Choosing the right pump for a tankless water heater is an important decision that requires careful consideration of your home’s water pressure and flow rate needs. Tankless water heaters provide hot water on demand without the need for a storage tank, but they require a minimum flow rate to activate the heating elements. The pump pushes water through the heater quickly enough to ensure continuous hot water delivery. Selecting a pump that is too small can lead to intermittent hot water while an oversized pump wastes energy. This article provides guidance on picking the optimal pump based on your tankless water heater’s specifications and home water pressure.
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How do tankless water heaters work?
Tankless or on-demand water heaters instantly heat water as it flows through a heating coil or heat exchanger. Cold water enters the unit when a hot water tap is opened. Sensors detect the flow and activate gas or electric heating elements to raise the water temperature. The now hot water exits the heater and runs to the tap. This just-in-time heating avoids storing hot water in a tank that can lose heat over time.
A minimum flow rate, measured in gallons per minute (GPM), is required to trigger the heaters. Flow rates under this threshold means the elements won’t turn on. The minimum activation rate can range from 0.5 GPM for small point-of-use units up to 6 GPM for whole house models. Maximum flow rates during peak demand periods also determine the right size heater.
Reasons for insufficient hot water flow
Some common reasons your tankless heater may not produce enough continuous hot water include:
- Water pressure too low – Tankless heaters need at least 40 PSI for proper operation.
- Flow rate too low – The pump cannot deliver the minimum GPM required to activate the heating elements.
- Pipe sizes too small – Undersized supply lines and fixtures restrict water flow.
- Heater sized too small – Peak demand exceeds the GPM capacity of the tankless unit.
In many cases, adding a properly sized water pump resolves low flow issues, ensuring a constant supply of hot water.
Sizing a pump for a tankless water heater
Follow these steps to select a pump with sufficient power to work with your tankless water heater:
- Determine your household’s peak water demand in GPM. Consider periods where multiple sinks, showers and appliances may run simultaneously.
- Verify your home’s water pressure without the heater connected. Pressure should be 40 PSI or above for tankless heaters.
- Check the minimum and maximum flow rate specifications of the tankless unit in GPM. This is provided by the manufacturer.
- Choose a pump capable of producing flow rates equal to or above the heater’s activation threshold. Add some extra capacity to account for pressure drops and future demand.
- Confirm the pump discharge pressure matches your household plumbing system needs.
- Select an energy efficient model to save on operation costs.
In addition to flow rate, calculating the right pump head pressure is also important. Select a pump that provides pressure above your system’s static head but below the maximum fixtures are rated for. Installing a pressure reducing valve helps regulate higher pressures from oversized pumps.
Common pumps for tankless water heaters
Here are some typical pumps used to support tankless water heaters:
| Pump Type | GPM Range | Pressure Range (PSI) | Power Source |
|---|---|---|---|
| Circulator pump | 10-45 GPM | 20-65 PSI | Electric |
| Submersible well pump | 15-50+ GPM | 30-60 PSI | Electric |
| Inline booster pump | 15-100 GPM | 40-100 PSI | Electric |
| Pressure booster pump | 30-100+ GPM | 40-100+ PSI | Electric or Gas |
Circulator pumps are commonly used in hydronic heating systems or solar water heaters. Submersible and inline pumps boost low well water pressure. Pressure booster pumps increase both flow rate and pressure as needed.
Installing the water heater pump
Proper installation of the water heater pump ensures efficient operation. Follow these guidelines:
- Locate the pump as close to the tankless unit as possible.
- Ensure flows match the direction of arrow markers on the pump body.
- Install a check valve to prevent backflow.
- Use isolation valves to facilitate maintenance and repairs.
- Support inline pumps with brackets to reduce vibration and strain.
- Follow all manufacturer instructions for electrical and plumbing connections.
It is also recommended to install a pressure gauge before and after the pump. This allows proper pressure settings and helps identify drops indicating worn pump components.
Configuring pump controls
Pumps may run continuously or activate based on demand via a pressure switch or flow switch. Continuous operation ensures immediate hot water delivery but uses excess energy during periods of no water flow. Flow or pressure activated pumps engage only when fixtures are opened to save power. Adjust activation and deactivation setpoints based on your household usage patterns for optimal efficiency.
Maintenance tips for tankless water heater pumps
Routine maintenance keeps your pump and tankless water heater working reliably for years. Recommended tasks include:
- Inspecting for leaks and fixing any drips or weeping seals.
- Checking that electrical connections are tight and wires free of damage.
- Listening for unusual noise like grinding or squealing bearings.
- Clearing any debris accumulated in the pump impeller or inlet.
- Testing and replacing old check valves prone to fouling.
- Confirming proper pipe support and hangers to reduce vibration.
- Lubricating motors and bearings per manufacturer specifications.
- Verifying pump output pressure and flow have not deteriorated over time.
Keep a log book noting maintenance checks and any repairs made. Catching problems early prevents more expensive breakdowns and extends the service life. Most pumps require a rebuild or replacement every 5-10 years depending on usage and water quality.
Signs it’s time to replace the pump
Consider replacing your water heater pump if you notice:
- A significant drop in water pressure or flow rate.
- Noisy operation with squeaks, grinding or knocks.
- Overheating motor causing the pump to periodically shut off.
- Rust colored water indicating internal corrosion.
- Continual buildup of mineral deposits even after cleaning.
- Electrical shorts tripping breakers.
It is also recommended to proactively replace pumps older than 10 years. The older internal components become, the higher the chance of failure.
Choosing a replacement pump
Select a replacement pump using the same sizing process as choosing the original unit. Do not assume that swapping in the same model pump is advisable. Your home’s water pressure and demand may have changed over time. New tankless water heaters often have different activation flow rates. Always double check the specifications and choose the correctly sized pump.
Look for improved efficiency in new pump models. Variable speed and digital pumps precisely match output to demand while using less electricity. Higher efficiency motors, impellers, and bearings reduce energy consumption as well. Consider upgrading to a smart internet-connected pump for remote monitoring and control via a smartphone app.
Conclusion
The right water heater pump provides the flow rate and pressure needed for a tankless system to deliver continuous hot water. Determine your household’s peak demand in GPM and choose a pump sized to exceed the heater’s activation threshold. Consider circulator, well, booster and pressure pumps to match required performance. Install the pump as close to the heater as possible following all codes. Maintain the pump to ensure longevity. Replace worn pumps or upgrade to improved efficiency models for optimal hot water delivery and energy savings.