What is the name of this silver vent attachment thing at the bottom of the picture?

It is attached to the side of our gas furnace. The black part is an insulated air duct which goes to a vent outside. The furnace is in the basement of our house. We have cold winter climate in Canada. The vent seems to pour in cold air from outside though.

Furnace Photo

2 Answers 2


That's your fresh air supply for your gas appliances. Newer high efficiency appliances are directly vented so you don't have the cold air dumping directly into your home. But for older style gas appliances, you have to have a fresh air supply to your utility room for combustion.

  • 2
    THAT much fresh air supply is surely overkill. I wonder if its connected to a powered damper? Looks like a builders quick fix to (over)satisfy a code requirement. I'll take a look at my IRC..
    – HerrBag
    Commented Aug 21, 2013 at 15:45
  • 5" duct? I think they used the same on my place. Builders were lazy before everything went high efficiency. Admittedly mine has an adjustable vent on the end of the intake and I just close it since the utility room has a louvered door.
    – BMitch
    Commented Aug 21, 2013 at 15:50

@bmitch has the correct answer, a combustion air supply

If you are governed by the IRC (International Residential Code), you might look to total volume or ACH to see if the air inlet is over engineered. You might also discuss if an ERV (energy recovery ventilator) could supply combustion air in a more energy efficient manner, with your HVAC provider.

IRC Section 24 addresses gas appliances and G2407.5 discusses indoor combustion air:

G2407.1 (304.1) General. Air for combustion, ventilation and dilution of flue gases for appliances installed in buildings shall be provided by application of one of the methods prescribed in Sections G2407.5 through G2407.9. Where the requirements of Section G2407.5 are not met, outdoor air shall be introduced in accordance with one of the methods prescribed in Sections G2407.6 through G2407.9. Direct-vent appliances, gas appliances of other than natural draft design and vented gas appliances other than Category I shall be provided with combustion, ventilation and dilution air in accordance with the appliance manufacturer’s instructions.

G2407.5 (304.5) Indoor combustion air. The required volume of indoor air shall be determined in accordance with Section G2407.5.1 or G2407.5.2, except that where the air infiltration rate is known to be less than 0.40 air changes per hour (ACH), Section G2407.5.2 shall be used. The total required volume shall be the sum of the required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section G2407.5.3, are considered to be part of the required volume.

G2407.5.1 (304.5.1) Standard method. The minimum required volume shall be 50 cubic feet per 1,000 Btu/h (4.8 m3/kW).

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