Diagrams are provided in this section to show how the tankless water heater works in several different applications, ranging from a single whole-house heater to space heating system applications. The models chosen for these illustrations are examples for use in these types of applications. However, they are not necessarily the correct model for an actual application. It is important to size and match the tankless water heater for each individual application according to the selection criteria found at the beginning of this section and using the ratings in the Product Specification Tables.
Whole House Application (See Diagram)
The most common application for a home is using a single RA-28. The RA-28 was specifically designed with the power necessary to provide hot water for a moderately sized home with standard faucets. Most homes qualify for this application. Exceptions are when there is not enough electrical capacity in the home (below 200 amps), the cold water inlet temperatures are below 50 degrees F or there are higher than standard flow rate faucets in the home. If any of these conditions exist, it may be necessary to look at other feasible options, such as the booster or backup application or the multiple tankless water heater arrangement. Also, in warmer climates, where the inlet water temperatures are above 65 degrees F, it is very possible to use a RA-22 with a 150 amp whole-house electric service.
Booster Or Backup Application (See Diagram)
When a home or building does not have the electrical capacity (200 amps) for a whole-house model, the booster or backup application is a very effective option for providing endless hot water in combination with a storage tank heater. This is generally the case in homes that primarily use gas or oil for heating and the electrical service is only 100 or 150 amps. With the tankless water heater utilized as a booster or backup downstream from the storage tank heater, it is still possible for a large family or heavy users to enjoy endless hot water. In this arrangement, the tankless water heater will not turn on until the storage tank is depleted. While the storage tank is recovering, the tankless water heater will turn on and continue to provide hot water. Models to be considered for this application are the RA-18 and the RA-22. Refer to the Product Specification Tables for the ratings of these two models to determine the one that will work with the electrical capacity of the home.
High Flow Applications (See Diagram)
Combining two or more tankless water heaters in the parallel plumbing configuration (as shown in this section) is the most effective design for high flow applications. However, split systems, such as using a tankless booster application in series with the main tankless water heater, are also effective when the parallel configuration cannot be located closer to the high flow faucet. Body spa showers (single shower stalls with multiple nozzles or sprayers), whirl pool and Jacuzzi tubs are among the fixtures with the highest flow rates found in the home (7 to 14 GPM’s). Other high flow fixtures may be the standard tub faucet, shower, utility sink or the washing machine (3 to 6 GPM’s). In addition, the life style of using hot water in the home needs to be evaluated. For instance, if two or more showers will be required to run at the same time, then the flow rate of the combined shower faucets must be added together to arrive at the peak flow rate demand.
It is important to start with the tankless water heater selection criteria to first determine the design parameters, such as the cold water inlet temperature, combined peak flow rate, and the electrical capacity in the home. It is recommended to install multiple tankless water heaters in parallel or in a split series configuration so that the peak flow is matched. Avoid zoning multiple tankless water heaters on individual branches of the plumbing system, as this will not work in keeping up with flow rates that exceed the capacity or flow rating of the tanlkess water heater.
Circulating System Application (See Diagram)
Some homes have a hot water circulating or re-circulating system designed to maintain hot water in the plumbing system throughout the house. This allows the user at any faucet on the system to receive hot water instantaneously. In most cases, these systems maintain the temperature between 90 and 125 degrees F with an auxiliary thermostat connected to the circulating pump. The tankless water heater control works independently in this type of system and does not require wiring to the pump or the auxiliary thermostat. The tankless water heater control is designed to detect flow and heat the water, which in this case occurs when the pump is activated by the auxiliary thermostat. The tankless water heater works very effectively with this arrangement as shown in the application diagram in this section. However, the same selection criteria applies to matching the proper model for this application and should be done using the cold water temperature entering the home and not the re-circulated water temperature in the system. Like any other high flow application, it is appropriate to install multiple tankless water heaters in parallel on this system if necessary. Refer to High Flow Applications in this section for details and the High Flow Application Diagram.
Space Heating – Radiant Floor Heating Systems (See Diagram)
Radiant floor heating systems are growing in popularity in the north, but also in new homes across the mid-section of the U.S. as well. Many feel that radiant floor heat is one provides the most comfort and warmth of any heating system. Using tankless water heaters in radiant floor heating systems can help make the Tankless Water Heater Installation and operating costs more affordable. As shown in the application diagram in this section, most radiant floor systems are plumbed in a closed-loop configuration and generally use antifreeze as the heating fluid. Note, that the tankless water heater works independently and does not require wiring to the circulating pump or the auxiliary thermostat.
