Tankless Water Heaters


How do Tankless Water Heaters work?

Tankless Water Heaters heat water directly without the use of a storage tank. Therefore, they avoid the standby heat losses associated with storage water heaters. When a hot water tap is turned on, cold water travels through a pipe into the unit. In an electric Tankless Water Heater an electric element heats the water. In a gas-fired Tankless Water Heater a gas burner heats the water. As a result, Tankless Water Heaters deliver a constant supply of hot water. You don't need to wait for a storage tank to fill up with enough hot water. Typically, Tankless Water Heaters provide hot water at a rate of 2 – 5 gallons (7.6 – 15.2 liters) per minute. Typically, gas-fired Tankless Water Heaters will produce higher flow rates than electric Tankless Water Heaters. Some smaller Tankless Water Heaters, however, cannot supply enough hot water for simultaneous, multiple uses in large households. For example, taking a shower and running the dishwasher at the same time can stretch a Tankless Water Heater to its limit. To overcome this problem, you can install a “whole house” type Tankless Water Heater or install two or more Tankless Water Heaters, connected in parallel for simultaneous demands of hot water. You can also install separate Tankless Water Heaters for appliances—such as a clothes washer or dishwater—that use a lot of hot water in your home.

Other applications for Tankless Water Heaters include the following:

Remote BBQ, garage sink or outdoor sink
Poolhouse lavatory or shower, greenhouse heating
Remote bathrooms or hot tubs. Hot water far from your primary water heater.
To serve as a booster, eliminating long pipe runs, for solar water heating systems, dishwashers and sanitation.

Potential Fuel Savings

For homes that use 41 gallons or less of hot water daily, Tankless Water Heaters can be 24% – 34% more energy efficient than conventional storage tank water heaters. They can be 8% – 14% more energy efficient for homes that use a lot of hot water, around 86 gallons per day. You can achieve an even greater energy savings of 27% – 50% if you install a Tankless Water Heater at each hot water outlet. Your fuel savings do vary with how the water is used, the flow rates and the schedule of users. For example, if you are not home most of the time because you travel, then a tankless becomes more viable from a fuel saving perspective.

Endless hot water

Where Tankless are particularly valuable is in long runs of use - ENDLESS HOT WATER - If you have lots of kids that take showers one after the other then the "endless hot water" characteristic of the tankless heater is very desirable. Unit sizing is important as the flow and temperature characteristics must be seriously considered when buying the machine.

Before buying a Tankless Water Heater, consider the following:

Fuel Type , Location, Size, Water-demand, Application

  1. Fuel Type

    The first thing that you'll need to decide when selecting a Tankless Water Heater is the fuel type. You will need to select between an Electric Tankless Water Heater or a Gas-Fired Tankless Water Heater . Natural gas is the preferred fuel, if available. (Electricity cost is 147% the gas cost here in Seattle).

    Requirements for Electric Tankless Water Heaters
    If you plan to purchase an Electric Tankless Water Heater, consider the following Electrical Requirements:

    Amperage - Different Electric Tankless Water Heaters will have various requirements in amp draw. You will want to ensure that you can support the electrical demands of your Electric Tankless Water Heater.

    Wire Size - very important if you don't want a meltdown and potential fire hazard.

    Circuit Breaker
    You must ensure that you have a circuit or circuits that will support your Electric Tankless Water Heater. It may be necessary to put your Electric Tankless Water Heater on its own circuit or circuits. This sometimes requires updating your electrical panel especially older homes.You should consult with a qualified, licensed electrician for more information.

    Gas-Fired Tankless Water Heater, consider the Gas-Type and Venting Requirements:
    You will first need to identify whether your gas type is Natural Gas or Propane. It is imperitive that you examine your current gas line to ensure that it will meet the requirments of your new Gas-Fired Tankless Water Heater. The requirements of the Tankless Water Heater may exceed that of your existing tank-style water heater. Tankless water heaters need bigger gas pipes than tank-type storage heaters.

    Next, you will need to consider venting requirements for your specific installation scenario. There are a few important things to keep in mind when engineering the gas venting for your Gas-Fired Tankless Water Heater.

    Be sure that you comply with the manufactures recommended flue piping, for example many models require Category III stainless steel (UL1738 certified) venting for your Gas-Fired Tankless Water Heater. "Type B" venting accessories are not acceptable for power vented models. Also, be sure to check local building code to ensure that your specific needs will be completely met.

