Buffer storage? Combi storage? Hygiene storage?

Hello dear forum,

for our single-family house, we have decided on a 15 KW pellet heating system. There is initially no solar support. Now the heating installer asked us whether we want a normal buffer tank, a combi tank, or a hygiene tank. The surcharge from the buffer tank (Cosmos buffer tank CPS 500) with soft foam insulation compared to a hygiene tank 800 L with internal stainless steel water heater (flow-through principle) with 90mm rigid foam insulation is 490.00 EUR plus VAT.
We do not have an offer for a combi tank.

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

I am grateful for any advice.

Hello

Clearly hygienic storage tank or fresh water station. Both systems offer a high level of drinking water hygiene. The first is very simple and without potential problems, the second even a bit more efficient but also equipped with various additional components.

I can only advise against the combination storage tank. At the connection between heating and drinking water, tensions often occur and thus corrosion in the drinking water tank. Replacement of the storage tank is then necessary.

I find the variant with a simple buffer and separate drinking water storage only sensible in cases of low installation space or required large flow rates of hot water preparation.

Olli

We have a 15 kW pellet boiler and a separate buffer tank, i.e. a simple tank only for heating water, completely separate from the drinking water system. The drinking water is heated separately (with electricity). Our consideration here was that we do not want to run the heating in summer (by heating I mean the boiler), just to heat some drinking water. For showering, 35° is more than enough. So the heating system is completely off in summer and only the water that is directly consumed is heated. So far, we use instantaneous water heaters for this. Soon, however, a domestic hot water heat pump will take over this task. And before anyone complains about the "high electricity costs" for hot water with instantaneous water heaters: we have an annual electricity consumption of 3000 kWh INCLUDING hot water (!) for a two-person single-family house. Of this, we generate about 1200 kWh ourselves and buy an additional 1800 kWh.

Update: We are now leaning towards a hygiene storage tank of 800 - 1000 L with an instantaneous water heater with 90mm rigid foam insulation. The domestic hot water should be heated by a [thermische Solaranlage]. We are omitting the water jacket from the wood stove since the stove only burns in winter anyway and the pellet heating provides energy.

What do you think of this combination?

Hello again

The hygienic storage tank is a good decision.

How actively would you heat the stove?
With frequent use, one might consider foregoing the pellet boiler
and instead choosing a water-bearing stove.

Another approach is to use a water-bearing pellet stove in the living area and do without the boiler in the utility room.
I used this option in my last [Immo] and will build it the same way in the new house.
A manufacturer from Tübingen offers good products, and for those unsure, e.g. about the winter vacation, both options can be equipped with a heating element in the buffer.

Olli