ᐅ What size should a heating buffer tank have – single-family home

Hello everyone,

Here is our situation: We are planning our single-family house with a ground source heat pump and have obtained several quotes from heating contractors. I am surprised by the different approaches to planning the domestic hot water or storage tanks (are these terms interchangeable, or is a storage tank something completely different?). The sizes vary from 180 liters to 300 liters and up to 800 liters (for example, the model SBS 801 W Sol Stiebel Eltron).

The question is, what makes sense?

I am also concerned about the space these units take up, as we are planning without a basement and the utility room space is limited.

Some additional information: Living area about 200m² (2153 sq ft), 2 children, 2 adults, so a 4-person household (which is likely to stay the same), showering and bathing habits are "normal," if there is such a thing.

I hope I haven’t forgotten anything and look forward to many responses 😉

If it’s only about the hot water supply, consider about 12 liters per minute (3 gallons per minute) when showering. Everyone wants to shower. With an average of 5 minutes, that amounts to 240 liters (63 gallons). For an average of 10 minutes, it’s 480 liters (127 gallons). Maybe this thought exercise helps you—regardless of the heat replenishment in the stratified storage tank.

With comparable parameters: 200 liters (53 gallons) buffer tank and 300 liters (79 gallons) domestic hot water tank.

Are you planning a rain shower? Then significantly more water will flow through. We have a standard shower and a 230-liter (60-gallon) integrated hot water tank, which is more than sufficient for us.

With a well-configured and properly sized heat pump plus hydraulics for the underfloor heating, you only need a domestic hot water tank and an expansion vessel for the heating circuit. No buffer tank is necessary!

You need a buffer tank for:
- Solar thermal systems
- If you want/need to use a fresh water station
- Heat generated from combustion (oil, gas, wood, pellets, etc.)
- Heat from self-generated wind/solar/hydro power, although in this case, a battery would be more efficient (less loss)
- If you want to qualify for the Bafa subsidy for SmartgridRead (buying a buffer tank just for this is not worthwhile)
- An oversized heat pump

Domski schrieb:
With a well-adjusted and properly sized heat pump plus the hydraulic system of the underfloor heating, you only need a domestic hot water tank and an expansion vessel for the heating circuit. No buffer tank!

A buffer tank is needed for:
- Solar thermal systems
- If you want or need a fresh water station
- Heat from combustion (oil, gas, wood, pellets, etc.)
- Heat from self-generated wind/solar/hydro power, although a battery would be more practical here (less loss)
- If you want to take advantage of Bafa funding for SmartgridRead (buying a buffer tank only for this is not worthwhile)

- oversized heat pump

Nothing to add! No buffer tank. Domestic hot water tank is something different.

Make sure the heat pump matches the heating load. Don’t plan for extra capacity.

Domestic hot water tank: 200 to 300 liters (53 to 79 gallons) for a standard single-family home.