To install a tankless water heater, you must mount the unit, connect water and gas lines, and set up a proper exhaust vent. You also need to ensure your home has enough gas pressure or electrical power to handle the high energy demand. While the process is doable for a skilled DIYer, it requires following local building codes and safety rules to prevent leaks or fires.
Switching to an on-demand system is a smart way to save space and lower energy bills. This guide will walk you through the entire tankless water heater installation from start to finish. We will cover the tools you need and the exact steps for both gas and electric models.
What Is a Tankless Water Heater?
A tankless water heater is a compact device that heats water only when you turn on a faucet. Unlike old-style tanks, it does not store hot water. Instead, water flows through a heat exchanger inside the unit. A gas burner or electric element quickly heats the water to your set temperature.
People often call these “on-demand” heaters. They are great because they never run out of hot water. You can take back-to-back showers without waiting for a tank to refill. They also last about 20 years, which is twice as long as most tank units.
What Should You Consider For The Installation Process?
Before you start your tankless water heater setup, you must plan carefully. These units have different needs than old tanks.
Sizing and GPM
You must pick a unit that matches your home. Look at the Gallons Per Minute (GPM) rating. A small unit might only handle one shower. A large unit can handle two showers and a dishwasher at once. You also need to know your “Temperature Rise.” This is how much the heater must raise the temperature of the cold water coming into your home. If you live in a cold state, you need a more powerful heater.
Gas Line and Meter Capacity
Most gas tankless heaters need a lot of fuel. They often require a 3/4-inch gas line. If your home has a 1/2-inch line, you may need an upgrade. Check your gas meter too. It must be able to handle the high BTU (British Thermal Units) rating of the new heater. If the gas pressure is too low, the unit will not fire correctly.
Tankless Water Heater Venting
Gas units produce exhaust that must go outside. You cannot use the same vent from your old tank. Modern heaters use special tankless water heater venting pipes. High-efficiency units can use PVC or CPVC because the exhaust is cooler. Standard units need Category III Stainless Steel to handle the high heat.
Water Quality
Hard water is the enemy of tankless systems. Calcium and lime can build up in the heat exchanger. If you have hard water, you should install a water softener. This keeps your system running for a long time.
Tools and Materials Needed
Having the right tools prevents rushed mistakes.
Basic tools:
- Adjustable wrench
- Pipe cutter
- Pipe wrench
- Drill and bits
- Screwdrivers
Plumbing materials:
- Copper or PEX piping
- Shut-off valves
- Service isolation valves
- Teflon tape and pipe sealant
Electrical or gas parts:
- Proper breaker and wiring
- Gas shut-off valve
- Sediment trap
- Vent pipes and wall thimbles
Step-by-Step Guide: How to Install Tankless Water Heater
The process changes depending on if you have a gas or electric model. Always turn off your water, gas, and power before you start.
Installing a Gas Tankless Water Heater
Remove the Old Tank
Drain your old tank completely. Disconnect the water and gas lines. Take the tank out and clean the area. Check the wall for any water damage.
Mount the Unit
Find a solid place on the wall. Tankless units are heavy when full of water. Use a piece of plywood or 2×4 studs to create a strong base. Use a level to make sure the unit is straight.
Set Up the Water Lines
Connect the cold water inlet and hot water outlet. Use an isolation valve kit. These valves allow you to flush the system with vinegar every year. Without them, you cannot clean out mineral buildup. Use copper pipes or PEX-B depending on your local codes.
Connect the Gas Supply
Run the gas line to the heater. Install a shut-off valve and a sediment trap. The trap catches dirt before it enters the heater. Use a manometer to ensure the gas pressure is correct. Check for leaks using a spray bottle with soapy water. If you see bubbles, tighten the connection.
Install the Venting
Run the exhaust pipe to the outside of your house. Make sure you follow the clearance rules. The vent should not be near windows or doors. If your unit is a “condensing” model, you must also install a condensate trap and drain line. This handles the acidic water the unit produces.
