How Long Does It Take to Install a Tankless Water Heater?
Quick Answer
4–8 hours for a standard installation. Switching from a tank to tankless system can take 8–12 hours due to additional plumbing and venting work.
Typical Duration
Quick Answer
Installing a tankless water heater takes 4–8 hours for a straightforward replacement of an existing tankless unit. Converting from a traditional tank-style water heater to tankless typically takes 8–12 hours because it requires upgrading gas lines, adding new venting, and rerouting plumbing.
Installation Time by Scenario
| Scenario | Time Estimate | Cost Range |
|---|---|---|
| Electric tankless (replacing electric tank) | 3–5 hours | $1,000–$2,500 |
| Electric tankless (new install) | 4–6 hours | $1,500–$3,000 |
| Gas tankless (replacing gas tank) | 6–10 hours | $2,500–$5,000 |
| Gas tankless (replacing tankless) | 3–5 hours | $1,500–$3,500 |
| Gas tankless (new install, no existing gas line) | 8–12 hours | $3,500–$6,000 |
Gas vs. Electric Comparison
| Factor | Gas Tankless | Electric Tankless |
|---|---|---|
| Installation time | 6–10 hours | 3–5 hours |
| Venting required | Yes (direct vent or power vent) | No |
| Gas line upgrade | Often required (¾" minimum) | N/A |
| Electrical upgrade | Minor | May need 200-amp panel |
| Operating cost | Lower | Higher |
| Flow rate | 8–12 GPM | 3–8 GPM |
| Complexity | High | Moderate |
Gas tankless heaters require more installation time primarily because of venting requirements. Category III stainless steel venting must be routed to an exterior wall or through the roof, which involves cutting through walls and proper sealing.
Step-by-Step Installation Timeline
| Step | Gas Unit | Electric Unit |
|---|---|---|
| Shut off water/gas/electric and drain old unit | 30–45 minutes | 20–30 minutes |
| Remove old water heater | 30–60 minutes | 20–30 minutes |
| Mount new tankless unit | 30–45 minutes | 30–45 minutes |
| Upgrade gas line (if needed) | 1–3 hours | N/A |
| Install venting | 1–3 hours | N/A |
| Connect water lines | 45–90 minutes | 45–90 minutes |
| Connect gas/electrical | 30–60 minutes | 1–2 hours |
| Test and commission | 30–45 minutes | 30–45 minutes |
| Total | 5–10 hours | 3–6 hours |
Factors That Add Time
- Gas line upgrade: Many homes have ½" gas lines, but tankless units require ¾" or 1" lines, adding 1–3 hours of work
- Electrical panel upgrade: Electric units drawing 120+ amps may require a panel upgrade (adds 4–8 hours, often a separate appointment)
- Relocation: Moving the unit to a different wall adds 2–4 hours of additional plumbing
- Permit inspection: Most jurisdictions require a plumbing or mechanical permit; scheduling the inspection may delay final sign-off by 1–5 business days
- Condensate drain: Condensing gas units require a drain line, adding 30–60 minutes
- Recirculation loop: Adding a recirculation pump for instant hot water at distant fixtures adds 2–4 hours
DIY vs. Professional
Tankless water heater installation is generally not a DIY project. Gas units require a licensed plumber in most states, and improper venting can cause carbon monoxide buildup. Electric units require working with high-amperage circuits (typically 40–60 amp breakers per unit), which most building codes require a licensed electrician to install. Professional installation also preserves the manufacturer warranty, which is often voided by unlicensed installation.
Permits and Inspections
Most municipalities require a permit for water heater installation. The permit process itself typically takes 1–5 business days and costs $50–$200. The inspection is usually scheduled within a few days of completing the work. Professional installers typically handle the permitting process as part of their service.