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# Troubleshooting Tips

### How much attic ventilation do I need for my attic?

The final step is to figure out how many vents would be needed to provide 4 square feet of attic ventilation. To do this let's start by converting the number to square inches by multiplying by 144. Thus, 4 x 144 = 576 square inches of attic ventilation for intake and 576 for exhaust. Air Vent ridge vents provide 18 square inches of Net Free Area per linear foot. To determine how many feet of ridge vent would be needed the formula looks like this: 576 divided by 18 = 32 feet of ridge vent. A typical 8" x 16" undereave vent provides 56 square inches of Net Free Area per vent. To determine how many undereave vents would be needed, the formula looks like this: 576 divided by 56 = 10.2 (which can be rounded up to 11).

If using Air Vent’s The Edge™ Vent, ProFlow Vented Drip Edge or continuous soffit vents simply double the amount of needed ridge vent linear footage because all of those intake vents provide 9 square inches of Net Free Area per linear foot.

### I have attic ventilation but why doesn't my attic seem to be any cooler?

With any attic ventilation system, the attic could be about 20 degrees hotter than it is outside. Attic ventilation is meant to protect the roof sheathing, insulation and shingles from temperature and moisture extremes. However, many variables will affect the temperature that the attic can reach. For example, the color of the shingles will have a large impact on the temperature. Black shingles will cause the attic to be much hotter than if white shingles were used. Other factors are the geographical location, intensity of the sun, orientation of the primary roof plane, and amount of total ventilation NFA.

### What size slot do I cut for your ridge vent?

For ridgepole construction, cut a 3/4" slot on each side of the ridgepole. For truss construction, cut a 1.5" slot at the peak of the roof.

### Do I have to close off my gable vents when I use a ridge vent?

Yes, the gable vents (a type of exhaust vent) should be closed off whenever a ridge vent (which is also a type of exhaust vent) is installed because vents installed at the roof’s edge or in the overhang should supply the intake air needed by the ridge vents. Air should flow in through the intake vents evenly along the roofline and exhaust out the peak. Any vents in place between the ridge vents and the intake vents may interrupt or short-circuit that flow of air along the roofline. The gable vents will end up becoming intake for the ridge vent — an undesirable situation that could lead to weather infiltration through the gable vents and also could prevent the attic from being properly ventilated. The same is true with mixing wind turbines or roof louvers with ridge vents.

### Can I install a power fan if I have a ridge vent already on my roof?

Mixing a power vent with a ridge vent can short-circuit the attic ventilation system just as a gable vent can as discussed above. This happens because air follows the path of least resistance. When the power vent turns on, it can pull air from the ridge vent, which could lead to weather infiltration and unbalanced airflow along the underside of the roof deck. When the power vent turns off, it acts like a roof louver — an opening on the roof without a motor. In this scenario, the ridge vent pulls its intake air from the power fan leading to possible weather infiltration and less than optimal ventilation along the underside of the roof deck.

### Can I use your ridge vent on the hips?

Yes. Air Vent makes a ridge vent specifically designed for use on hip roofs called Hip Ridge Vent.

### How important is intake ventilation for ridge vent?

Intake ventilation is very important for all types of exhaust vents, including ridge vents. Each attic should have an equal amount of intake ventilation low at the roof’s edge or in the overhang or undereave and exhaust ventilation at or near the peak of the roof. This is known as a balanced ventilation system.

### I have a knee wall. What should I do?

In a knee wall situation the goal is to get the intake airflow past the wall. There are two ways to do this.

If the roof deck is being replaced, install insulation baffles in every rafter from the overhang or undereave level to the peak of the roof. This will allow an even flow of air along the roof deck that will flow past the knee wall.

Slide wood slats up the underside of the roof deck (for short spans only) and then flip them on edge to force down the insulation. Pull down the fascia to allow access to the underside of the roof deck from outside the house. Someone can feed the wood slats from outside while someone in the knee wall area guides the slats toward the ridge.

### My power attic ventilator has burned out completely. What do I need to check to make sure this doesn't happen again?

Check the intake ventilation. Make sure that the attic insulation has not covered the intake vents preventing air from feeding the power vent. It might be necessary to either insert insulation baffles or to pull the attic insulation back to ensure the intake vents are not blocked.

Also check to make sure that the plywood the intake vents are installed in have actually been cut or opened to allow for air to flow into the vent.

Finally, make sure that the power vent has enough intake vents. To determine how many intake vents the power vent requires, take the CFM (cubic feet of air moved per minute) of the vent and divide it by 300. This will determine the square feet of intake ventilation needed. Take that number and convert it to square inches by multiplying by 144. For example, 1500 CFM divided by 300 = 5 square feet of intake ventilation needed. Converting to square inches looks like this: 5 x 144 = 720 square inches of intake ventilation needed for the power vent.

If you don't know the CFM of the power vent or the net free area of the intake vents, check with the manufacturer.

### Can I use Air Vent power attic ventilators around chemicals?

The motor on Air Vent power vents is not closed, which means chemicals could affect the motor. Air Vent recommends not using power vents around chemicals.

Can I use a gable-mount power attic ventilator to vent a workshop, restaurant, dry cleaners, etc?

### Why do I need a humidistat with my power attic ventilator?

The thermostat control on a power attic ventilator monitors the attic solely for temperature or heat buildup. Thus, the power vent will only run in the hot summer months. During the winter, moisture can build up causing a reduction in the effectiveness of your insulation. The humidistat allows the power vent to run in the winter, which will keep the moisture from building up.

### Can I mount the whole-house fan vertically?

Air Vent whole-house fan cannot be mounted vertically. There are several reasons for this. First, the shutter will not open or close in a vertical position. Second, the fan blade will eventually crack over time. Third, if mounted on a vertical wall facing the outside the fan will pull the air from outside into the attic rather than attic air being vented to the outside. Unfortunately, the fan blades and motors are not reversible. If the motor is reversed, it will burn out. If the fan blades are reversed they will crack. The warranty on Air Vent whole-house fans requires installation in a horizontal position.

The rough opening that is cut for the shutter is a different size so the whole-house fan can be pushed through the opening from inside the hallway rather than try to get it through a smaller attic opening.

### Can I use a rheostat with your fan?

No, if a rheostat is used on Air Vent fans, the motor will burn out.

### My fan is vibrating a lot. Anything I can do?

Remove the fan blade and see if the motor still vibrates. If the vibration is gone, it means the fan blade is out of balance. If there is still a lot of vibration, a bearing could have been knocked loose.

### My whole-house fan will only run on low. What is wrong with it?

Check to make sure there is enough “exhaust” ventilation, including intake vents at the roof’s edge or in the overhang or undereave as well as exhaust vents high on the roof at or near the ridge. Possibly there isn't enough “exhaust” ventilation for the whole-house fan to run at the higher setting.

Call the manufacturer to find out the net free area of all the vents in your attic (intake vents and exhaust vents). Most net free areas are less than half the size of the vent. For example, a 12" x 12" gable vent's unobstructed airflow is 56 square inches even though the opening measures 144 inches. Calculate the unobstructed airflow of all the vents in your attic, whether it is a ridge vent, gable vents or undereave vents. If they equal the minimum requirements for the whole-house fan, the fan should run on high.

Our exclusive Contractor Locator will allow you to find contractors in your area who can assist with Air Vent product installation—including solar attic fans and skylight tubes. Click the link below to register and get started.