The building I rent was built in 1958. It has Lennox Furnace of unknown age that certainly is out of any maintenance and so produces unburned gas odor. Gas Company provides only visual (Philippine or Hispanic) observation, nothing else. They are blue blooded - let entrepreneurs repair. And they do it, like they can. So we have non-maintained for years apartments, but excessive amateurs to repair everything. I sent a request to the company headquarters address and attach pictures with ask to recognize their Lennox year of manufacturing. The headquarters is failed with response. Please response me at email: >E-mail Removed< and I attach you those pictures again. I need to resolve this situation. You are required just recognize the year of manufacturing and provide the requirements for maintenance or terms of replace. Thanks.

Age makes no difference it is condition that counts. A heat exchanger test is in order for older units and the rest is up to your qualified service people. If you do get a new style furnace there is probably no one around that will have enough training to fix it.