As with most circulating or re-circulating systems, some of the heat or BTU’s produced by the tankless water heater is recovered. For instance, the fluid that is initially heated to 125 degrees F by the tankless water heater may return to the heater at 80 or 90 degrees F, depending on the heat loss rate or BTU loss of the building. Generally, qualified HVAC Contractors are capable of calculating the heating requirements of a building, in BTU’s per hour. For radiant floor heating applications, it is recommended to use two heaters plumbed in parallel, not in series. The BTU per hour rating of the combined tankless water heaters should equal no less than 125% of the BTU per hour requirements to heat the building. Refer to the chart in the application diagram for suggested heater sizes for a variety of home sizes in square feet.
Space Heating – Hydro-Heating Systems (See Diagram)
Hydro-Heating technology is generally used for indoor space heating systems in apartments and condominiums across the middle and southern sections of the U.S. The system was designed to extract heat from hot water circulating through an open loop heat exchanger. The small and compact size of the Sesico heater saves valuable space generally occupied by a boiler or large storage tank heater used with this application. Also, the tankless water heater provides the domestic hot water needed for household sinks, showers and tubs as well. See the Hydro-Heating Application Diagram in this section, illustrating the components generally used with this system.
Because of the high demand for hot water in this application, it is necessary to utilize a priority flow valve that helps insure all the hot water is available for the domestic needs. The priority flow valve detects flow to the domestic side and temporarily turns the hydro-heating pump off. The tankless water heater’s output temperature setting should be between 125 and 130 degrees to enable the hydro-heating system to provide the required output rating (BTU per hour rating). Note, that today’s building codes may require the use of a mixing valve on the domestic hot water supply to limit the temperature to 120 degrees F. The hydro-heating systems used for apartments and condominiums, are generally rated from about 27,000 to 40,000 BTU’s per hour. However, the BTU requirements for the domestic hot water side may exceed 75,000 BTU’s per hour during periods of peak flow, such as running the bath tub or the washing machine. The output of Model RA-28 is about 96,000 BTU per hour and is ideal for this application.
Solar Backup Application (See Diagram)
Heating water with solar collectors in certain geographic regions is one of the most efficient systems. The sun is obviously free energy, but when the sun is not available for replenishing the heat used from the storage tank or batch collector, the tankless water heater provides the perfect back-up. As a back-up heater, the tankless water heater allows the passive system do what it was designed to do, to recover on it’s own. Solar heating systems are particularly vulnerable of running out of hot water during the evening and early morning hours. Particularly, if the tank only holds 40 or 50 gallons. Two or three baths or showers taken during this period can deplete the tank when there is no sun available to recover or replenish the tank. The tankless water heater will only turn on and provide hot water when it senses the temperature from the storage tank or batch system is lower than it’s set point, making it the perfect back-up. In addition, the tankless water heater will only use the energy necessary to raise the temperature it senses to the set point, typically 120 degrees F.
Refer to the Solar Backup Diagram in this section and note that a mixing valve must be used between the storage tank and the tankless water heater. Temperatures generated by the solar collectors can exceed 160 degrees F, too hot for domestic use. Also, the tankless water heater is equipped with a 180 degree F high temperature shut down switch. So temperatures of 180 or greater will disable the tankless water heater and require a manual reset. Because there will be periods when the solar collectors are not heating the water and the storage of hot water can be depleted, the tankless water heater should be sized to heat the water as if there were no solar heating system. Use the selection criteria at the beginning of this section the Product Specification Tables to size and match the model for this application using the cold water inlet temperature.
Geothermal Backup Application (See Diagram)
There are geothermal heat pump systems used for space heating that are also designed to heat water for domestic use. These systems utilize an auxiliary de-super heater (or heat exchanger) designed to heat water in a storage tank heater. This is a closed loop system that transfer heat from the de-super heater to heat exchanger coils inside the storage tank. The tankless water heater located down stream from the storage tank provides the perfect back-up for this application. Refer to the Geothermal Backup Application diagram for an illustration of how this system is configured.
As with the backup to the solar water heating system, the tankless water heater allows this passive geothermal heating system to recover the hot water in the storage tank when not in use. The tankless water heater will heat water only when the tank is depleted or drops below the set point of the heater during usage. The unit will not turn on during periods of standby while the geothermal system is recovering. Because there will be periods when the geothermal heat pump is not operating (spring and fall months), the storage of hot water can be depleted, the tankless heater should be sized to heat the water as if there were no geo-exchange heating system. Use the selection criteria at the beginning of this section the Product Specification Tables to size and match the model for this application using the cold water inlet temperature.