Madrid resident blocks communal boiler upgrade over flue plans
A Madrid flat owner demanded an approved project before allowing his building's communal boiler replacement. The flue ended up using the old chimney.
English · Original discussion in Spanish · Published
Boiler flue: rooftop or internal courtyard
The flue for a communal gas boiler cannot be solved with a pipe at ground level next to a first-floor neighbour's window. That, at least, is the position of a flat owner in Madrid who has dug in his heels over his building's boiler replacement: without a project approved by the city council, nobody is entering his home. The residents' association wants to replace the old atmospheric boiler with a new one, presumably a condensing model, and move the flue discharge to the shared internal courtyard. The problem is that this courtyard faces his window.
The regulations cited in this case — ITC-07 of the Spanish Gas Fuels Regulation (RD 919/2006) and the Spanish Technical Building Code — establish as a general rule that combustion products must be discharged through the roof. Only exceptionally, for room-sealed or fan-assisted appliances with a rated useful output of 70 kW or less, is direct discharge to a façade or ventilation courtyard permitted. In existing buildings undergoing renovation, if there is a flue suitable for the new appliance, discharge must go through the existing flue. The key, therefore, lies in the boiler's output and whether the building already has a chimney.
How powerful is the communal boiler?
A communal boiler serving 30 flats will hardly come in under 70 kW. Domestic boilers for heating and hot water typically run around 24 kW, so a centralised unit for a six-storey block with thirty flats shoots well above that threshold. That figure is what separates the cheap-and-nasty solution — a pipe at window height — from the legal obligation to take the discharge up to the roof. If it exceeds 70 kW, the installation requires a project filed with the Industry authority and the discharge must be routed vertically.
That is where the calculations in this case come in. The affected owner has already announced that he will request the rated output of the installation: if it is above 70 kW, he will demand a full project; if it is below 5 kW, a technical report. And in both cases, that the installers prove they are registered and authorised for this type of work. The paperwork is not a whim: it is what turns a botched job into a certified installation.
The real risk of combustion gases
The toxicity of the gases depends on the fuel. With natural gas, the combustion of methane produces carbon dioxide and water, and the risk is limited to a hypothetical carbon monoxide leak. With heating oil, things change: the sulphur in the fuel forms sulphur oxides which, reacting with the water in combustion, generate sulphuric acid. That acid ends up corroding the flue, and it does so at the bottom, where the gases are hottest. In other words, right where the downstairs neighbour passes by.
In this case, the boiler appears to be a condensing model, which lowers the gas temperature and, due to the difference in densities, reduces the draught. This requires sealed, well-insulated flues. Standard UNE-EN 13384-2 governs chimney sizing, and for a communal installation serving 30 homes, stainless steel grade 304 minimum is recommended, with a sealed joint and insulation to prevent condensation. The diameter, moreover, will be considerable.
The solution: the old chimney and a compensation grille
In the end, the residents' association opted to use the old chimney for the flue discharge. What they wanted to install in the first-floor neighbour's courtyard was not the flue, but an air intake grille to compensate for the overpressure in the sealed boiler room. On the other side of the courtyard there is a forced air intake: if it brings in 100 units of air and the boiler needs 80, the remaining 20 have to go somewhere. That somewhere was the grille next to the window.
The project has been filed with the Industry authority and, once completed, will be certified. Without that certification there is no grant for the boiler. The affected owner has calmed down, but the lesson stands: in a renovation of this kind, a neighbour who stands firm and demands paperwork can turn a botched job into a legal installation. The question that remains is how many buildings are doing the opposite: installing without a project, without certification and with nobody checking.
The flue for a communal gas boiler cannot be solved with a pipe at ground level next to a first-floor neighbour's window. That, at least, is the position of a flat owner in Madrid who has dug in his heels over his building's boiler replacement: without a project approved by the city council, nobody is entering his home. The residents' association wants to replace the old atmospheric boiler with a new one, presumably a condensing model, and move the flue discharge to the shared internal courtyard. The problem is that this courtyard faces his window.
The regulations cited in this case — ITC-07 of the Spanish Gas Fuels Regulation (RD 919/2006) and the Spanish Technical Building Code — establish as a general rule that combustion products must be discharged through the roof. Only exceptionally, for room-sealed or fan-assisted appliances with a rated useful output of 70 kW or less, is direct discharge to a façade or ventilation courtyard permitted. In existing buildings undergoing renovation, if there is a flue suitable for the new appliance, discharge must go through the existing flue. The key, therefore, lies in the boiler's output and whether the building already has a chimney.
How powerful is the communal boiler?
A communal boiler serving 30 flats will hardly come in under 70 kW. Domestic boilers for heating and hot water typically run around 24 kW, so a centralised unit for a six-storey block with thirty flats shoots well above that threshold. That figure is what separates the cheap-and-nasty solution — a pipe at window height — from the legal obligation to take the discharge up to the roof. If it exceeds 70 kW, the installation requires a project filed with the Industry authority and the discharge must be routed vertically.
That is where the calculations in this case come in. The affected owner has already announced that he will request the rated output of the installation: if it is above 70 kW, he will demand a full project; if it is below 5 kW, a technical report. And in both cases, that the installers prove they are registered and authorised for this type of work. The paperwork is not a whim: it is what turns a botched job into a certified installation.
The real risk of combustion gases
The toxicity of the gases depends on the fuel. With natural gas, the combustion of methane produces carbon dioxide and water, and the risk is limited to a hypothetical carbon monoxide leak. With heating oil, things change: the sulphur in the fuel forms sulphur oxides which, reacting with the water in combustion, generate sulphuric acid. That acid ends up corroding the flue, and it does so at the bottom, where the gases are hottest. In other words, right where the downstairs neighbour passes by.
In this case, the boiler appears to be a condensing model, which lowers the gas temperature and, due to the difference in densities, reduces the draught. This requires sealed, well-insulated flues. Standard UNE-EN 13384-2 governs chimney sizing, and for a communal installation serving 30 homes, stainless steel grade 304 minimum is recommended, with a sealed joint and insulation to prevent condensation. The diameter, moreover, will be considerable.
The solution: the old chimney and a compensation grille
In the end, the residents' association opted to use the old chimney for the flue discharge. What they wanted to install in the first-floor neighbour's courtyard was not the flue, but an air intake grille to compensate for the overpressure in the sealed boiler room. On the other side of the courtyard there is a forced air intake: if it brings in 100 units of air and the boiler needs 80, the remaining 20 have to go somewhere. That somewhere was the grille next to the window.
The project has been filed with the Industry authority and, once completed, will be certified. Without that certification there is no grant for the boiler. The affected owner has calmed down, but the lesson stands: in a renovation of this kind, a neighbour who stands firm and demands paperwork can turn a botched job into a legal installation. The question that remains is how many buildings are doing the opposite: installing without a project, without certification and with nobody checking.
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Summary of a discussion on Burbuja.info - Foro de economía, actualidad y política., translated from Spanish and reviewed before publication. Read the full discussion (27 replies).
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