Tankless Water Heater Installation Cost: Gas vs Electric

Gas Tankless Installation Breakdown

A gas tankless installation includes the unit cost ($800 to $2,500), installation labor ($500 to $1,500), and materials/upgrades ($200 to $1,000). The total ranges from $1,500 for a simple unit swap on existing infrastructure to $5,000 for a full conversion from a tank system in a challenging location.

Gas Line Requirements

Gas tankless units have higher BTU input ratings than tank models, typically 150,000 to 199,000 BTU for whole-house units compared to 30,000 to 50,000 BTU for standard tanks. This higher demand usually requires a larger gas supply line. Most tank water heaters run on a 1/2-inch gas line, while tankless units need a 3/4-inch or 1-inch line.

If the gas meter and main supply line to the house are adequate, the plumber only needs to upgrade the branch line from the main to the water heater location. This costs $300 to $800 depending on the distance and whether the pipe runs through accessible or finished spaces. If the gas meter itself does not have enough capacity to handle the additional demand (particularly in homes that also have a gas furnace, gas dryer, and gas cooktop), the utility company may need to upgrade the meter at no cost, but this can add days to the project timeline.

Venting

Gas tankless units require Category III stainless steel venting, which is a different and more expensive material than the standard B-vent used by atmospheric vent tank models. Condensing tankless models can use PVC venting, which is less expensive but still requires running a new vent line because the existing B-vent from the old tank is not compatible.

Most tankless units vent horizontally through a sidewall rather than vertically through the roof, which actually simplifies the vent installation in many cases. The vent run should be as short and direct as possible, as longer runs reduce the unit's efficiency and may exceed the manufacturer's maximum allowable vent length. A typical sidewall vent installation adds $200 to $600 in materials and labor. If the unit must vent through the roof due to location constraints, the cost increases to $400 to $1,000.

Electrical Connection

Gas tankless units require a 120-volt electrical outlet for the control board, ignition system, and vent fan. If an outlet does not already exist near the installation location, adding one costs $100 to $300. Some installations also include a dedicated surge protector ($50 to $150) to protect the unit's electronics from power surges.

Electric Tankless Installation Breakdown

An electric tankless installation includes the unit ($500 to $1,500), labor ($300 to $800), and electrical work ($200 to $1,200). The wide electrical cost range is the defining characteristic of electric tankless installations.

Electrical Panel Requirements

Whole-house electric tankless units draw substantial power. A unit sized for a three-bathroom home in a moderate climate typically needs 100 to 150 amps across two to four dedicated 40 to 60-amp circuits. This is a significant electrical load that many older homes cannot support without a panel upgrade.

If your electrical panel has sufficient spare capacity (200-amp service with available breaker slots), adding the dedicated circuits costs $400 to $800 in electrician labor and materials. If the panel is full or the home has only 100-amp service, a panel upgrade to 200 amps costs $1,000 to $3,000, which can make the total electric tankless installation cost exceed that of a gas tankless.

For this reason, electric tankless is most cost-effective to install in newer homes built with 200-amp electrical service that has available capacity. In older homes with limited electrical infrastructure, a heat pump water heater is often a better electric option because it runs on a single 30-amp circuit, the same as a standard electric tank.

No Venting Required

The significant advantage of electric tankless is that it requires no venting at all. There are no combustion gases, no exhaust pipe, and no concerns about carbon monoxide. This simplifies the installation and removes one of the more expensive components of gas tankless installations. It also allows installation in enclosed spaces like interior closets where gas units would require specific combustion air provisions.

Tank-to-Tankless Conversion Costs

Converting from a tank to a tankless system costs $500 to $2,500 more than a simple unit replacement because of the infrastructure changes required. For gas conversions, this premium covers the gas line upgrade, new venting, and possibly relocating the unit. For electric conversions, it covers new circuit installation and potential panel upgrades.

The old tank must also be removed, which includes draining the 40 to 80 gallons of water it contains and hauling it out. If the tankless unit mounts on the wall where the tank previously stood, the plumber also needs to cap and conceal the old vent penetration through the roof. If the unit relocates to a different wall (common because tankless units mount closer to an exterior wall for shorter vent runs), the old water heater location needs the abandoned water and gas lines capped and the area cleaned up.

Tankless-to-Tankless Replacement

Replacing an existing tankless unit with a new one is significantly cheaper than a first-time conversion. The gas line, venting, and electrical connections are already in place and usually compatible with the replacement unit, especially if you stay with the same manufacturer or a comparably sized model. Labor for a tankless-to-tankless swap runs $500 to $1,000, bringing the total to $1,300 to $3,500 depending on the unit selected.

The main complications in a tankless replacement arise when upgrading to a larger unit that exceeds the existing gas line or venting capacity, or when the old unit was mounted in a location that no longer meets current code requirements for clearances and ventilation.

Location Considerations

Where you install the tankless unit affects both cost and performance. The ideal location minimizes the vent run (for gas units), is close to the main hot water demand points (to reduce pipe runs and waiting time), and is accessible for future maintenance.

Common installation locations include utility rooms, garages, exterior walls in basements, and outdoors (some gas models are rated for outdoor installation, which eliminates venting entirely). Outdoor installation is popular in warm climates and costs $200 to $400 less than indoor installation because no vent piping is needed. In cold climates, outdoor installation requires a freeze protection system built into the unit and may not be practical in areas with extended sub-zero temperatures.