How to Hook Up a Tankless Water Heater to Your Home Plumbing Properly

If you want to hook up a tankless water heater to your home plumbing safely and avoid future problems, follow the manufacturer’s instructions, local codes, and rely on trusted expert advice for proper installation.

A correct installation ensures the unit delivers hot water on demand with a continuous flow, leak-free connections, and protection from freezing. It also eliminates problems like hot water delays, scalding, leaks, and noise.

It’s important to note that the performance and lifespan of your tankless water heater depend on factors like plumbing design, water quality, pressure, and the environment in which it operates.

For a seamless setup, we invite you to explore our expert tips on everything from control valves and regulators to safety devices and the installation checklist.

Key Factors to Hook Up a Tankless Water Heater Properly

Installing Expansion Tanks to Prevent Pressure Issues

Expansion tanks are essential in closed water systems, where thermal expansion can cause increased pressure as water heats up. The expansion tank absorbs this extra pressure, preventing stress on the tankless water heater and the plumbing system. Without it, the pressure relief valve may open frequently, leading to unnecessary wear and possible water damage.

When choosing an expansion tank, ensure it matches your system’s size and pressure specifications. Install the expansion tank on the cold water inlet side of the system, following the manufacturer’s guidelines. Regularly inspect and maintain the tank by checking its air pressure with a tire pressure gauge.

Adding Mixing Valves to Prevent Scalding

Mixing valves are vital for protecting against scalding by blending hot and cold water to maintain a safe and consistent water temperature. These valves are particularly useful in homes with children, elderly individuals, or anyone at risk of burns from high water temperatures.

When selecting mixing valves, opt for models with low water resistance to ensure efficient water flow. Install the valve downstream from the water heater, where it can mix hot and cold water before it reaches faucets or fixtures. Some advanced models include thermostatic controls, which automatically adjust to maintain a set temperature, even when there are fluctuations in water pressure.

Using Recirculating Pumps for Faster Hot Water Delivery

Recirculating pumps are designed to deliver hot water instantly to taps and showers, eliminating the wait for hot water and reducing water wastage. These pumps are especially beneficial in larger homes with long pipe runs, where hot water may take longer to travel from the heater to the fixture.

Choose a recirculating pump with an integrated timer or motion sensor for maximum efficiency. These features allow the pump to operate only when needed, reducing energy consumption. Install the pump according to the manufacturer’s instructions, often near the water heater or at the farthest fixture in the plumbing system.

Protecting Your Tankless Water Heater with Water Treatment Devices

Hard water can cause significant issues for tankless water heaters, including scale buildup in the heat exchanger, reduced efficiency, and shortened lifespan. Installing water treatment devices, such as sediment filters, descalers, or water softeners, can mitigate these problems.

• Sediment Filters: Remove debris, sand, and rust from the water supply, protecting the heater and plumbing from clogs and damage.
• Water Softeners: Use ion exchange to remove calcium and magnesium ions that cause hardness, preventing scale formation.
• Descalers: Use electronic or chemical methods to reduce scale buildup, ideal for areas with moderate hardness levels.

Install these devices on the cold water inlet side of the tankless water heater for optimal protection. Regularly maintain them by replacing filter cartridges or regenerating softeners as needed.

Regulating Water Pressure with Pressure Reducers

High water pressure from municipal supply lines can damage plumbing fixtures, cause leaks, and stress the tankless water heater. Installing a water pressure reducer ensures a stable and safe water pressure throughout the system.

Choose a pressure-reducing valve (PRV) that matches your home’s water pressure needs. Most homes require water pressure to be between 40 and 60 psi. Install the PRV near the main water supply line entering your home. Additionally, consider adding backflow preventers or check valves to stop water from flowing in the wrong direction, further protecting your plumbing system.

Water Line Installation

When hooking up a tankless water heater to your plumbing, it is crucial to use materials approved for potable water systems, such as copper, PVC, CPVC, or PEX. These materials ensure the durability and safety of the water supply. Install union couplings or flexible pipes to allow for easier adjustments and to minimize stress on the system caused by expansion or movement.

Keep piping as simple and short as possible, as longer pipes lead to greater heat loss and increased energy usage. Avoid unnecessary joints or bends, which can reduce water flow and efficiency. Ensure that all connections are secure and leak-free, as leaks can compromise both performance and safety.

Additionally, the water pressure in the plumbing system should meet the manufacturer’s minimum requirements, typically around 50 psi, to activate the heater and maintain consistent hot water flow. Always purge air and debris from the lines before starting the system to prevent potential damage to the unit.

Adding a Manual Control Valve for Easy Maintenance

A manual control valve must be installed at the water inlet of the tankless water heater, positioned before the plumbing system connects to the heater. This valve allows you to easily shut off the water supply when needed for maintenance, repairs, or emergencies.

To improve convenience during installation and servicing, use unions on both the hot and cold water lines. Unions allow for quick disconnection of the water heater without cutting pipes or making extensive modifications. This not only reduces downtime but also simplifies future maintenance tasks.

Installing Isolation Valves for Simplified Servicing

Isolation valves are essential for maintaining and servicing a tankless water heater. These valves are typically installed on both the cold water inlet and hot water outlet. They allow you to isolate the water heater from the rest of the plumbing system, enabling tasks such as flushing, descaling, or cleaning the unit without disrupting the household water supply.

Many manufacturers provide isolation valves as part of the water heater package, but if not, they can be purchased separately. When choosing isolation valves, opt for models that include integrated drain ports for convenient flushing and maintenance. Properly installed isolation valves can significantly extend the lifespan of your tankless water heater by making regular maintenance easier.

Installing a Pressure Relief Valve for Safety

A pressure relief valve is a mandatory safety feature when you hook up a tankless water heater to plumbing, ensuring the system operates within safe pressure levels. The valve must be rated for up to 150 psi and should match or exceed the BTU input of the water heater. Install the valve on the outlet line, as close to the water heater as possible, to monitor and release excess pressure effectively.

The valve must be connected to a discharge line that directs hot water safely to an appropriate drain. The discharge line should be constructed from materials that can withstand high temperatures, such as copper or CPVC, and must comply with local plumbing codes. Additionally, the discharge line’s length should not exceed the maximum allowed by code to ensure proper functioning.

Do not install any plugs, reducing fittings, or valves between the pressure relief valve and the water heater, as these can restrict its operation. Periodic discharges from the valve are normal and occur due to thermal expansion, but you should test the valve annually to confirm it operates correctly. Replacing the pressure relief valve if it shows signs of wear or malfunction is inexpensive and straightforward, ensuring continued safety and efficiency.

Plumbing Checklist for Tankless Water Heaters

• Flush water lines. This removes debris before installation and ensures a clean water supply.
• Connect the water inlet and outlet. Properly connect hot to hot and cold to cold to avoid cross-connections.
• Inspect pipes and fittings. Check for leaks to prevent water damage and inefficiency.
• Verify water pressure and flow. Ensure they meet specifications, and purge air from the system for smooth operation.
• Install and annually test the pressure relief valve. This ensures safe pressure release and protects the system from over-pressurization.
• Route condensate pipes. Ensure they lead to an appropriate drain for safe disposal of acidic waste.
• Insulate plumbing lines. This helps reduce heat loss and improve system efficiency, especially in unheated areas.