ᐅ Buffer tank? Combi tank? Domestic hot water storage tank?

Hello dear forum,

For our single-family house, we have decided on a 15 kW pellet heating system. There is currently no solar support planned. Now the heating installer asked us whether we would prefer a regular buffer tank, a combined tank, or a hygienic tank. The additional cost for the buffer tank (Cosmos buffer tank CPS 500) with soft foam insulation compared to a hygienic tank of 800 liters (210 gallons) with an internal stainless steel domestic hot water heater (flow-through principle) and 90mm (3.5 inches) rigid foam insulation is 490.00 EUR plus VAT.
We have no offer yet for a combined tank.

What exactly are the differences between these systems?
What experiences do you have with the three options?
How does the type of insulation (soft foam, rigid foam, EPP, EPS) affect ongoing costs (fuel, electricity)?

I appreciate any advice.

Hello,

Clearly, either a hygienic storage tank or a fresh water station is recommended. Both systems provide a high level of drinking water hygiene. The first option is very simple and without potential issues; the second is slightly more efficient but also includes various additional components.

I would not recommend the combined storage tank. At the connection between the heating and drinking water, stress often occurs, leading to corrosion inside the drinking water tank. This then requires replacement of the storage unit.

I find the option with a simple buffer tank and a separate domestic hot water tank only sensible in cases of limited installation space or when large flow rates of hot water preparation are required.

Olli

We have a 15 kW pellet boiler and a separate buffer tank, meaning a simple container only for heating water, completely separated from the domestic water system. The domestic water is heated separately (using electricity).

Our reasoning was that we do not want to run the heating system (by heating system, I mean the boiler) during summer just to heat some domestic water. For showering, 35°C (95°F) is sufficient. This way, the heating system stays off completely in summer, and only the water that is actually used is heated.

So far, we have been using instantaneous water heaters for this. Soon, a domestic hot water heat pump will take over this task.

And before anyone raises concerns about the "high electricity costs" for using instantaneous heaters for hot water: our annual electricity consumption is 3000 kWh, INCLUDING hot water, for a single-family home with two occupants. Of this, we generate about 1200 kWh ourselves and purchase 1800 kWh.

Update: We are now leaning towards a hygienic storage tank of 800 - 1000 liters (210 - 265 gallons) with an instantaneous water heater and 90 mm (3.5 inches) rigid foam insulation. The domestic hot water will be heated by a solar thermal system. We are foregoing the water jacket from the wood stove since the stove only operates in winter and the pellet heater provides the energy.

What do you think about this combination?

Hello again,

The hygienic storage tank is a good choice.

How actively would you operate the stove?
If you use it frequently, you might consider skipping the pellet boiler and instead choosing a hydronic stove.

Another approach is to install a pellet stove with water heating in the living area and do without the boiler in the utility room.
I used this setup in my last property and plan to do the same in my new house.
A manufacturer from Tübingen offers good products, and for those unsure—such as when going on a winter vacation—both options can be equipped with an electric heating element in the buffer tank.

Olli