How They Work

How Conventional Electric Hot Water Heaters Work:
Most homes use a storage type hot water heater; an insulated tank with an electric or gas heating unit. A conventional hot water heater typically will heat 40 to 80 gallons of water, and keeps it hot both day and night. With a conventional water heater, heat escapes through the tank jacket causing a loss of energy (called stand-by-heat loss). Therefore, wasting money to heat the water over and over again!

HowTankless Electric Hot Water Heaters Work:
When a hot water tap is opened, the cold water entering the heater passes through the first heat chamber from right to left over the first thermostat turning on the first electrical heat coil, heating the water up to 125°F as it passes directly over it.
As you change the mixture at the hot and cold faucet, the other converting thermostats recalculate the flow of energy sequentially adding or subtracting energy to maintain a constant temperature. (The amount of energy needed is in direct proportion to the volume of hot water flow being used, thereby using only the energy needed.)
All fixtures will receive up to 125°F of hot water, however at your largest flowing fixture (your bath tub) you might find the water not hot enough. Simply lower the hot water flow mixture with no cold water added until you find the temperature required. Then, if you wish, you may add a little cold to the desired temperature.
All other minor fixtures will heat up to 125°F.
When the hot water is turned off, the flow of energy turns off as well.
Your hot water tap is an ignition key for energy used to heat all the hot water you need.

Tankless water heaters, also called combination or "combi" boilers, instantaneous, continuous flow, inline, flash, on-demand or instant-on water heaters, are also available and gaining in popularity. The chief advantages of tankless water heaters is a continuous flow of hot water and by saving energy (as compared to continuously heating tank water heaters). These water heaters heat the water as the water flows through the device, and do not retain any water internally except for what is in the heat exchanger coil. Point-of-use tankless (POU) heaters may be installed at the faucet or in a bathroom, laundry sink or garage faucet, far from the central water heater, or larger models can be used to provide all the hot water requirements for an entire house.

The high efficiency condensing combination boiler provides both space heating and water heating, an increasingly popular choice in houses. In fact, combination boilers now account for over half of all the new domestic boilers installed in Britain.

Tankless water heaters can be divided into two categories: "full on/full off" and "modulated". Full on/full off units do not have a variable power output level; the unit is either on or off. Modulated tankless water heaters base the heat output on the flow of water running through the unit. This is usually done through the use of a 'flow sensor', modulating gas valve, inlet water temperature sensor and an outlet water temperature sensor-choke valve and means that the occupants should receive the same output temperature of water at differing velocities, usually within a close range of ±2°C.

Tankless heaters can ideally be more efficient than storage water heaters. In both kinds of installation (centralized and Point-of-use) the absence of a tank saves energy because conventional water heaters have to reheat the water in the tank as it cools off, called standby loss. With a central water heater, water is wasted waiting for water to heat up because of the cold water in the pipes between the faucet and the water heater.

Point of use tankless water heaters are located right where the water is being used, so the water is almost instantly hot, which saves water. They also save even more energy than centrally installed tankless water heaters because no hot water is left in the pipes after the water is shut off. Point of use tankless water heaters are usually used in combination with a central water heater.

Under current North American conditions, the most cost effective configuration from an operating viewpoint is usually to use a central tankless water heater for most of the house, and install a point of use tankless water heater at any distant faucets or bathrooms. However, this may vary according to how much electricity and water costs in the area, the layout of the house, and how much hot water is used. Electric tankless water heaters are used for almost all point of use heaters.

If a storage water heater is being replaced with a tankless one, the size of the electrical wiring may have to be increased to handle the load. For electrical installations, AWG, 10 or 8 wire, corresponding to 10 or 6 mm², is required for most Point-of-use heaters at North American voltages. Larger whole house electric units may require up to AWG 2 wire. In gas appliances both pressure and volume requirements must be met for optimum operation. (http://en.wikipedia.org/wiki/American_wire_gauge)

The two main advantages of tankless water heater (continuous hot water and energy conservation):

1) A tank water heater tends to heat the water in the surrounding piping by virtue of convection (http://en.wikipedia.org/wiki/Convection). A tankless water heater only heats water upon demand and all water in the piping is cold. There is a "flow delay" for hot water to reach a distant faucet as a greater amount of cold water must be flushed from the piping first.

2) Since a tankless water heater is not active when hot water is not being used. However, tankless water heaters can be used in recirculation applications when designed correctly.

3) When water flow is turned off and on repeatedly, there is often a short delay before the water flow detector is triggered and the heating element activated. This can result in a brief flow of cold water (following the "flow delay") when one reopens the hot water tap after having closed it. Picture this as segments of water in the piping, some of which are hot (tap, water flow and water heater on) and the other cold (tap, water flow and water heater off).

4) There are typically minimum flow requirements that can result in a gap between the coolest warm water that can be achieved with a hot and cold water mix and straight cold water. On the other hand, more sophisticated tankless heaters often come with remote thermostats that can allow the water temperature to be changed interactively to suit the immediate purpose. This is impossible with tank heaters (but also not needed, since they have no trouble supplying hot water at a very low flow rate).

5) Adjusting the temperature of water with a non-temperature compensating valve can result in water temperature variations after the "flow delay". The slower that water flows to a point, the more time that water is allowed to heat and thus the hotter it becomes. If you increase the flow of water (increase the hot water tap), the flow of water increases, the water has less time to be heated in the tank and thus is less hot. The solution is to either install a temperature compensating valve (typical in modern showers) or only to adjust the cold water tap (constant hot water flow rate).

TANKLESS INC. 2040-A Whitfield Park Avenue, Sarasota, Florida, USA 34243
Phone: 1-800-TANKLESS 1-800-826-5537 Fax: 941-755-6529