Gas or heat pump in a KfW55 house

We were told that in single-family houses this can mostly be neglected; especially if the tanks are under 300 liters.
Opinions seem to be divided when it comes to legionella...

It would be nice - but those critters don’t care how big the hot water tank is. They’re just too stupid for that.

They only need water at the right temperature (27-45 degrees, as far as I know). Preferably stagnant. That’s why a frequent water exchange (as mentioned here) is beneficial.

There really is no disagreement here: wrong temperature and a bit of bad luck, and you’ve got the critters on your hands.

They don’t like temperatures above 55 degrees, then they die. That’s why 60 degrees is generally recommended for hot water. But you don’t always have to have it that way. A legionella colony in the tank and hot water pipes doesn’t grow in just a few days. That’s why there’s this thermal disinfection function (flushing the pipes with hot water, otherwise the little bastards sit in the pipes, not in the tank).

In the pipes, this is only a problem if there is circulation for hot water. Legionella are actually always present in normal water, but in low concentrations. If you have a sufficiently high turnover rate (i.e., small storage) or a fresh water station, or occasionally thoroughly heat your circulation pipe, that is usually enough.

if you have circulation for hot water

Right. If you have it.

I, for example, don't have it. Short pipe runs, it wasn't worth it to me.

Or to put it another way: A lot of people don't have a circulation pipe.

In my opinion, these people then really have to pay attention to that.

Best regards
Thorsten

I rather suspect that very many people in new buildings also have circulation. I do not have any, and among other things, I paid attention to short distances during the planning.

I rather suspect that many people in new buildings also have circulation. I don’t have it, and among other things, I paid attention to short distances during planning.

I also planned everything so that the utility room is next to the guest bathroom and below the large bathroom. The longest hot water route is to the kitchen. The plumbing installers also said at the time: Here circulation, do we have that on the list!? Never ever, as unnecessary as a goiter. We won’t install it. There’s a discount. It wouldn’t have been so expensive after all – but as said, unnecessary for me. And then the circulation pump keeps running (electricity + wear).

In the suggested floor plan from the house manufacturer, the large bathroom would have been upstairs on the other side... then I would have needed circulation, also according to building standards... but I only learned this later from the specialists during the plumbing installation.

I don’t see a loss of comfort. When all pipes have cooled down:
Bathroom upstairs: Quick, run water for 4 seconds
Kitchen: 7
Guest WC: 6-7 (if the kitchen hasn’t run before, it’s branched and about 60% of the route runs first in one pipe)

This means: In the small house we have 3 rooms with hot water points that are used regularly. And regularly disinfected as well. Zero effort, except for the above-mentioned few kWh every 4-5 months to heat up to 80 degrees. It’s worth it to me / us for our health.

Best regards
Thorsten

We also don't have a pump (all lines under 3 L) Regular water withdrawal is actually everywhere except the bathtub - but the branch line is off the upstairs bathroom and 1 m long. Just started the legionella program and turned on the heating element - heated water up to 75°C. Then I read that you also have to open the withdrawal points every 3 minutes... then the temperature dropped to the basement -. - The experiment cost 1.5 €. But well - you can probably do that every 3 months.