Advantages/Disadvantages: Gas + solar + water-heated fireplace for domestic hot water?

Hello everyone,

we are planning to build a solid wood house and would like to qualify for the KfW funding. Since we already have gas on the property, we prefer a gas condensing boiler. However, without solar, we will only qualify for the funding if we increase the wall thickness or if we use an air-water heat pump. As mentioned, the gas is already on the property, and I also do not find heat pumps particularly attractive due to the noise (we will build without a basement). Since we have always dreamed of a fireplace/tiled stove, we were advised to install a water-bearing fireplace to also heat the heating and domestic water. This way we would have an energy mix that I find quite appealing at first, although I cannot yet assess the economic aspects. Does such a solution make sense?

Best regards Telramund

I must also add that the water-bearing fireplace was recommended to us because it directs a large part of its output into hot water production; otherwise, the room would overheat too quickly.

Hello,

... However, without solar, we will only qualify for the subsidy if we increase the wall thickness...

This is not a mistake, but rather an advantage, as the heating energy demand will be lower.

... Since we have always dreamed of a fireplace/tiled stove at the same time, it was suggested to us to install a water-bearing fireplace in order to also heat the heating and domestic water.

A water-bearing fireplace fits better, if at all, with gas condensing boilers than, for example, with a heat pump. However, its energy contribution is only partially recognized in the verification. Not entirely without reason, because after the initial enthusiasm, usage declines significantly over the years due to the manual effort involved.

..., but one cannot yet assess the economic aspects. Does such a solution make sense?

As always, this depends on the specific conditions. If you have to buy wood, the profitability will suffer. Likewise, the additional investment cost or capital service will have an effect.
The overheating problem (without water guidance) only occurs with very low space heating loads of the installation room as well as with too little storage mass or secondary heating surfaces (the typical DIY store fireplaces). There are also combustion chambers with low heating output.

Best regards

Hello Euro,

thank you very much for the answers. As expected, I naturally still have a few questions and comments afterwards

Hello,
This is not an error, but rather an advantage, as the heating energy demand is reduced.

The question, of course, is how this ultimately affects the price. However, this must be discussed with the house manufacturer to see how an accordingly adjusted wall thickness affects the additional costs.

A water-bearing wood stove fits, if at all, better with gas condensing boilers than, for example, with a heat pump. However, its energy contribution is only partially recognized in the certification. This is not unfounded, because after the initial enthusiasm, the use significantly decreases over the years due to the manual effort required.

We currently also live with a tiled stove, which we actually prefer to operate over the heating system, as the warmth is more pleasant. Most of the time, however, we only use it when the whole family is present (e.g. weekends, vacation).

The overheating problem (without water circuit) only occurs with very low room heating loads of the installation room as well as with too little storage mass or supplementary heating surfaces (the typical DIY store wood stoves). There are also combustion chambers with low heating output

We were recently advised to take a stove that delivers only about 1/3 of its output to the room and uses the rest to heat the water. What exactly does too low room heating load mean? Does this mean it is better to take a larger stove with appropriate storage capacity, which then radiates slower but longer? How can the interaction of the gas condensing boiler and the wood stove be optimally controlled? We are going to install underfloor heating, which is slower than radiators.

Best regards, T

...The question, of course, is how this will ultimately affect the price. But you have to discuss with the house manufacturer how a correspondingly adjusted wall thickness will reflect on the additional costs.

The installation effort is almost identical, here only the additional material costs have a slight impact!

...We were currently recommended to take a stove that delivers about only 1/3 of its capacity to the room and uses the rest to heat the water. What exactly does a too low room heating load mean?

When dimensioning heating systems, the standard heating load and, for the individual room, the room heating load are necessary.
If the room heating load is not known, one is dealing with guesswork, estimates, assumptions, or suppositions. Whether this is a reliable basis for a significant investment decision must be answered individually.

...We will install underfloor heating, which is more sluggish than a radiator.

Exactly. Underfloor heating is sluggish and therefore less suited in terms of operational behavior to a stove without heat storage.
Completely different is a masonry heater with, for example, radiator heating.

Because of competing requirements, you cannot have everything but have to weigh according to priorities.

Best regards.

ok, understood, you have to have everything calculated by someone who knows something about it. Can any architect or energy consultant do that, or are there "trademarks" that show me I am dealing with a "knowledgeable" person?