Tankless Water Heaters: How They Work and What They Cost (2026)

Tankless water heaters heat water on demand rather than storing it in a tank. They're more energy-efficient, last longer, and never run out of hot water. But they also cost significantly more upfront. Is a tankless water heater worth it for your home?

This guide covers how tankless water heaters work, what they cost to buy and install, and how they compare to traditional tank units so you can make an informed decision.

How Does a Tankless Water Heater Work?

A traditional water heater keeps 40–80 gallons of water hot at all times, using energy even when you're not using hot water. A tankless unit works differently:

You turn on a hot water faucet.
Cold water flows through the unit and triggers a flow sensor.
A gas burner or electric heating element activates and heats the water instantly as it passes through.
Hot water flows to your faucet without any storage tank.
When you turn off the faucet, the heater shuts down.

This on-demand approach means you never run out of hot water (no more cold showers after the second person) and you only pay to heat water you actually use.

How Much Does a Tankless Water Heater Cost?

Cost Component	Gas Tankless	Electric Tankless
Unit cost	$800–$2,000	$400–$1,000
Installation labor	$1,500–$3,000	$800–$1,500
Total installed	$2,500–$5,000	$1,200–$2,500
Annual operating cost	$150–$250	$200–$350

Gas tankless units cost more to install because they often require upgrading the gas line, adding a new vent, or running a dedicated gas line. Electric units are simpler but may require an electrical panel upgrade.

For comparison, a traditional 50-gallon tank water heater costs $1,200–$2,500 installed in Los Angeles. See our complete plumber cost guide for more pricing details.

Tankless vs. Tank: Full Comparison

Factor	Tankless	Traditional Tank
Upfront cost	$2,500–$5,000	$1,200–$2,500
Lifespan	20–25 years	8–12 years
Energy savings	24–34% more efficient	Baseline
Hot water supply	Unlimited (on demand)	Limited to tank size
Physical size	Wall-mounted, compact	Large floor-standing tank
Maintenance	Annual descaling ($100–$200)	Annual flushing (DIY-friendly)
Wait time for hot water	2–5 seconds longer	Immediate (pre-heated)
Simultaneous use	Limited by flow rate (GPM)	Limited by tank volume

What Size Tankless Water Heater Do I Need?

Tankless units are sized by flow rate (gallons per minute, or GPM) and temperature rise (how many degrees the water needs to be heated). In Southern California, incoming water temperature is about 62°F, so you need a ~50°F rise to reach 112°F at the tap.

Household Size	Recommended GPM	Typical Unit
1–2 people	4–6 GPM	Small gas or electric
2–4 people	6–8 GPM	Mid-size gas unit
4+ people	8–10+ GPM	Large gas unit or multiple units

A shower uses about 2.5 GPM. A dishwasher uses 1.5 GPM. If you want to run a shower and dishwasher at the same time, you need at least a 4 GPM unit. Add up the fixtures you typically use simultaneously to determine your minimum GPM.

Gas vs. Electric Tankless

Gas tankless

Higher flow rates (8–11 GPM) — can serve the whole house
Works during power outages (some models)
Requires gas line and venting — installation is more complex and costly
Lower operating cost in most areas

Electric tankless

Lower upfront cost and simpler installation
No venting required — more flexible placement
Lower flow rates (2–5 GPM) — best for single-point use or warm climates
May require electrical panel upgrade (200-amp service recommended)

For most LA homes, a gas tankless unit is the best choice for whole-house hot water. Electric units work well for single-point applications like a bathroom addition or as a booster for a distant fixture.

Installation: What to Expect

A tankless water heater installation in Los Angeles typically takes 4–8 hours and may require:

Removing the old tank unit and capping off connections
Upgrading the gas line (tankless units need 3/4" gas lines; older homes may have 1/2")
Installing new venting (stainless steel category III or IV vent through an exterior wall)
Mounting the unit on an interior or exterior wall
Connecting water lines with isolation valves for maintenance
Pulling a permit (required in LA for water heater replacement)

Always hire a licensed plumber for installation. Improper gas or venting work is a safety hazard. In Los Angeles, verify your plumber holds a CSLB C-36 license. Browse verified plumbers in our directory.

Maintenance

Tankless water heaters need annual descaling to remove mineral buildup, especially in areas with hard water (LA water hardness varies by neighborhood, typically 10–18 grains per gallon).

Professional descaling: $100–$200 per visit. The plumber circulates a vinegar solution through the unit for 45–60 minutes.
DIY descaling: With a descaling kit ($100–$150 one-time purchase), you can do this yourself. It requires a small pump and two hoses.
Inlet filter cleaning: Clean the mesh filter on the cold water inlet every 6 months. Takes 5 minutes.

Skipping maintenance voids most warranties and can reduce efficiency by 30% or more over time.

Is a Tankless Water Heater Worth It?

A tankless unit makes financial sense if:

You plan to stay in the home 7+ years (to recoup the higher upfront cost through energy savings)
You frequently run out of hot water with your current tank
You want to reclaim the floor space a tank occupies
Your current tank is at end of life anyway and you're comparing replacement costs

A traditional tank may be the better choice if:

You're on a tight budget (tank units cost roughly half to install)
You're selling the home soon
Your gas line or electrical panel would need a major upgrade

Frequently Asked Questions

How much does a tankless water heater cost installed?

In Los Angeles, a gas tankless water heater costs $2,500–$5,000 fully installed. An electric tankless unit costs $1,200–$2,500 installed. Costs vary based on whether gas line or electrical upgrades are needed.

How long does a tankless water heater last?

Tankless water heaters typically last 20–25 years with annual maintenance, compared to 8–12 years for traditional tank units. Most manufacturers offer 10–15 year warranties on the heat exchanger.

Do tankless water heaters save money?

Yes. The U.S. Department of Energy estimates tankless units are 24–34% more energy efficient for homes that use 41 gallons or less of hot water daily. Annual savings are typically $80–$150, which adds up over the unit's 20+ year lifespan.

Can a tankless water heater run out of hot water?

A properly sized tankless unit provides endless hot water for sequential use (one shower after another). However, it can struggle with too many simultaneous demands. If you run two showers and a dishwasher at once, you may exceed the unit's flow rate and get lukewarm water.