Installing a Tankless
Water Heater

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Installing a tankless water heater article is your step-by-step, DIY guide for the successful and efficient installation, while keeping the costs down.

From my experience as the engineer who worked on combi boilers and on-demand water heaters I was always suggesting a professional installation by the qualified and licensed technician, and that is what I am recommending here as well. Local plumbing, venting and electrical codes have to be followed.

But, if you prefer to install a tankless water heater by yourself, use manufacturers guide and our guide (as a reference) to collect all the necessary information, tips and knowledge.

There are so many manufacturers of the tankless water heaters; Rheem, AO Smith, Titan, or Japanese Rinnai, Noritz, Paloma, or European Bosch, Stiebel Eltron, using gas or electricity to run and, which are different in design.

In order to insure a proper tankless water heater installation and keep the warranty valid, Noritz, for example, is selling units, venting and other parts only through the licensed contractors. These heaters are not sold by the manufacturers online through the Amazon or Yahoo stores, so you have to follow the manufacturer's recommendation and find the certified technician for installation and startup.

Installing a tankless water heater is a challenge, and it can be hazardous if it is not done properly. Majority of these on demand models can be installed virtually anywhere, inside or outside, in the garage, bathroom, and with a goal to maximize your convenience and water heating experience.

There is no need anymore, like with conventional tank type models, to have a designated room and occupy precious home area for this purpose. There is a lot of flexibility when installing a tankless water heater. They are wall-hanging with an option to be installed even in the bathroom like with the sealed combustion gas models or small point of use electric heaters.

What you need when installing a tankless water heater

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 for 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

  • Knowledge of plumbing

  • Knowledge of electric

What to consider when installing a tankless water heater:


Based on the water heater selection, your preference, home size and design, and available installation or mounting location, mount the unit close to the point of use and the most frequent used outlet; bathroom, laundry or kitchen, where it is convenient to use, service and is safe to run.

Secure your home by installing a tankless water heater in the area where water leakage will not result in damage. If it is needed, suitable drain pan should be installed under the appliance.

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 the reinforcement. Recommendation is to fasten the tankless unit to the wall studs or additional piece of wood between the wall studs.

emergency plumber

Providing the electric power outlet

Follow the electric local and national codes when Installing a tankless water heater, as the tankless unit requires higher voltage power supply - 120-240 VAC, 60Hz, sufficient amps and properly grounded wall outlet. When installing a tankless water heater it is important to make sure 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 match the gas type it is being installed for. 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 the connections must be checked for the gas leaks using the soap-water solution.

Gas supply line based on the gas type, gas pressure and other factors must be able to provide recommended gas flow.

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 contaminates.

Use pipes not smaller that the diameter of the water heater connections. Recommendation is to install unions and flexible copper connections so it 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 water heater and pipeline from freezing temperatures.

Manual shut off valve must be placed on the water supply line before it is connected to your tankless water heater.

Make sure water supply has sufficient pressure and connections are tight and there is no leak.


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


With the improperly installed venting system, (i.e. obstructed pathway) tankless gas water heater is producing dangerous gases like carbon monoxide that can leak into the living space. This is why installing a tankless water heater with the proper venting and according to the recommendation and code, and using the appropriate material will provide safe operation and peace of mind.

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

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

Exterior models are installed outside, in a recessed enclosure or flush with the outside wall with no need for the vent.

Approved venting materials are required and every connection must be accessible for inspection, cleaning and replacement. 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.

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

Installing devices to enhance the performance

Water softener installation is important in the areas where hard water is the problem. Due to sediment build-up water heaters are losing their effectiveness and reduce the performance.

Installation of the temperature controller is also recommended. It is not only that it controls the temperature but some of the manufacturers are having error codes to diagnose any problem, which helps in troubleshooting and repairs.

By installing a temper or mixing valve you will limit hot water temperature to a safe temperature not scalding.

Properly sized thermal expansion tank should be installed on all closed loop systems and is used to protect the water heater from the excessive pressure and repeated operation of the relief valve.

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 less factors to consider. Meeting a minimum supply pipe diameter is one of them.

Following the above step by step guide, combining it with a manufacturer's guide, your DIY skills and necessary tools you will probably have the answer on how to install a tankless water heater without calling plumber or the expensive contractor.

(Photo credit to Amazon)