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Attic Ventilation Question

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Background info:

First off, I am new here. So, if this is the wrong place for this question, please let me know. My home is 2200 sq ft built in 2004 and is located in Central Oklahoma. I recently had a new roof put on and in the process one of the 5 cap vents was replaced with a powered vent. Powered vent seemed to run all the time so I installed a wirelss thermometer in the house so I could monitor temperature. I adjusted the thermostat so it would turn on at approximately 115 degrees to help keep the house cool (contractor had it set at 70). I made sure the vents on the underside of the house are cleaned. I keep the attic door in the garage open for added ventilation.

Question: Are there ways to tell if my powered vent is working properly, or is it just robbing energy? Lately it has been about 105 degrees here lately. Fan will come on at noon and stay on until 8 pm. At 5:00 its 127 degrees in the attic, even thought it is mid 90's outside. It is possible the vent is just sucking in hot air from one of the cap vents nearby rather than pulling air up through the vents on the edges of the house?

Possible answer to my own question: If I can figure out how to turn off the fan, I can chart the temperature variations between fan on and fan off with the same weather patterns outside. Then I will know if it is effective... but I will still not know if it is working properly.

Sorry for the lenthy post, just wanted to get as much info as possible. If pics are needed just let me know!

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It's pulling air from the source of least resistance, whatever that is, most likely the nearest roof vent.

I've never found any of the power fans to do much of anything in cooling attics; they move air, but they don't cool attics.

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Background info:

First off, I am new here. So, if this is the wrong place for this question, please let me know. My home is 2200 sq ft built in 2004 and is located in Central Oklahoma. I recently had a new roof put on

Just curious, but why is that? Most people don't replace 5-year old roofs.

and in the process one of the 5 cap vents was replaced with a powered vent. Powered vent seemed to run all the time so I installed a wirelss thermometer in the house so I could monitor temperature. I adjusted the thermostat so it would turn on at approximately 115 degrees to help keep the house cool (contractor had it set at 70). I made sure the vents on the underside of the house are cleaned.

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?

I keep the attic door in the garage open for added ventilation.

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.

Question: Are there ways to tell if my powered vent is working properly, or is it just robbing energy?

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.

Lately it has been about 105 degrees here lately. Fan will come on at noon and stay on until 8 pm. At 5:00 its 127 degrees in the attic, even thought it is mid 90's outside. It is possible the vent is just sucking in hot air from one of the cap vents nearby rather than pulling air up through the vents on the edges of the house?

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.

Possible answer to my own question: If I can figure out how to turn off the fan, I can chart the temperature variations between fan on and fan off with the same weather patterns outside. Then I will know if it is effective... but I will still not know if it is working properly.

Sorry for the lenthy post, just wanted to get as much info as possible. If pics are needed just let me know!

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.

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Background info:

First off, I am new here. So, if this is the wrong place for this question, please let me know. My home is 2200 sq ft built in 2004 and is located in Central Oklahoma. I recently had a new roof put on

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.

and in the process one of the 5 cap vents was replaced with a powered vent. Powered vent seemed to run all the time so I installed a wirelss thermometer in the house so I could monitor temperature. I adjusted the thermostat so it would turn on at approximately 115 degrees to help keep the house cool (contractor had it set at 70). I made sure the vents on the underside of the house are cleaned.

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.

I keep the attic door in the garage open for added ventilation.

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.)

Question: Are there ways to tell if my powered vent is working properly, or is it just robbing energy?

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.

Lately it has been about 105 degrees here lately. Fan will come on at noon and stay on until 8 pm. At 5:00 its 127 degrees in the attic, even thought it is mid 90's outside. It is possible the vent is just sucking in hot air from one of the cap vents nearby rather than pulling air up through the vents on the edges of the house?

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.

Possible answer to my own question: If I can figure out how to turn off the fan, I can chart the temperature variations between fan on and fan off with the same weather patterns outside. Then I will know if it is effective... but I will still not know if it is working properly.

Sorry for the lenthy post, just wanted to get as much info as possible. If pics are needed just let me know!

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!

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It's pulling air from the source of least resistance, whatever that is, most likely the nearest roof vent.

I've never found any of the power fans to do much of anything in cooling attics; they move air, but they don't cool attics.

I used to have a copy of a DOE report indicating that the load added by the fans is greater than the reduction in AC load. I always equated that to indicate the minimal effects of them. IMHO, static roof vents have always been the way to go.

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It's pulling air from the source of least resistance, whatever that is, most likely the nearest roof vent.

I've never found any of the power fans to do much of anything in cooling attics; they move air, but they don't cool attics.

I used to have a copy of a DOE report indicating that the load added by the fans is greater than the reduction in AC load. I always equated that to indicate the minimal effects of them. IMHO, static roof vents have always been the way to go.

You learn fast. Are you an inspector? Why not fill out your profile?

Marc

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It's pulling air from the source of least resistance, whatever that is, most likely the nearest roof vent.

I've never found any of the power fans to do much of anything in cooling attics; they move air, but they don't cool attics.

I used to have a copy of a DOE report indicating that the load added by the fans is greater than the reduction in AC load. I always equated that to indicate the minimal effects of them. IMHO, static roof vents have always been the way to go.

Can you find your copy of that report and provide a link?

Goes without saying I'll search as well.

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I've been doing some reading and had a further question. If a 2400sq ft house has no soffits,2 roof vents and 2 gable vents= would installing a ridge vent be advisable? Would intake airflow now come from the gable vents(after installing ridge vent)? Should I close off the roof vents? Dont really want to install continuous soffit vents at this time.

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The majority of power vents that I've encoutered have a switch installed before the thermostat to shut them off. Look around for one. Sometimes they are in the living space below.

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