Two basic principles:
- Produce the energy with highly efficient equipment!
- Don’t let the generated energy go to waste!
The transformation of the living room:
As much as it’s a priority to steer the population away from gas consumption, let’s admit that in an apartment block without district heating (central heating), heating and hot water can primarily be provided by gas, and secondarily by electricity. If many people switched from gas to electric heating, it would also cause problems, as many apartment block infrastructure and stairwell electrical systems are not designed for mass electric heating. Therefore, the possibility of massively increasing the amperage of apartments would also face limitations. Naturally, heating with air conditioning could be an alternative to direct electric heating, as it represents roughly a quarter of the electrical load, but many people do not like the warm air blowing, and the numerous outdoor units attached to the façades are already a terrible sight. For this reason, I believe gas will remain predominant to a greater extent.
But what can we do to keep our gas bill low?
Anyone looking to replace their convectors or old, inefficient boiler with a condensing boiler will face challenges. The necessity of chimney lining, coordination with the residents above and below, obtaining permits, chimney sweep paths, and other details! If this is not feasible, then installing a condensing convector boiler may seem more promising in light of the previous obstacles, but I like challenges, so I wanted a boiler. 🙂
Things that had to go:
It is not only important to produce energy efficiently but also how our system delivers it. The efficiency of condensing boilers is higher at lower heating temperatures. This requires larger heat exchange surfaces than before. This can be achieved with larger radiators, as there are even 3-layer radiators available. This is not ideal, as it is also important to know that for radiant heating, a few degrees lower air temperature is sufficient for the same warmth feeling. It is easy to understand that the more layers a radiator has, the smaller the proportion of heat it radiates. In a 3-layer radiator, only one side out of six will radiate towards us, while the rest can only improve our thermal comfort by heating the air.
Therefore, it is advisable to think in terms of radiant heating. Underfloor heating is the most straightforward solution. Before someone thinks of a 10 cm thick concrete layer, there are thin-layer solutions. Based on the experience described below, in a sufficiently insulated apartment, only underfloor heating is entirely adequate, with no need for additional radiators or wall heating.
Naturally, underfloor heating can only be used for heating. If we want to cool as well, we need to set up ceiling or wall heating-cooling systems. However, this cannot be done with a gas boiler because cooling requires a heat pump. Yes, heat pumps are the future, and ideally, there would be a common heat pump on top of every building. Wake up! – I want to write about what we can do individually, and it is not a quiet reality if everyone had a heat pump buzzing on their balcony (I know there is a night silent mode, but not everyone has a balcony), although quieter solutions are expected in the future – so shall we wait? – but now – now is now.
Regarding the specific renovation:
DIY movement: Convector removal (3 wall-mounted and 1 bathroom chimney convector), and the open-flame instantaneous water heater. Two windows were replaced with triple-glazed windows with shutters. The balcony door and adjacent window were restored to the original floor-to-ceiling window solution from the 1950s, with double-glazed plastic windows, except for one balcony door, the other three parts became fixed glass. When gas convectors replaced the tile stoves, one door leaf was bricked up to the threshold, and the convector was placed there. The door leaf was turned into a window. This was reverted.
If you think the noise from Budapest comes through the old window, and everything will be solved with triple glazing, but you leave the convector under the window, you’ll only achieve partial noise reduction. The convector acts as a speaker. Once the convectors were removed and the parapet openings sealed, the noise reduction became even more pronounced. For the thermal insulation of the boundary walls, a steel frame for plasterboard was prepared, filled with self-supporting fiberglass. Rock wool is denser and better at noise reduction, but it irritates me, so I can’t work with it. Heat-reflective foil was glued to the frame, and two layers of plasterboard were added. This not only provided thermal insulation but also further noise reduction.
The removal of partition walls and the reconfiguration of the space (complete renovation) will be covered in another article.
Below, I will describe a 24kW combi condensing boiler system with underfloor heating, window replacement, 10 cm thick internal mineral wool insulation on the boundary walls and ceiling, and polystyrene insulation under the underfloor heating.
Many are shocked by internal insulation and consider it a terrible idea. Yes, it can be done poorly or well.
If the condominium later decides to install external thermal insulation, this apartment will still have an additional 10 cm. The 12 cm lost from the useful floor area due to the internal thickening of the boundary walls is somewhat regained by removing the space occupied by the convectors.
