Choosing a tankless water heater means deciding between two fundamentally different power sources, each with distinct installation requirements, operating costs, and performance characteristics. This choice affects everything from your utility bills to how many showers can run simultaneously.
You’ll learn the core differences between gas and electric tankless water heaters, how to determine which type fits your home’s infrastructure and hot water demands, and what each option requires for safe, efficient operation.
Are Tankless Water Heaters Gas or Electric?
Tankless water heaters are available in both gas and electric models. Gas units burn natural gas or propane to heat water on demand, while electric models use high-powered heating elements. Your choice depends on your home’s existing utilities, hot water needs, budget, and installation constraints, as each type offers different flow rates, energy efficiency ratings, and upfront costs.
How Gas Tankless Water Heaters Work
Gas tankless units ignite a burner when you open a hot water tap, sending water through a heat exchanger that raises the temperature in seconds. The burner modulates its flame intensity based on flow rate and desired temperature, shutting off completely when you close the tap.
These systems require both a gas supply line and proper venting to exhaust combustion gases safely outdoors. Most models need either direct vent, power vent, or condensing vent systems, each with specific clearance and material requirements set by local building codes.
Gas Unit Flow Rate Capacity
Gas models typically deliver higher flow rates than electric units, often providing 6 to 10 gallons per minute depending on the temperature rise needed. This makes them better suited for homes where multiple fixtures run simultaneously or where incoming water temperatures are very cold.
A gas unit rated for 8 gallons per minute can usually handle two showers running at once in moderate climates. In northern regions where groundwater enters at 40 degrees, that same unit might support only one shower and a sink.
Installation Requirements for Gas Models
Installing a gas tankless heater often requires upgrading your gas line to a larger diameter pipe, as these units demand higher BTU inputs than tank heaters. You may need a line capable of delivering 150,000 to 200,000 BTUs, which can mean running new pipe from the meter.
Venting requirements add complexity and cost. You’ll need to install approved vent pipe that terminates outdoors with proper clearances from windows, doors, and air intakes, and most installations require a licensed plumber and gas fitter to meet code and maintain warranty coverage.
How Electric Tankless Water Heaters Work
Electric tankless units pass water over electric heating elements that warm it instantly as it flows through the device. These models use no combustion, produce no exhaust, and require no venting, making installation considerably simpler in some situations.
The trade-off comes in electrical demand. Most whole-house electric tankless heaters draw 15,000 to 36,000 watts at full capacity, requiring dedicated circuits with substantial amperage that many older homes cannot provide without service panel upgrades.
Electric Unit Power Demands
A typical whole-house electric tankless heater needs three or more 40- to 50-amp double-pole breakers to operate. Your home’s electrical service must have enough spare capacity to handle this load on top of your existing appliances, HVAC system, and other electrical draws.
If your home has 100-amp or 150-amp service, you may need to upgrade to 200-amp service before installing an electric tankless heater. This upgrade requires a licensed electrician and often involves utility company coordination and permit inspections.
Flow Rate Limitations of Electric Models
Electric tankless heaters generally provide lower flow rates than comparably priced gas units. A whole-house electric model might deliver 2 to 5 gallons per minute, depending on inlet water temperature and desired output temperature.
These units work well for point-of-use applications or smaller homes with modest simultaneous demand. You can also install multiple smaller electric units at different locations rather than one central system, though this increases total installation cost.
Comparing Operating Costs
Your ongoing costs depend on local utility rates, which vary dramatically by region. In areas where natural gas costs significantly less per unit of energy than electricity, gas tankless heaters typically cost less to operate even though electric models convert energy to heat more efficiently.
Electric tankless heaters achieve 98 to 99 percent energy efficiency because nearly all electrical energy converts directly to heat with no exhaust losses. Gas models rate between 80 and 96 percent efficient, with condensing models reaching the higher end by capturing heat from exhaust gases.
Calculating Your Fuel Costs
To estimate operating costs, compare your local rates for natural gas (measured in therms) and electricity (measured in kilowatt-hours). A family using 64 gallons of hot water daily might spend $200 to $400 annually with gas or $400 to $700 with electricity, but these figures shift dramatically based on regional utility pricing.
