ᐅ Gas or heat pump in a KfW55 energy-efficient house

BeHaElJa schrieb:
We were told that in a single-family house this is rather negligible, especially if the storage tanks are under 300 liters (80 gallons).
Opinions seem to differ regarding Legionella...

That would be nice – but these bacteria don’t care about the size of the hot water tank. They are simply not intelligent enough for that.

They only need water at the right temperature (27-45 degrees Celsius (81-113°F), as far as I understand). Preferably standing water. That’s why frequent water exchange (as mentioned here) is beneficial.

There really is no disagreement: wrong temperature and a bit of bad luck, and you have the bacteria on your hands.

They don’t like temperatures above 55 degrees Celsius (131°F), at which point they die. That’s why 60 degrees Celsius (140°F) is usually recommended for hot water. However, it’s not always necessary to maintain that constantly. A Legionella colony in the storage tank and hot water pipes doesn’t develop in just a few days. That’s why there is the thermal disinfection function (flushing pipes with hot water, since the bacteria settle in the pipes, not in the tank).

This is only an issue in the pipes if there is circulation for hot water. Legionella bacteria are generally always present in regular water, but in low concentrations. Usually, having a sufficiently high turnover rate (i.e., a smaller storage tank), a domestic hot water unit, or occasionally thoroughly heating the circulation line is enough to control it.

Saruss schrieb:
if you have hot water circulation

Exactly. If you have it.

For example, I don’t. Because of short pipe runs, it wasn’t worth it to me.

Or put differently: Many people don’t have a circulation pipe.

In my opinion, those people need to pay close attention then.

Best regards
Thorsten

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

Saruss schrieb:
I rather suspect that many people in new homes have circulation systems as well. I don’t have one and made sure to design for short water routes, among other things.

I also planned everything so that the utility room is next to the guest bathroom and below the main bathroom. The longest hot water run is to the kitchen. The plumbers back then said: Circulation system here? On our checklist!? Never ever, totally unnecessary. We’re not installing it. That reduces the cost. It wouldn’t have been very expensive—but as I said, it’s unnecessary for me. Plus, the circulation pump would constantly be running (electricity + wear and tear).

In the manufacturer’s proposed floor plan, the main bathroom upstairs would have been on the other side… then I would have needed a circulation system, also according to building regulations… but I only learned that from the plumbing professionals during installation.

I see no loss of comfort. When all the pipes have cooled down:
Upstairs bathroom: Just 4 seconds of water running
Kitchen: 7 seconds
Guest WC: 6–7 seconds (if the kitchen hasn’t been used previously, the line is branched and about 60% of the distance is first flushed through one pipe)

That means: In this small house, we have three rooms with hot water outlets that are regularly used—and regularly disinfected. Zero effort, except for the few kWh mentioned above every 4–5 months for heating to 80°C (176°F). That’s worth it for my/our health.

Best regards,
Thorsten

We don’t have a pump either (all pipes are under 3 liters).

Regular water use occurs everywhere except the bathtub – but the branch line comes off the upstairs bathroom and is 1 meter (3 feet) long.

Just started the legionella prevention program and switched on the heating element – heated the water up to 75°C (167°F). Then I read that you also have to open all the outlets for 3 minutes each... that caused the temperature to drop significantly.

The experiment cost 1.5 €. But well, it seems you can really do this every three months.