On-Demand Water Heater Install: A DIY Guide
A comprehensive guide to installing an on-demand water heater safely. Learn planning, tools, steps, permits, and maintenance for DIY homeowners.
According to Install Manual, you can complete an on-demand water heater install yourself if you have solid plumbing, electrical, and gas-safety knowledge. This quick answer highlights what you’ll accomplish, essential preparations, and when to call a pro. The full guide below covers planning, required tools, safety steps, precise mounting, connections, and proper commissioning to prevent leaks and outages.
What is an on-demand water heater and why homeowners choose it
An on-demand water heater, also called a tankless unit, heats water only as it’s needed. That means no storage tank and no standby heat loss, which can save energy and free up space in tight utility rooms. For homeowners, the decision often comes down to efficiency, endless hot water, and the potential to shrink the home’s overall footprint. The Install Manual team notes that while these units can deliver reliable hot water, they require proper sizing, correct venting or electrical connections, and adherence to local codes to perform well and safely.
Sizing, location, and planning for an on-demand water heater install
Sizing is critical for on-demand water heaters. Manufacturers publish flow rates and temperature rise data; selecting a unit that matches peak demand prevents cold-water sandwiches and inadequate supply. Plan for a location with easy service access, clearance for venting (gas models), and a solid mounting surface. Consider electrical service or gas supply capacity, and be prepared to alter combustible-clearance distances or vent runs as required by code.
Safety, permits, and code considerations
Before you begin, check local codes and permit requirements. Many jurisdictions require a permit and inspection for gas or electrical work, and improper venting can create serious safety hazards. Always shut off power, gas, and water before starting; use a gas detector and a leak-testing solution to verify joints. If you’re unsure about venting, gas piping, or electrical disconnects, consult a licensed professional.
Typical installation scenarios and what to expect
Your install path depends on whether you’re replacing a traditional electric tank, converting from a gas-supplied tank unit, or adding a new unit in a previously unserved location. Expect new venting or a dedicated circuit, wall mounting considerations, and potential changes to nearby plumbing. The first run should be slow and deliberate to purge air and check for leaks.
Maintenance, troubleshooting, and long-term care
After installation, schedule regular maintenance such as descaling (if you have hard water), flushing the lines, and inspecting connections for signs of corrosion. Keep a log of service intervals and verify the venting and gas connections periodically if you have a gas unit. When in doubt, consult the manufacturer’s warranty guidelines and your local building authority.
Tools & Materials
- Safety gear (gloves, goggles)(ANSI-rated PPE)
- Voltage tester(to confirm circuits are de-energized)
- Adjustable wrench(for nuts and fittings)
- Pipe wrench(for stubborn joints)
- Pipe cutter(for copper pipes)
- Pipe thread sealant or Teflon tape(apply on male threads)
- PEX crimp tool or copper fittings(depends on piping)
- Gas-rated flexible connector(for gas models)
- Vent kit or vent piping(for combustion venting)
- Mounting hardware and wall anchors(to secure unit)
- Replacement shut-off valves(new and easily accessible)
- Drill/driver(for mounting and hardware)
- Electrical tester/multimeter(verify circuits and grounding)
- Leak-detection solution or soapy water(test joints for leaks)
Steps
Estimated time: 2-6 hours
- 1
Plan and assess suitability
Review the unit type, local codes, and whether your space supports venting or a dedicated electrical circuit. Check existing plumbing and electrical/gas capacity and prepare a plan before touching any hardware.
Tip: Take measurements and photo-document existing connections for reference. - 2
Shut off utilities and relieve pressure
Power down the electrical supply and close gas and water shut-offs. Open a hot tap to relieve residual pressure and purge the line of air.
Tip: Have towels ready and confirm power is off with a tester. - 3
Remove old unit or clear installation space
If you’re replacing an existing heater, disconnect and remove it carefully, keeping the area clean. If this is a new location, prepare a clean wall mount with studs and clearances.
Tip: Label remaining pipes and wires to simplify reassembly. - 4
Mount the tankless unit
Position the unit on a studded wall or suitable mounting surface. Use the manufacturer’s mounting bracket and ensure level, plumb, and secure with hardware.
Tip: Use a wall anchor kit and verify load rating before tightening. - 5
Connect cold and hot water lines
Attach cold inlet and hot outlet lines with appropriate fittings. Tighten gradually and apply sealant or plumber’s tape to male threads; check for kinks, then inspect for leaks.
Tip: Leave a small service loop to accommodate expansion. - 6
Connect the energy source and venting/ wiring
Gas models require venting and a gas supply with a shut-off; electric models require a dedicated circuit. Install venting per code and secure electrical connections with proper strain relief.
Tip: Follow the manufacturer’s wiring diagram precisely. - 7
Install valves, pressure relief, and expansion as needed
Install shut-off valves on both water lines and a pressure relief or expansion device per code. Verify all fittings are accessible for future maintenance.
Tip: Test the relief valve orientation and clearance. - 8
Fill, purge air, and test for leaks
Slowly open water supply and watch for air pockets. Use a leak-detection solution on joints and verify gas/electrical supplies are stable.
Tip: Check that there are no leaks before turning the unit fully on. - 9
Commission, document, and finalize
Power up the unit, perform startup checks, and compare output with manufacturer specs. Document the installation for future service and obtain any required inspections or permits.
Tip: Keep a copy of manuals and permit records with the unit.
Got Questions?
Do I need a professional to install an on-demand water heater?
Gas venting and electrical work can be hazardous; many neighborhoods require a licensed professional for safety and code compliance. If you’re unsure, hire a pro.
Yes, in many cases you should hire a licensed professional for gas and vent work. Safety first.
What safety permits are typically required?
Most areas require permits for gas or electrical work and for major plumbing changes. Check with your local building department and obtain inspections as needed.
Permits are usually required for gas and electrical work; have inspections completed.
How long does the installation typically take?
A typical install can take several hours depending on existing plumbing and wiring. Plan for a half to full day and coordinate with utility shutoffs.
Plan for several hours, often half a day or more.
Can I install in any climate?
Tankless heaters can operate in a wide range of climates, but outdoor or poorly vented installations require appropriate protection and venting. Dry, conditioned spaces simplify setup.
Yes, with the right venting and protection, though some setups may be more complex.
What maintenance is required after installation?
Descale if you have hard water, inspect joints periodically, and follow the manufacturer’s service schedule. Keep documentation and warranty information accessible.
Regular descaling and inspection keep the unit running efficiently.
Watch Video
Main Points
- Plan, size, and match to demand.
- Check permits and code compliance before starting.
- Prepare tools and a safe workspace.
- Test thoroughly for leaks and proper operation.
- Consider professional help for gas and vent work.
