Choosing the Right Buffer Tank Size for Your Heat Pump

Choosing the correct buffer tank size for your heat pump is essential for ensuring efficiency, long-term performance, and indoor comfort. It stores thermal energy, helps maintain stable temperatures, and prevents short cycling of the heat pump, extending its service life.

Why a Buffer Tank Is Important

It acts like a thermal battery. It stores hot water, reducing the frequency of the heat pump‘s on and off cycles. This helps avoid short cycling, which can cause wear on the compressor. A properly sized tank also improves temperature stability and helps meet peak heating demand.

Key Factors in Sizing Your Buffer Tank

1. Type of Heat Pump System

• Air Source Heat Pump (ASHP): Since outdoor temperatures vary, these systems benefit from a larger one to manage those fluctuations.
• Ground Source Heat Pump (GSHP): These provide more consistent output, so a smaller one may be enough.

2. Heat Pump Output Power

As a rule of thumb, plan for 10 to 20 liters of buffer per kilowatt (kW) of heat pump output.
For example:

• A 10 kW heat pump needs a 100–200 liter buffer tank.

Use the higher range if:

• Your home’s heat demand changes a lot during the day.
• You have underfloor heating or low thermal mass that leads to frequent cycling.

3. Heating System Design and Load

• Underfloor heating: Needs a larger one because it has lower water temperatures and heats up quickly.
• Radiator systems: May need less buffer since they retain heat longer.

Consider how many hours per day the heating runs and how demand changes over time.

4. Zoned Heating Systems

If your home has multiple heating zones, the system needs to manage varying demands. A larger one supports simultaneous heating across different zones more effectively.

5. Manufacturer Guidelines

Always check your heat pump manufacturer’s recommendations. Many brands specify a minimum size to ensure correct compressor operation. Using a tank below the recommended size can reduce system efficiency.

6. Installation Space and Budget

• Consider the physical size.
• Make sure it fits in your mechanical room or utility space.
• Oversizing the buffer tank adds cost and often gives a limited extra benefit.

Recommended Buffer Tank Size (Summary)

To size your buffer tank properly:

• Plan for 10–20 liters per kW of heat pump power.
• Increase the size if your system has quick cycling or wide load variations.
• Respect the manufacturer’s minimum requirements.
• Consider how many heating zones your home has.
• Balance performance with space and budget.

Need Help Sizing Your Buffer Tank?

Tell us your heat pump system size, whether you use underfloor heating or radiators, and how your home is zoned. Our technician team will recommend the right buffer tank size tailored to your setup.