Solar attic fan, etc. Is it worth it? The answer. (how much, house)

[behtypa]

OK, guys. For those of you skeptical about the use of a solar fan in the attic, here is the temps after completion of my attic insulation project.

GARAGE BEFORE:
Outside: 100F
Garage: 105-110F (no ventilation)
Attic: 115F (120F at the top?) (no ventilation)

GARAGE AFTER:
Outside: 100F (105F at the top)
Garage: 86F (no ventilation) (R10 on garage doors and standard builder insulation (R15?) on walls)
Attic: 88F (solar fan, soffit vents, ridge vent + R30 insulaltion and foil radiant barrier)

HOUSE ATTIC BEFORE:
Outside: 100F
Attic: 120F (135F top) (no ventilation)

HOUSE ATTIC AFTER:
>>>>installed today, will provide data tomorrow<<<<<<<

Conclusions? I think it is worth it. Now I have:

Garage:
- great cool ventilated storage space in the attic (around 20x20ft)
- well cooled and insulated garage comfortable to work inside
- less hot air coming through the house back door = cooler house space.

House:
- around 10-15 deg cooler attic
- better overall ventilation/heat exchange
- less power usage by A/C unit
- less heat wear for the roofing

How much is the solar attic fan?
I found a combined unit (solar panel attached to the fan unit) for $230 at HomeDepot. Plus paint your shingles color (i.e. black grill spray paint). Lowes has a detached panel version. Costco has similar for $320 or so.

How much will it save electricity (what is ROI)?
I can't answer to this question yet. If considered in combination with other insulation (batt, loose fill, radiant barrier) and vents (ridge, gable, etc.) it will definitely save 10-20% plus. I will give you the stats in a few months.

[tstone]

You only have a 20x20 attic?

Mine is roughly 65x40 with 8-12 ft celings (except on the edges), how many of those fans would I need? Some quick math says that's roughly 20,000 cubic feet.

[behtypa]

Originally Posted by tstone

You only have a 20x20 attic?

Mine is roughly 65x40 with 8-12 ft celings (except on the edges), how many of those fans would I need? Some quick math says that's roughly 20,000 cubic feet.

My garage attic is 20x20.
The house attic is appr. 40x40 +2 more smaller crawl spaces.

The fans come in various sizes. Mine are 500 cfm (cubic feet per minute) and 10watt solar panel.

Here is my comps:

1600 sq ft of attic floor space X average 4ft height (average between roof top and roof slopes)= 6400 cubic feet of space

500cfm peak = maybe 300cfm of real-life performance. This means that the fan will move 6400 cubic feet in about 230 minutes. Right?

500 cfm is the maximum output, in ideal conditions, direct sun, etc etc. So the actual would be 50-70% of 500 = 300 sq ft.

You can start with one or two and see how this goes. Or you can install exactly the number that the fan output tell you. Up to you.

[behtypa]

Originally Posted by tstone

You only have a 20x20 attic?

Mine is roughly 65x40 with 8-12 ft celings (except on the edges), how many of those fans would I need? Some quick math says that's roughly 20,000 cubic feet.

Here is the link to a tech spec of the fan sold at Home Depot. Its PRSOLAR1. 2nd page.

http://www.gaf.com/Roofing/Residential-Roofing/Roofing-Products/Attic-Vents-Roof-Ventilation/MasterFlow-Solar-Intake-Booster/Documents/MasterFlowSolar-PoweredRoofIntakeBooster-BrochuresDataSheets-255-68-5079.pdf (broken link)

[behtypa]

Originally Posted by tstone

You only have a 20x20 attic?

Mine is roughly 65x40 with 8-12 ft celings (except on the edges), how many of those fans would I need? Some quick math says that's roughly 20,000 cubic feet.

Here is the link to a tech spec of the fan sold at Home Depot. Its PRSOLAR1. 2nd page.

In case the moderator removes the link, here is the Manufacturer name: Master Flow, Green Machine EcoSmart Solar Power Vent. Model PRSOLAR1.

[behtypa]

Originally Posted by tstone

You only have a 20x20 attic?

Mine is roughly 65x40 with 8-12 ft celings (except on the edges), how many of those fans would I need? Some quick math says that's roughly 20,000 cubic feet.

Is it 8-12 ft at the highest attic point? I would then average the height to about 6ft. Because it is a roof-sloped attic, right?

In this case I guess this would be 65x40= 2600 sq ft x 6ft height = 15600 cubic feet of air.