What is a Tankless Water Heater?

Tankless water heaters produce hot water only when you need it.   Other names for this is “on demand”or “instant”hot water. Unlike traditional heaters,a tankless water heater does not have a huge storage tank.

How do Tankless Water Heaters Work?

When ground water flows through one end of the pipe,heating elements convert the cold water to hot water and passes out the other end of the pipe. Most models have a minimum flow rate before the heating mechanism actually turns itself on. Depending on the model and manufacturer,this may take up to 15 seconds or more. The two big differences here compared to a conventional water heater is that water is heated only when needed and,the hot water supply is endless.   On demand hot water heaters come in different models depending on the needs of your household.  To accurately determine the water needs of your home,you should calculate the total GPM water requirements by adding up the GPM flow rate for each water fixture (shower,dishwasher,etc.),determine the coldest temperatures during the year for where you live,and know the desired hot water temperature you’d like to set for your unit.

Choosing a Tankless Water Heater

1. Basics
2. Determine Ground Temperature
3. Decide on Temperature Setting
4. Calculate Temperature Rise
5. Calculate Total GPM Usage
6. Final Specifications

1. Basics: Tankless water heaters are rated by the amount of water produced GPM (Gallons Per Minute) given a specific desired temperature setting,and the amount of temperature rise (sometimes referred to as the temperature delta)needed to heat your ground water temperature to your desired temperature setting.

2. Determine Ground Temperature: The first information that’s required before selecting a specific heater is knowing your ground water temperature (sometimes called ambient temperature).   This is basically the temperature that sits inside your water pipe before it comes into contact with any heating devices. You’ll want to find the lowest average ground water temperature during the year in your city because doing this will accurately tell you which unit will be able to heat your water even at the coldest times of the year.

To do this,go here: temperature check

3. Decide on Temperature Setting:This is the temperature that you want the heating unit to produce.

4. Calculate Temperature Rise:Use this formula to find out your Temperature Rise.

( Set Temperature ) – ( Incoming Temperature ) = ( Temperature Rise )

110F (Set Temperature) – 60F (Incoming Temperature) = 50F (Temperature Rise)

5. Calculate Total GPM Usage:

a) Turn the water on to its maximum.

b) Put a container underneath the water for 10 seconds exactly.

c) Convert the water in the container to gallons.

Go to  Google and type:

”X (unit of measure) to gallon ”    e.g.     “3 liters to gallon”

or:

You can go to the “Unit Conversion”section here.

d) Use the following formula to caculate the GPM flow rate for your shower or other water fixtures.

no. gallons x 6 = GPM        .25  gallons x 6 = 1.5 GPM

e) Add the number of water fixtures together to arrive at the total hot water usage for your home.

1st Shower   = 2.5 GPM

Laundry        = 2.0 GPM

2nd Shower  = 2.5 GPM

———————————-

Total            =  7.0 GPM

NOTE:This total number of 7.0 GPM represents the water requirement if all 3 were being used at the same time.  If you know that your normal household uses only 1 bathroom shower at a time throughout the year,you’d probably adjust the total above to 4.5 GPM.

6. Tankless Water Heater Sizing  | Final Specifications

You now have the three  final numbers needed to start the tankless water heater sizing selection process.  These are the three  essential numbers required to make an informed purchasing decision.   In our example above,we would need a tankless water heater that can handle:

• 120 F (Set Temperature)
• 7.0 GPM
• 35 F (Temperature Rise) or (Temp Above Ambient) or (Temperature Delta)

According to our example above and using Stiebel’s chart,  it appears that all of the tempra series can handle up to 131° F.  The Stiebel 36 Plus seems to fit our needs here.

If your household generally uses 2 showers at the same time and can remember to hold off on using the laundry machine during those times,the following numbers could be used:

• 120F (Set Temperature)
• 5.0 GPM
• 35 F (Temperature Rise) or (Temp Above Ambient) or (Temperature Delta)

In this case,the Stiebel Eltron Tempra 24 Plus would be the best choice.

Applications

Armed with your final specifications,you can now start to consider the various kinds of tankless water heaters.  While the final specifications are the most important information to use as a buying guide,the following specific tankless water heater applications can further help you decide and understand what’s available in the market today.  For example,in many cases,home owners want to keep their existing storage tank water heater,but would like to add a tankless water heater to their shower fixture.  Or maybe the wood working shop is far from the main water tank.  In both cases,this would call for a single point of use model.  Using your final specification numbers would,in most cases,automatically guide you to choose a single point of use model.

