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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 / condensing furnaces use either single or double PVC pipe (2″ and larger).
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:
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.
Combustion 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.
One 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.
Example:
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
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.”
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
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