Attic fan pros and cons

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  #1  
Old 08-05-02, 02:09 PM
cheeseslice
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Attic fan pros and cons

I have a newly built home (2000) with plenty of soffit vents. But several of my neighbors have added attic fans to supplement ventilation in their attics. They all say their upper levels are much cooler and they are very satisfied with the results (I have not been in their homes to testify this--perhaps I should). But my builder says an attick fan really isn't that neccessary, that it doesn't 'cool' that much, it needs to be replaced frequently (5 years), and it can sometimes be noisy.

On really hot days, I can tell that my top floor is not as cool as the lower floor (naturally), but does an attic fan really help this variation in temperature? Is it worth putting in an attic fan if I already have what appears to be adequate ventilation? What are the pros and cons of attic fans in my situation?

Thanks in advance for your time.

Greg
 
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  #2  
Old 08-05-02, 02:25 PM
Hershey
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Where do you live? In a humid area, the attic fan will bring in humid air, and you will feel sticky. I think before anyone can help you, they need to know what city, state you live in.
 
  #3  
Old 08-05-02, 02:28 PM
cheeseslice
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I live near Chicago.
 
  #4  
Old 08-05-02, 02:36 PM
Hershey
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I live in south Texas where it is hot and humid. We have an attic fan in our house (50 years) old. We don't use it for cooling because of the humidity, but what we are going to do is stand it up and let it blow the hot air out of the attic. The attics in south Texas get very hot. Also, I would recommend that you visit your neighbors with the attic fans and see what they recommend and why they recommend it, or don't as the case may be. The attic fan will keep the air circulating and although it doesn't feel like air conditioning, it will probably feel good. Maybe the next response will come from someone in your area.
 
  #5  
Old 08-05-02, 03:56 PM
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  #6  
Old 08-06-02, 07:09 AM
DJK
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the solar powered attic fan, mentioned in the above site
given by twelvepole sounds very interesting.
 
  #7  
Old 08-06-02, 03:58 PM
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Lightbulb Solar fans

No way they can get 600 CFM out of an 11 watt motor !!!!!

A regualr fan uses 300W to get 1200 CFM, so what gives ??

Thes ratings are crazy, a roof turbine would work just as good and cost 1/10 the price.
 
  #8  
Old 08-07-02, 09:19 PM
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Geetings,

Your builder is partially correct.

Hot air rises. It cannot enter the home unless there is a positive air presseure in the attic. It would then be forced into the house thru ceil'g openings. Electric attic fans are a joke. For one thing they do not operate in the winter when you need them most. You vent an attic to prevent moisture buildup which is worst during winter.

The most efficient way to vent an attic is with a ridge vent. Your builder didn't want to install one because he didn't want to spend the money. Ridge vents work summer and winter automatically using the laws of physics. Try: cor-a-vent.com the best

The reason it gets hot on the second floor is because your builder chose to install an insulation that is only about 10% efficient. On a 95% degree day your "ceiling" is probably 110 degrees hot. This is about 25 degrees hotter than a radiant ceiling heat systm.

I have been upgrading attics like yours for about 30 years and besides a ridege vent I would suggest that you install a radiant barrier (RB) over the top of your insulation. That will drop the upstairs temperature about 10 to 15 degrees. You can't do that with any other insulation. Your upstairs will also be warmer in the winter.

If you ask your builder about RB he will say they don't work, BECAUSE, when you install in your attic everybody else is going to be on his case BIG TIME and he knows it.

This can be a DIY job if you are so inclined.
 
  #9  
Old 08-08-02, 05:20 PM
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To answer your question, an attic fan might make the 2nd level cooler, but it will be so slight, that it won't be noticable to you. The attic fan will lower you cooling bill.
 
  #10  
Old 08-08-02, 05:28 PM
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Lightbulb Attic fan WON'T lower the bill !!

Any savings in air condirioning will be offset by the usage of the fan.

Use passive ventilation if possible.
 
  #11  
Old 08-08-02, 10:50 PM
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Let us assume an attic fan is 300 watts and that fan is set at 110 degrees F. For the Chicago area, that would mean the fan would probably operate 700 hours during the cooling season. And let us assume the cost per kilowatt is an outrageous $.14. To determine the annual cost 300 watts x $.14 x 700 hours/ 1000 = $29.40 per year. There is a default the the U. S. Dept. of Energy uses, which is a 3 degree difference results in an 1% savings in energy costs. You may be familar with this when it comes to your thermostat settings. It cannot only be used in your heating and cooling but can also be applied to attic temperatures that affect cooling costs. Even if this is applied conservatively, you can go to http://www.cpc.ncep.noaa.gov/product...t/weekass.html and look up the cooling degree days (CCD) for Chicago and you'll see that the if you used air conditioning only 1/3rd of the year, the saving would exceed the cost of operation of the fan.

