What is a tankless water heater


Mounted on the wall in your garage, utility room, or outside your home, a tankless water heater can service the hot water heater needs of your entire home, from faucets and showers, to soaking tubs, dishwashers, laundry and more.


Tankless water heaters provide hot water on-demand, meaning that assuming you install an appropriately-sized unit, you can have hot water when you need it, in as many locations as you need it, for as long as you need it. In fact, these are two of the greatest benefits of tankless water heaters: 1) you don’t have to waste energy continuously keeping a large volume of water hot, and 2) you can generate an unlimited flow of hot water, so you don’t have to worry about not having enough hot water to take a long shower or completely fill a soaking tub.

tankless water heaters


There are three types of tankless units currently available on the market: non-condensing, condensing, and hybrid condensing. While each one operates in a slightly different way, the basic premise for all three is the same. 

When a tap is turned on, a gas burner ignites and a heat exchanger coil transfers heat to incoming cold water flowing through the coil, delivering hot water to your faucet. (Electric tankless heaters that use elements instead of a gas burner also exist, but aren’t as effective for whole-home use.)

In order to get the water to a sufficient temperature, the units use a high volume of gas, typically between 150,000 and 200,000 BTUs, which in most homes requires the upsizing of a gas line.

A condensing tankless water heater takes things one step further by introducing a second heat exchanger to take advantage of excess exhaust heat, further heating your water and increasing the efficiency while decreasing the operating cost.

A hybrid tankless water heater includes a small reservoir of 2 or more gallons to compensate for “short draws” – hot water needs that don’t use much hot water such as hand washing. Keeping this small reservoir full of hot water prevents the unit from having to fully fire up, which increases its overall efficiency.

Important to note: Tankless units do not provide literally “instant hot water”, as hot water still takes time to flow from the unit to the tap.


Endless hot water

A tankless water heater is a great solution for a homeowner who currently has a standard tank water heater and is looking to replace it because their current tank is old, inefficient, and/or leaking. Other folks switch to tankless because they simply want to lower their annual water heating bills, and/or use endless hot water. Though tankless water heaters have been in use in Europe and Asia for over 20 years, they are just starting to gain wider acceptance and use in the United States.

 more energy efficient 

Tankless water heaters are gaining popularity for several reasons: a tankless water heater saves valuable floor space in your garage or utility room, lasts 20-30 years because the unit is less susceptible to rust and leaks, can increase home resale value, and is rated at 40-50% more efficient than today’s standard tanks. While the average home using a standard gas tank water heater spends roughly $250 heating their water each year, a tankless heater can bring costs down $75-$120 annually. Whether you’re concerned about environmental impact or just bringing down the cost of heating your water, a tankless water heater is a winner in both of these categories. Some utility companies even offer rebates for installing a tankless water heater.

high quality/longer lasting product

Another important factor to consider involves the changing federal regulations affecting water heaters, which go into effect in 2015. If you have a gas water heater that’s larger than 55 gallons, from 2015 on, you will be required to install a water heater with at least an 82% efficiency. This rating will only be found in tankless water heaters and more rare, less well-tested condensing tank water heaters.



  • Endless hot water: Since a tankless unit heats on demand, hot water will not run out. This is especially useful for large families or for homes with larger hot water demands – for example, homes with a soaking tub or spa system are often good candidates for a tankless system.
    If you’re considering upsizing your tank from 40 or 50 gallons to 66 or 80 gallons, or are replacing a larger tank, we strongly recommend you consider a tankless water heater.
  • Saves space: The footprint of a tankless unit is much smaller, freeing up valuable space in the home or garage.
  • Energy efficient: The most efficient traditional gas tanks today currently operate at 62-67% efficiency, compared with 82-96% for today’s tankless water heaters, resulting in around $100 in annual savings for most homes.
  • Longer lasting: Tankless units typically have longer warranties, and can last twice as long as a traditional tank. This means you’ll have to replace your tankless unit half as often as you would your tank.
  • Home resale value: In some cases, homeowners may be able to recover the cost of a tankless installation as a tankless water heater may increase the sale value of your home.