Point of Use: A point of use tankless water heater is designed to produce water for only 1 water appliance or fixture.  For example one shower,a laundry machine,or a kitchen sink.  It is often also used for remote water fixtures such as a guest house bathroom that is located far away from the main house and its traditional water heater.

Whole House Tankless Water Heaters: This kind of model will be able to handle more demanding water consumptions,usually 2 or more simultaneous points of use.

Commercial Tankless Water Heaters: For hospitals,apartment buildings,or any kind of large water consumption application.  Manufacturers either have an industrial version of their heaters or  a series of  tankless water heaters are installed  together to meet the water heating requirements.

Thermostatic: For buildings like hospitals or labs that require precise water temperatures.

Indoor Tankless Hot Water Heaters: Some units are designed solely for indoor usage,while others can be used indoors and outdoors.  Indoor units require more planning in most cases due to venting and electrical circuit evaluations.

Outdoor Tankless Hot Water Heaters: Outdoor instant water heaters are sometimes easier to install because venting is a simpler process and venting wall holes don’t usually need to be cut out.  However there may be a need to cut holes for the gas piping.  A common placement is outside bathroom walls.

Fuel Types

• Electric
• Gas-fired

Electric tankless water heater requirements:

Power is measured by the following formula:

I = V/r
(V) = volts and uses Voltage units
(I)  = current uses Amps units
(r)  = resistance and uses Ohms units

Actual electrical power usage is measured in watts:

P = VI ->Watts = Volts x Amps

You’ll want to gather the specific Voltage,Amperage,and Wattage information for the specific
tankless water heater model you intend to purchase. An electrician will need this information to determine if your circuit breaker can meet those requirements.

Many times it’s necessary to change your circuits to accomodate an electric tankless water heater or provide a separate circuit breaker for an electric instant water heater.

To determine if your circuit breaker can handle the electrical requirements,go to your circuit breaker panel,find the room label in which you plan to install the unit,look for the specific Amps number on the breaker switch.  Multiply the amps  x volts (for United States this would be 120 v ) to arrive at the Watts.  After arriving at that number,you’ll want to mulitply the watts by .80 because the IEC ( International Electrotechnical Commission ) recommends this as a safety gap.

e.g.

60 amps x 120 volts x .80 = 5760 Watts

In many cases,an electric tankless water heater will require what’s called a double pole breaker.  A single breaker (single pole ) will provide 120v,while a double pole provides twice that voltage,which is 240 v.

The amps for a double pole breaker is what the label indicates.

e.g.

A 60 amp label on a double pole breaker does not mean 2 x 60 amps,it means 60 amps.  You can identify double pole breakers by  the single arm that connects the two breaker legs.

Please consult with a licensed electrician.

Gas tankless water heater requirements:

All gas models will require venting and proper venting is crucial to any installation. The venting material must be a type Category III stainless steel which is UL1738 Certified. DO NOT USE any other type of venting material because the condensate which is produced by tankless water heaters is acidic and can cut through other venting materials such as type “B”. Each brand and model will have its own maximum allowable venting lengths,and therefore we recommend you refer to the installation manual for specific venting requirements and call the manufacturer for further details. Additional local building codes may also need to be met. To reduce the costs of a tankless water installation,generally you will want to have the unit near a wall where horizontal venting distances can be kept to a minimal rather than through a longer vertical venting system that goes through the roof. It is sometimes possible to use existing chimneys for the venting routes which would prevent the need to cut through any roofing.

Most manufacturers will provide venting kits,but we advise you assess the location of your installation before buying their kits as each situation will most likely require a unique venting solution.

Another consideration is that your home may need to change the gas pipe line to accommodate a gas tankless water heater.

In some areas natural gas prices may be cheaper than electriciticy prices which may help you decide the most cost effective choice between gas tankless water heaters and electric tankless water heaters.

Tankless Water Heater Installation

A few things to keep in mind if you intend to hire a professional tankless water heater installer:

• Make sure the plumber and electrician are licensed.
• Check to see if the plumber has had any traning by the manufacturer and then call the manufacturer to verify this.  Alternatively you can check websites of specific brands for their list of approved installers.
• Check references before hiring a plumber or electrician.
• Ask for more than one plumber to come by and give their estimates. You’ll be in a better position to decide who has the best knowledge and expertise to handle the installation.  We recommend a minimum of 3 estimates.
• Make sure you ask them about any local building codes that need to be considered.
• Ask for all cost estimates in writing.
• Make sure they understand the manufacturer’s instructions and requirements for installation and warranty compliance. If not installed properly,in some cases,the manufacturer will void any warranty.