Gas vs. Electric Tankless Water Heaters: Costs & Efficiency Guide

Tankless water heaters heat water on demand instead of storing it in a tank, so you get continuous hot water and save space. But once you decide to go tankless, the next question is gas or electric. They differ sharply in flow capacity, installation requirements, efficiency, and cost. This guide breaks down each factor so you can choose the right tankless water heater for your home.

By Anthony Hamilton, Co-Founder, THE Water Heater Company (21+ years in water heaters). Reviewed by THE Water Heater Company's factory-trained technical team.

Definition: how tankless units differ

A gas tankless heater fires a powerful burner to heat water as it flows through, and is available from brands like Noritz, Navien, and Rinnai. An electric tankless heater uses high-wattage heating elements instead. Both eliminate the storage tank, but gas units generally produce far more hot water per minute than electric ones.

GPM and flow rate: keeping up with demand

Flow rate is measured in gallons per minute (GPM) — how much hot water the unit can deliver at once. This is the single biggest practical difference:

• Gas tankless units typically deliver higher GPM, enough to run multiple showers and appliances simultaneously, even in cooler weather when incoming water is colder.
• Electric tankless units deliver lower GPM and are better suited to smaller homes, single bathrooms, or point-of-use applications.

The colder your incoming water, the harder a unit works to reach temperature, which lowers its effective flow rate. SoCal's mild climate helps, but household size still drives the right capacity.

Panel and gas-line requirements

Installation needs are very different, and this often decides the choice:

• Gas tankless usually requires a larger-diameter gas line than a standard tank heater, plus dedicated venting (often stainless or PVC for condensing models). The high burner output demands adequate gas supply.
• Electric tankless requires substantial electrical capacity — often multiple dedicated high-amperage 240V circuits and, in many cases, an electrical panel upgrade. Many older panels simply can't supply enough power.

Both involve permits and code compliance. A specialist should verify your gas line or panel can support the unit before installation.

Efficiency

Electric tankless units convert nearly all their energy into heat at the point of use, so they rate very efficiently on paper. Gas tankless units — especially high-efficiency condensing models from Noritz, Navien, and Rinnai — are highly efficient too and often cost less to operate where natural gas is cheaper than electricity, as it often is across Southern California.

Upfront vs. lifetime cost

Electric tankless units typically cost less to buy and install when your panel already has capacity. Gas tankless units cost more upfront — the unit, gas-line work, and venting add up — but for larger households they often win on lifetime cost thanks to lower gas rates and high flow capacity. The right value depends on your home's hot-water demand and utility rates.

Failure mode: undersizing the unit

The most common mistake is installing a tankless unit that can't meet demand — an electric model that runs cold when two fixtures run at once, or a gas unit fed by an undersized gas line. Proper sizing and infrastructure are everything with tankless. We serve homeowners across Ventura, Los Angeles, and Orange County; see our service areas.

Proof you can trust

THE Water Heater Company is a residential water-heater-only specialist, factory-trained on Noritz, Navien, and Rinnai tankless systems. With 42 years of combined experience, a 4.9-star rating across 2,100+ reviews, and an A+ BBB rating, we size and install tankless units correctly the first time.

Ready to go tankless?

We'll assess your gas line, panel, and hot-water demand and recommend the right unit. Same-day service, 7 days a week. Call (877) 798-7487 or book online to get started.