We can increase our comfort while simultaneously reducing heating costs.
It is well known that the lower the temperature of the water used to heat the house by our boiler, the more economical it is. This is especially true for condensing boilers. Whether it’s an old open fire or a turbo gas boiler, caution is needed because the return water temperature to the boiler must be higher than the dew point of the flue gas. This is approximately a threshold value between 55–60 degrees Celsius. In condensing boilers, the key is that the return water temperature is as low as possible, as the condensation of the flue gas below the dew point is stronger, meaning the precipitation of water vapor from the flue gas. This precipitation, the change of state, comes with additional energy release. The lower the temperature of the water used to heat our home, and by better dissipating this heat, making the return water as low in temperature as possible, the better efficiency we can achieve in operating our condensing boiler.
Here, the heating pipe is already in the living room wall:

All of this is fine and good — however, the lower the temperature of the heating water, the more difficult it is to give off heat, as the temperature difference between the room temperature and the advancing water temperature becomes smaller. This problem can only be solved by increasing the surface area of the heating element. Beyond a certain size limit, implementing this with a radiator would be impractical. Especially considering that multi-panel radiators increasingly enhance heat dissipation through convection (i.e., by heating the air) and to a lesser extent through radiation. This is not advantageous, as heat emitted through radiation provides a more pleasant sensation even at lower temperatures.
On the other hand, if we use underfloor, wall, or ceiling heating, we can heat a larger surface area. This warm, radiant heating ensures a comfortable feeling of warmth.
If we want to live in the apartment during heating system improvements (now specifically discussing water heating), among the three surface heating methods, wall heating comes with the least dust, clutter, and inconvenience, using the following method — provided there is available wall space. And there was.
In a new construction, wall heating is implemented by piping the raw brick wall and then applying mortar in such thickness that it not only conceals the piping but also forms the required thickness above the pipes.
The walls shown in these pictures were partly plastered and had an additional layer of plasterboard attached during a renovation. Removing the plasterboard and plaster was not a feasible option due to potential dust. While theoretically it seemed promising to carve grooves in the plasterboard layer, in practice, it would also generate a lot of dust and noise. Moreover, almost 200 meters of pipe were installed on the wall, meaning an equal amount of grooves would need to be carved. Contemplating these issues, I discarded the idea. A more practical approach seemed to be an overlay, where strips of plasterboard are attached to the existing plasterboard, leaving a gap for the piping. It is a quiet and dust-free process since the cut-to-size plasterboard pieces are inserted into the apartment. True, the apartment became about 2 cm smaller, but this was bearable. 😀
Wall heating in the living room
The living room wall with plasterboard strips and piping:

I secured the plasterboard strips with adhesive polyurethane foam and temporarily fixed them with screws. Once the polyurethane foam had solidified, I removed the screws and trimmed any protruding parts of the foam that might have emerged from under the plasterboard. The plasterboard was 9.5mm thick, and the heating pipe was 8mm, so there was a comfortable fit. I applied fiberglass mesh to prevent any possible movement of the pipe. I pressurized the heating system to the 1.5-bar pressure required by the boiler, allowing the pipes to settle a bit (they creaked a little), and then filled the gaps with flexible tile adhesive.
As a mirror was mounted on this wall (it was there before), I measured and installed the two plugs in advance for mirror hanging, ensuring that there wouldn’t be any pipes behind the finished wall.
Upper layer of the living room wall with plastered top layer of plasterboard:

For the upper layer, another 9.5 millimeters (3/8 inch) layer of plasterboard was glued with flexible adhesive. It was then smoothed and painted.
I am aware that there are gypsum boards specifically designed for better heat conduction in wall heating. I used the readily available standard version and trusted that it also had sufficient heat conductivity. It worked.
Wall heating between the dining area and kitchen
Plasterboard strip installation on the wall between the kitchen and dining area:

I created 4 heating circuits on both wall sections with nearly identical lengths of 19–22 meters (20-24 yards) each.
Wall between the kitchen and dining area with piping, fiberglass mesh, and plaster:

On this wall, the upper layer is not plasterboard but stone porcelain. I fixed these with flexible tile adhesive and fiberglass mesh, also secured with flexible tile adhesive.
During the heating season, it’s a pronounced pleasure to walk by the wall, feeling the radiant heat, as if there were a peculiar-shaped ceramic stove on the wall.
The kitchen-dining area wall with ceramic tiles — with wall heating underneath:

Where does the heating water come from?
The pipes for the wall heating in the living room are hidden in the built-in furniture base of the adjacent entrance hall, distributed discreetly. The radiator pipes in the entrance hall were cut, and a T-joint was inserted to install a manual control forward and a return valve, each equipped with a Eurocone threaded 4-way mini-distributor. The branches have 8mm quick connectors.
Mini-distributors of the living room wall heating pipes concealed in the built-in furniture base of the entrance hall:

In the picture above, it’s explicitly mentioned that each of the 4 branches has a quick-connect mini-ball valve installed. However, such a photo was not taken. These valves helped with air bleeding. While air escaped effortlessly from the pipes on the other wall section when the circulating pump of the boiler started, in these 4 circuits, air got trapped in 3. The 4 small ball valves made it easy to release the trapped bubbles by individually breaking the branches, allowing the water pressure to push the air out of the thin pipes. The external diameter of these pipes is 8mm, but the internal diameter is only 6mm — just the size of the bubbles. 🙂
Accessibility is only provided for the radiator valves. The forward valve can be accessed by removing the grid cut into the furniture board, while the return valve can be reached from above with an Allen key.
Covering the mini-distributors in the entrance hall:

The mini-distributors of the dining area kitchen wall are concealed in the ceiling plasterboard enclosure. This enclosure was already in place, as on one side, the heating pipes run, and on the other side, it accommodates recessed spotlights. Similarly, the 18mm ALUPEX pipe was cut here, and by inserting two T-joints, the radiator valve and the 4-way mini-distributor pair were installed.
One might wonder why a thermostatic head or a thermoelectric valve opener wasn’t installed. In this space, the only boiler controller thermostat is present. The boiler only operates when there is a heating demand in this combined living-dining-kitchen area. Therefore, providing a separate thermostatic shut-off option doesn’t make sense.
Mini-distributors of the heating pipes on the dining area kitchen wall are hidden in the ceiling plasterboard channel:

The curtain rod in front of the terrace door is recessed into the plasterboard. This rod is secured to the plasterboard frame with 3 bracket screws. By unscrewing these 3 screws, the rod easily comes off, and access to the radiator valves is available. In reality, touching these valves only makes sense in an emergency situation, which I cannot even guess what it might be. Still, it could be useful that they are relatively easily accessible yet hidden. Actually, the bracket screws could be replaced with, say, black recessed head screws if they were bothersome — but they are not. At least, it might seem bothersome in the photo, but somehow — I don’t usually notice.
The dining area kitchen heating pipe mini-distributors are covered by the built-in curtain rod:

The entrance hall painted in turquoise
Since the living room’s lime-green wall has been repainted turquoise, the opportunity arose to give a new color to the entrance hall, previously painted red 17 years ago. Well, it also became turquoise. However, while the dark brown wall and wood elements in the living room give it a stronger character, here, the gray wood and metal parts remain gray.
The entrance hall in turquoise:

The plasterboard shelf running along the top received a rounded edge design back in the day. Now, two metal edge protection profiles have been inserted to make it square.

The floor previously had red grout matching the wall. I didn’t scrape off the red grout; I simply painted over it with turquoise dispersion wall paint. I thought we would wear it off with muddy shoes, but so far, nothing.

Wondering how the entrance hall looked in red? Check it out: HERE!
Energy savings are in focus, so I’m sharing this now, but this work was done last summer, so there’s already a year of positive experience. It has only brought benefits; there are no drawbacks.
My video about the project:
– in 6 minutes.