There is one major difference between wind turbine fans and electric attic fans. Wind is an intermittent power source and electric is a firm reliable power source. What that means is the attic fan will come on when the temperature in your attic rises above 110 degrees or what ever setting you have and will not go off until the temperature drops below that setting. No intermittent power source, solar or wind, can make this claim. This is because these fans are not governed by attic temperature. It is the attic temperature that affects the life of the roof, which is the primary purpose of attic fans. The secondary aspect of attic fans is that it reduces your cooling costs.

There is a simple rule one should follow when it comes to condensation in attics. WARM AIR CONDENSES AGAINST COOLER SURFACES!!! Since most attics are warmer than the outside in the summer, the only cooler surfaces in your attic must come from your air conditioning. And the number one source for it is air leakage.

Can increased venting reduce attic temperatures in the summer? The answer is NO. This is because the dominant heat transfer mechanism in cooling is radiant. Any object that gets warm, like your roofing shingles, will radiate heat. The warmer that object, the more heat it will radiate. Though opposing temperatures have the tendancy to equalize, the materials found in attics, like insulation and roofing materials are considered thermal masses and free venting will take too long to equalize the temperatures.

As stated in my previous post, the attic fan might reduce the temperature difference between the 1st and 2nd floors, but it will be so slight, you probably won't notice it. IT WILL REDUCE YOUR ENERGY BILLS!

At the bottom of this message is a www icon, if you click on it it will bring you to my site. The first topic is "Compairing Energy Bills", it shows you how to compair energy bills from one month to another. If you install the attic fan, it will show you if there was a savings as a result of installing the attic fan and it doesn't matter if last year was warmer than this year or vice-versa.
 
  #12  
Old 08-09-02, 06:06 AM
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Red face Real tests

Government tests have proven power attic fans save no $$$ in moderately to well insulated attics.

Data measured at FSEC and elsewhere show that attics with nominal natural ventilation and R-19 ceiling insulation do not need powered vent fans. Such fans cost more to operate than they save in reduced cooling costs, so they are not recommended.
http://www.fsec.ucf.edu/Pubs/EnergyNotes/EN-13.HTM

Attic vent fans are thermostat controlled to force ventilation of the attic when solar heat accumulates and causes high attic temperatures. Testing done by FSEC shows that attic vent fans use more power than they save in attics with normal passive venting and code level insulation. If insulation is inadequate, or ventilation poor, it would be more cost-effective to improve insulation than to install vent fans.
http://www.lcec.net/Home/fans.htm

http://hem.dis.anl.gov/eehem/95/951103.html

http://www.askbuild.com/cgi-bin/column?236


http://www.philly.com/mld/philly/liv...in/3062074.htm

Show ME some GOVERNMENT or other non-biased source showing how much money attic fans save
NO data from sites trying to sell product !!
 

Last edited by 54regcab; 08-09-02 at 06:25 AM.
  #13  
Old 08-09-02, 12:24 PM
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http://www.eia.doe.gov/emeu/efficien...gy_savings.htm I am a Energy Conservationist. My site is listed on the U. S Dept. of Energy, Energy Information Administration list for Energy Savers. This lists the most notable Energy Conservation web sites inside the U.S. and outside. My site is the only independent listed. Advertising on these sites is strictly prohibited to be on this list.

For 15 years, my job was to resolve high energy complaints that went before the State Utility Regulatory Board. The home where these high energy bills occurred were visited by me, their energy bills were reviewed by me prior to going. After the home was inspected a report was generated by me and sent to the energy bill payer, Utility and State Regulatory Board. The report depicted energy consumption from a toaster oven to a central air conditioner. It identified sources of high energy consumption and made recommendations for the reduction of that high consumption.

Today, Energy Conservationists are involved in something where the stakes are much higher. That is Reduction of Peak Load Demand. Most of the programs associated with this are Pay for Performance. Some programs are more difficult than others. Comfort Partners program, the most difficult of all the programs, uses a concept known as the "House as a System of Energy Use." What makes this program so difficult is that every known energy conservation measure is applied to each and every home, including consumer education. Each measure must be measured and verified, calculated and documented. Pay for Performance means in this program that the energy bills for the home mentioned are reviewed every six months. If after the first year, the reduction of energy in that home is what I said it would be, I get a check. If not, there is a penalty clause.

