Frequently Asked Questions
Everything you need to know about tankless water heaters
General
What is a tankless water heater?
A tankless water heater, also called an on-demand water heater, heats water directly without using a storage tank. When you turn on a hot water tap, cold water travels through a pipe into the unit where it's heated by either a gas burner or electric element, providing a constant supply of hot water. Learn more in our Ultimate Tankless Water Heaters Guide.
How does a tankless water heater work?
When you open a hot water faucet, cold water enters the tankless unit. A flow sensor detects the water flow and activates the heating element (gas burner or electric coils). The water is heated instantly as it passes through the heat exchanger, delivering hot water at your desired temperature. When you close the faucet, the unit shuts off automatically.
What are the main benefits of tankless water heaters?
Key benefits include: endless hot water supply, 8-34% energy savings, space-saving compact design, longer lifespan (15-20 years vs 8-12 for tank units), reduced risk of water damage from tank leaks, and better water quality since water isn't stored in a tank. Read our detailed comparison of tankless vs traditional water heaters.
Installation
Can I install a tankless water heater myself?
While possible for experienced DIYers, we strongly recommend professional installation. Gas units require proper venting and gas line work, while electric units may need electrical upgrades. Improper installation can void warranties and create safety hazards. Most manufacturers require professional installation to maintain warranty coverage. Check our installation tips for detailed guidance.
Do I need to upgrade my electrical system for an electric tankless unit?
Most electric tankless units require significant electrical upgrades. Whole-house electric units typically need 150-200 amp electrical service and multiple dedicated circuits. Point-of-use units have lower requirements but still need dedicated circuits. Consult an electrician to assess your current electrical capacity, and see our guide to electrical requirements for real amperage and breaker figures by model.
What type of venting does a gas tankless water heater need?
Gas tankless units require proper venting to safely remove combustion gases. Most use either direct vent (sealed combustion) or power vent systems. Direct vent units draw air from outside and vent directly through an exterior wall. Power vent units use indoor air for combustion and require a fan to exhaust gases.
Sizing
How do I size a tankless water heater for my home?
Sizing depends on flow rate (GPM) and temperature rise needed. Calculate your peak hot water demand by adding up GPM of fixtures you'll use simultaneously. For temperature rise, subtract incoming water temperature from desired output temperature. Most homes need 6-10 GPM capacity with 70-80°F temperature rise. Read our complete sizing guide or use our sizing calculator.
Can a tankless water heater supply my whole house?
Yes, but proper sizing is crucial. Whole-house units typically provide 6-11 GPM depending on the model. For larger homes or high-demand situations, you might need multiple units or a high-capacity commercial-grade unit. Consider your family size, number of bathrooms, and simultaneous usage patterns.
What's the difference between point-of-use and whole-house tankless units?
Point-of-use units serve single fixtures or small areas, typically providing 0.5-3 GPM. They're ideal for remote locations or supplementing whole-house systems. Whole-house units provide 6-11+ GPM and can supply multiple fixtures simultaneously. Point-of-use units are less expensive but require multiple units for whole-house coverage.
Cost
How much does a tankless water heater cost?
Electric point-of-use units: $100-$500. Electric whole-house units: $600-$1,000. Gas units: $1,000-$2,600. Installation costs vary widely: $1,000-$3,500 for most installations. Total project costs typically range from $1,400-$5,600, with average around $2,800. Browse our best budget options or use our cost calculator.
Will a tankless water heater save me money?
Tankless units can save 8-34% on water heating costs (depends on usage patterns). Typical savings of $200/year in utility costs. Payback periods: 4-7 years for most units. Utility rebates, where available, can shorten that considerably. The main value comes from energy savings, convenience, and space savings. Calculate your specific savings with our cost calculator.
Are there rebates available for tankless water heaters?
The federal 25C tax credit for qualifying tankless units expired on December 31, 2025 and is no longer available. However, many utility companies and some states still offer their own rebates. Check with your local utility company, your state energy office, and the Database of State Incentives for Renewables & Efficiency (DSIRE) for programs currently available in your area.
Maintenance
How often should I maintain my tankless water heater?
Annual professional maintenance is recommended, with more frequent service in hard water areas. Key maintenance includes: descaling (every 6-12 months in hard water areas), cleaning air intake filter monthly, checking venting annually, and flushing the system. Regular maintenance extends lifespan and maintains efficiency.
Why is my tankless water heater not producing hot water?
Common causes include: insufficient gas supply or electrical power, clogged air intake or exhaust, mineral buildup requiring descaling, flow rate too low to activate unit, or malfunctioning components. Check for error codes, ensure adequate flow rate (usually 0.5+ GPM), and verify power/gas supply before calling for service.
How do I descale my tankless water heater?
Descaling removes mineral buildup and maintains efficiency. Use a descaling kit with food-grade vinegar or commercial descaling solution. The process involves connecting a pump to circulate the solution through the unit for 45-90 minutes, then flushing with clean water. Follow manufacturer instructions and consider professional service for warranty compliance.
Comparison
Should I choose gas or electric tankless?
Gas units generally provide higher flow rates, lower operating costs, and work during power outages. Electric units have lower upfront costs, easier installation (no venting), and higher efficiency ratings. Choose gas if you have existing gas lines and high hot water demand. Choose electric for smaller homes or where gas isn't available.
Which brands are most reliable?
Top-rated brands include Rinnai, Rheem, Noritz, and Navien for gas units. For electric units, consider Stiebel Eltron, Rheem, and EcoSmart. Look for units with long warranties, good customer support, and local service availability. Our product reviews provide detailed comparisons of reliability, features, and performance.
Technical
What is temperature rise and why is it important?
Temperature rise is the difference between incoming cold water temperature and desired hot water temperature. For example, if groundwater is 50°F and you want 120°F hot water, you need 70°F temperature rise. Higher temperature rise requirements reduce the unit's flow rate capacity, so it's crucial for proper sizing.
Can tankless units work with well water?
Yes, but well water often has higher mineral content requiring more frequent maintenance. Install a water softener if hardness exceeds 7 grains per gallon. Some manufacturers void warranties without proper water treatment. Well water may also have lower pressure, affecting unit performance, so check minimum flow rate requirements.
Do tankless water heaters work during power outages?
Gas tankless units with pilot lights can work during power outages, but most modern units have electronic ignition and controls requiring electricity. Some units offer battery backup options. Electric units cannot operate without power. Consider a whole-house generator if hot water during outages is critical.
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Why Choose a Tankless Water Heater?
Tankless water heaters represent a significant advancement in home water heating technology. Unlike traditional tank water heaters that continuously heat and store water, tankless units heat water on-demand, providing numerous benefits for homeowners.
Energy Efficiency and Cost Savings
Tankless units avoid the standby losses of a storage tank. Actual energy use and savings depend on household demand, fuel, efficiency, inlet-water temperature and installation. See the DOE and ENERGY STAR references below for current test criteria and consumer guidance.
Space-Saving Design
Tankless units mount on walls and take up significantly less space than bulky tank water heaters. This space-saving design is particularly valuable in smaller homes, apartments, or utility rooms where every square foot matters.