ᐅ Achievable minimum indoor temperature with KfW55-standard building

Hello everyone,

I hope this post is in the right place.

We have a new apartment in a building constructed to the KfW55 standard. The apartment has underfloor heating and does not get warmer than 20 degrees Celsius (68°F). According to the developer, this is due to the KfW55 standard. So the maximum room temperature would be expected. However, 20 degrees Celsius (68°F) is too cold for us. Cooking is minimal, and the apartment is unoccupied during the day. There is also not enough solar gain, meaning no other heat sources are present. Therefore, the heating should be able to reach 21 or 22 degrees Celsius (70–72°F) for a comfortable climate.

Does anyone have information on whether the statement that the heating system can only reach 20 degrees Celsius (68°F) due to the KfW55 standard is actually correct? Thank you very much.

P.S.
Are you a tenant or an owner?

In rental law, the minimum temperature is 20-22 degrees Celsius (68-72°F). In the bathroom, it should be 21 or 22 degrees Celsius (70-72°F), although court rulings vary slightly on this. Since the heating system usually also supplies your hot water, which needs to be hot, the heating should be capable of properly warming the entire home.

The claim that this is due to the KfW55 standard is obviously incorrect and is meant just to reassure you. Since this is a new build, I will assume you have a heat pump. It just needs to be properly adjusted, then it can provide more heat. In our KfW55 apartment, we currently have the opposite problem — it tends to get too warm rather than too cold. We are almost reaching 22°C (72°F) even with little heating.

However, to assess this more accurately, we need a bit more information.

Sorry, my first post was removed because I used a bad word and received a warning. This bad word (besides the paragraph with the specific information related to the question) caused the forum software to mark my post as “no added value.”

So, again:
No, the statement from the developer is complete nonsense. Modern houses (by the way, KfW 55 is the current minimum standard that a new build must meet) are so well insulated that heat can no longer escape. Or rather, cold does not penetrate, making it quite easy to heat to comfortable temperatures.
If 20 degrees Celsius (68°F) is not exceeded, it could be due to:
- incorrect heat generator (heating system)
- incorrect design of the underfloor heating
- incorrect heating load calculation
- incorrect settings on the heat generator
- incorrect settings on the underfloor heating
and so on.

ALL of this is within the builder’s responsibility. Please report the defect and have it corrected. Since you haven’t yet responded to my question above and you are the owner, please ask to be provided with the documents you are entitled to. Then you will know more. Nowadays, it is really difficult not to reach 20 degrees Celsius (68°F) in a new build, unless the heating is simply turned off.

I am the owner. The apartment is rented to a young lawyer from Turkey, who is not yet accustomed to the cold temperatures in Germany and feels cold even at 20°C (68°F) in the living room with the heating turned up fully. I had assumed that the KfW55 standard was just an excuse to dismiss my objection. Now, they refer to the standard indoor temperature according to DIN EN 12831:2003-08, section 6.2, which is set at 20°C (68°F).
I am asking how the house is heated.

Correct. According to the DIN standard, a reference temperature of 20 degrees Celsius (68°F) is specified. However, the DIN is intended for heating system design and holds no relevance for the tenant.
You might want to ask how the standard temperature of 24 degrees Celsius (75°F) for the bathroom is supposed to be achieved. This is also specified in the DIN as far as I know. As a landlord, you are responsible for a higher temperature than 20 degrees Celsius (68°F) in the bathroom. Otherwise, your tenant could reduce the rent slightly.

The DIN refers to the standard outdoor temperature, which is somewhere between -10 and -15 degrees Celsius (14 and 5°F).

P.S. You purchased a newly built apartment but have no information about the unit and the building? Legally and by court decisions, the following documents are required, for example:

• building permit / planning permission
• fire protection certificate
• structural safety certificate – sound insulation certificate
• thermal insulation certificate
• planning documents, calculations, and drawings created for the construction of the building, such as execution planning, structural engineering, and building services plans for heating, water, ventilation, and exhaust air systems
• maintenance instructions
• operating and user manuals
• calculation models, e.g., for underfloor heating
• access cards / locking plans
• energy performance certificate