Tankless water heater replacement costs
| Job | What's included | Typical market range | Fair price* |
|---|---|---|---|
| Tankless → new tankless (gas) | Condensing gas tankless unit, ~199k BTU · Remove old tankless unit · Isolation (service) valves if missing · Reuse existing venting and gas line | $3,000–$5,500 | $3,600 |
| Tank → tankless conversion (gas) | Condensing gas tankless unit, ~199k BTU · Remove and haul away old tank · New PVC venting and condensate drain · Isolation valves and mounting | $4,200–$8,000 | $5,200 |
*National base price before local adjustment and add-ons. Prices are current estimates while our provider network finalizes local pricing. Market ranges come from published contractor prices and national cost guides (sources). Updated October 2026.
Common add-ons for tankless jobs are gas line upsizing (tankless burners need far more gas than a tank), permit and hard access. Typical prices for each are in the tool above.
Tank to tankless: what’s involved
- Gas supply: a whole-home gas tankless unit is typically rated near 200,000 BTU/hr, several times a typical tank. Many homes need a larger gas line from the meter.
- Venting: condensing units vent through PVC, usually on a new path out a wall or roof.
- Condensate: condensing units make acidic condensate that needs a drain (and sometimes a neutralizer).
- Mounting and valves: the unit mounts on a wall, and isolation valves are installed so it can be flushed.
Not sure a tankless unit can keep up with your home? Use our tankless size calculator.
Is tankless worth it?
| Gas tank | Gas tankless | |
|---|---|---|
| Installed price | $2,100 (50 gal) | $5,200 (conversion) |
| Hot water supply | Limited to the tank, then recovery time | Continuous, limited by flow rate |
| Space | Floor footprint | Wall-mounted |
| Typical lifespan | About 8–12 years | Often 15–20 years with maintenance |
| Maintenance | Flush and check the anode | Descale and clean the filter |
Tankless makes the most sense if you’re staying in the home for a long time, run out of hot water often, or need the floor space. If you just need hot water back fast at the lowest cost, a like-for-like tank replacement wins.
Tankless filter and flow sensor maintenance
Cleaning the inlet filter (DIY)
- Turn off power to the unit and close the cold-water isolation valve.
- Open the hot isolation valve’s drain port into a bucket to relieve pressure.
- Unscrew the inlet filter (on the cold-water inlet at the bottom), rinse the screen under a tap, and use a soft brush to clear debris.
- Reinstall, open the valves, restore power and check for leaks.
Descaling
In hard-water areas, tankless units need a periodic descaling flush with a small pump, hoses and a descaling solution, run through the isolation valves. Follow your manufacturer’s interval and procedure.
Flow sensor replacement
If the unit won’t fire even with good flow and a clean filter, or shows a flow-related error code, the flow sensor may have failed. Seeing a code? Look it up: Navien, Rinnai, Rheem tankless. It’s a model-specific part inside the unit, so we recommend a pro diagnose it before you order parts.
Frequently asked questions
How much does it cost to replace a tankless water heater?
Replacing an existing gas tankless unit with a new one costs about $3,600 at a fair price. Converting from a tank to tankless costs $5,200, because it needs new venting, a condensate drain and often a larger gas line.
Why does a tankless conversion cost so much more than a tank?
Gas tankless units need a much larger gas supply than a tank, and condensing models need new PVC venting and a condensate drain. That extra labor and material is most of the difference.
How often should I clean the tankless inlet filter?
Check and rinse the inlet water filter screen every few months to once a year, depending on your water quality. A clogged screen causes low flow and error codes.
What does a tankless flow sensor do?
It detects water flowing through the unit and tells the burner to fire. A failing flow sensor causes no hot water, or hot water that cuts in and out, at faucets that normally work. It’s a model-specific part, usually best replaced by a pro.