Just curious, but why is that? Most people don't replace 5-year old roofs. There was a massive hail storm last year that totaled the roof. From the information I acquired it would be beneficial to get a powered vent which would help cool my attic, which in turn would save on my electric bills. Because of negotiating with the contractor this was installed, wired by an electrican at no cost to me. What are the "vents on the underside of the hosue?" Is that the foundation vents under the floor? Or do you mean soffit vents at the eaves? The soffit vents under the eaves. I made sure they were cleaned out so they would provide proper ventilation to the attic. That's a poor idea. If a fire were to start in the garage, it would spread to the attic quickly. There's supposed to be a separation wall between the garage and the rest of the house to slow the spread of fire. Keeping that door open defeats the purpose of that separation. The attic vent is a hatch in the ceiling of the garage. I never thought about a fire spreading more rapidly because it was open, but I guess it would allow it to have a larger supply of oxygen, which it turn would allow it to be able to spread into the attic. A quick search on the internet also showed that I need to seal off that door because the paneling on my attic door is way too thin for fire safety. I plan on doing this right away. One benefit of leaving the attic door open and cracking open the garage door is that my garage doesn't stay 120 degrees when I pull a car in the garage during the summer as air fresh air is pulled in from the garage and the hot air from the garage is pulled up into the attic. While I thought it was important keeping my attic cool, it is even more important keeping my garage cool.(This garage issue is something I will have to address later without comprising fire safety.) With a powered vent fan in the attic, there's no difference between those two things. The function of a powered vent fan is to waste energy. Building science concluded this over 20 years ago. This is the reason I am searching for more information. Apparently there is a lot of misinformation different places and I am trying to get all of this figured out. It's funny how roofing contractors and new builders are still putting these on houses in place of the static(cap) vents or the wind powered vents. Unless you have specially trained air that knows where you *want* it to come in, it's coming in through every single opening in the attic in proportion to the pressure difference at each opening. Most of the air is coming in through the nearest, largest opening. Some of the air is coming in through the farthest, smallest opening. A certain quantity of the air is coming in from the interior of your house, through the gaps around plumbing vents, electrical wires, light fixtures, etc. If you have air conditioning, this is expensive air that you're sucking into your attic. Yes, with the 105 degree heat the A/C is running a LOT. The last thing I need is the cool air pulled from the house. I will eal gaps in outlets and plumbing and see about turning off attic fan. Listen carefully, here comes an epiphany: It's not about the air; it's about radiation. Heat in your attic come primarily from radiation. The sun hits the roof, causing it to get hot. The underside of that roof, *radiates* heat into the attic. You could remove all of the air from the attic and the surfaces in the attic would still get hot. You could replace all of the air in the attic with 30-degree air, and the surfaces in the attic would still get hot because there's a huge radiant surface there to warm everything up. Try this experiment: put a steak under the broiler and blow a fan over it. The steak still cooks. That's because of radiant heat. If you want the interior of the house to stay cool, make sure that you have a generous layer of insulation at the ceiling plane. Then don't worry about the temperature in the attic. Alternatively, if you want a cooler attic, put the insulation at the underside of the roof plane. Sucking air out of an attic is not an effective or efficient method of controlling the temperature inside your house. It just makes your attic into a convection oven instead of a regular oven. My initial thought was: Install a power vent for when the attic gets hot... then it will kick on and ciruclate the air and it will be cooled down. The radiation example is very helpful as I know now the previous statement is not possible. I wan to say "Thank you!" as this post has been extremely helpful. I am very fortunate to have stumbled onto THIS website, unlike other websites where the 'experts' don't have a clue. Everything was explained very well and I think I finally understand how an attic functions. Because the items in my attic are not sensative to temperature, I will see if there is a switch on the thermostat fan to turn it off. My local energy company just did an energy audit on my house and said I have plenty of insulation in the attic, and no additional is recommended. As a result my house will be more better prepared for fire safety, my electric bills will be lower, and I won't have to hear that annoying quiet hum from the fan in the attic when it is on. Thank you!