ᐅ Gas condensing boiler technology combined with a solar thermal system

Hello, our builder is offering a gas condensing boiler system (Viessmann Vitodens 200W) combined with a solar thermal system (Vitosol 200F with a 300-liter (79 gallons) hot water storage tank).

Is this combination necessary or efficient? We are a household of three; wouldn’t a 150-liter (40 gallons) storage tank be sufficient?

Single-family house, underfloor heating on the ground and upper floors, 125 square meters (1,345 square feet) of living space, mechanical ventilation with heat recovery.

As an alternative, he is offering an air-to-water heat pump installed indoors, also with a 300-liter (79 gallons) storage tank.

Best regards

300 liters (79 gallons) is standard – usually, people choose a larger capacity.
Why should the solar system only be able to heat 150 liters (40 gallons)? The more, the better.

Question for the experts: is there even a smaller storage tank???

Hmm, I think if only 150 liters (40 gallons) need to be heated, it requires less energy as well as a smaller collector?

The first question is whether the solar system is economically viable or if it is only used to make the KfW or energy saving regulation proof look better.

With solar energy, you won’t get any favorable calculations at first. Without using at least some renewable energy, it is already very challenging to meet the energy saving regulations (15% rule).

I wouldn’t be discouraged by the liters mentioned. We haven’t reached the point of dealing with heating systems yet. But what I’ve heard in passing is that there are also “3-part” boilers. Although they store a lot of water, about one-third is cold, one-third lukewarm, and one-third hot. That’s why these units can easily be 300 liters (79 gallons) or more in size.

Did I misunderstand something? 🙂

Hello,

300 liters (79 gallons) is definitely suitable, and even a slightly larger tank would be fine. The question is, what are your usage habits? If you plan to use a lot of hot water for bathing, I would recommend going larger than 300 liters (79 gallons).

The concept of the stratified storage tank is correct, and with an appropriately sized tank, the solar system can be well integrated. The purpose of the cooler layer is to make the heat collected by the solar panels usable at a lower temperature, so the surrounding storage water should ideally not be heated to a higher temperature.

Best regards, Erik