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A tankless water heater does not provide “instant” hot water in the sense that hot water comes out the moment you turn on the tap. Instead, it provides “on-demand” hot water. This means that the water is heated instantly as it passes through the unit, but there is still a delay between the moment the tap is turned on and when the heated water reaches the tap. The time it takes for the hot water to arrive depends on the distance between the water heater and the faucet.

How Tankless Water Heaters Work:

  • When a hot water tap is turned on, cold water travels through a pipe into the tankless water heater.
  • An electric element or gas burner heats the water as it passes through the unit.
  • Since the water heater starts heating water only on demand, it doesn’t supply hot water instantaneously. The delay you experience is due to the time it takes for the heated water to travel through the plumbing to reach your tap.

Factors Affecting Hot Water Delivery Times:

  1. Distance: The further the water has to travel from the heater to the tap, the longer it will take to receive hot water.
  2. Flow Rate: The flow rate of your plumbing fixtures can also impact delivery times. A higher flow rate means water moves faster through the pipes, reducing the wait time.
  3. Type of Plumbing: The type of pipes (e.g., copper vs. PEX) and their diameter can affect how quickly the water heats up and how long it retains heat as it travels.

Solutions for Instant Hot Water:

For those who want truly instant hot water, there are a couple of solutions that can be used in conjunction with a tankless water heater:

  1. Recirculation Systems: These systems circulate hot water through your plumbing so that hot water is always available near the points of use. Some tankless water heaters are equipped with built-in recirculation pumps, while external pumps can be added to others. This system can greatly reduce the wait time for hot water but may increase energy usage.
  2. Point-of-Use Tankless Water Heaters: Installing smaller, point-of-use tankless water heaters near specific fixtures (e.g., under a sink) can provide nearly instant hot water to that fixture by eliminating the distance the hot water must travel.


While tankless water heaters offer the convenience of on-demand hot water, eliminating wait times entirely usually requires additional solutions like recirculation systems or point-of-use heaters. Understanding the distinction between “on-demand” and “instant” hot water can help set realistic expectations for the performance of a tankless water heater in your home.

A tankless water heater, also known as an on-demand water heater, is an energy-efficient appliance designed to heat water directly without the use of a storage tank. When a hot water tap is turned on, cold water travels through a pipe into the unit, where it is heated by either an electric element or a gas burner. This process ensures that hot water is available in a continuous supply, eliminating the wait time for a storage tank to fill up and heat.

GPM stands for Gallons Per Minute, and it is a crucial metric when considering tankless water heaters. GPM measures the flow rate of water that the heater can provide at a given temperature rise. Essentially, it tells you how much hot water the unit can produce in a minute, which is vital for understanding whether a particular model can meet the hot water needs of your household.

Why GPM is Important:

  1. Determines Capacity: The GPM rating helps determine the capacity of the water heater, indicating how many hot water applications (like showers, washing machines, and sinks) can be used simultaneously without running out of hot water.
  2. Sizing Your Water Heater: Properly sizing a tankless water heater to your home’s needs involves calculating the total GPM required at peak usage times. This ensures that the water heater you choose can handle the demand when multiple fixtures are in use at the same time.
  3. Efficiency and Comfort: A water heater with a GPM rating that matches your household’s demands ensures efficient operation and continuous comfort, providing a steady supply of hot water without unnecessary energy use.

Calculating Your Needs:

To calculate your needs, you’ll need to add up the GPM of all fixtures that could potentially be in use simultaneously. Here’s an example:

  • Shower: 2.0-2.5 GPM
  • Kitchen Sink: 1.0-1.5 GPM
  • Dishwasher: 1.0-1.5 GPM
  • Washing Machine: 1.5-3.0 GPM

If all these could be in use at the same time, you would need a tankless water heater that can provide somewhere between 5.5 to 8.5 GPM to ensure you don’t run out of hot water.

Consider Temperature Rise:

The actual GPM output of a tankless water heater can also depend on the temperature rise required, which is the difference between the incoming cold water temperature and the desired hot water temperature. A unit may produce a higher GPM of hot water in a warm climate where the incoming water temperature is higher compared to a cold climate where the water heater needs to work harder to heat the water to the desired temperature.

Choosing the Right Unit:

When selecting a tankless water heater, consider both the GPM rating and the temperature rise at that flow rate to ensure it meets your hot water needs in the most energy-efficient manner. This approach will help you choose a unit that not only saves energy but also provides the convenience and comfort of continuous hot water.

When it comes to choosing a tankless water heater, one of the key decisions homeowners face is between condensing and non-condensing models. Understanding the differences between these two types of water heaters is crucial for selecting the right one for your needs, ensuring energy efficiency, and optimizing long-term savings.

What are Condensing Tankless Water Heaters?

Condensing tankless water heaters are designed to capture and utilize the energy from exhaust gases that would otherwise be wasted. These heaters have a secondary heat exchanger that condenses the exhaust gases to extract additional heat, pre-warming the incoming cold water. This process enhances efficiency, with many models achieving energy efficiency ratings of 90% or higher.

Benefits of Condensing Models:

  • Higher Efficiency: By utilizing exhaust gases, condensing models are more energy-efficient, reducing energy bills.
  • Environmental Impact: Lower greenhouse gas emissions due to better energy utilization.
  • Reduced Venting Costs: Since the exhaust gases are cooler, PVC pipes can often be used for venting, which is less expensive than the stainless steel venting required for non-condensing models.


  • Higher Initial Cost: Condensing units are generally more expensive upfront due to their complex design.
  • Maintenance Requirements: The additional components and the condensation process may require more frequent maintenance.

