Attic ventilation is not quite as simple as just installing a fan. If you want to ensure that your attic is properly ventilated, you need to do some homework before investing in an attic fan. Many residential attics only need one 30watt fan. However, this is not always the case. It is important to properly calculate the size of your attic so you know exactly how much ventilation is required for your unique circumstances. Proper ventilation requires 10-12 complete air exchanges each hour. If these air exchanges are executed correctly, the temperature of the attic should be approximately 5-15 degrees Fahrenheit above ambient. Please see the following calculations or check with your roofer, green energy audit company, builder, contractor, or other attic ventilation expert to verify the following information in relation to what you are looking to ventilate:
- Attic Sizing: length x width x average height = total cubic feet of air
- Cubic feet of air per minute (CFM) x 60 minutes = cubic feet per hour
- Total cubic feet of air divided by cubic feet per hour = number of air exchanges
- Number of air exchanges x .7 = the average number of air exchanges
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|---|---|---|---|
| Attic Size | CFM Required | Net Air Intake (sq.in.) |
Ave.Pitch ~6/8 |
| 1800 sq.ft. | 1260 | 604 | 1 Fan |
| 2100 sq.ft | 1476 | 705 | 1 Fan |
| 3500 sq.ft | 2450 | 1176 | 2 Fans |
Always remember that proper ventilation is a direct result of proper installation. Even if you do your homework and get the best fan for your attic, it still won’t work without proper installation. This is why we always recommend using a certified roofing contractor to install your fan(s).
Optimal Orientation for Proper Ventilation
The optimal direction to orient your solar fan is south. This allows the greatest sun exposure as long as there are no trees or buildings blocking the UV rays. If south is not an option, then orienting the fan either east or west is your next best option. Utilizing the position of the unit and panel angel to optimize the best exposure to the sun will ensure the fan operates at peak efficiency. If none of the above options are viable, you can orient the fan north. You need to angle the panel as much as possible to ensure the best sun exposure. No matter which direction the fan is oriented, it is critical to ensure there are no barriers blocking the incoming UV rays anytime during the day. This ensures that the fan is operating at peak efficiency to create proper ventilation.
[SunCalc is a great reference site to determine optimal solar panel orientation. <Click-here> and enter your own address]
Attic Air Intake
There are several types of air intake for attics. The air being exhausted must be replaced by outside air drawn through unobstructed air vents. This is often done through soffits that are normally found under the eaves of a home. However, for air to properly be exhausted, the intake vent, regardless of type or location, must be completely unobstructed.
To calculate the total minimum vent intake area in square inches, divide the CFM ratings of the solar ventilation by 300 and multiply the result by 144 which will give you the Net Air Intake as recommended by hvi.org. So, here is a calculation demonstration:
(1300 ÷ 300) 144 = 624 net air intake required
The Solar Royal Attic Fan moves up to ~78’000 cubic feet per hour. The intake must be balanced for it to do its job. ~4.2 sqft of Net Free is suggested per fan.
Additional Cost Benefits: One of the best features of a solar attic fan is the cost savings. Please note that this is only an estimate. However, it gives a clear comparison of solar fans vs. electric ventilation. The figures also do not take into consideration the energy savings from keeping your attic cooler.
For more solar attic fan FAQs, CLICK HERE.
