ᐅ Add wood gasification boilers, hydronic fireplaces, and solar systems to gas heating.

Dear forum community,

I would like to ask for advice regarding the upgrade of our heating system. I am quite skilled in some areas of DIY, but not when it comes to heating. Please excuse me if my questions seem amateurish. Ultimately, a professional will carry out the work, but I would like to better understand the topic myself in order to be able to assess everything.

I am attaching sketches of the current and planned setups, as well as pictures of the buffer storage tank.

Currently, we heat our house (an old building from 1930 with an extension from the 1970s) with a Viessmann Vitodens 300 condensing boiler connected to a simple 300 L (79 gallons) domestic hot water tank. Additionally, there is a wood stove with an external chimney.

The house is now being energy renovated, and to avoid dependence on gas, the primary energy source is intended to be wood combined with solar thermal energy.

This means:

- Installation of an Atmos wood gasifier with 25 kW output
- Installation of two water-jacketed wood stoves, each with 12 kW output (7 kW room air, 5 kW water jacket)
- Installation of a 550 L (145 gallons) buffer storage tank
- Installation of a 15 m² (161 sq ft) solar thermal system

The two stoves will be regularly fired during the day and evening.

We basically have free access to wood.

So far, so good, but I still have the following issues / questions:

- I would like not to have to reload the wood gasifier constantly but rather bring the buffer tank up to temperature once a day. Are 550 L buffer tanks sufficient for 270 m² (2,906 sq ft) of living space? If not, how many liters would be recommended?

- Is the buffer tank suitable for this setup in terms of connections? Unfortunately, I have no data on this. It came together with one of the water-jacketed stoves. The flange still has three inlets and outlets. For example, I do not know if it is suitable for domestic hot water production (it of course has insulation, which is not shown in the photos). I would also appreciate alternative purchase recommendations.

- I assume that the current 300 L (79 gallons) tank can be removed completely, as it will no longer be needed? Or will I need a tank for domestic hot water in the future, with the buffer tank only used for heating water?

- Is it advisable to place the buffer tank in the outbuilding or would it be better located in the basement next to the gas boiler? Or does the location not matter?

- How / by which device (controller?) can the system be set up so that the gas boiler starts automatically when the temperature in the buffer tank drops too low? The gas boiler should remain as a backup in case the stoves, wood gasifier, and solar thermal system fail to provide sufficient heat for any reason.

- What share of the energy supply can the solar thermal system roughly be expected to contribute?

- Now a difficult question: approximately how high might the costs be for the connection work / piping?

Thank you very much and best regards,

Josef

Do you know the maximum heating capacity you will need after the energy retrofit? If a 22 kW condensing boiler is sufficient now, then 25 kW afterwards is probably oversized. Why 15 m² (160 ft²) of solar thermal instead of photovoltaic panels? Have you considered a heat pump if you don’t want gas, supplemented by the fireplaces?

Best regards

Hello, thank you very much for your message. We received the solar thermal modules from the neighbor. We will also have photovoltaic panels combined with a battery storage system.

Yes, maybe the heat pump would be a good option then!

Why even install something like this when wood is free?

Rumbi441 schrieb:

Why install something like that at all when wood is free?

I brought the wood inside the house, but it still stayed cold.

Jansepp schrieb:

- I don’t want to constantly add fuel to the wood gasifier; instead, I want to bring the buffer tank up to temperature once a day. Are 550L (145 gallons) buffer tanks sufficient for 270sqm (2,900 sqft) of living space? If not, how many liters would be advisable?

It depends. With only buffer tanks and no domestic hot water tank, at least 1,500 liters (400 gallons) are needed. Alternatively, 800–1,000 liters (210–265 gallons) of buffer tanks combined with an 800-liter (210 gallons) domestic hot water storage tank, which can also function as a buffer tank, are recommended.