Before You Convert to a Tankless Water Heater

“Endless” hot water still has a flow limit

A tankless unit heats water as it moves through the appliance. It avoids storing a full tank, but it can deliver only the temperature rise and flow for which it is designed. Two showers and a dishwasher may ask more of the unit than one low-flow fixture.

Sizing begins with simultaneous demand, incoming water temperature, desired outlet temperature, and fuel or electrical capacity. Choosing by bedroom count or marketing label alone can produce disappointing performance.

Conversion is the real project

Replacing one tankless unit with a compatible model can be relatively direct. Converting from a storage tank may involve:

• a larger gas line or different gas-meter capacity;
• new combustion-air and vent routing;
• condensate drainage for a condensing model;
• electrical service for controls or an all-electric unit;
• water-line changes and service valves;
• wall structure and clearances; and
• a new equipment location.

Each item should be evaluated before a final quote. A compact appliance does not guarantee a simple installation.

Symptoms on an existing unit

Temperature swings, reduced flow, ignition errors, rumbling, or shutdown under heavy demand can have different causes. Scale, clogged filters, fuel or airflow problems, control faults, inadequate sizing, and crossed plumbing are among the possibilities.

A technician should read fault history, verify flow and temperature, inspect filters and venting, and compare actual demand with the model’s capacity. Repeatedly resetting an error without identifying the cause is not a durable repair.

Maintenance depends on the water and model

Tankless heat exchangers have narrow passages. Mineral scale can reduce heat transfer and flow. Manufacturer procedures commonly call for periodic inspection and may call for flushing or descaling, but the interval depends on water quality, use, and equipment instructions.

Ask whether isolation/service valves are installed and accessible. Keep air inlets, vents, and condensate paths clear. Never improvise a vent or disable a safety code.

Compare proposals by inputs and outputs

A useful proposal identifies:

1. model and fuel type;
2. rated flow at the design temperature rise;
3. household fixtures assumed to operate together;
4. gas, electric, vent, condensate, and water-line changes;
5. permits and inspection;
6. startup and combustion testing where applicable; and
7. maintenance requirements and warranties.

If a contractor promises savings, ask for the assumptions. ENERGY STAR describes potential efficiency benefits for qualifying gas tankless equipment, but actual energy and cost outcomes depend on the home, usage, fuel prices, and installation.

Safety is not a homeowner adjustment

Fuel-burning appliances require correct gas supply, combustion air, venting, and carbon-monoxide protection. Leave gas and vent modifications to qualified professionals. If a carbon-monoxide alarm sounds or anyone has symptoms, leave and call emergency services. Do not restart equipment until it is evaluated.

Electric tankless systems can require substantial electrical capacity. Panel and circuit work belongs to a qualified electrician working under applicable permits.

Philadelphia checks

Plumbing permits in Philadelphia are issued by the Department of Licenses and Inspections (L&I) under the Philadelphia Plumbing Code, and permitted plumbing work is done by a Philadelphia-licensed master plumber. Pennsylvania home-improvement (HIC) registration is not a plumbing license. Ask who will pull the permit and confirm the license before work starts. This directory does not endorse a listed business.

Sources

1. Whole-Home Tankless Gas Water Heaters, ENERGY STAR
2. How Whole-Home Gas Tankless Water Heaters Work, ENERGY STAR
3. Carbon Monoxide Fact Sheet, U.S. Consumer Product Safety Commission
4. Carbon Monoxide Poisoning Prevention, U.S. Fire Administration
5. Tank and Tankless Maintenance, Rheem
6. Descaling a Tankless Water Heater, Noritz
7. Tankless Water Heater Sizing Guide, Navien
8. 34 Pa. Code § 403.42, Pennsylvania Code
9. Home Improvement Contractor Registration, Pennsylvania Office of Attorney General
10. Contractor Licensing, Pennsylvania Department of Labor & Industry
11. How to Install a Tankless Water Heater, This Old House
12. PB_022 FAQ — Summary of 2018 Philadelphia Plumbing Code Amendments, Philadelphia Department of Licenses and Inspections