Published by All Systems Pros · Updated October 12, 2026
The Baseline Cost Range for Conversion
A tankless conversion needs a project-specific estimate. The selected heater, installation location, and necessary gas, venting, water, and electrical changes determine the scope and price.
Transitioning from a traditional storage tank to an on-demand water heating system is a major plumbing upgrade, not a simple appliance swap. The unit itself represents only a portion of the total investment. The majority of the cost variance comes from adapting your home's existing infrastructure to safely support the new technology. Traditional tanks store hot water and heat it slowly over time, requiring relatively low energy input. Tankless systems, however, heat water instantly as it flows through the heat exchanger. This requires a massive, sudden draw of energy. Preparing a home for this shift often involves upgrading gas delivery systems, altering exhaust venting, and reconfiguring water pipes. Understanding these distinct components helps clarify why the installation range is broad and why a customized assessment is necessary for an accurate price.
Gas Line Modifications and Capacity
Tankless water heaters require a significantly larger volume of gas on demand compared to traditional tanks. Upgrading your gas line to meet this demand is a primary cost factor.
A gas tankless unit can have a substantially higher input rating than the tank it replaces. A qualified installer must evaluate total connected appliance load, supply pressure, developed pipe length, fittings, and the manufacturer’s approved sizing requirements. Existing pipe diameter alone does not establish capacity; some projects need modified piping or utility coordination. This process involves calculating the total gas load for all gas-connected appliances in the home to ensure the entire system operates safely without pressure drops. We handle all necessary gas connections to the water heater unit, though we do not perform appliance repair on other household gas appliances.
Venting and Air Intake Requirements
Proper venting is critical for safety and performance. Tankless units require specialized venting materials that can withstand acidic exhaust and often need new pathways to the exterior.
Traditional atmospheric water heaters typically vent vertically through a standard metal flue, relying on the natural buoyancy of hot air to carry exhaust gases up and out of the roof. High-efficiency, condensing tankless water heaters operate differently. They extract so much heat from the combustion process that the resulting exhaust gases are cooler and highly acidic. This requires specialized venting materials, such as specific grades of PVC or concentric venting systems, which resist corrosion. Because the exhaust is cooler, it is often pushed out horizontally through a side wall using an internal fan. Creating these new ventilation pathways, sealing them to prevent dangerous carbon monoxide leaks, and ensuring the unit has adequate intake air for combustion adds specific labor and material requirements to the conversion process.
Water Line and Electrical Updates
Relocating hot and cold water lines, installing isolation valves, and adding a dedicated electrical outlet are necessary steps that influence the final installation price.
Because a tankless water heater is much smaller and mounts directly to a wall, the physical location of the water connections changes. The existing hot and cold water pipes must be extended, rerouted, and neatly secured to align with the new unit. Professional installations also include isolation valves and flush ports, which are essential for future maintenance and descaling. Depending on your home's plumbing configuration, thermal expansion control may also be necessary. As noted in manufacturer documentation for closed water systems, expansion tanks are a common approved solution, though not universally required in every system. Additionally, even gas-powered tankless units require electricity to operate their internal computer boards, sensors, and electronic ignition systems. If there is no standard electrical outlet near the new installation site, one must be installed to power the unit.
Permits and Code Compliance
Securing the proper permits and passing local inspections is a mandatory part of the conversion process. Permit fees and requirements vary by city and add to the total cost.
Converting to a tankless system involves significant alterations to gas piping, water lines, and venting, which triggers the need for building permits. Under the 2025 California Building Standards Code, which took effect January 1, 2026, these modifications must be inspected for safety and compliance. Local authorities having jurisdiction manage this process, and their fees and submission routes vary. For example, Pasadena utilizes its own city Permit Center, Glendale Development Services handles permits on property, and Burbank lists water heaters and gas piping among its permit categories. Unpermitted plumbing work can lead to severe safety hazards, warranty issues that depend on the manufacturer's terms and the installation, and complications during future real estate transactions. General code education provided here is for informational purposes as of October 12, 2026; homeowners must always confirm current requirements and fees with their actual local building department.
Next Steps for an Accurate Quote
Because every home's infrastructure is different, an in-person assessment is the only way to determine your exact conversion cost. We provide free estimates for all installations and replacements.
The variables involved in a tankless conversion make it impossible to provide a single flat rate over the phone. During a free installation estimate, a qualified technician will evaluate your current gas supply capacity, identify the safest and most efficient venting route, and assess your water line configuration. This evaluation supports a written quote for your actual project. Review the proposed equipment, included modifications, and process for approving additional work before accepting the estimate. Financing options are also available for those who qualify, subject to terms and eligibility. Contact All Systems Pros to schedule your evaluation and determine exactly what it will take to upgrade your home in the San Gabriel Valley to an endless hot water system.
Sources and further reading
About All Systems Pros
All Systems Pros is a plumbing service company based in Monrovia, CA. The company lists Rheem ProPartner, A. O. Smith Certified Contractor, and Raypak credentials. These general guides help explain plumbing topics; equipment instructions and project requirements must be checked for the specific property.
