Gas tankless water heater replacement cost in St. Louis, MO
Installed, About 180,000–199,000 BTU (2–3+ bathrooms)
A typical tankless water heater (About 180,000–199,000 BTU (2–3+ bathrooms)) costs about $2,900 installed in the St. Louis area, 4% above the national figure, because plumbers here earn a median $37 an hour against $31 nationally.
Prices by size in St. Louis
| Size | Low | Typical | High | National typical |
|---|---|---|---|---|
| About 150,000 BTU (1–2 bathrooms) | $2,100 | $2,750 | $3,750 | $2,650 |
| About 180,000–199,000 BTU (2–3+ bathrooms) | $2,650 | $2,900 | $4,100 | $2,800 |
Local labor: what plumbers earn here
| Hourly wage | St. Louis metro | United States |
|---|---|---|
| 25th percentile | $28 | $24 |
| Median | $37 | $31 |
| 75th percentile | $50 | $41 |
The St. Louis market
The City of St. Louis Building Division issues plumbing permits only to licensed plumbing contractors certified by the city, and mechanical permits only to city-certified licensed mechanical contractors. No homeowner route is stated. The plumbing fee schedule prices a water heater as a fixture at $10, plus a $30 application fee. For homes, mechanical permits carry a $25 application fee plus $40 for each furnace, condensing unit or combination furnace and condensing unit. Heat pumps are not named. After approval you print the permit and schedule inspections through the STL City Permits dashboard. EIA found furnaces are main heat in 76% of Missouri homes and central air serves 83%. St. Louis County, a separate government from the city, has its own permit office, and so do the Illinois counties in the metro.
A gas tankless unit may require new gas piping and its own vent. If the old tank shared a chimney with the furnace, ask how the furnace will vent once the heater leaves it. Ask the plumber whether the gas meter and line can carry the tankless unit's input, and where the new vent will exit. Cold winter water lowers tankless output, so ask what flow rate it delivers in January.
Permits in St. Louis
| Permit for this job | Yes (inferred: plumbing permit fee schedule prices 'water heater' as a fixture; permit pages do not name water heaters) (source) |
|---|---|
| Fee | Plumbing: $30 application fee + $10 per fixture (water heater listed). Mechanical (R1-R3 residential): $25 application fee + $40 per furnace, $40 per condensing unit, or $40 per combination furnace/condensing unit. |
| Who can pull it | City-licensed contractor only (City plumbing contractor or mechanical contractor license); homeowner route not stated |
| Inspection | Yes (scheduled through STL City Permits dashboard after approval) |
Rebates in Missouri
HEAR: announced, not open yet. HOMES: announced, not open yet. Source: Missouri DNR Division of Energy, checked October 13, 2026.
What these programs cover, and other states
Other systems in St. Louis
- Gas tank water heater
- Gas furnace
- Central air conditioner
- Heat pump (ducted, outdoor unit + air handler)
Gas tankless water heater cost in other metros
Sources
- City of St. Louis: Mechanical permits
- City of St. Louis: Plumbing permits
- City of St. Louis: Plumbing permit fees
- City of St. Louis: Mechanical permit fees
- Missouri DNR: IRA home energy rebates
- EIA, 2020 RECS: Highlights for space heating in U.S. homes by state
- EIA, 2020 RECS: Highlights for water heating in U.S. homes by state
- EIA, 2020 RECS: Highlights for air conditioning in U.S. homes by state
- BLS OEWS May 2025, St. Louis, MO-IL (47-2152 plumbers)
- DOE Gas-fired Instantaneous Water Heaters Final Rule TSD (Dec 2024), Table 8.2.6 (2023$)