    Additionally, many Tankless Water Heater manufacturers offer gas venting "kits". It is recommended that customers evaluate the needs of their specific installation to ensure that they will be getting all of the necessary gas venting accessories. Depending on where you will be installing the Tankless Water Heater, a pre-made kit will probably not meet your needs. Ensure that you measure out the vent route and consider where the discharge will go through the wall or ceiling, consider the necessary clearances, and consider ample access to air for combustion, then buy the appropriate gas venting pieces. *Note: Gas-Fired Tankless Water Heaters may still require a minimal electrical connection. Be sure to review installation requirements for the units you are considering for purchase.

  2. Location, Size, and Demand

    When deciding which Tankless Water Heater to purchase, you will also need to consider where you will need hot water. Are you looking for a unit that will heat the water at one bathroom sink (single point application), an entire bathroom (multipoint application), or an entire house, apartment, or condo (whole house application)? It is important to recognize the number of fixtures that will require hot water. Each fixture will have its own demands. The chart below illustrates the typical flow rates (demand) for some standard fixtures:

    Typical Flow Rates in Gallons per Minute (gpm)
    Fixture Type Lavatory 0.5 Bathtub 2.0 – 4.0 Shower 1.5 – 3.0 Kitchen Sink 1.0 – 1.5 Pastry Sink 1.5 – 2.5 Laundry Sink 2.5 – 3.0 Dish-washer 1.0 – 3.0
    The flow rate is especially important, since Tankless Water Heaters will generate a temperature rise based on the flow rate demanded.

    For example, a typical small electric model, running on 240 Volt power, will raise the water temperature by 54°F at 1.5 gpm, 36°F at 2.25 gpm, and 27°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F.

    A larger unit, running on 240 Volt power, will raise the water temperature by 92°F at 1.5 gpm, 85°F at 2.25 gpm, and 82°F at 3.0 gpm, above the ambient incoming water temperature, up to 125°F. The manufacturers specifications are critical when engineering these tankless systems.

    Temperature Rise Based on Flow Rate, Up to 125°F
    Typical Flow Rate Small model = 1.5 gpm 54°F , 2.25 gpm = 36°F, 3.0 gpm = 27°F
    Typical Flow Rate Large model = 1.5 gpm 92°F , 2.25 gpm = 87°F, 3.0 gpm = 82°F

    This means that if you are using a 1.5 gpm shower and a 1.5 gpm kitchen sink simultaneously, a total demand of 3.0 gpm, the small model will raise the temperature 27°F, whereas the larger model will raise the temperature 82°F.

    Next, you should look at your ambient incoming water temperature. If you live in a cold climate, like New York, your incoming water temperature will likely be much lower than if you live in a warm climate, like Florida. Your best bet is to find out how much temperature rise you will need in order for your hot water to reach the desired heat. If the ambient incoming water temperature for your shower is 65°F, you are using a 2.0 gpm shower, and you want to raise that temperature to 115°F, you will want to look for a Tankless Water Heater that will provide at least a 50°F temperature rise at 2.0 gpm (115°F - 65°F = 50°F). However, if you anticipate additional simultaneous demand, such as the hot water from a sink being used while someone is showering, you will need to add the sink's gpm to the shower's gpm in order to determine your overall gpm demand and then find the temperature rise necessary to meet your overall needs.

    EXAMPLE of sizing formula
    60° F Incoming Water
    2 gpm Shower @ 110° F Desired Output Water Temperature
    You will need a Tankless Water Heater that produces a 50°F temperature rise at 2 gpm

  3. Application

    You may have a specific application in mind for your Tankless Water Heater.

    Here are a few examples of the different models and their unctionality for a specific application:

    Single Point Application - each fixture has an independent local heater. Example: Isolated garage with utility sink. Warehouse hand-wash sink.

    Multi-fixture use - Two or more fixtures can share a water heater. An example would be the new bath addition on the other side of the house. The unit takes care of this isolated bathroom only with both a shower and a lavatory sink. The older part of the house has it's own old water heater separate from the new.

    Whole House Indoor Mount - This is probably the most typical installation. The unit is usually in the basement or garage but sometimes elsewhere.
    Larger Whole House units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist.

    Whole House Outdoor Mount - Same as Indoor mount except that it is physically located outside. Typically mounted onto the side of the house. These units make venting easy as they do not require a flue pipe as they are already outside. They are suitable for freezing envirnments (some models). Larger Whole House units are designed to serve an entire house, apartment, condo, or cabin, where multiple points of use will exist.

    Proper installation depends on many factors. These factors include climate and local building code requirements. You should have a qualified, licensed plumbing and heating contractor install your Tankless Water Heater. (And insure they used licensed plumbers, gas techs and electricians). The installer should be a licensed plumber with electrical experience so that it is code compliant and safe to operate. Here in Seattle a gas technician license is required for gas piping as well.

SeattleHotWater.com welcomes comments and requests for consultation on any hot water heater issue.