There is one exception to protocol in this program. You guessed it, wind turbine fans. What that means is if I installed one, the Utility would pay me for it regardless if it reduced energy consumption in that home. I have refused to do so, to the ire of the Utilities I work for, State Regulatory Board and Energy Conservationists. My job is the actual reduction of energy consumption and I will not install something where the measurement and verification is questionable. This is because it is totally dependent on the weather. There are other reasons why I disapprove of wind turbines, which I cannot use when dealing with the Utilities. If the turbine is not plumb or installed properly or maintained, it is noisy. Though there are many contractors that do take the time to install them properly, that is not true when it comes to contractors dealing with low income housing. Whenever you cut a hole in your roof, you increase the chances that the roof will leak. I don't even like using roof vents and never use ridge vents. The only time I'll use a roof vent is when I'm forced to like with a hip roof. Even then I will take extra precautions to prohibit that vent from ever causing a leak in that roof. These people cannot even afford to pay their energy bills, let alone a roof leak.

When it comes to installing electric thermostatically controlled attic fans, vast majority gable mounted, it depends upon the energy bill payer usage. Protocol dictates installation. In the vast majority of installations in this program, medical reasons was the cause of air conditioner usage. I can measure, verify and calculate the saving on cooling cost as a direct result of attic temperature reduction because of the fan. On the other hand, if cooling is not or infrequently used, protocol disallows the installation of the fan. What I find somewhat humorous here is reduction of cooling costs is a secondary aspect of attic fans. The primary aspect is the prolonging of the life of the roof by temperature reduction. Which automatically justifies its installation.
 
  #14  
Old 08-09-02, 01:41 PM
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Lightbulb Nothing works properly

When incorrectly installed
A powered roof vent doesn't work worth 2 cents either if not installed correctly.
So if you don't like roof, ridge and turbine vents are you saying that powered attic fans are the best way to go regardless of what alll the above articles I linked to say ??
Please show us just on test done by an independent agancy showing energy savings.
Also compare a power vented attic with one PROPERLY vented using natural convection.
Just curious, why such a hate of ridge vents ??
 
  #15  
Old 08-10-02, 10:07 PM
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54regcab

I would like to apologize first for not being clear on my position. I will try to do better this time.

You will not find another energy conservationist like me. This is because I openly disapprove of renewable energy resources for residential use, to the dismay of many of my collegues. Before I answer your question on the articles, I'd like to answer the other questions.

Besides the fact I don't like cutting holes in roofs, I live in the northeast, where we get snow in the winter. On several occassions I inspected homes that have ice damming on their roofs. When I calculated to see if they had adequate ventilation, they did. The problem was when the snow fell on the roof it covered the roof and ridge vents, rendering them useless. In all my years of experience, this never occurred with gable vents. To be honest, I never seen a turbine fan covered by snow. After careful consideration, I might just put a turbine fan in the next hip roof I have to ventilate, but I will be extremely careful in its installation.

Forced ventilation verses convection or wind turbines. What everyone wishes for on those very hot days in urbans areas is a breeze. So when you need the ventilation the most, there's no wind. To illustrate convection is an object out in the sun and another put in the shade. The object in the sun will become much warmer than the object in the shade and it will radiate more heat. This is a major reason why attic temperatures are usually higher than the outside during the summer. Natural convection cannot alleviate the temperature in attics because of the enormous radiant heat energy created by the roof exposure.

The Building Specialists of America (Architects) are very fond of beginning their conferences on energy conservation by stating "There is no documented occurance where an Architect destroyed a structure." This is a dig towards energy conservationists because there are several documented cases where they have destroyed structures. When I first started as an energy conservationist, I was a zealot. I consumed all the information I could get my hands on and applied it. Many were test results done by notable organizations. You could say, I learned my lesson the hard way.

As far as any non-profit organizations that have test results for forced ventilation, I do not know of any. Then again, I don't pay too much attention to them. I will state openly, based on my experience, I disagree with their findings.
 
  #16  
Old 08-11-02, 07:19 AM
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Lightbulb Hip Roof

What is YOUR recommendation for venting a hip roof ??
Seems to me a hole must be cut in the roof no matter what for proper venting.

Seems to me the Turbine is the only thing that WOULDN'T cover up with snow.

