For flushing a tankless water heater, use a submersible pump with at least 5-10 gallons per minute (GPM) flow rate for effective cleaning.
Flushing your tankless water heater is essential maintenance to prevent mineral buildup and maintain efficiency. Choosing the right pump size ensures effective descaling without damaging your system.
Ideal Pump Size for Tankless Water Heater Flushing
For most residential tankless water heaters, a pump with 1-2 gallons per minute (GPM) flow rate is ideal. This provides sufficient circulation for descaling solutions while preventing excessive pressure that could damage internal components.
Recommended Pump Specifications
- Flow rate: 1-2 GPM (60-120 GPH)
- Pressure: 30-50 PSI maximum
- Material: Acid-resistant (polypropylene or stainless steel)
- Power: 1/6 to 1/4 HP sufficient
Many professionals use specialized descaling pumps designed specifically for this purpose, but smaller submersible pumps can work effectively when properly matched to your system.
Why Pump Size Matters
The right pump size ensures proper circulation of descaling solution through your tankless unit’s heat exchanger without causing damage.
Consequences of Wrong Pump Size
| Pump Too Small | Pump Too Large |
|---|---|
| Incomplete descaling | Potential damage to heat exchanger |
| Longer flush times | Wasted cleaning solution |
| Poor mineral removal | Excessive system pressure |
Alternative Pump Options
If you don’t have access to a specialized descaling pump, these alternatives can work:
1. Small Submersible Pumps
80-120 GPH pond or fountain pumps can be effective when used with proper descaling solution and adequate flush time.
2. Condensate Pumps
While lower in flow rate (typically 30-50 GPH), these can work if you extend the flush duration. They’re often acid-resistant.
3. Recirculating Pump Systems
Some homeowners create custom systems using small submersible heaters and pumps for controlled flushing.
Professional vs. DIY Approach
Professionals typically use higher-capacity pumps (3-5 GPM) to complete jobs faster, but for DIY maintenance, slower pumps with longer flush times can be equally effective.
Key Differences
- Pros use higher flow rates for efficiency
- DIYers can achieve same results with smaller pumps and more time
- Commercial pumps often include pressure gauges and flow controls
According to SpeedClean, the chemical action of descaling solutions does most of the work, not just pump turbulence.
Descaling Solution Considerations
The pump is only part of the equation – the descaling solution is equally important.
Common Descaling Agents
- White vinegar (5% acetic acid)
- Food-grade citric acid
- Phosphoric acid solutions
- Manufacturer-approved cleaners
Always check your water heater manual for recommended cleaning solutions to avoid voiding warranties.
Flushing Procedure Tips
Regardless of pump size, follow these best practices:
- Always turn off power/gas to the unit before flushing
- Use proper isolation valves or a flushing kit
- Circulate solution for 45-60 minutes
- Flush thoroughly with clean water afterward
- Check manufacturer recommendations for your specific model
Remember that regular flushing (annually or bi-annually) with a properly sized pump will keep your tankless water heater running efficiently for years to come.
