# Natural Ventilation through a Mechanically Ventilated Space?



## Mech (Jul 7, 2015)

2009 IMC (& IBC)

Warehouse building is supplied with outside air via natural gas direct fired make-up air units.  The amount of OA provided exceeds the code requirement by about 2400 cfm.

The internal 340 sq ft shipping office has one door, which opens into the warehouse, and the designer's plan is to utilize "natural ventilation" (airflow through the man door) from the mechanically ventilated warehouse, not the outside.  The door opening exceeds 4% of the office floor area (area to be ventilated.)

Would you allow this?

Would you allow this under Section 105.2 Alternative materials, methods, equipment, and appliances?

*402.1 Natural ventilation.* _Natural ventilation_  of an occupied space shall be through windows, doors, louvers or other  openings to the outdoors. The operating mechanism for such openings  shall be provided with ready access so that the openings are readily  controllable by the building occupants.   

*402.2 Ventilation area required.** The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated. * 

*105.2 Alternative materials, methods, equipment and appliances.* *The provisions of this code are not intended to prevent the  installation of any material or to prohibit any method of construction  not specifically prescribed by this code, provided that any such  alternative has been **approved**. An alternative material or method of construction shall be **approved**  where the code official finds that the proposed design is satisfactory  and complies with the intent of the provisions of this code, and that  the material, method or work offered is, for the purpose intended, at  least the equivalent of that prescribed in this code in quality,  strength, effectiveness, fire resistance, durability and safety.*

*Thanks in advance.*


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## mtlogcabin (Jul 7, 2015)

> *402.1 Natural ventilation. **Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors.** The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants.*


*I believe the office complies*

*However*





> *Warehouse building is supplied with outside air via natural gas direct fired make-up air units.*


*This sounds like mechanical ventilation tied to a heating system. Is there natural ventilation for the warehouse during the summer when the heat is not needed?*


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## Mech (Jul 7, 2015)

The designer said outside air exchanges will be provided while the building is occupied, so I take that to be year round ventilation.

I am not involved with the controls, but I suppose they could wire the blowers to operate independently of the burners.


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## mtlogcabin (Jul 7, 2015)

Normally a direct fired appliance combustion air does not communicate with the buildings ventilation air.

DIRECT-VENT APPLIANCES. Appliances that are constructed and installed so that all air for combustion is derived from the outdoor atmosphere and all flue gases are discharged to the outdoor atmosphere.

Make up air for a furnace can provide ventilation air. I would ask for more documentation/clarification.


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## steveray (Jul 8, 2015)

402.3 Adjoining spaces. Where rooms and spaces without openings to the outdoors are ventilated through an adjoining room, the opening to the adjoining rooms shall be unobstructed and shall have an area not less than 8 percent of the floor area of the interior room or space, but not less than 25 square feet (2.3 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.  

*Exception: Exterior openings required for ventilation shall be permitted to open into a thermally isolated sunroom addition or patio cover, provided that the openable area between the sunroom addition or patio cover and the interior room has an area of not less than 8 percent of the floor area of the interior room or space, but not less than 20 square feet (1.86 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.*


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## rgrace (Jul 27, 2015)

I believe that the proposed ventilation design would have to go through the code modification process per 105.2. 2009 IMC 401.2 states that every occupied space be ventilated by natural means OR mechanical means. The office is not being provided with natural means per 402.1 because there are no openings to the outdoors. It cannot be provided with natural means as an adjoining space per 402.3 because (1) the door is an obstruction, (2) the door opening is not 8% of the floor area, and (3) the warehouse (assumedly) doesn't meet the 402.2 requirement for natural ventilation. Alternately, if one were to propose the use of a fan to forcibly introduce some of the excess outdoor air located in the warehouse into the office, I could see that the intent of the code could be seen favorably based on the language contained in 403.2.1.


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