ᐅ Do Gas Condensing Boilers Significantly Lower the KfW Standard?
Created on: 11 Dec 2018 11:48
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netzplanHello everyone,
We have a two-family house (2 full floors) with a fully basement in solid construction from the 1960s. The exterior walls are made of 24cm (9.5 inches) pumice blocks starting from the ground floor.
The major renovation includes the following:
The pitched roof will be completely removed and rebuilt. All windows and doors will be replaced. Most of the windows face south or west. Full thermal insulation with a thickness between 12–16cm (5–6.3 inches) should be applied, including the basement exterior walls. A balcony overhang and the entrance canopy also need to be fully wrapped with insulation. The basement ceiling should be insulated as well. Underfloor heating is also planned.
1. We were unsure about the heating system. As soon as the energy consultant heard "gas condensing boiler," he mentioned that only KfW 100 standard would be achievable at best. Does a gas condensing boiler really reduce the energy performance that much, or is it generally difficult to improve much in an older building with the measures roughly described above?
Regarding heating, a heat pump would naturally be an alternative. Solar collectors to heat the domestic hot water are also an option. One floor will have a wood stove, which might also be able to heat water pipes. Whether a ventilation system with heat recovery should be considered needs to be clarified, especially whether it is financially viable and technically feasible in this building.
2. Shouldn’t KfW 55 or 70 standard be easily achievable with these measures?
We have a two-family house (2 full floors) with a fully basement in solid construction from the 1960s. The exterior walls are made of 24cm (9.5 inches) pumice blocks starting from the ground floor.
The major renovation includes the following:
The pitched roof will be completely removed and rebuilt. All windows and doors will be replaced. Most of the windows face south or west. Full thermal insulation with a thickness between 12–16cm (5–6.3 inches) should be applied, including the basement exterior walls. A balcony overhang and the entrance canopy also need to be fully wrapped with insulation. The basement ceiling should be insulated as well. Underfloor heating is also planned.
1. We were unsure about the heating system. As soon as the energy consultant heard "gas condensing boiler," he mentioned that only KfW 100 standard would be achievable at best. Does a gas condensing boiler really reduce the energy performance that much, or is it generally difficult to improve much in an older building with the measures roughly described above?
Regarding heating, a heat pump would naturally be an alternative. Solar collectors to heat the domestic hot water are also an option. One floor will have a wood stove, which might also be able to heat water pipes. Whether a ventilation system with heat recovery should be considered needs to be clarified, especially whether it is financially viable and technically feasible in this building.
2. Shouldn’t KfW 55 or 70 standard be easily achievable with these measures?
netzplan schrieb:
Does a gas condensing boiler worsen the energy rating that much, or can you already achieve little improvement in an older building with the measures described above?Achieving better than KfW-100 with a gas condensing boiler is quite challenging.
What helps a lot is solar thermal hot water preparation, and if you have enough roof space with a suitable orientation, heating support is also worthwhile. Since you are planning underfloor heating, this makes sense financially as well. There are additional subsidies available through BAFA (2500€), and the primary energy demand is significantly reduced. Moreover, if you are renewing the roof anyway, it can be done as an integrated (in-roof) system. This reduces heat loss from the system and also slightly lowers the roofing costs.
If you already have gas in the house, I would stick with it rather than switching to a heat pump. You should be able to reach at least KfW 70, but this always needs to be verified through an individual energy balance. Achieving KfW 55 would require mechanical ventilation with heat recovery, which is probably no longer cost-effective.
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