An electric fan That I see you recommend so highly won't run due to low temps unless you add a humidistat for the fan, Less than 1 out of 10 attic fans are sold with humdistats. The ones that are tend to be out of the price range for most consumers. Also there is the isssue that here in the south the cheap shaded pole motors used in these fans (the same as the motor in the 20" box fan they sell at Wal-Mart for $10) don't normally last more than 5 years in the 120 degree heat. Go into Home Depot or Lowes and you will find a stack of replacement motors for sale (about $30.00 each) in the same isle and the attic fans. Interestingly enough there are no replacement capacitor run motors for sale at the stores. The fans that use a capacitor run motor tend to last longer, use about the same amount of power (are much more efficient than shaded pole) and have a higher CFM rating. The downside to the Capacitor run motor is they are 1725 RPM vs the 1150 RPM for the shaded pole motors resulting in increased noise, not to mention the increased price $$$

I just fail to see how an electric fan saves more money on electric bills than a attic vented with an adequate (don't stick two up there no matter how big your attic is, for some reason two always seems to be the perfect # LOL) number of turbines. I use turbines and my attic, in full sun rarely exceeds 20 degrees above ambient, I doubt the electric fan would make the attic cooler to the point I would see any electric savings. I will say Oklahoma has more wind avalible to turn the turbines than most areas of the country, hence why they are so popular here.

Other than snow, ridge vents also have a problem with the "filters" plugging up with dust an debris over time rendering them useless, so if a ridge vent is chosen be sure it doesn't use a fiber/cloth "filter"
 

Last edited by 54regcab; 08-11-02 at 07:44 AM.
  #17  
Old 08-11-02, 10:10 PM
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After replying to this post, I will seriously consider using a turbine fan on a hip roof, but it will depend on the site. Here in the northeast our housing stock is old and quite large. For some reason people like old homes up here. When that tree was planted 70 years ago, it was quite small. Today, it towers over the house. There is a term we use up here known as "Widow Maker." I'm trying to imagine the number of calls I would get, even after a small storm.

20 degrees above ambient. Based on what you described, I'll make an assumption that your roofing shingles are light colored, depending on the size of the roof, a turbine every 600 to 800 square feet of attic floor area and your averaging 3 knots of wind a day. There is no way a 1750 cfm fan could accomplish that temperature drop. Most electric attic fans accomplish an average 20 degree drop and not 20 degrees above ambient.

However, even an average 20 degree drop is significant in prolonging the life of the roof.
 
  #18  
Old 08-12-02, 04:58 AM
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Lightbulb Properly vented

Yes I have probably overvented going with a 1/150 ratio instead of the conventional thinking of 1/300

12 soffit vents about 2.5" x 22" using 1/4" hardware cloth and 2 turbines on the roof.

House is 900 sq ft, has relatively light colored shingles with little shade.

Wind is typically 5-10 mph average which helps the turbines do there job

Even when there is no wind I can see the turbines turning just from the hot air rising, on these days I'm looking at 25 degrees above ambient at 3:00 in the afternoon with it quickly cooling after the sun goes down.

Most attics that are supposedly properly vented don't even get the 1/300 right, normally closer to 1/600 after considering NET free vent area !!

Passive venting works great BUT you MUST use enough of it !!!!
 
  #19  
Old 08-13-02, 02:31 PM
rbisys
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Greetings,

Ridge vents can be installed on a hip roof also.

Check cor-a-vent.com

Another thing, contrary to what the mfgr tells you, you can get rain thru them, particularly if they jam and there is a driving rain.
What, a machanical device jamming? Who would have thought.

Thank you for considering my opinion.
 
  #20  
Old 08-22-02, 01:38 PM
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i too live in northeast & have a much needed hip roof to vent

Resercon, I live Northern NJ & am finally ready to vent my hip roof. Any 2nd thoughts on saying you probably would use a turbine on your next hip roof?

I bought the hse 2 yrs ago; its 30 yrs old, 2700 sq ft living area, and is in an area that is always windy. The roof currently has only 2 roof vents and 6 soffit vents; totally under-vented correct? Yes, its hot in the summer!

I really like the idea of an passive-powered solution. Also, Is there a turbine anyone would recommend?

Appreciate your help and really liked your resercon website!
 
  #21  
Old 08-22-02, 02:50 PM
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2 turbines

Always seems to be the "right" amount regardless of attic size LOL

You need 5 turbines total so you will need to add 3 (one per 500-600 sq ft)

Also you will need 120 sq in free vent intake area MINIMUM per turbine, 200 per vent would be ideal.

