Installing a tankless water heater can boost your home’s energy efficiency and provide endless hot water. This guide walks you through planning, tools, safety, and step-by-step installation—even if you’re a beginner.
Key Takeaways
- Plan carefully: Assess your home’s water demand, fuel type, and location before buying a unit.
- Turn off utilities: Always shut off power, gas, and water supply before starting any work.
- Use proper venting: Tankless heaters need correct exhaust systems to operate safely and efficiently.
- Check local codes: Permits and inspections may be required—don’t skip this step.
- Test after install: Run a full system test to ensure no leaks, proper heating, and safe operation.
- Consider professional help: If you’re unsure about gas or electrical work, hire a licensed pro.
- Maintain regularly: Flush the system yearly to prevent mineral buildup and extend lifespan.
How to Install a Tankless Water Heater
Upgrading to a tankless water heater is one of the smartest moves you can make for your home. Not only do these units save space, but they also deliver hot water on demand—no more running out mid-shower! Plus, they’re far more energy-efficient than traditional tank models, which means lower utility bills over time.
In this guide, we’ll walk you through everything you need to know to install a tankless water heater safely and correctly. Whether you’re replacing an old unit or installing one for the first time, we’ve got you covered—from choosing the right model to testing your finished setup.
Step 1: Choose the Right Tankless Water Heater
Before you even think about tools or pipes, you need the right unit. Tankless water heaters come in gas, electric, and propane models, each with different power requirements and installation needs.
Determine Your Hot Water Demand
Calculate how many gallons per minute (GPM) your household uses during peak times. For example, a shower uses about 2.5 GPM, while a dishwasher might use 1.5 GPM. Add up all fixtures that could run simultaneously—this gives you your required flow rate.
Pick the Fuel Type
- Gas models heat water faster and are ideal for larger homes but require proper venting and gas line upgrades.
- Electric models are easier to install and great for small spaces but need heavy-duty wiring and may struggle in cold climates.
Consider Size and Location
Measure the space where you plan to install the unit. Most tankless heaters mount on walls and need clearance for ventilation. Also, choose a location close to major water lines to minimize heat loss.
Tip: If you’re unsure which model fits your needs, check out our guide on how to choose the right HVAC appliance—the same principles apply when sizing systems for home efficiency.
Step 2: Gather Tools and Materials
Having the right tools makes all the difference. Here’s what you’ll likely need:
- Pipe wrench or adjustable wrench
- Teflon tape and pipe sealant
- Pipe cutter or hacksaw
- Drill and masonry bits (for wall mounting)
- Level
- Screwdrivers
- Safety goggles and gloves
- Venting kit (if required)
- Gas flex line (for gas models)
- Electrical conduit and wire (for electric models)
Always double-check your unit’s manual for specific requirements—some manufacturers include mounting brackets or vent pipes, while others don’t.
Step 3: Turn Off Utilities and Prepare the Area
Safety first! Before touching anything, shut off all utilities:
Water Supply
Close the main water valve to your house. Open a faucet to relieve pressure and drain remaining water from the lines.
Power
Turn off electricity at the breaker panel. For electric units, this means switching off the dedicated circuit. For gas units, turn off the gas valve near the old heater.
Clear the Space
Remove the old water heater if present. Clean the area and ensure the wall can support the new unit’s weight (most weigh 30–60 pounds). If mounting outdoors, protect the unit from rain and extreme temperatures.
Step 4: Install the Mounting Bracket
Most tankless heaters come with a wall-mounting bracket. Follow these steps:
Mark the Wall
Use a level to mark where the bracket will go. Ensure it’s high enough to allow clearance below for pipes and ventilation.
Drill Holes and Secure
Drill pilot holes into studs or use heavy-duty anchors for drywall. Screw the bracket firmly in place—this is critical, as the unit will hang from it.
Pro tip: If you’re installing near an exterior wall (common for venting), make sure the bracket aligns with your planned vent exit point.
Step 5: Connect Water Lines
Now it’s time to hook up the plumbing. Tankless heaters have two connections: cold inlet and hot outlet.
Cut and Prepare Pipes
Use a pipe cutter to trim existing copper or PEX lines to the correct length. Deburr edges to prevent leaks.
Install Shutoff Valves
Add isolation valves on both inlet and outlet lines. These let you service the unit without shutting off your whole house’s water.
Connect with Fittings
Wrap Teflon tape around threaded connections and hand-tighten fittings. Use a wrench for a snug fit—but don’t over-tighten, or you’ll crack the ports.
Note: Some units require dielectric unions to prevent corrosion between dissimilar metals. Check your manual!
Step 6: Set Up Venting (Gas Models Only)
Gas-powered tankless heaters produce exhaust and must be vented properly—this is non-negotiable for safety.
Choose Vent Type
Most use concentric (pipe-in-pipe) vents that expel exhaust and draw in combustion air through a single wall penetration. Others may use separate vents.
Install Vent Pipe
Measure the distance from the unit to the exterior wall. Cut the vent pipe to length and connect it securely to the heater’s outlet. Seal all joints with high-temperature silicone.
Pass Through Wall
Drill a hole slightly larger than the vent diameter. Insert the vent from inside, seal the exterior with flashing and caulk, and attach the outer cap.
Warning: Never use PVC for high-temperature exhaust unless specifically rated for it. Always follow local building codes.
Step 7: Connect Gas or Electrical Supply
For Gas Units
Attach a flexible gas line to the unit’s inlet. Use pipe dope or Teflon tape rated for gas. Turn the gas back on slowly and check for leaks with soapy water—bubbles mean trouble.
For Electric Units
Run heavy-gauge wire (often 6 AWG or thicker) from your electrical panel to the heater. Connect to the terminal block inside the unit. Ensure the breaker matches the amperage requirement.
Safety reminder: If you’re not confident working with gas or electricity, hire a licensed professional. Mistakes here can be dangerous.
Step 8: Mount the Unit and Test
With everything connected, it’s time to hang the heater.
Hang the Heater
Lift the unit and slide it onto the mounting bracket. Ensure it’s level and secure.
Turn On Utilities
Restore water, then gas or power. Open the hot water tap at a nearby sink and let it run for a minute to purge air from the lines.
Check for Leaks and Errors
Inspect all connections. Watch the unit’s display for error codes. Most modern heaters will self-test and show status lights.
Adjust Settings
Set your desired temperature (usually 120°F is ideal). Some models let you adjust flow rate or energy mode via a digital panel.
Troubleshooting Common Issues
Even with careful installation, problems can arise. Here’s how to fix the most common ones:
- No hot water: Check if the unit is powered, gas is on, and water flow is above the minimum threshold (often 0.5 GPM).
- Water too hot or cold: Adjust the temperature setting. Mineral buildup can also affect performance—flush the system.
- Leaking connections: Tighten fittings slightly or reapply sealant. Never overtighten.
- Venting errors: Ensure the vent isn’t blocked and is the correct type and length.
- Unit won’t ignite (gas): Verify gas pressure, check for air in the line, or reset the unit.
If issues persist, consult your manual or contact customer support. And remember—regular maintenance prevents most problems. Learn how to clean internal components safely to keep your system running smoothly.
Conclusion
Installing a tankless water heater might seem daunting, but with the right preparation and attention to detail, it’s totally doable—even for DIYers. You’ll enjoy endless hot water, lower energy bills, and a smaller carbon footprint.
Just remember: safety comes first. When in doubt, especially with gas or electrical work, don’t hesitate to call a pro. And once your system is up and running, keep it in top shape with annual flushes and inspections.
Ready to upgrade your home’s comfort? Your future self (and your shower) will thank you.
