulative total of about one hour per day, yet they typically keep 40 or 50 gallons (oftentimes more) of water hot 24 hours a day. Having a system that eliminates the storage and heats water only as you use it can dramatically reduce your energy consumption.

Can it really provide an endless supply of hot water?
Yes. Because storage tank water heaters store a finite amount of water, when that amount is used up your shower goes cold and you have to wait for the heater to heat the water back up (this is known as recovery time). Because a tankless water heater heats the water as it passes through the heater, you can never run out, provided flow limitations are not exceeded.

Are there other benefits of a tankless water heater?
There are many advantages of having a tankless water heater in your home. Besides the money savings, endless hot water and smaller impact on the environment, a tankless water heater:

• Is very small and can hang on the wall, thereby saving you valuable floor space.
• Is designed with replaceable parts and is built with such materials as copper, stainless steel, and aluminum (the AquaStar) so as to last a lifetime. Energy savings is only one segment of savings—with proper care this could be the only water heater one needs in a lifetime.
• Is almost entirely recyclable, so if you ever decide to replace it, it doesn’t have to go to the landfill.
• Will not develop a corrosive leak like a storage tank water heater, saving you from expensive water damage in your home.
  Note: A tankless water heater can leak if it is exposed to freezing temperatures or has a manufacturing defect.
• Maintains its efficiency throughout the lifetime of the unit. Storage tank water heaters decrease in efficiency over time due to mineral build-up inside the tank. This is due to the fact that storage tank water heaters store hot water, giving those minerals a chance to settle out and bake from the heat onto the walls of the tank, and onto the heating element in electrical models, thereby reducing heat transfer.

Will I still get the hot shower I’m used to now?
Yes, provided you buy the right tankless heater for you (see Shopping Consultant to choose the right model for you). Tankless water heaters are able to function at a variety of temperatures that you can choose, and can produce hot water at the same flow rate as your standard single-headed shower provides now (since 1992 all showerheads are designed to deliver a maximum of 2.5 gallons per minute, as mandated by federal legislation).

Will one tankless water heater do my entire house?
Yes. You must choose the size model to suit your home’s hot water needs, which is based upon the maximum flow of hot water you need at any one time (see Shopping Consultant to choose the right model for you). We sell tankless water heaters that are capable of handling one shower at a time and others that can sustain a maximum of two showers at a time.

What if I have very hard water?
Since tankless water heaters do not store hot water, minerals do not have as much of a chance to settle onto the heater. Therefore, you won’t see the same corrosive or scale build-up problems with tankless water heaters that you do with storage tank water heaters. And it is fine to use a water softener with a tankless water heater, if you choose.

What limitations do tankless water heaters have?
Because this type of water heater heats the water as you use it, the volume of hot water that it can deliver is directly correlated to the amount of its energy input. The bigger the burners or heating elements in the unit, the higher the volume of hot water that it can deliver. Today tankless water heaters come in various sizes to suit most homes’ needs. Even if you need to be operating multiple showers at once, tankless water heaters can keep up (see Shopping Consultant to choose the right model for you).

How do I properly size a tankless water heater for my home?
You need to choose the model that can deliver the volume of hot water to meet your needs. The best method for sizing this type of water heater is to know how many showers each model can run simultaneously. We have models that can run either one or two showers at a time. Our most popular sized model is the one that delivers one shower at a time. (Remember, although it will only deliver one shower at a time, it can do so endlessly, shower after shower after shower.) See our Shopping Consultant to determine which tankless water heater would be right for you.

Can I fill a hot tub with a tankless water heater?
Yes. Because tankless water heaters provide an endless supply of hot water, you can fill a tub of any size. It is only a question of time, meaning that our larger units can fill a tub faster than our smaller units. Keep in mind that some tubs draw water at high flow rates, so it may be necessary to limit the flow so that the tankless water heater can adequately heat the water that is being called for.

Is this a new technology?
No. Europe, Asia and South America, where energy costs are more expensive than here in the U.S., have been using tankless water heaters for 75 years. Controlled Energy Corporation has been selling and supporting tankless water heaters in the United States since 1979. However, most Americans are just now learning of this technology and its benefits.

What is a point-of-use water heater?
A point-of-use water heater is a very small water heater, tank or tankless, that is designed to be installed at the point of use, thereby eliminating a long pipe run. They are mostly sized to supply hot water to one specific application, usually a sink. These can be either a mini storage tank or a tankless water heater. A common application is a remote sink, such as a bathroom in an office building or a service station. The other sensible application is for distant sinks in the home that typically take too long to receive hot water.

What are the advantages of a point-of-use water heater?
Point-of-use water heaters are usually used for one of two reasons. One is to supply hot water to a remote location that is not served by a larger water heater. The other is to eliminate the wait time for hot water you may have at a particular faucet. Both offer the advantage of not having to wait for hot water. You can install a point-of-use water heater right at the source, e.g., under a sink. Therefore, when you turn on the faucet you have hot water instantly available to you. This both eliminates your wait for the hot water and saves water, our most valuable resource, from being wasted down the drain as you wait for hot water to arrive.

Can I use point-of-use water heaters for applications other than a sink?
Yes. You can place a mini storage tank (see Ariston) in-line with your main water heater. These are available in 2.5-gallon, 4-gallon and 6-gallon sizes. These provide you instant hot water at your washing machine or dishwasher, for example, and by the time you exhaust that supply, the main water heater that serves these locations has caught up, so you have a continuous supply of hot water.

Are your products difficult or expensive to install?
No, they are not difficult to install. The installation expense depends on many factors. Although tankless water heaters are “on” for only a small fraction of the day in most home uses, when hot water is being called for they require a lot of energy because they are heating water instantly. Because of this, Aquastars (gas tankless water heaters) sometimes require expansion of the vent pipe and PowerStars (electric tankless water heaters) sometimes require the electrical service in the home to be upgraded.

Can any plumber install your products?
Yes, they should, after all it is just another appliance. But experience has shown us that many will not because, as they say, they are not familiar with the unit. To locate an installer in your area please use the following link: http://www.controlledenergy.com/html/dealer/index.html