I use turbines and my attic rarely exceeds 20 above outside tempature.
 
  #22  
Old 08-22-02, 03:28 PM
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Re: 2 turbines: Any recommendations?

Thank you!

I believe you like aluminum ones any other features or brands you have found to be best?
 
  #23  
Old 08-22-02, 04:02 PM
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Lightbulb Aluminum

Yes they are 1/2 the weight, therefore easier for the wind to turn
I don't think they vary much from brand to brand, but Whirlybird makes an excellent turbine.

Pay the extra for the colored ones if they match your roof, they will be much less noticable.

Don't forget to add soffit vents if needed, turbines need plenty of air to work properly
 
  #24  
Old 08-22-02, 05:01 PM
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Greetings,

Since you have to cover turbines in the winter and the purpose of a venting system is to remove the winter moisture, what do you use to replace the turbine during winter?
 
  #25  
Old 08-22-02, 05:18 PM
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Talking Don't cover turbines

Leave the turbines open, the attic SHOULD be insulated from the house anyways.

Do you block the cor-a-vent in the winter ??
According to some, the ridge vents allow MORE air through than turbines do ....
 
  #26  
Old 08-23-02, 06:21 AM
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Re: Don't cover turbines

Thanks again!
 
  #27  
Old 08-23-02, 06:26 AM
gubs18
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Re: 2 turbines - WHAT SIZE?

which size did you calculate for to get 5 total turbines (think they are 12" & 16?)?
 
  #28  
Old 08-23-02, 07:50 AM
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Wink 12"

Standard size at home centers.
I haven't seen any other size except online.
The sqft per turbine is nornmally listed on the outside of the box along with intake requirements.
Most say 500 to 600 sq ft per turbine, check to the box to verify
 
  #29  
Old 08-23-02, 01:27 PM
rbisys
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Greetings,

No, you don't cover ridge vents, but then you don't have the problems with ridge vents that you do with turbines. Under the right conditings turbines can let snow and rain in. Seems to me the manufacturer recommends covering in the winter.

If I remember correctly, years ago a Texas University did in field testing of turbines and the weren't too impressed. In every independent test I ever saw ridge vents were far superior to turbines.

Wjen I did remodeling work I took alot of turbines out, at customers request, never put one in.


Thank you for considering my opinion.
 
  #30  
Old 08-23-02, 02:26 PM
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Lightbulb Evidence

We have already seen evidence of many brands of ridge vents with filters clogging up .
How effective can that be ??
Even clean a cloth mesh restricts airflow by a significant amount.
Cor-a-vent doesnt use the mesh but the product isn't widely avalible at home centers (at least in my area anyways)
Wind driven rain has also proven to be an issue with ridge vents.
I personally haven't had any leakage problems with my turbines even in hurricane alley Oklahoma.
Cor-a-vent already did a low pressure experiment on airflow, I would think a 12" basically unrestricited hole in the roof would provide very low backpressure (notice they never tested it)
You can even see the vents turning on a still day from the heat rising out of them.
Also the amount of labor to install the ridge vent can be an issue.
I assume you arer using the cor-a-vent in YOUR attic, what is the temp up there on a 95 degree day ???
 
  #31  
Old 08-25-02, 10:35 AM
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Greetings,

Glad you mentioned the clogging of the mesh, that's why I recommend cor-a-vent to the new home customers. Cor-a-vent doesn't use mesh. Their new design includes a flapper seal to prevent infiltration during high winds. I never had a problem with the old product either. When one of the firt mesh type products came out I called the company and asked their engineer about this very thing, even before it was a problem, and he hung up on me.

Instead of asking me those questions about vent area, I suggest you call cor-a-vent 800 number and ask them direct.

While you're asking that question you could also ask them where to buy in your area. Have we gotten so lazy that if it isn't in the store it's not worth pursuing? Is this part of the immediate gradification virus that is so common?

By the way, I'm sure they can also give you more detailed info about the problems with turbines and/or where to get such info.

Besides if you have the radiant barrier up there it really doesn't matter how hot it gets.

Thank you for considering my opinion.
 
