Different Heating Concepts Compared

Under optimal conditions … Legionella can double approximately every 3 hours. This means that from one Legionella, a colony of 65,000 Legionella can develop within 48 hours….

Well, when I go on vacation, I prefer to keep it at 60 degrees.
Running a few liters through a 300 or more liter water tank in the basement is by far not sufficient as a measure.

You can rationalize it… I am not a fan of these lukewarm storage systems because of this issue.

When using the heating element for the legionella program, it is always at 60 degrees.
So, hundreds of euros extra per year.

Under optimal conditions ... Legionella can double about every 3 hours. That means from one Legionella a colony of 65,000 Legionella can develop within 48 hours....

Yep. But that requires standing water at 35 degrees. In a single-family house with +/- 50 degrees in the hot water tank and daily use, there is practically no danger.

Well, when I go on vacation, I prefer to keep it at 60 degrees. Running a few liters in a 300 or more liter water tank in the basement is by far not sufficient as a measure.

The temperature in the hot water tank does not change during vacation either, and the legionella program continues running. So where is the problem?

You can talk yourself into it ... I am not a fan of these lukewarm tanks because of this issue.

So you are not a fan of normality and daily practice (installed hundreds of thousands of times every year) or of the future, when only heat pumps will be in use anyway. You can see it that way, but you will become an endangered species with double parachutes and suspenders. And you don’t trust scientific facts like those from the Robert Koch Institute or studies on legionella diseases in single-family houses (under 100 per year with an average resident age over 60 and thus probably not necessarily heat pump users)? Then size your heating accordingly and spend additional money on high-temperature hot water production. I do not want to dissuade you from that, but other readers are surely interested in this thread and can form their own opinion.

If the heating element is used for the legionella program, there are always 60 degrees. So hundreds of euros extra per year.

How do you calculate hundreds of euros extra? I would calculate as follows: - in almost all regions in Germany there is no deep winter from March to November, so a heating element is not necessary per se - then there are some weeks (in far from all of Germany) where the daily average temperature is -10 to -20 degrees - and finally, we are talking about a temperature increase for the legionella program from 50 degrees (normal hot water temperature) to 60 degrees. That means the water needs to be raised by 10 degrees once a week. With a typical 3kW heating element, we are talking about weekly costs of 50 cents - own heat pump experience: never used the heating element in winter (except for defrosting the system, but that is specific to my heat pump manufacturer) Of course, one can talk everything down. But then one leaves a factual path. And that is what you are doing right now. As said, do what you think is right for you. You are not damaging or doing anything wrong by doing so. It just isn’t absolutely necessary.

You could also, when you come home from summer vacation - mostly in countries where worrying about water quality would be a lot more worthwhile - run the Legionella program and sadistically boil and eliminate your newly bred strain along with its reigning queen. And afterwards, continue with the usual everyday water consumption as if nothing had happened. That doesn't cost hundreds of euros.

If Legionella are really his only problem, he could simply install a hygiene storage tank or a drinking water station. They only cost a few percent efficiency and have no problems with Legionella.

One could also simply run a circulation pump for a few hours daily (mine has a power of 7 watts) and it can be time-controlled via the air-to-water heat pump. It is true that Legionella only multiply in stagnant water. If the fluid is constantly moving, nothing develops. There is no need for 60 degrees either. According to our latest analyses (I work professionally with water circuits), reproduction above 50°C is no longer detectable. For around 50€ you can have your sample tested as a private person at the regional lab if you want to be on the safe side. I do this annually and have the best water quality.

This legionella discussion somehow reminds me of the asbestos panic. Abstract, exaggerated, mostly not really relevant and quite easy to manage in a private setting.

Now the best thing is, since heat pumps do not have chimneys, the "Glücksbringer in Schwarz" comes once a year to the single-family house and carries out government-mandated legionella inspection for 75 euros plus lab and travel costs.