Derogation for gas heater emissions

After having the gas boiler replaced in my apartment, I was told by the installer that the set-up no longer meets environmental standards. The flue sends the emissions directly into a main street in Ixelles. They said that you can ask for a derogation (exemption) from the Commune ("Service Urbanisme"). Otherwise, a chimney must be installed on outside of the building. By chance, does anyone of experience of asking for this exemption, and what was the response? (If it is likely to be in the negative, I will save myself the trouble of asking.)