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FAN FAQ TOPICS:
How should the fan (or fans) be positioned/placed for optimum PPV?
- Also on this page: Placement of Multiple Fans
Coming soon: Analysis of third party testing showing how well VENTRY Fans do compared to the leading box fans at different distances from the door. It is remarkable data! Please call Joan if you can not wait to see the analysis and she will share the rough draft over email.
WHERE TO PLACE A VENTRY FAN: A good rule of thumb is to set the fan back 1.5 times the height of the opening you are ventilating through (illustration). For balloonists, this is farther back than most are used to. For firefighters on residential fires, it is generally 10 to 15 feet from the entry point, allowing fire fighters to access the door without delay and without tripping over the fan. With VENTRY Fans, it is better to be too far away than too close because volume drops off much slower if you are too far than it does if you are too close. When a PPV Fan blows air in and smoke pours back out the top of the door, the fan is too close to the entry point. It is the tight air cone of VENTRY Fans that allows them to be placed far back from the target. |
 Click illustration above for larger view of PPV Fan placement |
The tripod frames also help allow VENTRY fans to be set further back, because they elevate the air stream over the stairs instead of needing to be tipped. (Legs also prevent the pickup/ejection of debris, allow greater air supply to the prop, and stand on uneven ground and over obstacles like hose…) Ground-hugging fans must be propped up with additional items, or must be aimed upwards which often activates the engine oil alert features and shuts them down, just when they are most needed. By aiming horizontally/directly into the structure from a ways back, VENTRY Fans also provide minimal disturbance to the thermal balance – they don’t bounce the air off the ceiling but instead push fresh air directly into the lower portion of the structure.
Further, the quality of the air stream on a PPV Fan is very important. If you hold a handkerchief in front of any multiple-blade fan and move it around within the air stream, you will find that the strength of flow varies greatly within the circular plane. The strongest points are often at the outer edges of the circle and hit the outside of the door when properly sealed, thereby leaving the weakest points in the center to enter the structure. With VENTRY Fans, the air cone is very focused and uniform across the entire stream. You won’t lose the strongest part of the air stream on the edges of the door – instead, the air is directed into the structure.
The elevated position of a VENTRY Fan allows the geometry of aiming squarely at the entrance so a door seal is much easier to establish. Also, air stream momentum is preserved so fresh air drives deep into the structure instead of bouncing off the ceiling.
We did a lot of engineering and design work on the prop to create a uniform tight air stream. Put our fan in the rose garden and let your firefighters use the sidewalk for advancing their hose line.
How should multiple fans be placed for ventilation?
When multiple fans are required, placement side-by-side generally yields more volume while placement one-behind-the-other yields more pressure. This is a simplistic rule, so please call us regarding your specific placement questions. If you have a large fan and a small fan, again, side-by-side is probably best. If this is not possible, we recommend placing the larger fan in front (closer to the entry point) and putting the smaller fan behind it to seal the doorway. |
 Multiple propane-powered VENTRY Fans are shown above being used to ventilate millions of cubic feet of air at a shopping mall. Click the image to enlarge. |
In the photo shown above (which was pulled from a video so the quality is lacking), multiple (propane-powered) VENTRY PPV Fans are positioned side by side to ventilate a huge shopping mall in the Seattle area. Far in the background, two more fans have been positioned at another entryway. Eventually, three fans were set at each of the two entry points. This dynamic combination pressurized a portion of the mall and ventilated the other. We were able to use three fans to pressurize unaffected areas of the mall and three fans to push the smoke out. This combination did a terrific job of clearing all smoke in just 8 minutes and proved that extremely huge, over-priced fans are just not necessary to ventilate and protect enormous structures. Please give us a call if you would like more details on this amazing experiment.