If you’re considering propane rather than natural gas, factor in delivery costs and price fluctuations. Propane often costs more per BTU than natural gas, narrowing the cost advantage over electricity in some markets.
Installation Cost Differences
Gas tankless installations typically cost more upfront due to venting requirements, potential gas line upgrades, and the need for condensate drainage in condensing models. Professional installation often ranges from $2,500 to $5,500 including the unit, depending on how much infrastructure work your home needs.
Electric installations may cost less if your electrical service already has adequate capacity and space in the panel. However, if you need a service upgrade from 100 to 200 amps, that work alone can add $1,500 to $3,000, making the total project comparable to or more expensive than gas.
Climate and Regional Considerations
Incoming water temperature dramatically affects tankless heater performance. In southern regions where groundwater enters at 65 to 75 degrees, you need less energy to reach 120-degree output, allowing smaller, less expensive units to meet household needs.
In northern climates where winter groundwater temperatures drop to 35 to 45 degrees, you need a higher-capacity unit to achieve the same flow rate. This often makes gas models more practical for cold-climate whole-house applications, as electric units may struggle to heat enough water quickly.
Choosing Based on Existing Infrastructure
If your home already has gas service and adequate venting access, a gas tankless heater often makes practical sense. The existing infrastructure reduces installation barriers, and you avoid electrical service upgrades.
For all-electric homes or situations where running new gas lines is impractical or prohibited, electric tankless heaters provide a viable solution. Condominiums and apartments often favor electric models because venting through shared walls and roofs creates complications.
Outdoor vs. Indoor Placement
Gas tankless heaters designed for outdoor installation eliminate venting concerns entirely, as combustion air comes from outside and exhaust disperses naturally. These units must be rated for outdoor use and protected from freezing in cold climates.
Electric models install almost anywhere indoors, as they require no combustion air or venting. This flexibility allows placement closer to point-of-use locations, reducing the wait time for hot water and minimizing heat loss in long pipe runs.
Maintenance and Longevity
Gas tankless heaters require annual maintenance including burner cleaning, flame sensor inspection, and air filter replacement. Hard water areas demand more frequent descaling to prevent mineral buildup in the heat exchanger, which can reduce efficiency and damage components.
Electric units need less maintenance because they have no combustion components, but they still require periodic descaling in hard water areas. Both types benefit from annual flushing with vinegar or commercial descaling solution, a task you can perform yourself or hire a plumber to complete.
Expected lifespan for quality tankless heaters ranges from 15 to 20 years with proper maintenance, regardless of fuel type. This exceeds the typical 10- to 12-year life of tank water heaters, though replacement parts for tankless units can be more expensive.
Making Your Decision
Start by evaluating your home’s current utilities and electrical service capacity. If you have natural gas service and standard electrical capacity, gas likely offers better flow rates and lower operating costs in most regions.
Consider an electric tankless heater if you have or can afford to install adequate electrical service, if your hot water demands are modest, if you’re installing point-of-use units, or if gas venting is impractical. Get quotes for both options including all necessary infrastructure upgrades before deciding.
Professional Assessment Recommendations
Before purchasing either type, have a licensed professional evaluate your home’s specific requirements. A qualified plumber can calculate your peak hot water demand, assess your gas line or electrical capacity, identify venting options, and provide accurate installation cost estimates.
For electrical assessments, consult a licensed electrician to determine whether your panel has capacity for an electric tankless heater or what service upgrade would cost. This prevents discovering mid-project that your chosen option requires expensive additional work.
Start With Your Hot Water Needs
Both gas and electric tankless water heaters deliver endless hot water when sized correctly for your household. Gas models generally provide higher flow rates and lower operating costs where natural gas is affordable, while electric models offer simpler installation when adequate electrical service exists.
Calculate your home’s peak hot water demand by adding up the flow rates of fixtures you might use simultaneously, check your electrical panel capacity or gas line size, and get professional assessments for both options. This comparison reveals which technology fits your infrastructure, budget, and performance expectations.
We hope this guide helps you make an informed decision about your home’s hot water system and encourages you to explore more helpful Home and Garden articles for your next project.