What are Non-Condensing Tankless Water Heaters?

Non-condensing tankless water heaters are the more traditional design. They heat water directly without the additional step of capturing heat from exhaust gases. As a result, their efficiency ratings are usually lower than those of condensing models, typically around 80-85%. The exhaust gases are hotter, which requires specific venting arrangements to handle the higher temperatures.

Benefits of Non-Condensing Models:

  • Lower Initial Cost: These models are less expensive upfront, making them attractive for budget-conscious consumers.
  • Simplicity and Reliability: With fewer moving parts and a simpler design, non-condensing models can be more reliable and easier to maintain.


  • Lower Efficiency: Less efficient than condensing models, leading to potentially higher operating costs over time.
  • Venting Requirements: The need for special venting materials can increase installation costs and complexity.

Choosing Between Condensing and Non-Condensing

The choice between condensing and non-condensing tankless water heaters depends on several factors:

  • Budget: If initial cost is a primary concern, non-condensing models might be more appealing. However, for those willing to invest more upfront for lower operating costs, a condensing model is the way to go.
  • Installation Considerations: The location of installation and the feasibility of venting can influence the choice. Condensing models offer more flexibility with venting options.
  • Energy Savings Goals: For homeowners prioritizing energy efficiency and long-term savings, condensing water heaters offer significant advantages.


Both condensing and non-condensing tankless water heaters have their place in residential settings, offering unique benefits tailored to different homeowner needs and preferences. By understanding the distinctions between these two types, you can make a more informed decision that aligns with your budget, environmental values, and efficiency goals. Regardless of your choice, transitioning to a tankless water heater is a step forward in enjoying continuous hot water supply and energy savings.

At Water Heater Doctor, we prioritize providing reliable, efficient, and practical solutions for our clients. As such, we have opted not to install or service electric tankless water heaters. These models can sometimes require substantial modifications to your home’s electrical system, including the addition of extra circuits, due to their high electrical demand.

Implementing these modifications is not only potentially complex but can also result in significant costs, which can make electric tankless water heaters a less economically feasible option compared to their gas counterparts.

Furthermore, we have found that electric tankless water heaters can sometimes fall short in terms of reliability. To ensure we’re offering you the most dependable and efficient solutions for your hot water needs, we focus on servicing and installing gas tankless water heaters, which we believe offer a superior balance of reliability, efficiency, and cost-effectiveness.

We value your comfort and satisfaction, and our team at Water Heater Doctor is always on hand to guide you through the process of choosing the most appropriate water heating solution for your specific needs and circumstances. Rest assured, we’re committed to helping you make an informed decision and providing the high-quality service you deserve.

Regular maintenance is essential for the optimal functioning and longevity of a gas tankless water heater. A well-maintained unit can last up to 20 years or more.

Professional servicing should be conducted at least once a year. This service typically involves checking for and fixing any leaks, inspecting the burner and venting system, descaling the heat exchanger, and checking the overall operation of the unit.

Regular maintenance is especially important if you have hard water, as the mineral deposits can build up over time and affect the efficiency and lifespan of the unit. Descaling or flushing the system can help prevent this buildup.

In addition to professional servicing, there are also some things homeowners can do, such as regularly checking for any visible signs of damage or leaks and cleaning the air filter as needed.

At Water Heater Doctor, we provide comprehensive maintenance services for gas tankless water heaters, ensuring they continue to provide efficient, reliable hot water for many years.

Tankless water heaters are designed for longevity. On average, they can last up to 20 years or even longer with proper maintenance, almost twice as long as traditional tank-style water heaters. Of course, this can vary depending on factors like usage, water quality, and regular maintenance. At Water Heater Doctor, we recommend scheduling regular servicing to ensure your tankless water heater stays in top shape for as long as possible.

Tankless water heaters heat water on-demand, which means they start heating water as soon as you turn on the tap. However, the time it takes for the hot water to reach your faucet will depend on the distance between the water heater and the faucet. If the faucet is far away from the heater, it may take a few seconds longer for the hot water to reach you. One way to overcome this delay is to install a dedicated recirculation line and recirculation pump however this can be costly.

While some homeowners may feel confident in their ability to install a tankless water heater on their own, we generally advise against it. Proper installation of a tankless water heater involves handling gas, electricity, and water, which can be dangerous if not done correctly. Additionally, a professional installation ensures the unit operates efficiently and safely. Incorrect installation can void the manufacturer’s warranty and potentially lead to significant repair costs down the line. At Water Heater Doctor, our experienced team can handle the installation process seamlessly, ensuring your peace of mind.

Non-Condensing Water Heaters: These traditional models heat water and immediately vent the exhaust gases to the outside. This process unfortunately allows some heat energy to escape, reducing the heater’s overall energy efficiency. Typically, non-condensing water heaters achieve energy efficiency ratings around 80-85%.

Condensing Water Heaters: Designed with energy efficiency in mind, condensing water heaters capture and repurpose some of the heat from the exhaust gases. They employ a second heat exchanger to extract heat before the gases are vented. This ‘recycled’ heat preheats the incoming cold water, reducing the energy needed to reach your desired temperature. With this innovative method, condensing water heaters can reach energy efficiency ratings up to an impressive 98%.

While the upfront cost for condensing water heaters is generally higher than for non-condensing models, their superior energy efficiency can lead to significant savings over time. Please note, condensing water heaters need a drain for the condensed water, which may impact installation location options.

At Water Heater Doctor, we’re committed to helping you make an informed decision that aligns with your specific needs, budget, and property layout. Whether you prioritize upfront cost, long-term energy savings, or installation simplicity, we’ve got you covered.

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