  • Retrofit cost: The costs to switch to a tankless unit can be prohibitive: total cost for a project generally ranges from $2,000 to $4,500 installed due to gas line, venting, and water line changes. The good news is, your next tankless installation will be significantly less expensive because it won’t involve these retrofit costs.
  • Longer wait time at the tap: Lots of homeowners think that installing a tankless water heater will decrease the time it takes for water to get hot at a faucet. This is untrue – in fact, in most cases, hot water will take approximately 15 seconds longer to get water to the tap with a tankless water heater.
  • Lower operating costs not guaranteed: Because of the ability to get unlimited hot water, some homeowners will use a lot more hot water on a regular basis. This increased usage can eliminate the reduction in electricity costs from installing an efficient tankless water heater.
  • Tankless units require electricity: Because tankless water heaters require electricity, they cannot provide hot water in the event of a power outage.

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What is a flow rate and what should I ask for?

While traditional hot water tanks are compared based on gallon capacity, recovery rate, and first hour rating, tankless water heaters are compared based on their per minute flow rate. Typical flow rates for most major brands range from 4 to 12 gallons per minute (GPM). Consider these common hot water needs and the flow rate requirements of each: 

0.5 – 1.0 GPM
Bathroom sink
0.5 – 1.5 GPM
Kitchen sink
1.5 – 2.0 GPM
Utility sink
1.5 – 2.0 GPM
Washing Machine
2.0 – 2.5 GPM
1.5 – 2.5 GPM
Bath tub
2.5 – .0 GPM
Jacuzzi/Hot tub
4.0 – 5.0 GPM

Consider how many of these needs you may have simultaneously to determine the maximum flow rate you require. For a home with 1 bathroom, we recommend 6-7 GPM; 2 bathrooms, 8 – 9 GPM; and 3+ bathrooms, 9-11 GPM.

In our experience, smaller 4-5 GPM units are suitable for studio apartments and small one bathroom homes or other application specific needs. For very larger homes, there are other options including installing multiple tankless units in series.

What is temperature rise & how does it factor into my choice of max GPM?

Water enters the home at different temperatures depending on where you live. If you live in the northern U.S., your average entering winter water temperature is 40-50˚F. If you live in the southern U.S., your average entering winter water temperature is 50-65˚F.

Where do I want to locate my tankless water heater?

Many homeowners decide to relocate their water heater when converting to tankless. Consider where you want to install your water heater, as there are both indoor and outdoor units on the market. The outdoor units are typically less expensive to install.

What should I look for in an Efficiency Factor (EF)?

The higher the EF, the less the tankless water heater will cost to operate. Efficiency is a measure of heat transfer from the energy source to your hot water. The best tankless water heaters have an EF of .92 – .96, which means that they are 92-96% efficient.

What brand should I select?

Important things to consider when choosing the brand of your tankless water heater are warranty, availability of local service providers, and reliability. Make sure there are installers in your area who are certified to work on the product, in the event your water heater needs to be serviced.


When choosing a tankless water heater, the two most important considerations are:

Fuel type:

If you currently have a gas tank water heater (natural gas or propane), you can install a gas tankless water heater. However, you will probably have to upsize the gas line coming from your meter to your heater, as tankless units typically require a dedicated line to service their high demands of up to 200,000 BTU. If you currently have an electric water heater, you will either have to apply for gas or propane service to your home, or connect an existing gas connection to your water heater setup. Some utility companies offer significant rebates for switching from electric water heating to gas water heating, and switching to gas tankless is a great choice and great opportunity to take advantage of these rebates. We do not recommend electric tankless water heaters for most whole-home water heating needs because of the poor feedback, less-than-desirable temperature and flow capabilities of these units.


Determining the desired location of your tankless water heater is important for achieving space savings and most economical installation costs. Talk with your installer about where might be the best place to locate a tankless water heater in your home. You will also need dedicated power to the unit so consider that. Keep in mind, in the event of a power outage, the unit will not provide hot water. However, installers can install a backup battery system if you want. When estimating a total cost for the installation of a tankless water heater, your installer should go over the current plumbing codes and permit costs with you before they begin work in your home. Make sure you understand the requirements so your water heater is installed safely. Also, ask your installer to help you understand the periodic maintenance requirements of a tankless water heater. While maintenance costs are low, some manufacturers do recommend a descaling process, the frequency of which will depend on the quality of the water where you live. This will help extend the lifetime of your tank. Read your owner’s manual for further tips and recommendations.

so, why go tankless?


Some utility companies offer incentives to help bring down the upfront cost of purchasing and installing a tankless water heater. Call your utility company to find out about incentives available in your area, or visit our rebates and incentives page.

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Call Fast Water Heater Co. TODAY for more information on tankless hot water heaters.

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