The two published ranges
| Source | Tankless, installed | Average | Date |
|---|---|---|---|
| This Old House | $1,200 to $3,500 | $2,800 | June 2026 |
| Fixr | $2,500 to $4,500 | $2,811 | January 2025 |
The averages agree almost exactly, at $2,800 and $2,811. The ranges do not. Fixr's floor is more than twice This Old House's, and Fixr's guide is 17 months older than the other figures on this page. Where the two conflict we lean on This Old House, because it is current and it separates unit cost from labor.
The part that is specific to converting
A tankless unit replacing another tankless unit is a straightforward job. Replacing a tank is not, because a tank and a tankless heater want different utilities. These are the line items that exist only because you are converting:
| Conversion item | Cost | Source |
|---|---|---|
| Gas line upsize, half-inch to three-quarter inch | $400 to $800 | This Old House |
| Gas line conversion, stated separately on the same page | $350 to $750 | This Old House |
| Adding a gas line, conversion from tank | about $500 | Fixr |
| New stainless venting through wall or roof | $400 to $800 | This Old House |
| New dedicated circuit, electric units | $200 to $600 | This Old House |
| Full electrical panel upgrade, electric units | $1,000 to $2,000 | This Old House |
| Removing the old tank | $100 to $500 | This Old House |
Fixr puts the whole conversion at about $1,700 for a gas unit including the gas line, against $90 to $450 to install an electric tankless unit where the electrical supply is already adequate.
What this means in practice. A gas tankless unit almost always needs a bigger gas line than a gas tank did, because it fires at several times the input rate for short bursts instead of a low rate continuously. An electric tankless unit needs a service most houses do not have: This Old House puts it at 120 to 160 amps dedicated and multiple 240-volt circuits. Those two facts, not the price of the appliance, are what make or break a conversion budget.
Cost by fuel
| Fuel | Unit | Labor | Total installed | Source |
|---|---|---|---|---|
| Electric | $500 to $1,500 | $150 to $1,000 | $650 to $2,500 | This Old House |
| Propane | $500 to $2,000 | $900 to $1,500 | $1,400 to $3,500 | This Old House |
| Natural gas | $750 to $2,000 | $900 to $1,500 | $1,650 to $3,500 | This Old House |
Plumbers charge $75 to $150 an hour for this work and the job takes 4 to 8 hours (This Old House). A tank swap takes 1 to 3 hours. The extra labor is most of why the conversion costs more.
Sizing, which drives the unit price
| Size | Flow rate | Suits | Unit cost |
|---|---|---|---|
| Point-of-use | 1 to 2 GPM | Single faucet or appliance | $150 to $500 |
| Small whole-house | 2 to 4 GPM | Small apartment or condo | $500 to $1,000 |
| Medium whole-house | 5 to 7 GPM | 2 to 3 bedroom home | $1,000 to $2,000 |
| Large whole-house | 8 to 10 GPM | 4+ bedroom home | $1,500 to $3,000 |
All from This Old House, June 2026. Natural gas models reach the highest flow rates, up to 11 GPM; electric models deliver 3 to 8 GPM depending on the model.
What you get back
| Measure | Figure | Source |
|---|---|---|
| Energy saved, homes using up to 41 gallons a day | 24% to 34% | Energy Star, via This Old House |
| Tankless lifespan | 15 to 20 years | This Old House, Fixr |
| Tank lifespan | 8 to 12 years | This Old House, Fixr |
| Running cost, tank | $440 to $580 a year | This Old House |
| Running cost, tankless electric | $300 to $540 a year | This Old House |
| Running cost, tankless gas | $192 to $264 a year | This Old House |
| Federal tax credit, gas units at 0.95 EF or higher | up to $600 | This Old House |
| Utility rebates | $100 to $300 | This Old House |
| Manufacturer rebates | $100 to $400 | This Old House |
The payback arithmetic, done openly. Take the middle of This Old House's figures: a gas tankless unit installed at $2,800 against a gas tank at $1,200 to $2,300 installed, so roughly $500 to $1,600 extra. Running cost falls from $440 to $580 a year to $192 to $264, saving roughly $250 to $315 a year. On those numbers the extra cost is back in two to six years, and the unit lasts roughly twice as long. That calculation is ours, built from the figures in the table; neither source publishes it.
It breaks down in three cases: if the gas line and venting work pushes the conversion well past $2,800, if your household uses far more than 41 gallons a day (the savings percentage is stated for households at or below that), and if you are on electricity at a high rate.
What the sources say goes wrong
- A 3 to 5 second delay before hot water arrives at the tap (This Old House). Tankless units heat on demand, so there is no reservoir already hot.
- No hot water in a power outage, including on gas units, because the controls and ignition need power (Fixr). A tank holds hot water for hours.
- Hard water needs descaling, at $100 to $500 a year (This Old House). Skipping it shortens the life of the unit and costs efficiency.
- One unit may not serve the whole house. Fixr notes that each demand point may need its own unit in some layouts, which multiplies the cost.
How to read a quote for this conversion
Insist that the quote lists the gas line work, the venting and any electrical work as separate lines, and that it states the size of your existing gas line and what it is being changed to. A conversion quote that shows one number has hidden the only figures that distinguish a $1,600 job from a $4,000 one. Get three quotes: This Old House notes that prices for identical tankless work vary by $500 or more between contractors.
Related: repair or replace, how long a water heater lasts, replacement cost calculator.
Sources
- This Old House, How Much Does Tankless Water Heater Installation Cost?, updated June 12, 2026
- Fixr, Tankless Water Heater Installation Cost, updated January 31, 2025
- This Old House, How Much Does Water Heater Installation Cost? (2026), updated June 17, 2026
Price figures are national US ranges from the sources above as of the date shown. Your local price depends on labor rates, permits and site conditions. Read how we get our numbers.