A tankless water heater costs $2,500 to $5,500 installed, with most gas units landing between $3,000 and $4,500. Electric models run $1,800 to $4,000, and often more if your panel needs an upgrade. The hardware itself isn’t the expensive part. Getting gas, venting, and condensate up to spec is where the money goes, and it’s why the same unit that costs $1,400 online turns into a $4,000 job.
What Drives the Price
Gas tankless units demand more from a house than a tank ever did. A burner that heats water on demand pulls 150,000 to 200,000 BTU, roughly triple what your old tank burner drew. If the house has half-inch gas line feeding the heater, that line has to be upsized or a new dedicated run added. Then comes venting: most tankless units need sealed stainless venting, not the B-vent over your old tank. Condensate from the heat exchanger needs somewhere to drain.
| Cost item | Typical range | Notes |
|---|---|---|
| Gas tankless unit | $900-$2,000 | Mid-tier brands cluster near $1,100-$1,500 |
| Gas line upsizing or new run | $250-$1,200 | Depends on distance to the meter and obstructions |
| Stainless venting kit | $300-$800 | Longer runs and wall penetrations cost more |
| Condensate drain or pump | $50-$250 | Pump needed when gravity drainage isn’t available |
| Installation labor | $700-$1,500 | Conversion jobs take six to ten hours |
| Electric unit | $500-$1,200 | Whole-house models, not point-of-use |
| Electric service upgrade | $1,500-$3,500 | Common when the panel is 100 amps or less |
Electric looks cheaper until you check the panel. A whole-house electric tankless unit draws 18,000 to 36,000 watts, which usually means four large breakers and a 200-amp service. If your panel is already tight, the electrical work can dwarf the plumbing.
Tank vs. Tankless: The Real Comparison
| Factor | Tank, 40-50 gal gas | Tankless, gas |
|---|---|---|
| Typical installed cost | $1,300-$3,200 | $2,500-$5,500 |
| Typical lifespan | 8-12 years | 15-20 years with regular flushing |
| Hot water supply | Finite, then a refill wait | Continuous if sized correctly |
| Standby losses | Roughly 10-15% of water-heating energy | Negligible |
| Annual maintenance | Basically none | Descaling flush, $150-$300 pro or DIY |
| Back-to-back showers | 30-60 min recovery | No recovery needed |
| Cold inlet water | No effect | Flow rate drops noticeably in winter |
| Power outage | Gas tank keeps working | Dead electronics, no hot water |
That lifespan column is where tankless earns back some dignity. A heat exchanger rated for 15 to 20 years against a tank that rusts out at 10 means you buy roughly half as many units over a 30-year stretch. Over a very long ownership, the gap narrows. Over most people’s actual ownership, it doesn’t.
Real-World Installation Scenarios
Scenario 1: electric swap in a 1-bath condo, panel already 200 amps. Unit at $1,000, labor at $600, flush valves and fittings at $150, permit at $100. Total: about $1,850. This is the best-case electric install, and it only exists when the electrical service is already generous.
Scenario 2: gas tankless replacing a gas tank, favorable house. Three-quarter-inch gas line already in place, exterior wall for venting, floor drain nearby. Unit at $1,400, short gas extension at $250, venting at $500, labor at $800, permit at $150. Total: about $3,100. This is what a smooth conversion looks like.
Scenario 3: 1970s house with half-inch gas line. Same unit, labor, and permit as scenario 2, but the short gas extension becomes a new three-quarter-inch run at $900, the venting stretches to $700, and a condensate pump adds $200. Labor climbs to $900. Total: about $4,250. Nothing went wrong. The house just wasn’t built for an on-demand burner.
The Payback Math, Honestly
Here’s the part most tankless marketing skips. A tank loses heat through its walls around the clock, and that standby loss runs roughly 10 to 15 percent of your water-heating energy. A tankless unit eliminates most of it. For a family of four spending $400 to $600 a year heating water with gas, that’s real savings of maybe $50 to $100 a year.
Now compare against the cost gap. Tankless typically runs $1,200 to $2,000 more than a comparable tank install, sometimes $3,000 more after gas line work. At $75 a year in savings, the payback period is 16 to 27 years, if the unit even lasts that long. Subtract $150 annual descaling in hard-water areas and the math can genuinely never close. We’ve run this comparison plenty of times, and the honest answer is that payback alone almost never justifies tankless.
The math works better in specific cases: big households running three showers a morning, cheap natural gas regions, homes you plan to keep for 20 years, and replacements happening anyway at end of tank life. It never works for vacation homes with light usage or electric setups needing a service upgrade. And if you expect to sell within five years, you won’t recoup the premium at appraisal. If a plain tank suits you better, the tank water heater replacement guide covers that job in detail.
Ways to Pay Less
Choose a mid-tier brand instead of the flagship model. The $1,800 premium units add recirculation and Wi-Fi features that matter little; the burner and heat exchanger are similar across the line.
Batch the gas line work. If a plumber is already on site for the swap, adding the three-quarter-inch run costs less than a separate visit. Get the gas line and venting quoted as line items so you can compare them across three bids. Spreads of $1,000 on identical conversions are common, and contractor quote red flags lists the padding patterns worth catching.
Check utility rebates before buying. Some gas utilities pay several hundred dollars back on high-efficiency tankless units. Search dsire.org and your utility’s promotions page. Skip anyone claiming a federal tax credit; those expired December 31, 2025.
Mistakes to Avoid
Undersizing is the classic error. Sizing a tankless unit to its rated flow at 77-degree inlet water when your groundwater runs 50 degrees means lukewarm showers in January. Ask the installer to size against your actual winter inlet temperature and your real simultaneous demand.
Skipping the flush is how $3,500 units die at year eight. Hard water scales the heat exchanger, efficiency drops, and the warranty claim gets denied for missing maintenance. If your water is hard, flush annually or install a softener. Put the flush on the calendar with the rest of your annual home maintenance budget so it actually happens.
Also, don’t accept a quote without confirming the gas line size. Plumbers who skip that calculation deliver units that error-code out every time the furnace kicks on.
Bottom Line
Budget $3,000 to $4,500 for a gas tankless conversion and $1,800 to $2,500 for a clean electric install. Buy tankless for endless hot water and long service life, not for savings, because the energy math rarely pays back the premium inside a normal ownership. If your household runs out of hot water daily and you’re staying put, the numbers can work. Otherwise a well-sized tank remains the smarter spend.
FAQ
How long do tankless water heaters last?
Fifteen to twenty years with regular flushing, and manufacturers back heat exchangers with 12 to 15 year warranties. Neglected units in hard-water areas can fail much sooner. Maintenance, not brand, is the biggest variable.
Do tankless water heaters really save money?
A little, not enough. Eliminating standby losses saves roughly $50 to $100 a year for a typical gas-heated household. Against a $1,200 to $3,000 price premium, payback takes 15-plus years, which is longer than most people own the unit.
Do I need to descale a tankless water heater?
In hard-water areas, yes, annually. A recirculating vinegar flush through the service valves takes 45 minutes and costs nothing DIY or $150 to $300 from a plumber. Skip it and scale chokes the heat exchanger, which kills efficiency and can void the warranty.
Is electric or gas tankless cheaper to install?
Electric is cheaper only when your panel can handle the load. The unit costs less and venting isn’t needed, but whole-house models need 100 to 150 amps of dedicated capacity. If that means a service upgrade, gas becomes the cheaper route fast.