Dimensions of fresh-air vent
NYC code says that a vent to the outside for an enclosed gas furnace must have an area of 144 sq. inches, or 12 by 12. Does this mean the louvre in the wall must be 12 x 12, or the duct running the length of a cellar must be 12 x 12? Or that…
NYC code says that a vent to the outside for an enclosed gas furnace must have an area of 144 sq. inches, or 12 by 12. Does this mean the louvre in the wall must be 12 x 12, or the duct running the length of a cellar must be 12 x 12? Or that from the furnace room to the outside there must be a minimum of 144 sq. inches? The vent I have is 26 inches circumference (or an area of 53 sq. inches) and runs 20 linear feet. Anyone have a clue?
Could also be that the external grill is 12×12 which is not a free space of 144. If you follow the 1in/3000 btu, you’d only need about 50-60 sq ins.
Molly,
The duct for fresh air to the furnace/boiler is the same as the duct to the room. Master Plumber explained it well.
But I am as frustrated as you. Getting a straight answer is obviously not easy, even from the pros posting here, and I am confronted with a similar situation.
The answer is complex depending on the use of your basement space, whether or not your make-up or combustion air is coming exclusively from the outside or perhaps also partially from the surrounding basement space, how air-tight your basement is, the BTU ratings of your equipment, and even potentially the exhaust duct sizes you currently have. I am afraid that the NYC Fuel Code, which seems to govern this, at least for natural gas-fired equipment, is not consistnent or clear in this regard.
I did not find 144 sq. inches anywhere, but I would conclude that 1 square inch per 3000 BTU (remember to reduce available air for elbows, louvres should cover you, even if the aggregate area of the existing “duct connectors” exceeds that. NYC is just trying to cover its ass. Get the ratings of your equipment and do the math. I need to do the same tonight.
Here is the text and link, including the rules for the multple configurations, for what I found:
http://www.ci.nyc.ny.us/html/dob/downloads/pdf/fuel_code.pdf
304.6.2 One-permanent-opening method. One permanent opening, commencing within 12 inches (305 mm) of the top of the enclosure, shall be provided. The equipment shall have clearances of at least 1 inch (25 mm) from the sides and back and 6 inches (152 mm) from the front of the appliance. The opening shall directly communicate with the outdoors or through a vertical or horizontal duct to the outdoors or spaces that freely communicate with the outdoors [see Figure 304.6.2] and shall have a minimum free area of 1 square inch per 3,000 Btu/h (734 mm²/kW) of the total input rating of all equipment located in the enclosure, and not less than the sum of the areas of all vent connectors in the space.
Well, the furnace uses the air within the room, which is fed by the duct
For what it’s worth, we’re not using the same mechanical code now as when the document in that link was written.
July 1, 2008 we switched to the National Code.
Smokychimp probably knows the answer to the new requirements, but from a practical standpoint I’ll offer the following:
When a boiler runs it expels a great deal of air out of the building’s chimney.
Because you can’t have less air inside your home than outside, that air has to be replaced.
So as that air flows out the chimney, a negative pressure (not quite a vacuum, but almost) developes inside the structure which pulls air from outside in through any cracks and leaks it can find.
We call this infiltration.
Infiltration lets cold air in from outside and mixes with your pricey, warm inside air. Then all of it heads for the boiler and is sent out the chimney.
Having a controlled path for new air, very necessary for efficient combustion, to get to the boiler reduces the natural tendency for infiltration and saves you fuel money.
The Code is smart and very necessary.
Based on the building code Vicki found, I would definitely try to enlarge the boiler room to include an exterior wall. It might be as simple as removing the current boiler room door and installing 2 hr rated doors leading into the basement. It appears that if the boiler is above ground you have the option of using an adjoining room to ventilate both.
I am having trouble finding the right chapter in the online code book, but found this instead:
Under the old building code there is a NYC Building Department memo that clarifies the 144 square inch (or 1 inch per 1,000 BTU gas) calculation. It also says taking fresh air from an adjacent basement room is not allowed.
http://www.nyc.gov/html/dob/downloads/pdf/bf918.pdf
In a basement installation of a boiler, it seems that a mesh grille or holes in a metal hatch to the exterior might fit the exterior wall louver description that is allowed by the memo. Any other interpretations?
I know that furnaces would do better if there were a dedicated vent, but this “code” requirement makes no sense.
So if there’s NO furnace room enclosure, you don’t need an outside vent, but if there is, it cannot draw air from the same source? Am I getting it wrong?
Personally, if you’re not getting inspected, I’d ignore it.
Does that mean outside as in outside the house or outside the furnace room, ie a vent into the basement?
This code changed recently and I don’t want to say the wrong thing here.
Mod squad, your boiler is taking room air which is sometimes fine, but if a boiler is in a mechanical room, it needs fresh air ducted from the outside.