How much does a gas tankless water heater cost to install?

Prices checked October 2026. Wages: BLS, May 2025.

The first tankless heater in a house is a conversion job, and conversions cost more than swaps. The range above is for a gas-fired tankless (instantaneous) water heater in two sizes: about 150,000 BTU for one or two bathrooms, and 180,000 to 199,000 BTU for two to three or more. Equipment prices come from public retailer listings. Installation is the Department of Energy's average from its December 2024 rule on gas instantaneous water heaters. It reflects DOE's sample of homes, which mixes like-for-like replacements with harder installs. Half of that figure is treated as labor and adjusted to plumber wages where you live.

A whole-house unit burns gas much faster than a tank burner, so the gas line may need to be larger. The old metal flue usually gives way to new plastic or stainless venting through a wall or roof. Condensing models need a condensate drain. Replacing an existing tankless with a new one should land near the low end. A first-time conversion belongs in the upper half, plus any separate extras shown below.

Installed price by size, national

Size	Unit (list)	Low	Typical	High
About 150,000 BTU (1–2 bathrooms)	$1,422	$2,050	$2,650	$3,500
About 180,000–199,000 BTU (2–3+ bathrooms)	$1,566	$2,550	$2,800	$3,850

Installation averages $1,213 nationally for the common size (DOE, inflated to August 2026); about 50% of that is labor, which we scale to local wages.

Extras that may be added

Item	Typical	Range
Thermal expansion tank (where code requires it)	$200	$150–$360
Condensate pump	$200	$160–$320

What moves the price

Burner size

Bigger units can run more showers and taps at once but cost more and draw more gas. Navien's installation guide shows a large model at about 195 cubic feet of gas per hour and tells installers to check the manual's pipe sizing tables. A line that fed a tank may not carry that much, especially on a long run from the meter.

Venting

Condensing tankless models can use plastic venting, which DOE's analysis notes lowers their installation cost compared with non-condensing units that need stainless. Approved materials in one major brand's guide include Schedule 40 PVC or CPVC and polypropylene. The vent run length and where it can exit the house set the labor.

Condensate disposal

Condensing units produce acidic water that must drain away, often through a neutralizer. With no floor drain nearby, a condensate pump is needed, which is shown as a separate extra on this page.

Mounting location

Units hang on a wall, so the old tank spot is not always the best place. Moving the heater means new water lines, gas pipe and vent routing. Keeping it where the old tank sat, near an outside wall, is usually the least expensive layout.

Regional plumber pay

The labor half of DOE's average is multiplied by your area's plumber wage compared with the national median. In high-cost metros, a first-time conversion with gas and vent work is where the difference shows most.

Repair or replace?

DOE assumes a gas tankless heater lasts about 20 years on average, longer than a tank, so repairs on a unit under about ten years old usually pay off. Common fixes include flame rods, igniters, fans, sensors and descaling a heat exchanger clogged by hard water. Check the heat exchanger warranty before paying for a large repair. Many brands cover it far longer than other parts. On an older unit with a failed heat exchanger or control board, hold the repair up against the replacement range above. A new unit can reuse the venting, gas line and water connections, so a like-for-like swap sits at the low end of the range.

Run the numbers for your unit.

What a complete quote lists

Model number, maximum BTU input and rated flow at your area's winter water temperature
Whether this is a new installation or a tankless-to-tankless replacement
Gas line work: pipe size from meter to heater, with a note if the existing line was checked and kept
Vent material, length and where it exits the house
Condensate drain and neutralizer, or a condensate pump
Isolation valves for future flushing and descaling
Removal and disposal of the old tank
Electrical outlet for the unit, if none is within reach
Permit fee for both plumbing and gas work
Heat exchanger warranty, parts warranty and labor warranty, each stated separately

Paste your quote and we'll tick these off for you.

Gas tankless water heater prices by metro

Common questions

Why does a tankless install cost more than a tank swap?

The equipment is pricier, and a first install usually needs new venting, a condensate drain, wall mounting and often a larger gas line. DOE's average installation cost for gas tankless units is higher than its figure for gas tanks for those reasons.

Do I need a bigger gas line?

Often for a whole-house unit. It depends on the total load of all your gas appliances and the length of pipe from the meter. The installer should check this against the manufacturer's sizing tables and say so on the quote.

How long does a tankless water heater last?

DOE's 2024 rule assumes an average of 20 years, with a median of about 18 years, and notes that field data is limited. Some inspection charts list as little as 10 years for on-demand heaters, so treat any single number with caution. Hard water shortens the life unless the unit is descaled.

Which size do I need?

Size is set by how much hot water you use at the same moment and how cold your incoming water is. Homes with two or more showers running together usually need the larger size. The installer should explain sizing in terms of gallons per minute at your incoming water temperature.

Can I install it myself?

No. Navien's guide says its units must be installed and serviced by a licensed plumber and that gas supplies should be connected only by a licensed professional. Gas line and vent work also need a permit in most areas.