Yes, many tankless water heaters use gas (natural gas or propane), but not all of them. The short answer to “does a tankless water heater use gas” is that it depends on the model: gas-fired tankless units are common, but electric tankless models also exist and are widely available. This guide from the MyTownPlumber Editorial Team will help you understand the differences, pros and cons, and what to consider before buying one for your home in 2026.
How a Gas Tankless Water Heater Works
A gas tankless water heater (also called an on-demand water heater) heats water only when you turn on a hot water tap. Cold water flows through a heat exchanger, and a powerful gas burner rapidly raises its temperature. Because there is no storage tank, you never run out of hot water as long as the gas supply and flow rate are adequate.
Key Components of a Gas Tankless Unit
- Gas burner: Typically powered by natural gas or propane.
- Heat exchanger: Usually made of copper or stainless steel to transfer heat efficiently.
- Venting system: Requires a dedicated flue pipe to exhaust combustion gases outside.
- Electronic ignition: Lights the burner only when water flow is detected.
Gas vs. Electric Tankless Water Heaters: A Quick Comparison
| Feature | Gas Tankless | Electric Tankless |
|---|---|---|
| Fuel source | Natural gas or propane | Electricity |
| Flow rate (typical) | 5–11 GPM (gallons per minute) | 2–5 GPM (lower for whole-house use) |
| Installation complexity | Requires gas line, venting, and often a larger electrical supply for ignition | Requires high-amperage electrical circuit (often 60–150 amps) |
| Operating cost (US average) | Typically lower than electric in most regions | Higher if electricity is expensive |
| Lifespan | 20+ years with proper maintenance | 15–20 years |
| Energy efficiency | Up to 96% (Energy Star rated) | Up to 99% (no standby loss) |
Should You Choose a Gas Tankless Water Heater?
Advantages of Gas Tankless
- Unlimited hot water: As long as the gas supply is on, you can run multiple showers, the dishwasher, and the washing machine simultaneously — provided the unit’s flow rate is sufficient.
- Lower fuel cost: Natural gas is often cheaper than electricity per BTU in most US states.
- Smaller electrical load: Gas units only need a small amount of electricity for the control board and ignition (often a standard 120V outlet).
Disadvantages of Gas Tankless
- Higher upfront cost: The unit itself and installation (gas line, venting, permits) can cost $1,500–$3,500 or more, depending on your region and existing infrastructure.
- Venting requirements: You must have a route to the outside for exhaust; retrofitting an older home may be expensive.
- Cold weather concerns: Some gas units can struggle if incoming water is very cold (below 40°F), reducing flow rate.
Installation Considerations for a Gas Tankless Water Heater
Installing a gas tankless water heater is not a DIY job for most homeowners. You need a licensed plumber and often a gas fitter or HVAC professional. Key steps include:
- Upgrading the gas line to supply enough BTUs (British Thermal Units) for the unit.
- Installing a proper venting system (usually PVC or stainless steel) that meets local building codes.
- Adding a condensate drain (high-efficiency units produce acidic condensation).
- Ensuring adequate combustion air supply, especially in a closet or basement.
If you already have a gas tank water heater, switching to a tankless may be simpler because the gas line and venting may already be in place — but it still requires professional evaluation. For expert help, check out our water heater repair services or schedule a consultation.
Maintenance Tips to Keep Your Gas Tankless Unit Running Efficiently
Annual maintenance is critical for a gas tankless water heater. Hard water can cause mineral buildup in the heat exchanger, reducing efficiency and lifespan. We recommend:
- Flushing the unit with white vinegar or a descaling solution once per year.
- Cleaning the air intake filter every 3–6 months.
- Inspecting the venting system for blockages or corrosion.
- Checking the gas pressure and burner flame (best left to a pro).
If you notice rusty water, strange noises, or error codes, call a professional. Our team also handles drain cleaning and leak detection if you suspect any plumbing issues.
Frequently Asked Questions
Do all tankless water heaters use gas?
No. While many tankless water heaters are gas-fired, electric tankless models are also common. Gas units are more popular for whole-house applications because they can heat water faster and at a higher flow rate.
Can I use a propane tankless water heater if I don’t have natural gas?
Yes. Propane tankless water heaters work similarly to natural gas models. You will need a propane tank on your property and a gas line to the unit. Propane is more expensive than natural gas in most areas but still often cheaper than electricity.
How much does it cost to install a gas tankless water heater?
Installation costs vary widely by region and home configuration. A typical total (unit + labor) ranges from $1,500 to $4,000. Retrofitting an older home with new gas lines and venting can push costs higher.
Is a gas tankless water heater better for the environment?
Gas tankless units are more efficient than traditional tank heaters (up to 96% vs. 60–70%), so they use less fuel overall. However, electric tankless units produce zero onsite emissions. The overall environmental impact depends on your local electricity generation mix.
How long does a gas tankless water heater last?
With proper maintenance, a gas tankless water heater can last 20 years or more. Many manufacturers offer warranties of 10–15 years on the heat exchanger.
Can a gas tankless water heater work during a power outage?
Most gas tankless units require electricity to power the control board and ignition. Without power, they will not operate unless you have a backup generator or battery system. Some models have a manual ignition option, but they are rare.
External Resources
For more detailed information, we recommend consulting the U.S. Department of Energy’s water heating guide and the International Association of Plumbing and Mechanical Officials (IAPMO) for code requirements.
Ready to Upgrade Your Water Heater?
Whether you choose a gas or electric tankless water heater, proper installation and maintenance are key to long-term performance. The MyTownPlumber team can assess your home, provide a free estimate, and handle everything from gas line upgrades to venting. Contact us today for a special offer on tankless water heater installation.