ᐅ Window frame ventilators – A good idea for uninsulated older buildings?

Good morning everyone,

I’m not sure if this is the right section for my topic, so please feel free to move it if necessary.

We bought a house built in 1964 in 2015. We have almost completely renovated it, including replacing the windows. The old windows were wooden double-glazed units, but the frame could be opened so you could get between the two panes of glass. I think you know what I mean. Obviously, they were far from airtight. Now we have installed airtight PVC double-glazed windows.

As expected, with these airtight windows in our uninsulated older building, we’ve been having some issues with moisture inside the house. By heating well and ventilating very thoroughly (at least 3 times a day), we’ve managed to get the humidity under control. The indoor relative humidity usually ranges between 50% and 65%. However, the windows still have some condensation on the lower part in the mornings. We successfully avoided mold last winter.

With the next winter approaching, I’m considering making some changes for the following reasons:
1. The frequent ventilation is annoying and time-consuming. Also, the rooms cool down a lot.
2. We are expecting our second child soon, and I doubt they will enjoy sitting in a 20°C (68°F) room when cold air suddenly keeps flowing in from outside.

I came across window frame ventilators (trickle vents).
What are your experiences with them?
I have already found out that they are designed to prevent drafts because they close at a certain airflow speed.
Some even have small “heat exchangers” integrated, so not all the heat is lost.
What I want to know:
Do these devices actually work? Will I really need to ventilate less to reduce moisture?
How much extra heating energy is lost?

My hope is to only have to ventilate well once a day (in the morning).
I don’t expect to have to heat significantly more since I would ventilate less.

I would appreciate your experiences and insights.

Best regards,
Specki