New underfloor heating instead of radiators and controlled residential ventilation; yes or no?

... What about rooms like e.g. bedrooms? Usually, we have the window open at night there.

But that will then have to end with a controlled residential ventilation system and of course contradicts KFW 55!

Hello,

We are currently planning a new build of a single-family house with 134 sqm floor area in Lower Saxony through a developer. The house should have KfW 70 standard. Now we are considering using underfloor heating instead of regular radiators.
According to the developer, the additional cost would be about €8,000. Is it worth it? What about rooms like, for example, the bedroom? Usually, we have the window open at night there.

I would suggest you ask the provider again exactly. KfW 70 with radiators is actually not feasible; at least not without a lot of additional effort. The stated additional cost for the underfloor heating confirms this suspicion, as it is much too high if the other parameters for KfW 70 are correct.

Regardless of the fact that you can install the underfloor heating with individual room control, it is extremely unhealthy to sleep at night with the window open – especially at low outside temperatures. Try Aunt Google and you will be surprised what you can catch with constantly open windows.

Furthermore, we are considering installing a controlled residential ventilation system. Through the ventilation, we could achieve standard 55 and thus have further funding opportunities. The ventilation would cost us about €4,000 after funding.

Sorry, but a lot of this is not right. Either you did not listen properly to the seller or he found a good victim in you. KfW 55 is not available that cheaply – not even in Lower Saxony – as if it could be done with just underfloor heating and controlled residential ventilation.

Rhineland regards

The house costs €152,000 gross without any extras and has the Standard 85. In the wishes, the surcharge KFW 70 (triple glazing and floor insulation) with €4,500 is included. According to the standard, we would have a normal gas condensing boiler with radiators. The €8,000 is the extra cost for a complete underfloor heating system. According to an independent building expert, this is supposed to have the advantage that we only need to heat with about 35 degrees when we heat only with underfloor heating.

I have actually always slept with the window open, all year round. The waterbed also makes it easier for me not to be cold at night. However, I have concerns that the ventilation in the bedroom cannot replace the fresh air of an open window.

The developer is a reputable company that has existed for 30 years and carries out about 150 constructions annually. They have their own energy consultant who will calculate the house on the computer and can tell us whether the measures are sufficient for KFW 55.

According to the standard, we would have a normal gas condensing boiler with radiators. The €8000 is the surcharge for a complete underfloor heating system.

Well, that's nonsense... they want to make money at your expense... underfloor heating in a new building should cost about the same for purchase and installation as a "normal" heating system, you can ask any reputable plumbing company... they will say the same...

I have actually always slept with the window open, all year round. The waterbed also doesn’t help me not to freeze at night. But I’m concerned that the ventilation system in the bedroom cannot replace the fresh air of an open window.

Nonsense again... the controlled residential ventilation system can and will replace the fresh air of a window with the positive side effect that the air is also warmed...

Hello,

......KfW 70 with radiators is practically not achievable; at least not without great additional effort.....

Unfortunately, that is a misconception. Some time ago, I completed the planning for a KfW40, with radiators!

....Regardless of the fact that you can have underfloor heating installed with individual room control,...

The option does not actually exist. ERR (individual room control) is required according to the Energy Saving Ordinance.
At best, a justified exemption application can be submitted.

Best regards

How glad I am that I am not building through a developer but awarding all trades individually and myself...

Just for you as a reference, I awarded last week:

175 sqm underfloor heating system = 7,000 euros + VAT

Controlled residential ventilation with central supply and exhaust air = 6,000 euros + VAT