Ventilation: central or decentralized?

It is about an air-to-water heat pump with underfloor heating, so hot water. Air heating is not up for discussion.

Then first have the architect give you the key data... then you can discuss whether it would be a good choice...

Thermal insulation insulates walls Because in modern thermally insulated houses the building envelope is so tight that little to no air can enter the interior through joints and cracks, assistance is necessary. "Either through frequent manual ventilation around the clock or through technical measures that ensure constant air exchange," explains Thoma. In highly thermally insulated buildings, and thus in virtually all buildings constructed according to the current Energy Saving Ordinance (Energieeinsparverordnung), air exchange must take place approximately every two hours.

Risk of mold formation This is a problem: In a four-person household, up to eleven liters of water accumulate daily in the indoor air. If they remained inside for a longer period, mold formation threatens – with serious health consequences. Opening the windows every two hours for five minutes would not be bearable for the residents. "The solution is a ventilation system that continuously ensures the removal of moist air," says Thoma.

But not everyone needs a ventilation system. Whether it is sensible and necessary in a specific case is determined by architects, energy consultants, or specialist planners using the so-called Blower-Door Test to determine the airtightness of the building. This makes clear how much air enters the building through infiltration. Depending on the result, specialists develop a concept with proposals for ventilation technology.

Some technical solutions have many drawbacks Sometimes window rebate ventilators are enough to bring in sufficient fresh air. "They are installed in the rubber lips of the windows and allow outside air to enter the rooms," explains ventilation expert Thoma. However, the air exchange here depends on the weather: On calm, warm days little happens. In strong wind, a whistling can occur at the windows.

"Moreover, in the cold season the heat generated with valuable energy is constantly cooled down this way," observes Günther Mertz from the Professional Association for Building Climate. He therefore advises ventilation systems that constantly expel indoor air and let fresh outside air in. "The most energy-efficient solution is ventilation systems with heat exchangers," says Mertz. They can extract 80 to 90 percent of the heat from the exhaust air and return it to the building. This can significantly reduce heating costs.

Filters clean the air Additionally, pollutants and pollen can be removed with the help of filters. "This makes the air overall fresher and healthier because chemicals released from furniture, carpets, paints, tobacco smoke, cleaning and detergent agents do not remain long inside the house," explains Michael Conradi from the Initiative Wärme+.

Professionally installed systems do not cause drafts because the air exchange takes place in closed systems. "Operators also do not have to fear that cold air constantly flows into the rooms," clarifies Thoma. "Ventilation systems are not air conditioners; they do not cool down the air."

For new buildings, centrally controlled systems that exchange the air throughout the whole house are recommended. In existing buildings, however, according to Conradi, they are often not usable for structural reasons. "Decentralized ventilation systems are suitable there." Individual rooms such as bathrooms, bedrooms, or kitchens, where particularly much moisture occurs, are ventilated in a controlled manner. The devices can usually be well integrated and also find space in suspended ceilings or kitchen units.

Source: FOCUS Online

For the people who think from 12 to noon.

Getting offended right away? Is that necessary?

Back to the topic:

With controlled residential ventilation you could skip the pointless solar thermal: save 4-5k.

I don’t have solar thermal. Air-to-water heat pump and exhaust air. There was no gas. So you can’t generalize.

The exhaust air system itself costs including installation etc. certainly about 1k. The difference to controlled residential ventilation shrinks to maybe 5k.

Please do a total cost calculation here: it’s not just about the devices. That is the smallest part in both ventilations. In my case: decentralized (or for that matter exhaust air) came to 2.4k including installation. A controlled residential ventilation could not have been realized under 10k after three offers. Fairly, an additional half square meter for the space should be included, which theoretically would have cost about another ~900 €.

Controlled residential ventilation itself doesn't pay for itself or only in the long term, but also saves about 200 EUR per year in heating costs.

I doubt that controlled residential ventilation saves me over a third of the heating costs. And even if it does, it surely consumes more electricity than the exhaust air solution. But if we assume 200 €, controlled residential ventilation would be paid off in 38 years (if maintenance costs nothing and nothing breaks). So you are right – it doesn’t pay off.

In the end, you get higher comfort, better coziness, and also a higher resale value practically almost for free.

It’s warm, the humidity is right, it doesn’t smell musty, I don’t have to ventilate more than I want to, there are no drafts anywhere, and I don’t hear the noises in any living room. But sure – it will never come close to the “coziness” of controlled residential ventilation!