Thermal Insulation
Internal Wall Insulation
The main problem with internal insulation is that the moisture generated in the apartment wants to escape through the walls. If we don’t prevent it, condensation will occur under the insulation on the wall, leading to mold. If the moisture continues to migrate outwards, the frost line (due to the internal insulation) moves closer to the inner wall in winter, causing damage from freezing. On this latter point, if we heat poorly due to high utility costs, the freezing boundary will shift towards the inner wall, causing the same damage. A frozen wet wall doesn’t care whether it froze due to lack of heating or internal insulation. The key is to prevent moisture entry, so before insulation, use vapor barrier foil under the plasterboard. Yes, there are methods without vapor barrier foil, such as the Xella Multipor product line, but that’s different. Leave those 5mm polystyrene or 12mm wool and other fiberboards aside. I understand they eliminate the feeling of cold radiation or reduce noise, but I wanted real thermal insulation.
Another criticism of internal insulation is that even with vapor barriers, thermal bridging is inevitable. To counter this, internal insulation is typically turned onto the boundary wall for 60-100cm on the side walls, ceiling, and floor. A downside of internal insulation can be that the walls take on a lightweight structural character. Despite the mass of the wall structure, it acts like a lightweight structure inwardly. Thus, the internal thermal mass decreases, meaning the heat inertia of the brick wall is less noticeable. The advantage of a large wall mass is that it warms up more slowly in summer and cools down more slowly once heated. The thermal mass of an internally insulated wall does not, or barely, impact the apartment. Naturally, the downside of a large wall mass is that it needs to be heated when warming the apartment and cooled when cooling. Conversely, the advantage of an internally insulated wall is the opposite: it heats up faster because the cold wall does not conduct heat away, meaning you don’t need to heat the wall, and it’s also easier to cool down. The general counter-argument is that in summer, you need to cool more because the warm summer air is immediately felt inside, whereas, with a brick wall, the summer heat must first heat the wall, meaning the cooler wall absorbs heat from the apartment until it warms up.
Ceiling Insulation:
The images show that the ceiling and floor received complete insulation due to underfloor heating, so there is no thermal bridging upwards or downwards. The ceiling did not receive a vapor barrier, given that the floor above is also an apartment.
Insulation for Underfloor Heating:
However, there was no turning of insulation towards the walls, except from the staircase, which must be considered as an exterior space due to its single-pane glazing and lack of heating.
Thus, the risk of thermal bridging for the walls remains. The walls only received a decorative one-person gypsum board cladding attached with PUR foam. By decorative, I mean the edges of the 60cm x 260cm gypsum boards are rounded without thinning, creating a built-in closet or mobile wall appearance when placed side by side. I think the repeated vertical division looks good. It was an easier solution than scraping off the plaster, which was ready for replacement due to numerous mini-cracks from 60 years of traffic.
The Decorative Effect of One-Person Gypsum Board without Putty:
At the same time, the reinforced concrete consoles received thick polystyrene insulation. The house, built in the 1950s, has these walls mostly removable despite being cross-walled, with double partition brick walls, making it easy to open up with neighbors. Thus, the reinforced concrete consoles run along the top of every wall in a transverse direction. These received insulation.
This insulation is a unique decoration: I scratched the surface of the polystyrene with a coarse, large-toothed wood saw blade, glued them together in an L shape, attached them to the consoles with PUR foam, and painted them with dispersive wall paint. It looks like hand-carved limestone, giving a rustic and eclectic touch to the minimalism.
The Unique Polystyrene Covering of Reinforced Concrete Consoles:
Moreover, from an energy perspective, it’s important to note that the lighting is LED, the stove is induction instead of gas, and a cooling-heating mobile air conditioner was placed on the balcony, along with a backup electric water heater in the bathroom. These two were very useful, as it took 11 months from the installation of the boiler and the lining of the chimney before gas heating could start. (This is another story, but it shows that planning is always essential in energy matters.) Naturally, an extractor hood was installed, which vents above the plasterboard insulated false ceiling. Additionally, due to well-sealing windows, hygroscopic air vents are indispensable. Therefore, managing indoor humidity is essential in a well-insulated apartment.Yes, in the West, recuperators are almost standard; however, I still neglect them in 57 m².
Window Replacement
I have previously experienced that the promised two-month production time for custom-sized windows often extends to four months. Therefore, the basic setup was to try to fit ready-made standard-sized windows into the old window spaces. A balcony door and three fixed windows with a coupling element fit perfectly into the original three-wing balcony door space, with the old wooden frame remaining in place. However, it isn’t visible due to the plasterboard and insulation.
Two windows could only be replaced with smaller standard-sized triple-glazed ready-made plastic windows, but it was successful. These two windows definitely needed shutters. Externally installed shutter boxes always intrude into the window, and if we’re lucky, the guiding rails don’t obstruct the view. To avoid this, frame extensions are used for custom-made windows on both sides, especially on the strap side and top, so the box doesn’t hang into the window. For standard-sized pre-manufactured windows, I couldn’t get frame extensions, so the plastic window frames were extended with wood. It sounds horrific at first, but the shutter box and guiding rail perfectly cover it from the street side, and internally, the insulation and plasterboarding cover it. For convenient strap handling, a strip of plastic paneling was placed inside next to each plastic window.
