Is this enough attic ventilation?

[smp7015]

I have sofet vents all arount the house. In the roof I have 3 vents that are like this picture:
http://www.geocities.com/sp7015/vent.jpg


Do you think this enough ventilation for a 1700 sq foot attic?

[rasmussen6880]

it should be ok. if you are concerned with ventilation try adding an attic ventilation fan. relitivly low cost and in most cases its like adding an other half ton to your a/c.

[uktra]

Adding a power vent is the worst thing you can do. While I understand Folks in the HVAC service end of the business like to work in cool attics, giving the wrong advice is not helping the homeowner.

[docholiday]

I dont think its wrong advice as long as there is no draw from the conditioned space. The alternative is to use a better insulation on the ducts. A 120+ attic is foolish. Insulation is one thing but you are looking at a 45 degree difference between your home temp and a 65 degree difference between your duct temps. The larger the difference, the faster the losses.

Why is it the wrong advice? Can you explain?

[johnsp]

Some say the energy used by the fan is a great as the loss in BTU cooling. Maybe a solar power exhaust fan would be the best option. Would only run during the sunny/hot part of the day.

[uktra]

Yes it is bad advice because the chances of having an air tight attic in a code buit existing home is nil. Even if the attic was air tight, the energy to run the fan offsets any savings in lowering the heat tranfer. The correct advice would have been to first seal all the holes in the attic. Then make sure you have enough insulation. Sealing the holes has one of the highest cost benefit ratios, because it can be a do-it-yourself project.

[Edited by uktra on 07-01-2005 at 08:34 AM]

[docholiday]

Respectfully, I must disagree, a sealed attic is not a good idea. They should indeed be well ventilated. Gable ends are better than soffit vents for power exhaust. Soffit vents and either gables or ridge vents are good for natural ventilation. The house should not be under positive pressure and the attic should not be under a negative pressure. Otherwise, this is when you leak conditioned air.

The drop in attic temp in a ranch home by 10-20 degrees can be a significant reduction in load and cooling requirements and the amperage to run the fan is likely less than the additional compressor requirements to accomplish the same thing.

Remember the equipment is already installed and the duct is done, I offer an exhaust fan as a viable option at this point.

[uktra]

When I said seal the holes, I was referring to the holes between the attic and rooms below. When you put a power vent in an attic you create a negative pressure that does pull conditioned air from the rooms below. In many tests on real homes this was found to increase a/c cost not decrease costs.

[millerman]

If you have proper ventilating like soffit, ridge or eve vents, a powered fan will not put negative pressure in an attic. That's why they make them in differant cfm sizes. The fans as well as the attic vents should be sized accordingly.
I agree with the Doc, this is good advice.

[uktra]

Millerman--That is absurd. Any hole whether from rooms below or to the outside will have a pressure differential on it. And when air comes from the rooms below, the replacement air comes from outside. Tracer gas tests have shown that the infiltration rate of the home increases from 30 to 100% over normal infiltration rates due to power vents.

[Panama]

smp7015,

Did you ever find out whether your system has a TXV?

I ask this because you seem to have ignored this issue in previous threads. A TXV can really make a big difference in the output of an AC system. This is mainly because many installers don't know how to properly charge a system with a fixed orifice. Overcharged systems are far more common than most pros realize. And an overcharged system won't put out the cool and will cost more to run. The charge is not as critical in a system with a TXV.

Maybe it's time to call Central City Air and get your house cool before August!



[Edited by Panama on 07-01-2005 at 12:00 PM]

[millerman]

Originally posted by uktra
Millerman--That is absurd. Any hole whether from rooms below or to the outside will have a pressure differential on it. And when air comes from the rooms below, the replacement air comes from outside. Tracer gas tests have shown that the infiltration rate of the home increases from 30 to 100% over normal infiltration rates due to power vents.
Absurd? Please. If you have an eve vent with an opening to allow 100 cfm and a fan pulling 100 cfm how could you be in the negative and pull air from the living space? As I said SIZED ACCORDINGLY! Power venting an attic is a good idea if all is done properly, your comic book articles may tell you differantly. I'm sure these articles are written about diyers that just slap a fan in without proper venting. :rolleyes:

[uktra]

Yes absurd! a 100 cfm fan is not pulling 100 cfm from one opening if there are other openings. If you don't think a power vent pulls air from below, go buy a smoke pencil and put it next to a non-airtight canned light and watch what happens to the smoke when the pav comes on. Thats not theory, that "in the real world".

