Heater savings: up to 95% heat recovery reliably calculable?

Good evening dear forum,


we are considering installing a (central) residential ventilation system in our new building.

When researching this topic, I keep coming across the argument:
“…up to 90%-95% heat recovery, with simultaneous heating savings.”

However, I cannot understand this further.

I understand a controlled residential ventilation system to work with heat recovery so that the generated heat remains as much as possible (up to 90-95%) inside the house. The warm indoor air is mixed with the colder (winter) / warmer (summer) outdoor air and brought back into the house.

This “heating savings” refers exclusively to the time in winter when one would otherwise, for example, ventilate by shock ventilation, right?

Is it even possible to calculate how much that saves? I imagine it to be very little if, for example, one ventilated twice a day for 5-10 minutes. Moreover, it is not even guaranteed that 90-95% heat recovery is achieved?

We will not base our decision on this, but I am just interested if it can be calculated reliably in advance with certain assumptions or if someone has any experience on this?



Best regards

Heat losses in a modern new building amount to about 40-50% from ventilation alone. The rest disappears through heat transmission through masonry, windows, the floor slab, and the roof. Yes, this is calculated during the creation of the thermal insulation verification and/or the heating load calculation to correctly size the heating system. Whether the stated 90% is realistic, however, remains to be seen. This is tested, among others, by the Passive House Institute. You can find the test results at passiv . de.

My impression is that the OP means with a controlled residential ventilation system you save 90% heating costs? You only recover 90% of the ventilation losses. How much you have to ventilate is standardized.

Is it even possible to calculate how much that saves? I imagine it’s very little if, for example, you ventilated twice daily for 5-10 minutes each time.

Hi. Since I ventilate decentrally and without heat recovery, I cannot provide any figures. However, since air is a poor heat storage medium, heat losses due to ventilation are generally low. And even if the above-mentioned 40-50% were the case, with 90% being recycled, we’re talking about savings of €15-20 per month. The system should therefore not incur any maintenance costs and ideally run for 20 years for it to be worthwhile at all! ;-)

It's not really about cost-effectiveness when it comes to ventilation systems. Either you have one and don't need to ventilate anymore, or you don't. How high the losses are depends heavily on the building. In a "typical" house from the seventies, it's around 25% of the energy used... in modern energy-efficient buildings, it can easily be 50%, because simply due to the construction method (insulation etc.), much less energy is needed to achieve and maintain the same temperatures.

Thank you very much for the previous answers, this clarifies the question regarding the argument "heater savings."


This is probably a misunderstanding, if a controlled residential ventilation system would save 90% of heating costs, everyone would have it. That is not what I meant.

In fact, it is only about ventilation losses, which was more or less my assumption.

I did not want to start any fundamental discussions.

Thank you all!