ᐅ Additional cost for KfW 70 energy standard

Hello everyone,

We are about to decide whether provider A or provider B will build our house. The design is exactly the same for both houses, with the difference that House A is equipped with a Dimplex air-to-water heat pump installed indoors and meets the KfW 70 energy standard. House B has a Viessmann split air-to-water heat pump and does not meet the KfW 70 standard. My advisor told me that the additional cost to reach the 70 standard would be around 7,500 euros.

How do you assess this? Both houses will be built with solid 36.5cm (14.5 inches) Poroton bricks.

Thanks in advance for your answers!

Best regards

Hello,

based on my experience with inquiries, I want to tell you that KFW70 is actually the standard. There is no additional charge.

What kind of Poroton blocks?

Not all 36cm (14 inch) blocks are the same.

With T12 or T14 blocks, you won’t achieve KfW 70 standards. But with T9 or T8 blocks, you will. If a supplier usually installs T12 blocks as standard, then the additional cost for T9 is justified.

We are building with 36cm (14 inch) T9 Poroton blocks and are also using an air-to-water heat pump as a split system, easily meeting KfW 70 standards.

@Bolzen based on my experience with inquiries, KfW 70 is not standard—it often needs to be specifically requested or mentioned upfront.

Oh, my mistake.
Provider A: aerated concrete blocks with 0.09 W/mK
Provider B: aerated concrete blocks with 0.27 W/mK

iomaju schrieb:

Supplier A: aerated concrete blocks with 0.09 W/mK

What kind of block is that supposed to be?
The standard offer from our supplier was, even without KFW70 (building energy standard), a 30cm (12 inches) Ytong block with, I believe, 0.32 W/m²K.
Our extended KFW70 offer, however, includes much more than just a different block. The KFW70 design features a 36cm (14 inches) Ytong block with 0.23 W/m²K, plus additional insulation for the slab foundation, roof, windows, and doors. The extra costs for this amount to just over 5500 euros.
Both offers, however, are planned with a gas condensing boiler and mechanical ventilation with heat recovery. I’m not sure if the air-to-water heat pump plays such a major role in your calculations that only a different block is sufficient, especially since the efficiency of an air-to-water heat pump strongly depends on insulation.

All in all, I find the 7500 euros quite realistic, depending on the size and type of the house.

Hello,

iomaju schrieb:
Oh, my mistake.
Supplier A: aerated concrete blocks with 0.09 W/mK
Supplier B: aerated concrete blocks with 0.27 W/mK

There still seems to be something wrong. In your original post you mentioned Poroton, and now you are referring to aerated concrete...

Regards, Bauexperte