Thread: retired safety engineer (ETL)

Does the Chicago code for energy efficient furnaces allow a 2 inch vent pipe (uses air inside the house for combustion) and if so, are there requirements for specific locations for exiting the premises?

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Whether a 2" or 3" vent pipe is allowed is specified by the manufacturer in the installation instructions. There are typically 1-3 pages outlining pipe size, length, number of elbows, etc in the install manual. Pipe size is based on BTU size of the unit.
Typically, and this is a generality so nobody bite my head off, up to 90K BTU is usually 2". 100K and over is typically 3". You can go to most manufacturer websites, type in the model number and a pdf will come up with all the necessary info about the unit and installation.
As far as where the vent exits there are rules. These rules specifically came about because of complaints by residents. Too many installers were venting the units into gangways across from the neighbors windows. Don't think I need to explain that further.
If we are talking about typical City housing, 25' lot, 3' gangway between houses, etc ... it is technically possible to vent out the side. However, in order to be compliant distances from doors and windows it is mostly NOT possible to vent into gangways any longer. There's usually one of your own or a neighbors window too close to make it feasible. This is a good thing. Even if it is a PIA for installers or some homeowners.
For the most part, the City wants units vented out the roof, at the back or front to avoid problems. Most good installers have adapted to the change by now and should know better than to vent into a gangway if that is your concern.
If you have a house in a less dense area of the City with wider lots, then yes it is possible to vent out the side if clearances can be met.
Hope that helps.