Buffer cylinder

A buffer cylinder is a water tank for heating water. With modern, modulating heat pumps in detached houses, it is often not needed at all.

A buffer tank is an insulated container filled with heating water, not drinking water. It is located between the heat pump and the heating circuits and can temporarily store heat.

What it is used for

• Preventing cycling: For heat pumps that can only switch on and off, according to the klimaaktiv guide, a sufficiently large cylinder must be provided so that they do not constantly switch on and off.
• Bridging blocking times: If the grid operator temporarily switches off the heat pump, the cylinder continues to supply heat.
• Complex systems: With multiple mixing groups, a cylinder may be necessary for hydraulic reasons.

When you don't need one

The klimaaktiv Wegweiser (guide) states: as a rule, no heating buffer cylinder is required in detached and semi-detached houses. Variable-speed heat pumps are more efficient and usually manage without a buffer cylinder. With underfloor heating, the screed also stores heat.

What you should look out for

A buffer cylinder causes heat losses. According to the klimaaktiv Ratgeber Warmwasser (hot water guide), a 1.000-litre buffer cylinder at 80 °C loses around 900 kWh per year, almost 50 % more than at 60 °C. If a buffer cylinder is installed, its temperature should be as little as possible above the required flow temperature, and it must be well insulated.

Ask in the quote why a buffer cylinder is planned. 'That's just how it's usually done' is not a justification. Read more under Check quote.

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