A tankless water heater heats water on demand using powerful burners, providing instant hot water without the need for a storage tank.
Tankless water heaters provide hot water on demand without the need for a storage tank. These innovative systems heat water instantly as it flows through the unit, offering energy efficiency and endless hot water. This guide explains exactly how they work, their advantages, and key considerations for installation.
How Tankless Water Heaters Operate
Tankless systems, also called on-demand or instantaneous water heaters, work fundamentally differently than traditional tank models:
- Cold water enters the unit when a hot water tap opens
- Flow sensors activate the heating elements
- Water passes through a heat exchanger where it’s rapidly heated
- Hot water exits the unit and travels to your faucet or appliance
Gas vs. Electric Heating Methods
Tankless heaters use one of two heating methods:
| Gas Models | Electric Models |
|---|---|
| Use a high-powered gas burner (natural gas or propane) | Utilize electric resistance heating elements |
| Produce higher flow rates (5-10 GPM) | Offer lower flow rates (2-5 GPM) |
| Require proper venting | Need adequate electrical capacity |
According to U.S. Department of Energy, gas models typically provide better performance for whole-house applications.
Key Components of Tankless Systems
Understanding the main parts helps explain how these units function:
Heat Exchanger
The core component where water gets heated. In gas models, this is a copper coil exposed to burner flames. Electric models use metal heating elements.
Flow Sensor
Detects when water starts moving through the system and activates the heating mechanism.
Temperature Controls
Maintain precise water temperature through thermostats and modulating valves.
Venting System (Gas Models)
Safely removes combustion gases. Some models use power venting technology for flexible installation.
Performance Factors
Several variables affect tankless water heater performance:
Flow Rate Capacity
Measured in gallons per minute (GPM), this determines how much hot water the unit can produce simultaneously. Most residential units provide 2-10 GPM.
Temperature Rise
The difference between incoming groundwater temperature and desired output temperature. Colder climates require units with higher temperature rise capabilities.
Energy Efficiency
Tankless heaters are 24-34% more energy efficient than tank models for typical homes, according to Home Depot’s research.
Advantages of Tankless Water Heaters
- Endless hot water: Never run out during long showers
- Space savings: About 80% smaller than tank heaters
- Longer lifespan: Typically last 20+ years vs. 10-15 for tanks
- Lower operating costs: Only heat water when needed
- Reduced risk of leaks: No large tank to corrode or burst
Installation Considerations
Proper installation is crucial for performance and safety:
Gas Models
- Require proper gas line sizing
- Need correct venting installation
- May need upgraded gas meter
Electric Models
- Often need electrical panel upgrades
- Require proper circuit breakers and wiring
- May benefit from advanced thermostat controls
Maintenance Requirements
While generally low-maintenance, tankless systems need:
- Annual descaling (especially in hard water areas)
- Periodic filter cleaning
- Venting system inspection (gas models)
- Component checks per manufacturer guidelines
Many homeowners opt for professional maintenance to ensure optimal performance and longevity of their investment.