  #32  
Old 08-26-02, 06:32 AM
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here's what I know

When I cut the 12" hole in the roof to install the turbines i could feel a quite powerful blast of hot air coming for m the attic.
Direct shot from the attic to the outside.
The turbines realtively open design offers very little resistance to the air flowing out (assuming no wind condition, with wind the turbine actually draws air from the attic)
The turbines will tun in no wind conditions just from the force of the hot air rising out of the attic.
The main downside to the turbines is appearence, when you have enough up there to do the job (not just 2) it can look "industrial" to some ppl.
Ridge vents are much less noticable on the roof, but I have my doubts about the actual airflow compared to hte turbines in real world conditions.
I have never seen an attic that uses ridge vents be only 20 degrees above outdoor ambient unless it was in the shade all day.
Turbines have giving me 20 degrees above ambient (It did go to 25 above ambient once when there was no wind and 100 degrees outside) even in full sun all day, so that has made ME a beliver !!
To me that is as good as an electric fan but with -0- operation costs.
I think ridge vents have a good deal of "friction losses" due to the surface area the air must pass over to exit.
I would love to see a ridge vent showing 20 degrees above ambient in full sun
 
  #33  
Old 08-26-02, 11:46 AM
rbisys
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Greetings,

I find it intresting that you come back on line expressing concerns that you have no knowledge of and apparently have no intention of finding the answers to. You blow your credibility when you do that.


Thank you for considring my opinion.
 
  #34  
Old 08-26-02, 12:21 PM
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Red face Insulation contractor

What kind of numbers are you seeing in the field with cor-a-vent ridge vents ??
Since you have been doing this for 28 years I'm sure you have run a few tests.
I haven't personally used cor-a-vent, maybe they perform much better than the average ridge vent.
I have yet to see any ridge vent installation with a 20 degree over ambient result.
If you have seen otherwise please tell us about it.
 
  #35  
Old 08-26-02, 05:55 PM
rbisys
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Greetings,

Ye gads man, call the damn company.

I don't care if it's 200 degs up there the foil will protect the interior. You're so concerned about the attic air temp and don't realize that radiant energy is radiating directly to the insulation that is absorbing and re emitting at a 90%+ rate to the house. The radiant energy doesn't care what the attic temp is. The ridge vent is for removing MOISTURE, as is the pupose of all vent systems. If you have a high efficiency RB up there the attic temp will be about 11 degs above ambient, about 1/2 less than you're all excited about. It takes acombination of the right products to get effective performance.

Done.

Thank you for my opinion.
 
  #36  
Old 08-26-02, 06:16 PM
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Question Cooling attic

So laying a radiant barrier on top of the insulation DECREASES the attic tempature ??
Doesn't it reflect the heat back into the attic (instead of going into the house) thereby INCREASING the attic temps
I could understand it keeping the attic cooler if it was a under the rafter application.
I do agree as far as cooling goes the radiant energy seems to be the bigger issue.
AS far as ridge vents go, for new construction and reroofing I can understand, but there is just too much labor involved for a plain ridge vent installation in most cases.
Turbines require a simple 12" hole in the roof and they are ready to go
Also where are you purchasing the cor-a-vent product ??
 
  #37  
Old 08-27-02, 11:47 AM
rbisys
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Greetings,

I can't tell you the exact reason, an engineer probably could. All I know is that I developed this system to make it easier to install and then got better results. I belive part of the reason is that the rafter and gable end sf surfaces are greater and there fore more energy is available.

The other thing about the temps is that it is believed that the roof does not see an abosorber of the heat it is holding, that the heat is reradiated to the atmosphere. On retrofit the attic will get very hot if there is not some ample venting. But then again the heat energy is going to be greatly reduced to the living quarters. Consider, a foil at 110 degs will radiate only about 2 BTUs/hr/sf . If memory serves me right going to 180 degs only inceases to 3 - 4 btus/hr/sf. A drywall ceil'g at 110degs (95 deg day) will radiate about 37 btus/sf/hr. Do you see now why I am not too concerned about how cool the attic is? You can check this in an Engineering Handbook, material emissivity sec. The formula for calculating the BTUs is there too.

I've put in many a retrofit ridge vent. Most homes have ample soffit area so the ridge vent is no problem. I always go end to end and put a s shot opening in the gable soffit if it is covered. I do this because you get condensation and rotting of the sheathing at the top.

There are 2 roofing companies that handle cor-vent. One is ABC Supply, you may have an outlet in your area.

Thank you for considering my opinion.
 
  #38  
Old 10-01-02, 09:11 AM
Member
Join Date: Sep 2002
Location: Michigan
Posts: 126
attic fans

For homes with two layers of shingles an attic fan is a best idea for prolonging roof life in hot weather.



 
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