Hygiene storage tank or regular hot water storage tank?

Hello everyone,

we are currently facing the decision of whether to install a 300L hot water tank "enameled" (gas + solar without heating support) or, for an additional cost of about €1700 gross, a hygiene tank in our new building. Since we have a baby, the topic of legionella concerns me a lot. Unfortunately, our sampling budget is almost empty; otherwise, I would have automatically opted for the hygiene tank. Therefore, two questions:

1. How high is the risk of legionella if I stick with the regular tank? There is the legionella program which heats the water up to 70 degrees from time to time, and I might run the tank at 60 degrees for safety. Of course, the question arises of what additional energy costs this causes per year. Also, I have read that it is suspected that the 70-degree program might actually harden the legionella, making the bacteria more resistant. Is there any truth to that? I am really uncertain.

2. What is the lifespan of the two variants, or when would they have to be replaced?

Thanks in advance!

Do you have a gas boiler? If yes, then simply set the water temperature permanently above 60 °C and there will be no more Legionella.

But even at below 60 °C, Legionella in single-family houses are rather rare according to various studies. Regular water exchange every 2-3 days is important. Then a normal domestic hot water tank is sufficient, and preferably no circulation, as this can even promote Legionella growth.

Yes, we have planned a gas boiler + solar. Is there a calculator where you can calculate how high the costs are for a permanent minimum temperature of 60 degrees or more? If the costs exceed a certain amount per year, it might make sense to take the hygiene storage tank right away, even if the additional costs currently sting.