Power and Test
Plug the unit into a grounded outlet. Open the water valves and check for leaks. Turn on a hot water tap to get the air out of the pipes. Finally, turn on the gas and set the temperature.
Installing a Tankless Electric Water Heater
Check Your Electrical Panel
Electric units pull a lot of power. You may need two or three 40-amp or 60-amp breakers. Make sure your panel has enough room.
Mount and Connect Water
Mount the unit near the main water line. Connect the water pipes using flexible hoses or copper. Include a pressure relief valve if your local code requires it.
Wire the System
Run the correct gauge of wire from your panel to the heater. Connect the wires to the lugs inside the unit. Make sure the system is grounded properly to avoid shocks.
Flush and Fire
Run water through the heater for a few minutes before turning on the power.This prevents “dry firing,” which can burn out the heating elements instantly. Turn on the breakers and test the water temperature.
You can read about: How to Install a Heat Pump Water Heater
How Much Does It Cost to Install a Tankless Water Heater?
The cost varies based on your home’s layout. On average, a tankless hot water installation costs between $1,500 and $3,500.
Item | Estimated Cost |
Electric Unit | $500 – $1,200 |
Gas Unit | $800 – $2,500 |
Labor (Pro) | $600 – $1,500 |
Gas Line Upgrade | $300 – $800 |
Venting Materials | $200 – $500 |
Electric models are cheaper to install but might cost more to run monthly. Gas models save more money over time but have higher upfront costs due to venting and gas lines.
Common Installation Mistakes to Avoid
Even pros make mistakes. Watch out for these common errors:
- Undersizing the gas line: If the pipe is too small, the heater will starve for fuel. This leads to error codes and cold showers.
- Forgetting the isolation valves: You must have these to descale the unit. Without them, the unit may fail in just a few years.
- Wrong vent material: Using a “B-vent” on a tankless unit can cause a fire. Always use the material the manufacturer lists.
- Improper sloping: Vent pipes must slope away from the heater. This stops water from dripping back into the burner.
- Neglecting the expansion tank: If you have a closed plumbing system, you still need a small expansion tank to handle pressure.
When to Hire a Professional
A tankless water heater install involves gas, fire, and electricity. If you are not comfortable soldering copper or working with gas lines, call a pro. A mistake with gas can lead to carbon monoxide poisoning or a house fire. Professionals also know the local permits you need. Getting a permit ensures your insurance will cover you if something goes wrong.
Find A Local Water Heater Professionals
While DIY installation saves money, some situations require professional expertise. If you need help with Tankless Water Heater Installation in Eagle Rock or surrounding areas, Derks Plumbing offers experienced installation services.
Professional installers handle permits, ensure code compliance, and warranty their work. This peace of mind matters when dealing with gas, electricity, and your home’s water supply.
Look for contractors who:
Hold proper licenses for plumbing and gas work
Carry liability insurance
Provide written estimates
Offer warranties on labor (typically 1-2 years)
Have experience with your specific unit brand
Get at least three quotes before choosing. The cheapest bid isn’t always the best value.
Conclusion
Learning how to install tankless water heater systems takes time and patience. It is a big project, but the reward is endless hot water and lower bills. Always put safety first. Follow the manual exactly and do not skip the maintenance valves. With the right setup, your new heater will keep your home comfortable for decades.
FAQs
Do I need a permit to install a tankless water heater?
Yes. Most cities require a permit for any new water heater. This ensures the gas and venting are safe.
Can I use my old chimney to vent a tankless heater?
No. Tankless units have high-pressure exhaust. A chimney is too large and will not vent properly. It could lead to dangerous gas buildup.
How often do I need to maintain my tankless system?
You should flush the unit with white vinegar once a year. This removes the mineral scale that lowers efficiency.
Will a tankless heater work during a power outage?
No. Even gas models need a small amount of electricity to run the computer and spark the burner. You would need a battery backup to keep it running.
Is a tankless water heater worth the cost?
Yes. While they cost more at first, they save up to 30% on energy. They also save space and last much longer than tanks.
