Installing a Tankless Water Heater Fast and Easy (DIY)

Navien tankless water heaterNavien tankless water heater

Installing a tankless water heater article is your step-by-step DIY guide for a successful and efficient installation. Check out the installation requirements, things to consider, tools and material needed for this job, venting and gas tips, whom to contact if professional help is required, and much more.

Note that the professional installation by the qualified and licensed technician is recommended, with the local plumbing, venting, gas, and electrical codes followed.

However, if you prefer to install a tankless water heater yourself, use the manufacturers' guide and our instructions (as a reference) to collect all the necessary information, tips, and tricks.

There are many manufacturers of tankless water heaters; Rheem, AO Smith, Titan, or Japanese Rinnai, Noritz, Takagi, or European Bosch, Stiebel Eltron, using gas and electricity, which are more or less complicated to install.

Installing an electric unit is simpler than gas type. Gas tankless water heater installation, in short, involves; mounting the unit, connecting electricity, gas, and water lines, and flue installation.

An electric type does not need venting but sometimes requires a new electric panels and more volt power.

Installing a tankless water heater is a challenge, and it can be hazardous if it is not done correctly. The majority of these on-demand models can be installed virtually anywhere, inside or outside, in the garage, attic, bathroom, or kitchen, and in places where it is possible to maximize your comfort and water heating experience.

There is no need anymore, like with conventional tank-type models, to have a designated room and occupy useful home area for this purpose. As opposed to heavy and large tank-type, there is a lot of flexibility when installing a tankless water heater.

Small and compact design allows easy wall mount while sealed combustion chamber, power, and direct venting, provide safe indoor installation and use.

Installing a tankless water heater - Things to consider 

Tankless models are small, nicely designed, wall-hanging, and flexible to install with an indoor and outdoor mount. Almost every water heater installation is different and specific to each home and application.

Skills needed when installing a tankless water heater:

  • Handling power tools
  • Working with flaming torches
  • Working with gas
  • Soldering copper pipes
  • Working with plumbing systems
  • Working with electric systems

What to consider when installing a tankless water heater:


An ideal location for your water heater depends on several factors, such as the water heater selection, your preference, home size and design, and available installation or mounting spots. The best is to mount the unit close to the point of use and the application where it will be used, mostly; bathroom, laundry, or kitchen sink, where it is convenient to use, service, and safe to run.

Secure your home by installing a tankless water heater in the area where water leakage will not result in damage, especially if planning to install tankless in the attic. To reduce the danger of water leaks, install a suitable drain pan under the appliance.

If considering the attic installation, the heat builds up, or freezing temperature might affect the normal operation, as the modern tankless units are equipped with delicate electronics.

Keep in mind that recommended clearances should be provided for the unobstructed, efficient, and safe work.

Wall Installation

Use the recommended number of bolts so the heater is securely attached to the wall. Using an installation bracket and its upper and bottom holes, simply attach the unit to the wall in the vertical position (unless otherwise requested).

If the wall is not strong enough to hold the heater, use reinforcement. The recommendation is to fasten the tankless unit to the wall studs or an additional piece of wood between the wall studs.

Providing the electric power outlet

Follow the electric local and national codes when installing a tankless water heater, as the tankless unit requires a higher voltage power supply - 120-240 VAC, 60Hz, sufficient amps, and an adequately grounded wall outlet. When installing a tankless water heater, it is essential to ensure that the voltage matches the rating plate.

Connecting the heater to the gas line and/or gas line upgrade

  • Ensure that your tankless water heater matches the gas type that will be used. Check inlet gas pressure to ensure that it is within the range found on the rating plate. Your tankless unit cannot use natural gas and propane without modifying the unit (conversion kit).
  • Propane water heaters should not be installed below grade (i.e., basement).
  • A manual gas control valve should be installed in the gas supply line, closed to your water heater. All connections must be checked for gas leaks using the soap-water solution.
  • A gas supply line based on the gas type, gas pressure, and other factors must provide recommended gas flow.
  • A sediment trap should be used at the bottom of the gas line.

Plumbing changes or upgrades to provide hot and cold water to the new unit

  • Use only potable water, free of dirt and other contaminants.
  • Use pipes not smaller than the diameter of the water heater connections. The recommendation is to install unions and flexible copper connections so they can be easily disconnected for maintenance and repairs.
  • Make sure that on the new installations, hot and cold water lines are not reversed.
  • Keep in mind to insulate hot and cold water lines to conserve water and energy. Protect both the water heater and pipeline from freezing temperatures.
  • A manual shut-off valve must be placed on the water supply line before it is connected to your tankless water heater. You can also install one on the hot water side.
  • Install the pressure relief valve.
  • Make sure the water supply has sufficient pressure and connections are tight, and there is no leak.


Venting is the most critical step in installing a tankless water heater.


With the improperly installed venting system (i.e., obstructed pathway), the tankless gas water heater produces dangerous gases like carbon monoxide that can leak into the living space.

According to the recommendations and codes, installing a tankless water heater with the proper venting and according to the recommendations and codes will provide safe operation and your peace of mind.

Water heaters with the concentric venting system and sealed combustion, such as direct vent models, must be installed with zero clearances, wall or roof penetration, allowing flexible and simpler installation.

In the indoor installation where the single vent system and the concentric vent pipe are utilized, a metal pipe is used for the exhaust gases and PVC or metal for fresh air intake. If the water heater uses inside air for combustion and is installed in the confined space, it is mandatory to provide provisions or two permanent openings.

Approved venting materials are required, and every connection must be accessible for inspection, cleaning, and replacement. A condensation collar or trap has to be installed correctly.

Venting should be as direct as possible and with a minimum length and number of elbows.

To avoid dips and sags, horizontal venting has to be supported every XX feet (per manufacturer's instructions). On vertical runs include condensate drain and vertical terminations (rain cap). Follow the manufacturer's guide for maximum lengths and other instructions.

Exterior models are ventless and installed outside, usually in a recessed enclosure for protection against the elements.

Installing devices to enhance the performance of a water heater

  • Water softener installation is essential in the areas where hard water is a problem. Due to sediment build-up, water heaters are losing their effectiveness and reduce performance.
  • Installation of the temperature controller is also recommended. The controller is used to control and monitor the temperature and diagnose the problem by displaying the error codes (check out these Rinnai error codes, as an example).
  • By installing a tempering or mixing valve, you will limit the temperature of hot water to the safe level, therefore, preventing scalding.
  • The adequately sized thermal expansion tank should be installed on all closed-loop systems. The expansion vessel is used to protect the water heater from excessive pressure and repeated relief valve operation.
  • If the pressure relief valve is not factory-installed, it is required by the ANSI CSA standard for all water heating systems. It must be rated up to 150 psi and to allow maximum BTU/hr gas input.
  • Electric tankless water heaters are less risky to install as they involve fewer factors to consider. Meeting a minimum supply pipe diameter is one of them.

Summary of installation requirements

  • All local/national codes are met.
  • Correct unit installation for the proper and safe operation, including electrical, gas, and water connections.
  • No adjustments were needed for gas pressure as it was factory set.
  • Proper space must be provided for installation, service, and maintenance.
  • The units should be installed in areas where sufficient air is available.
  • The vent termination must meet the requirements when it comes to the noise, clearance, and quality of air.
  • Venting must be per instructions; material, size, lengths...

As can be seen from the above guide, installing a tankless water heater shouldn't be hard as long as the directions are followed, but it is better to call a licensed technician.

Failure to install the tankless correctly results in improper and unsafe operation, shorter unit life, and possible warranty cancellation.

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