ᐅ Do radiators always need to be installed under windows in new constructions?

I always wonder why wood as a fuel is being phased out. Apparently, our current coalition government plans to gradually eliminate this type of heating (wood stove, tiled stove, pellet heating) in single-family homes over the coming years.

As far as I know, wood is considered climate-neutral because the CO2 emissions from burning it are balanced by the CO2 absorption of a tree during its lifetime.

In contrast, some politicians promote nuclear energy as environmentally friendly, and this view is quite widespread. However, most people can probably understand that nuclear waste (e.g., plutonium) is not exactly green. Not to mention the risks of power plant accidents—think Fukushima, Chernobyl, wartime events, power outages... Just one major disaster can cause a crisis lasting decades, leaving regions uninhabitable for centuries. In my opinion, nuclear power plants are not environmentally friendly but are an absolute catastrophe.

Sorry if this only partly fits here, but I wanted to mention it in relation to biomass power plants as well.

Bardamu schrieb:

I always wonder why people are moving away from wood as a fuel source.

Sorry, this only somewhat fits here, but also regarding biomass power plants.

This doesn’t really fit in this thread, but I’ll try to answer your question anyway. ;-)

Bardamu schrieb:

As far as I know, wood is carbon neutral because the CO2 emitted during combustion is the same amount as the CO2 absorbed by a tree during its lifetime.

That is also true for coal, oil, and gas, just like for wood. Unfortunately, with all of these fuels it’s not possible to regenerate them as quickly—whether industrially or naturally—as they are consumed. Wood regrows faster than the others mentioned, but the problem remains the same.

Bardamu schrieb:

Apparently, our current coalition government wants to phase out this type of heating (wood stove, tiled stove, pellet heater) in single-family homes over the years.

Yes, and that makes sense. Besides CO2, these heating methods emit a significant amount of fine particulate matter.

And we have no further potential for expanding timber production in Germany. The dry summers are already destroying more than what grows back. Overexploitation in the east is not a valid solution to any crisis.

On the contrary: the amount of biomass grown solely for energy production urgently needs to be reduced if we want to have enough food in the future. (The alternative could be giving up meat, but God forbid any politician should tackle that!)

Pinkiponk schrieb:

When I see your beautiful solution, I also prefer to have radiators. Now I have to ask the question that has been on my mind for a while: Did you design the interior yourselves, or did an interior designer do it? And if you did it all yourselves, where and how did you gain the experience, or were you simply born with excellent taste?

@Pinkiponk We furnished everything ourselves. Honestly, nothing special at all... many of the pieces have been with us for 20 to 30 years. Most of them are made of wood and leather, so we wanted to keep them. The real experience is probably this: don’t overload spaces with knick-knacks, avoid creating dirty corners, use plenty of (light) wood, not too many plants but care for the ones you have lovingly, don’t squeeze furniture into corners, use bright, warm lighting, and curtains also add coziness. A no-go for me are, for example, colorful pots, colorful towels in the bathroom (which I also rarely like), spices, kitchen appliances, etc. left out on the kitchen table... the same applies in the bathroom, where only the soap is left out—everything else is stored in cabinets. Wobbly plants, overflowing shoe cabinets, and clothes racks in the visible area... oh, actually, everyone knows that. If you then edit the photos a little (usually brighten them a bit)... you have a beautiful home.

Steffi33 schrieb:

@Pinkiponk We arranged everything ourselves. Honestly... nothing really special... many of the furniture pieces we’ve had for 20 to 30 years. Most of them are made of wood and leather, so we wanted to keep them. The main lessons we learned are: don’t overload with knickknacks, avoid dirty corners, use plenty of (light-colored) wood, not too many plants but care for those you do have lovingly, don’t squeeze furniture into corners, use bright, warm lighting, and curtains add coziness. For me, a no-go are colorful plant pots and I’m also reluctant to use brightly colored towels in the bathroom. Spices, kitchen appliances, etc., should not be left on the kitchen counter—same for the bathroom, where only soap is left out; everything else stays in the cupboard. Worn-out plants, overcrowded shoe cabinets, and clothes racks in sight—all of that is best avoided. Well... actually, everyone probably knows this. If you then edit the photos a little (usually just brighten them up somewhat), you end up with a beautiful home.

Your skills and sense of aesthetics go far beyond what you described, but I understand; you either have it or you don’t.

Bardamu schrieb:

Radiators are installed below windows because, as someone else already mentioned, windows are thermal bridges in the room.
Since the "cold" air coming through the windows falls downwards, it is guided through the top grilles of the radiator, warmed there, and then exits at the bottom as warm air, which rises again in the room.

No offense intended, just to prevent this statement from being repeated incorrectly by others: No.

1. Radiators have always been, and still are, installed somewhere on exterior walls, with exceptions being rare. This is because heat loss through transmission naturally occurs at the building’s outer envelope, and the temperature at radiators mounted on interior walls would be lower. This would lead to drafts, condensation on cold walls, and other issues. In new buildings with highly insulated exterior walls, this is less critical but still beneficial. Underfloor heating avoids these issues by providing an even heat distribution throughout the room, working better the higher the insulation level of the exterior envelope.

2. Windows are not thermal bridges (nor are they "cold bridges"). Thermal bridges are something different. For example, geometric thermal bridges occur at building corners, or construction-related thermal bridges appear at junctions between interior walls and roof or walls, etc.
Windows are simply components that typically (at the same energy performance level) have a higher U-value than the opaque exterior wall. This results in higher heat loss and a lower internal surface temperature at the window. In older windows (older than 1994), the U-value was so high that the indoor air near the window cooled significantly and, due to the higher density of the cold air, it effectively "fell" downward. It is not the case that large amounts of cold air enter there, except if you have a (poor) trickle ventilator in the window rebate or very old, drafty windows and strong wind outside.

3. Air inside radiators does not “fall” from top to bottom and warm up in between.
Convection radiators use the chimney effect for heat distribution, which occurs when the relatively cooler air near the floor is warmed in the gaps within the radiator, expands, and rises due to lower density (like a hot air balloon). The resulting lower pressure at the bottom intake of the radiator pulls in more air from below → natural convection on hot surfaces with a chimney effect.

When radiators are placed under windows, the effect of the cooling, sinking air at the windows is counteracted by the warm air rising from the radiators, resulting in—tada—no drafts, no cold surfaces, but dry windows due to the warm air flowing along the glass, and a more even temperature distribution in the room.

With newer windows, heat losses are significantly lower (less than one-third of the “old” windows). Because of this, this effect hardly occurs anymore, and underfloor heating can be used without limitations, allowing radiators to be installed elsewhere.

Typical temperatures of underfloor heating in new buildings are around 30–35°C (86–95°F), which cannot be reached with conventional radiators. Convection radiators require a temperature difference to room air of about 15–20°C (27–36°F) to utilize the chimney effect; below that, they mainly emit heat via surface radiation. To compensate for the lower temperatures and still provide sufficient heat through convection, radiators would need to be significantly oversized.
Therefore, well-designed systems typically require about 45°C (113°F) supply temperature and 35°C (95°F) return temperature. Alternatively, radiators can be actively ventilated, similar to air-to-air heat pumps—with the same reductions in comfort. But this way, radiator circuit temperatures below 40°C (104°F) can be achieved even without underfloor heating.