A tankless install usually takes a licensed pro 4–10 hours; tank-to-tankless conversions with gas, vent or electrical work can take one to two days.
The key steps are gas or electrical supply, venting, water connections with isolation valves, condensate drain, and commissioning.
Most areas require a permit, and most manufacturers require professional installation for full warranty coverage.
We don't install. Use this guide to vet local plumbers, electricians and gas fitters.
What a professional installation includes
Whether you plan to install on demand water heater equipment in a new home or replace water heater with tankless in an existing one, installing tankless hot water heater units follows the same core steps. How to install a tankless hot water heater safely is the installer’s job; this overview helps you know what to expect.
A typical tankless water heater installation follows these stages:
Site assessment. The installer confirms sizing, gas or electrical capacity, venting route, condensate disposal and wall space.
Removal of the old heater. The old tank is drained, disconnected and hauled away.
Mounting. The unit is fastened to a wall or framing with required clearances.
Water connections. Hot and cold lines are connected with isolation (service) valves for future flushing, and a pressure relief valve if required.
Fuel supply. For gas and propane, a correctly sized gas line with a shutoff valve and sediment trap. For electric, dedicated circuits, breakers and wire sized to the manual.
Venting. Approved vent pipe routed through a wall or roof with proper slope and terminal clearances (not needed for outdoor units).
Condensate drain for condensing units, usually with a neutralizer.
Power for gas units: a 120V outlet or hardwired circuit.
Commissioning. Leak testing, purging air, checking gas pressure, setting the temperature and confirming error-free operation.
Registration with the manufacturer to activate the warranty.
Replacing a tank water heater with tankless
Replacing a water heater with tankless is the most common job. The differences from a tank swap:
Gas demand jumps. Tankless units use up to 199,000 BTU, so the gas line often needs upsizing.
New venting. Tank vents can’t be reused for most tankless units.
Gas tankless water heater installation must follow the manufacturer’s manual and the fuel gas code adopted locally. The installer checks meter capacity, sizes the gas line for total household demand, installs a manual shutoff, tests for leaks and confirms inlet gas pressure. Propane tankless water heater installation adds regulator and tank sizing with your propane supplier.
Electric installation
Electric tankless water heater installation is mainly electrical work: dedicated double-pole breakers, wire sized for the amperage, and confirmation that the panel can carry the load. Many whole-house units need 100–150 amps. A licensed electrician should do the load calculation and connect the circuits.
Tankless electric water heater installation typically takes less time than tankless water heater gas installation, but only if the panel already has capacity.
Finding tankless water heater installation near you
We are an online store and don’t provide installation, but here is how to find a good local installer:
Check licensing. Most states license plumbers, electricians and gas fitters. Look up the license on your state’s licensing board website.
Ask about tankless experience. Ask how many tankless units they install each year and which brands they are trained on.
Use manufacturer installer locators. Brands like Rinnai, Navien and Rheem list trained or certified pros on their websites.
Get two or three itemized quotes covering labor, materials, permit, haul-away, gas line, venting, condensate and electrical work.
Confirm permits and inspections are included.
Ask about labor warranty, and whether they will install a unit you buy online.
Check reviews on several platforms and ask for references from recent tankless jobs.
A good plumber for tankless water heater jobs will have completed many tankless water heater installations and can show photos of recent work. How to replace a tankless water heater with a newer model is usually simpler, since the venting and valves exist.
Questions to ask your installer
Will my gas line or electrical panel need upgrading?
What vent material and route will you use, and how long is it?
Will you install isolation valves and show me how to flush the unit?
Where will the condensate drain go?
Will you register the unit with the manufacturer?
What is your labor warranty?
After installation
Keep the manual, invoice and permit paperwork. Set the temperature to around 120°F, register the warranty, and schedule annual descaling. Our maintenance guide explains what to do each year.
Buy the unit your installer recommends
Share our product pages with your installer; every listing includes the specs they need.
How long does it take to install a tankless water heater?
A straightforward replacement of an existing tankless unit can take 3–5 hours. Replacing a tank with tankless often takes 6–10 hours, and up to two days if a new gas line, vent route or electrical circuit is needed.
Can a plumber install a tankless water heater?
Yes. Licensed plumbers install most tankless water heaters. Gas connections may require a gas-fitter license in some states, and electric units need an electrician for new circuits.
Can I install a tankless water heater myself?
Small electric point-of-use units can be DIY projects for experienced homeowners where code allows. Gas, propane and whole-house electric installs involve safety-critical work, usually need a permit, and DIY installation may void the warranty.
How do I find tankless water heater installation near me?
Look for licensed, insured plumbers with specific tankless experience, ideally certified by the brand you choose. Manufacturer websites often list trained installers by ZIP code. Get two or three itemized quotes.
Where should a tankless water heater be installed?
Indoor units go on a wall near the old heater location or close to the most-used fixtures, with room for venting and service clearances. Outdoor units go on an exterior wall, away from windows and doors. Avoid unheated spaces for indoor units in cold climates.
This guide is general information for U.S. homeowners, not professional advice. Gas, electrical and venting work must follow the manufacturer’s instructions and local codes, and in most areas requires a licensed plumber, electrician or gas fitter and a permit. Specifications and prices change; always confirm details on the product page and in the installation manual.
