Heating energy and gas cost saving alternative?

Hello, I am looking for an affordable way to heat. There is space available; it is about a single-family house with approximately 250 square meters. A Vitodens 300 from Viessmann with a 160-liter hot water storage tank is being installed. It is a household of 3 people. All pipes such as gas, water, and heating are new. In the basement, there is complete underfloor heating, and heating is present upstairs. There is natural gas and wood, which we handle ourselves since we have 2 fireplaces. Solar is not yet planned but is under consideration because many say that in summer the boiler remains completely off and everything is heated via solar. Another consideration would be a wood gasifier that can be connected with the boiler so that the boiler can usually be bypassed and only turns on when it gets tight or if you forget to fire the wood gasifier.

The question is what is worthwhile for a household of 3 people? What would you recommend? We thought that maybe we would buy a wood gasifier for 4000 euros on the internet and then connect it with the gas boiler in such a way that when no one is heating, the boiler steps in. What do you think about that? And does the heating engineer who installs the gas boiler have to lay additional connections? If yes, which ones?

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The cheapest option is probably, if you already have a gas heating system, to simply do nothing, as the price per kwh of heat with gas is not too expensive. I don't think any investment other than a very good adjustment (hydraulic balancing, configuration of the boiler, etc.) is worth it.

In summer or from April to September, you usually don't have to heat depending on the location and Germany anyway, and a gas condensing boiler produces that little hot water so cheaply that you can make your hot water with those 4000 euros for 30 years, or longer.

If you don't have any heating at all, you can buy a brine heat pump and possibly solar power with higher investment, which then promises lower running costs, but is much more expensive.