ᐅ New Construction: Underfloor Heating Instead of Radiators and Mechanical Ventilation with Heat Recovery – Yes or No?

Heisenberg schrieb:
... What about rooms like bedrooms, for example? Usually, we have the window open at night there.

However, this will then have to be replaced by a controlled mechanical ventilation system, which of course conflicts with KFW 55 standards!

Hello,

Heisenberg schrieb:

We are currently planning a new build of a single-family house with 134 sqm (1,442 sq ft) of floor space in Lower Saxony through a developer. The house is supposed to meet the KfW 70 standard. Now we are considering installing underfloor heating instead of regular radiators.
According to the developer, the additional cost would be about €8000. Is it worth it? What about rooms like the bedroom? Usually, the window is open at night there.

I would suggest that you ask the provider for clarification. Achieving KfW 70 with radiators is actually not feasible; at least not without significant additional effort. The stated extra cost for the underfloor heating supports this assumption, as it is far too high if the other parameters for KfW 70 are correct.

Regardless of the fact that you can have the underfloor heating controlled individually for each room, it is highly unhealthy to sleep with an open window at night—especially when outside temperatures are low. Try searching online and you will be surprised what you can expose yourself to by constantly sleeping with an open window.

Heisenberg schrieb:

Furthermore, we are considering installing a mechanical ventilation system with heat recovery. With the ventilation system, we could reach the KfW 55 standard and thus have additional funding opportunities. After deducting subsidies, the ventilation system would cost us about €4000.

Sorry, but a lot of this does not add up. Either you didn’t listen carefully to the seller or they see you as an easy target. KfW 55 is not available that cheaply—even in Lower Saxony—and cannot be achieved just by installing underfloor heating and a mechanical ventilation system with heat recovery.

Best regards, Bauexperte

The house costs €152,000 gross without any additional options and meets Standard 85. In the options, there is an upgrade for KFW 70 (triple glazing and floor insulation) included for €4,500. According to the standard package, we would have a regular gas condensing boiler with radiators. The €8,000 is the extra cost for a complete underfloor heating system. According to an independent building expert, the advantage of underfloor heating is that we would only need to heat at about 35°C (95°F) when using underfloor heating alone.

I have actually always slept with the window open, all year round. The waterbed also helps me not to feel cold at night. However, I am concerned that the ventilation system in the bedroom might not be able to replace the fresh air from an open window.

The developer is a reputable company that has been around for 30 years and builds around 150 houses annually. They have their own energy consultant who models the house on a computer and can tell us whether the measures meet the KFW 55 standard.

Heisenberg schrieb:
According to the standard, we would have a normal gas condensing boiler with radiators. The €8000 is the additional cost for a full underfloor heating system.

That’s nonsense... they just want to make money at your expense... the cost of purchasing and installing underfloor heating in a new build should be roughly the same as a "normal" heating system. Any reputable plumbing company will tell you the same...

Heisenberg schrieb:
I usually sleep with the window open year-round. The waterbed also helps prevent me from feeling cold at night. However, I’m concerned that the ventilation system in the bedroom can’t replace the fresh air from an open window.

This is nonsense as well... a controlled mechanical ventilation system can and will replace the fresh air from an open window, with the added benefit that the air is also warmed...

Hello,

Bauexperte schrieb:
......KfW 70 with radiators is basically not achievable; at least not without significant additional effort.....

Unfortunately, that is a misconception. Some time ago, I completed the planning for a KfW 40 with radiators!

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

The option is actually not available. Individual room control (IRC) is required according to the energy saving regulation.
At best, a justified exemption request can be submitted.

Best regards.

I’m really glad that I’m not building through a developer but instead contracting all trades separately and managing them myself...

As a reference for you, here’s what I arranged last week:

175 m² (1,885 sq ft) underfloor heating system = 7,000 euros + VAT

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