ᐅ KfW 40 house with gas boiler

Hello,

we are planning to build a KfW40 house. Is this fundamentally possible using solid construction along with a gas boiler?

I am thinking of building a highly energy-efficient house: well insulated, with a ventilation system, solar collectors, and a wood stove connected to the heating system. The gas boiler would serve as the main heating source and for domestic hot water. I am considering replacing the gas boiler in 15-20 years, for example with a geothermal borehole system.

Is this heating concept reasonable, or should I reconsider it?

Looking forward to an active discussion.
Maccus

Additional information: the reason for the KfW40 standard, besides the high energy efficiency, is the exemption of 10% of the loan for a single-family house with a secondary apartment = 10,000 €.

Hello Maccus

You probably won’t manage that... most likely not even with a gas condensing boiler… it will already be very tight with the standard energy calculation. Possibly with a direct connection between solar, stove, and controlled ventilation system… But the weighted standard heating system today is the heat pump. Anything less efficient receives penalty points in the certification, which must then be compensated by other measures… But then costs and feasibility quickly become a problem.

For KfW40, the requirements are even stricter… So, skip the gas connection and the rental costs for the gas meter and invest that money in a heat pump instead; the extra cost won’t seem as high then… but keep away from the boiler!

What type of heat pump would you recommend then? I’m rather reluctant about air-source heat pumps (efficiency concerns). For geothermal via drilling, I consider the costs too high. Since there is no groundwater available, the only option is a heat pump with ground loops (I’m not familiar with the technical term here).

I haven’t researched the different heating options much yet and am not familiar with their exact initial and ongoing costs.

Should I also look further into pellet heating?

Thanks.

Thanks for the quick replies!!

I definitely want to have a wood stove, which means a chimney as well! A basement is also planned.
What are the price differences between an air-source heat pump and a pellet stove? And based on your experience, which would you lean towards?

Is it economically reasonable to achieve KfW40 standard with a pellet heating system? Or would you not even aim for that? For me, economy comes before ecology.

Thanks

Exact prices… so I can’t tell you the differences. It ultimately depends on the size of the system, the type, and the manufacturer.

However, an air-to-water heat pump is definitely cheaper than a pellet heating system. Both systems are suitable for a KFW-40 house.

You will probably have to consider the chimney for the wood stove separately, as a pellet heating system, depending on the kW rating and location (effective height from flue pipe connection to above the roof), will require its own chimney. You won’t be able to compensate for the different diameters. But you can easily find this out from the district chimney sweep responsible for your area, who will inspect and approve the system anyway. If he agrees to a single flue pipe… well, then you save yourself a chimney.

Once the planning is finalized, I would simply request quotes for the heating options. This way, you can see the exact price differences and still decide accordingly, weighing both economic and ecological factors.

Hello Maccus,

As far as I know, a gas condensing boiler is not possible for a KfW 40 house due to the CO2 balance. However, this varies and depends on many factors.

We are also building to the KfW 40 standard. Our options are limited to heat pumps (only air-to-air) or pellet heating. We are choosing pellet heating combined with a ventilation system and heat recovery.

By the way, solid construction is not a problem, although all prefab house manufacturers claim otherwise.

Feel free to discuss different aspects of the energy standard anytime.

Good luck!