U-value of windows: 1.3 - is an upgrade worth it?

The topic of windows continues to concern us.

Existing windows are 22 years old, double-glazed, with no burglary-resistant measures. The house has quite a lot of windows, so retrofitting for security would be correspondingly expensive.

That is why we are now very unsure whether, also in terms of heat loss, insulation... installing new windows might possibly be more cost-effective in terms of cost/benefit, upgrading the house, etc.

All the windows have a U-value of 1.3. This refers to the value relating to the entire window area.

We know there are windows with a value of 0.6. Can it be calculated that this would mean roughly only half the heat loss? We have 2 children, so we also heat the bathroom, children’s rooms accordingly... The house has many windows, and costs for retrofitting locks would be incurred anyway.

Or are new windows that approach passive house values so expensive that it wouldn’t pay off in the next 20 years anyway? Is this energy-saving thing overrated?

It is about 20 window sashes in total... 3 of them are floor-to-ceiling windows. For at least 11 sashes we would retrofit mushroom locks, and we were given an offer amounting to costs per window of just under 300 euros... So the retrofitting would cost around 3500 euros, but the windows would remain 22 years old, i.e., double-glazed with a U-value of 1.3.

1.3 is not dreadful. I wouldn't just throw away anything that is okay. That never saves money. Even the mushroom heads, ...tell me, how many break-ins have you had in 22 years? If upgrading security, then only downstairs anyway. Karsten

Let's say we have heating oil costs of 2500-3000 euros per year. That is somewhat realistic for 4 people in just under 200 sqm, right? Can one then say whether we would definitely save, say, 600 euros with windows that have a U-value of 0.8? Or can't you calculate it like that?

Regarding the topic of burglary: Yes, I am certainly sensitized because of a serious burglary within the family. But the house is located in an absolutely quiet edge location, behind it open fields, no real security through a fence, many windows on the back of the house, where someone could practically tamper unnoticed. I think that already speaks in favor of investing here, and on the ground floor there are already 11 window panes :(

Let's say we have 2500-3000 euros per year in heating oil costs. That is somewhat realistic for 4 people in just under 200 sqm, right? Can you say whether with windows with a U-value of 0.8 we would definitely save, say, 600 euros? Or can't you calculate it that way?

No, you can't.
If you want to know exactly, have an energy consultant come. They can provide an estimate...

To me, this sounds a bit like "I don't like my red car anymore, I want a blue one that also has 20 percent less consumption..."

On the subject of burglary protection:
Security companies/police offer free on-site consultations.
It is really recommended...

There can also be mold problems if the windows are not coordinated with the rest.

3000 euros gives about 6000 liters of oil. That seems too high to me for a house with double glazing 1.3. Saving 600 euros through different windows results in about 1200 liters saved. That also seems too optimistic to me. Karsten