Heating system new construction single-family house air-air / air-water?

I modernized from calorific value to condensing technology in my first house. I cannot provide actual figures. The problem is: condensing technology only realizes its potential if you have the lowest possible return temperature. That means: as long as you don’t perform a hydraulic balancing together with a reduction of the flow temperature, a condensing boiler hardly brings any benefit. You can simply insulate pipes in the basement, for example. I would continue to operate the old heating system as long as there is no obligation and until it is really defective. I would use the time to optimize the overall system and thus save through low investment.

Thanks for the information. Often, the person who installed something new is so enthusiastic that they no longer report or calculate quite objectively.
The return flow is the problem for me. Despite underfloor heating, I run a high flow temperature because I used "copper" pipes back then. There were some problems with plastic hoses, which is why I decided on that. Since copper might react with the concrete, the plastic-coated pipe was used at the time. To compensate for the expansion coefficient, there is some air between the copper and the coating (worse heat transfer) - but it has proven itself.
To achieve sufficient flow even in the remote areas, I have to run it a bit faster, which means the return flow is not so cold. The radiators in the basement were never even installed because it turned out that they were not necessary due to the lack of insulation. So I automatically heat the basement as well.
Since I chose a cast iron boiler back then (no corrosion), the unit is still almost like new.
I was able to elegantly solve the problem with efficiency (over the years, the flue gas loss specification changed from about ~14% to now ~10%).
The trick was not even known to the chimney sweep, and heating accessory companies also said it wouldn't work.
I now meet the values (down to 8%!), so the chimney sweep can only tick the box.
It is a simple, inexpensive solution that only requires a bit of DIY.
I will not rely on condensing technology but rather think towards the future, which I have already done, but was somewhat desperate because of the many options and therefore initially thought about condensing technology (only because of the oil price).
The 80-meter deep drilling for about 9000,- hit me in the stomach at first, and digging up my garden with the pipe coils at 1m depth is also too much effort for me.
"Only" the drilling divided by 15 years = 600,- per year! I can still get quite a bit of oil for that.
---Sidebar: Doesn't the drilling actually cool down over the years?? Which would reduce efficiency?
By the way:
If another reader has an older boiler whose values are slowly reaching the limit, I can gladly repost the "super solution" with details.
Greetings from a "seeker" who is not averse to the future but is not so enthusiastic about a 15-year amortization period, especially since I know from experience that some repairs also occur during this time that were not mentioned at the beginning.......

So if you have already done your best in terms of optimization, then switching to [Brennwert] almost certainly does not make economic sense. You could, since you seem to be handy, install pipes for a wall or ceiling heating system each time you renovate a room. This way, you might have the option to operate a heat pump economically when the oil heating system kicks the bucket.

Yes, my optimization thoughts are now also going into the exterior wall (25cm Ytong), but the effort is (even with self-assembly) relatively high if I attach the Styrofoam on the outside. Possibly directly with brick look to save on plastering. I am currently calculating how big the financial effort is and to what extent it is worthwhile. My interest in this also results from an extension project and the associated overall optical design. The tip about wall/ceiling heating was new to me, as I only knew it as electric heating—and heating electrically always means the more expensive solution overall. Pipes in the ceiling or wall are quite a bigger deal (suspending the ceiling, adding a wall in front). I have to get informed. Heat rises upwards, so when does the heat from the ceiling reach the floor? I had already posted that underfloor heating and tiles (in the living area—is great because of cleaning and appearance but....) are problematic in the intermediate seasons, since unfortunately we don’t live in Sicily. During the day it is warm, in the evening the tile radiates cold because it’s unheated. So the heating doesn’t run during the day; if you turn on the heating in the evening, the floor stores the heat until the next day and it becomes “super warm” during the day. It works, but is hard to control by regulation! Unfortunately, it’s not that simple at all to plan an overall concept, especially when you keep an eye on the “€”! I have already planned a few flat collectors for hot water because the effort is not so big, and I have practically seen what the sun can do. Photovoltaics is another matter and you have to think long term. The possibly optimal solution with storage technology seems to me financially more something for people who pursue it as an expensive hobby. I recently saw on YT that there is something “new” again! Wood stove with attached pelletizer elements. They convert the heat directly into electricity. This is then sold as a “super solution.” I know about these elements (it also works the other way around for cooling) since I know it for computer CPU cooling, where it works. But for electricity generation via wood stove you don’t have to question it, just forget it right away! Fortunately, the winters have been getting milder (climate catastrophe also has advantages (irony on!), may it stay that way. Greetings from the owner of warm, thick jackets, who can still remember -18°C! I’ve been considering in recent weeks whether I could donate these things to homeless aid. But first I will calculate the Styrofoam attachment........

How high are your supply and return temperatures? Oil consumption and postal code? Warm water collectors is absolute nonsense.

Heat rises, so when does the heat from the ceiling reach the floor?

The heating on the ceiling works differently than underfloor heating. Underfloor heating mainly operates by convection, ceiling heating works by radiation.