Installation Type for Tankless Water Heaters: How to Choose Yours

How to Measure and Establish Your Installation Requirements

To determine the correct installation requirements, you must measure the available clearance and confirm your utility capacities before ordering.

Measuring Physical Space for the Unit

Measure the height, width, and depth of the area where the unit will sit. Most tankless heaters require a minimum of 12 to 18 inches of clearance from surrounding walls or combustible materials to allow for proper airflow and maintenance access.

Verifying Gas Line Capacity

If you choose a gas-fired model, you must confirm your gas line’s diameter and pressure. The required BTU input for a tankless heater is often higher than a standard tank heater, and a standard 1/2-inch line may not provide sufficient volume for high-flow output.

Checking Electrical Amperage

Electric tankless heaters require a dedicated circuit with a specific amperage, often 150 to 200 amps depending on the unit’s power draw. You must check your main breaker panel to see if your electrical service can support a dedicated 240V circuit without tripping.

Mapping the Venting Route

For gas models, identify the shortest path from the unit to the exterior. Note the diameter of the exhaust pipe; standard 2-inch or 3-inch venting is common, but the length of the run affects the draft and the required blower power of the unit.

What Happens if the Installation Type is Incorrect?

Choosing an installation type that does not match your home’s infrastructure leads to specific functional failures during daily use.

The Risk of Under-Sized Gas Lines

If the gas supply cannot meet the unit’s demand, the heater will fail to reach the set temperature quickly enough. You will notice the water temperature dropping significantly when you turn on a second fixture, such as a shower while the dishwasher is running.

The Risk of Improper Venting

Incorrect venting leads to a buildup of exhaust gases or a lack of proper draft. This can cause the unit to enter a safety shutdown mode frequently or, in severe cases, create a carbon monoxide hazard within the living space.

The Risk of Inadequate Electrical Circuits

If an electric unit is installed on a circuit that cannot handle the peak load, the breaker will trip every time the heater activates. This results in a total loss of hot water until the breaker is manually reset.

What to Do if You Fall Between Installation Types?

Deciding between two installation types often comes down to a trade-off between convenience and performance capacity.

Choosing Between Gas and Electric

If your home is equipped for gas but the installation is difficult, and you are considering electric because it is easier to mount, consider the flow rate. Electric units often have lower flow rates than gas units; if you need to run two showers simultaneously, gas is usually the necessary choice despite the harder installation.

Choosing Between Wall-Mount and Floor Models

When space is tight but you need a high-output unit, choose the wall-mount option that matches your required BTU output. If a wall-mount unit is too large for your specific wall, you may need to move the installation point to a different wall rather than settling for a smaller, underpowered unit.

When to Hire a Professional Installer

Because tankless water heater installation involves gas lines, high-voltage electricity, and venting, it is a job for a qualified professional. A licensed plumber or electrician ensures that the installation meets local building codes and safety standards, which is required for insurance and warranty validity.

Reviewed by the Green Writer editorial team. Green Writer writes these guides from the 49 most-reviewed tankless water heater installation listings in our retail dataset, not from manufacturer copy.