Entrance door upgrade: insulated panels covered with laminate flooring:
The entrance door remained with its security lock, but the panel layers were brought flush with the frame using polystyrene boards and covered with laminate flooring on both sides. (You can do this if you dislike plastic entrance doors, as the beautiful and affordable ones come in fixed sizes, which aren’t suitable, and the beautiful custom-sized ones are deemed unaffordable – so it became nice and cheap – DIY, yet insulated.)
Condensing Boiler
The boiler was installed on a wall behind which is the chimney that other residents relinquished in writing. A professional handled the chimney lining, documentation, gas planning, new gas pipe installation, chimney sweep approval, and gas-MEO. The water side of the boiler, including the manifolds, room thermostats, underfloor heating piping, insulation under the pipes, and concreting, was a DIY project.
Combination condensing boiler and manifold hidden in a built-in cabinet:
The boiler is a 24kW Ariston Genus One combi gas boiler, providing domestic hot water. This choice was made due to its modulation range of 10-100%, meaning it can heat with just one-tenth of its capacity. Compared to a boiler with a 50-100% modulation range, it can run quietly and continuously at low power during transitional periods. A boiler with a higher minimum modulation turns on and off more frequently and is inevitably louder due to the higher minimum power. The underfloor heating operates directly, without a heat exchanger, so the boiler’s single pump circulates water for the entire system. This results in less noise and lower electricity consumption. The boiler was set up with a delayed start. When a thermostat activates the boiler and starts heating its associated thermo-valve, the boiler starts after a few minutes delay to allow the thermo-valve to open and avoid starting the heating in by-pass mode.
The underfloor heating was laid using 16mm five-layer alupex pipes, placed between the studs of special insulating boards, in a double spiral pattern. Five circuits were created, each ranging between 55 and 68 meters in length. The two smaller rooms each have their own circuit with individual thermostats, the living room has two circuits with a single thermostat, and the kitchen and bathroom share the fifth circuit, with the thermostat located in the kitchen. The bathroom’s underfloor heating pipes are laid twice as densely, so this setup does not pose any problems. The bathroom is tiled with porcelain stoneware, while all other rooms have laminate flooring.
There’s no need to worry about the thermal insulation properties of laminate flooring. While it was originally wood, it contains so much adhesive and is pressed so densely that it can practically be considered a thermal conductor. However, the choice of underlay for the flooring is crucial. Without underfloor heating, a few millimeters thick bubble wrap or foam underlay is typically used. Since these materials contain bubbles and air is a good insulator, the industry invented perforated foam underlays for underfloor heating. They might be good, but considering the ratio of holes to non-perforated insulating parts, I found them to be unfavorable and expensive. Seeking a better solution, I used asphalt paper under the laminate. While paper is also an insulator, this is a dense and heavy paper, so I trusted its thermal conductivity more than the perforated foam. It worked well.
To facilitate heat emission from the floor, all furniture has legs. The kitchen cabinets and large sliding door wardrobes also stand on legs. This setup proved advantageous for cleaning as well.
Actual Gas Consumption
According to the current regulations, the annual limit for discounted gas prices is 1729 m³, with a monthly limit of 144 m³.
This apartment is 57 m² according to the property deed, typically housing three people. The interior of the exterior walls and the ceiling received 10 cm of mineral wool insulation, with one layer of plasterboard on the ceiling and two layers on the walls, along with a vapor barrier thermal reflective foil under the plasterboard. Underfloor heating was installed in a thin-layer concrete bed with a studded polystyrene insulation system board, supplemented with an additional 2 cm of polystyrene insulation boards underneath. The plastic windows have 2 or 3 layers of thermal insulating glass. The entrance door is the old one, with the panels filled with 2×2 cm thick polystyrene. A condensing boiler provides both heating and domestic hot water. The following graph shows the monthly consumption of this boiler over the past three full years.
Monthly gas consumption for the past three full years, in cubic meters:
The average annual consumption is 532 m³, which is only 31% of the annual discounted limit. (2019: 564 m³/year, 2020: 508 m³/year, 2021: 523 m³/year.)
The highest monthly consumption was in January 2020, at 120 m³/month.
This consumption keeps the apartment at 21-23°C, allowing us to walk around in socks or even barefoot.
The low-utility-cost renovated apartment, completed:
Before and After
A summary of the apartment renovation in just 2 minutes.
This insulation method has proven effective not just in this apartment over the past four years, but in others I’ve worked on for seven and even thirteen years—no signs of problems.
Read up and do it yourself!
Complete Apartment Renovation – 9 Months in 30 Minutes – From 2 Rooms to 3 Rooms