ᐅ Is it possible to install a gas condensing boiler that meets the KfW 55 energy efficiency standard?

apokolok schrieb:

You can still consider switching later on.

However, this is often no longer as efficient as it would be with direct planning from the start. The requirements for underfloor heating and domestic hot water usually make separate approaches more practical. Designing now for gas may make a future conversion to a heat pump uneconomical for a long time.

Stefan001 schrieb:

However, this often isn’t as effective as when done through direct planning. The requirements for underfloor heating and domestic hot water frequently call for different system designs. A current setup optimized for gas might make a future switch to a heat pump uneconomical for a long time.

That used to be the case when underfloor heating systems were designed for high flow temperatures, resulting in loops that were far too large for low-temperature operation.
There is nothing preventing a modern gas boiler from operating at the same flow temperatures as a heat pump. Accordingly, the underfloor heating system can also be designed appropriately.

Regarding the environmental topic: it simply doesn’t belong here. As mentioned earlier, new construction is an environmental disaster at its worst. Compared to that, my old oil boiler in a 1970s house is a saint.

apokolok schrieb:

That used to be the case when underfloor heating systems were designed for high flow temperatures and, accordingly, the loops were much too large for low-temperature operation.
There is nothing wrong with running the same flow temperatures with a modern gas boiler as with a heat pump. The underfloor heating can be designed accordingly.

Is the water from the solar thermal system (which is required for condensing boilers to meet KfW55 standards) then mixed with cold water? Or is the flow rate in the underfloor heating system simply reduced significantly?

Stefan001 schrieb:

Is the water from the solar thermal system (which is required with condensing boilers for KfW55 standard) then mixed with cold water? Or do you simply reduce the flow rate in the underfloor heating significantly?

As far as I know, only enough hot water is mixed into the returning (cold) water to keep the supply temperature relatively low. In our underfloor heating system, the supply temperature is 29 degrees Celsius (84°F). This is sufficient even on very cold winter days. However, the domestic hot water is heated to 55 degrees Celsius (131°F) to prevent legionella.

We also decided on a combination of gas, solar, and ventilation to achieve KFW 55 standards. Regardless of KfW, we would have chosen this setup anyway. Our municipality has extended the gas supply to this new development area. Additionally, we did not want an external heat pump exposed to the weather.

Deep drilling is not permitted in our area. Therefore, the only option left was gas.

When it comes to heat pumps or gas, opinions differ greatly. Everyone has their own view. However, gas should not be universally dismissed here.

Pumpernickel1 schrieb:

We also chose gas + solar + ventilation to achieve KfW 55 standard. Regardless of KfW, we would have picked this combination anyway. Our municipality provided gas connections in this new development area. Additionally, we did not want an outdoor heat pump exposed to the weather.

Deep drilling is not allowed here. Therefore, the only option was the gas solution.

Whether heat pump or gas, opinions differ greatly. Everyone has their own view. However, gas should not be dismissed outright in this context.

Are you satisfied with it? In our case, the gas connection was offered as a special deal for 300 € (about 320 USD). We are especially surprised by the low costs and the fact that during the warmer months, the gas heating hardly needs to turn on.