Chicago Condo Inspection & Combustion Air Requirements

This part will cover Chicago condo inspection combustion air requirements for the gas furnace and water heater installed inside your condo closet / utility room.


This part will cover Chicago condo inspection combustion air requirements for the gas furnace and water heater installed inside your condo closet / utility room (not in the building common areas) – this is an extremely important section and you may need measuring tape.

All gas burning appliances require oxygen for a proper, complete and safe combustion process / without creating measurable and dangerous amounts of  Carbon Monoxide.

Because Carbon Monoxide has no taste, smell or color you must have a CO detector installed in your condo to alert you about any unsafe levels (check Chicago smoke and Carbon Monoxide detector requirements).

First we’re going to check if gas furnace and / or gas water heater installed in your condo require combustion air from within your apartment. In case you have two or three appliances installed in one room / closet, and only one of them requires combustion air, the minimum rules (or whatever the actual appliance requirements are) would have to be applied to this area anyway.

High efficiency gas furnace combustion air

High efficiency / condensing furnaces use either single or double PVC pipe (2″ and larger).

  1. If you have only one PVC pipe coming out of your furnace enclosure and penetrating room wall or ceiling, it is used for ventilation purposes only and this furnace requires air from within your apartment for combustion.
  2. If you have 2 PVC pipes coming out of your furnace enclosure and both of them continue through the furnace closet wall or ceiling, this furnace uses outside fresh air for combustion. The area where this appliance is installed (if single or all appliances the same type / using air from exterior) does not require any additional combustion air supplying ports.

This type of an appliance can be installed in your closet behind the air tight doors – just look-up the installation manual for minimum distances from surrounding walls and doors.

There might be also 2 pipes coming out of the furnace enclosure but one terminating inside the furnace closet / room (usually very short), and second continuing to building exterior – this appliance is like #1 / single pipe.

Regular efficiency furnace using metal vent pipe / regular chimney

The same combination as with PVC pipes but two metal pipes system (one for venting and one for combustion air) are very rare and I don’t think you’re going to find such furnace in your new Chicago condo (as a brand new installation of course /regular efficiency and sealed combustion chamber furnaces were common a little while ago).

If by any chance your condo has a brand new furnace with 2 metal pipes or exhaust metal and PVC air supply – this doesn’t require combustion air from interior.

Most common installation of a 80+ efficiency furnace:

  • Furnace with a single metal (vent) pipe – it requires combustion air supply from within the condo

Gas water heaters combustion air

There are two types of water heaters commonly installed in Chicago condo units:

1. Conventional tank water heaters with natural draft (metal vent pipe) and induced draft / power vent (PVC pipe). 100% of the installed tank gas water heaters in Chicago condos (whatever I had a chance to inspect) use combustion air from within the apartment.

Although, there are high efficiency tank type water heaters using outside air sources for combustion (PVC exhaust and air supply), they are expensive and I’ve never seen one installed in Chicago condos.

2. Tankless type water heaters – to determine where is it taking combustion air from, use the appliance manual because some models use a concentric pipe that looks like a single but it is actually pipe within a pipe. So depending on the installed model – it may or may not require interior combustion air.

This section below explains one of the most common installations.
If you have any other combination of air supplying /combustion air vents – let me know your total appliance BTU’s, send me a picture of this section of your condo with detailed description.

How much combustion air your condo utility / furnace closet requires

Chicago condo fuel burning appliances - furnace BTU rating labelChicago condo fuel burning appliances - water heater BTU rating labelCombustion air requirements are based on the BTU rating of your appliances (you can find BTU’s on manufacturer name plate attached to the appliance). However, there’s a minimum required combustion air supplying net free vent area and specific location which must be maintained.

  • If your condo furnace and / or water heater installed in a closet / utility room require combustion air from interior of the apartment, the room they are located in must have a minimum of two openings / vents that will supply that air.

Single combustion air port on the furnace closet door or wall is not sufficient and installed too high. The minimum requirement is one within 12 inches from the floor and second within 12 inches from the ceilingCondo inspection combustion air - no sufficient combustion-air vents within the furnace closetCondo inspection - furnace combustion air and air return through the same louver doorsOne interior combustion air vent must be located within 12” from the floor, second 12” from the ceiling of the appliance closet / utility room.

Each combustion air supplying vent must have at least 100 sq inches of a net free air flow area, and extra 1sq inch per 1000 BTU if 100 sq inches is not enough.

Because the combustion vents are usually covered with metal or wood grills with louvers the actual FREE air flow area is smaller than the louvered section of the vent.

  • Metal louvered combustion air vent cover provides 60%-75% of its net free area (10″x10″ louvered opening would only provide 60-75 sq inches)
  • Wood louvered combustion air vent cover provides  only 20%-25%

The furnace 100 000 BTU rating + water heater  40 000 BTU rating = 140 000 BTU Size of each of the two interior openings – 140000 BTU / 1000 = 140 sq inches of a net free air flow area

Click “combustion air” for calculations example.

For clothes dryers makeup air check Chicago condo laundry inspection section. If installed together with a furnace or water heater, just add  BTU’s rating to the example above.

Full louver doors as the only source of combustion air

As far as the amount of air that can pass through the door (in most cases) it would be acceptable and approved by the city building inspector. The questionable situation would be with an 8’ (or higher ceiling) and a regular size door where the top section of the louver door is not within 12″ from the furnace / water heater closet ceiling.

Per code, that additional vent is still required, and if your condo utility room / closet doesn’t have it, contact city of Chicago building department for clarification because I was once told (by the Chicago building inspector) that it was OK.

Also, according to Chicago Peoples Gas Construction Guide for Gas Usage – “In confined space situations, where there may be vertical and/or horizontal space limitations, it is permissible for the two permanent openings to about one another.”

  • Combustion air ports for the furnace – water heater closet (including louver doors) must not open into the sleeping area, no fuel burning appliances that require interior air for combustion can be installed in bedrooms or bathrooms.

One exception are vented and ventless fireplaces that require combustion air from interior, but this is a different story.

So, how is your Chicago new condo gas furnace and water heater combustion air?

For more inspection manuals go back to Chicago Condo Inspection Manual.

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