[ps]

Here we go again!

[whos on call]

uktra.
This is my first reply. Uktra your not making sense. Are you saying that a 100 cfm fan pulls more than what it is rated for? If so then I need to go back to school and complain to my teachers that I was taught incorrectly. I want my money back!! The fan will pull the air that is closest to it, and if that vent allows for 100 cfm or greater, then thats where the fan is going to pull the air..period. Thats not my opinion, thats the laws of physics. You can't argue with reality.

[ps]

And not all comments deserve (or warrant) a reply.

[tuccillo]

Originally posted by whos on call
uktra.
This is my first reply. Uktra your not making sense. Are you saying that a 100 cfm fan pulls more than what it is rated for? If so then I need to go back to school and complain to my teachers that I was taught incorrectly. I want my money back!! The fan will pull the air that is closest to it, and if that vent allows for 100 cfm or greater, then thats where the fan is going to pull the air..period. Thats not my opinion, thats the laws of physics. You can't argue with reality.

If you have a PV rated at 100 CFM, and it is indeed exhausting 100 CFM, then 100 CFM will be drawn into the attic from any source available. You cant assume it will only drawn from gable vents - it may, and probably will, draw from the conditioned space of the house. The ratio of air drawn from the outside via vents to air drawn from the conditioned space of the house will vary from house to house depending on how well sealed the conditioned space is from the house. Air moves in response to a pressure gradient force created by the exhausted air and will move to reduce the pressure gradient force.

[tuccillo]

Originally posted by docholiday
Respectfully, I must disagree, a sealed attic is not a good idea. They should indeed be well ventilated. Gable ends are better than soffit vents for power exhaust. Soffit vents and either gables or ridge vents are good for natural ventilation. The house should not be under positive pressure and the attic should not be under a negative pressure. Otherwise, this is when you leak conditioned air.

The drop in attic temp in a ranch home by 10-20 degrees can be a significant reduction in load and cooling requirements and the amperage to run the fan is likely less than the additional compressor requirements to accomplish the same thing.

Remember the equipment is already installed and the duct is done, I offer an exhaust fan as a viable option at this point.



Ventilated attics may make sense (and actually be needed) in cold climates but there is a growing body of evidence against it in warm climates. I have a non-ventilated attic - sprayfoam insulation on the underside of the roof sheathing. My attic temperature is between 80 and 90 degrees on the hottest days. We religously use bathroom fans to exhaust moisture from showers and the AC takes care of the rest. I am sure the absolute mosisture content of the air in our attic is less than the absolute moisture in the outside air and it is certainly cooler. There is no need for ventilation.

[ps]

Tuccillo - you are a kinder and more patient person than I.
The observed tone and lack of basic knowledge of some posts are usually a sign of someone looking to stir it up and hijack the thread. I like a good fight when opponents are evenly matched - but the previous poster was obviously way out of his league and just spoiling for some name-calling.

[tuccillo]

Originally posted by ps
Tuccillo - you are a kinder and more patient person than I.
The observed tone and lack of basic knowledge of some posts are usually a sign of someone looking to stir it up and hijack the thread. I like a good fight when opponents are evenly matched - but the previous poster was obviously way out of his league and just spoiling for some name-calling.

PS, thank you for your kind words, although my wife would argue with you ;-). The problem with a lot of these discussions is that they are not black and white - just a uniform shade of grey. There is a mixture of people's realife experiences and controlled, scientific experiments. My own experiences with PVs was not a good one. It was obvious to me that significant amounts of conditioned air were being drawn into the attic from the PVs, although some of it could also be the stack affect. The reason I know this is that I could see black dust accumulate between the floor molding and the carpet. Clearly the carpet was filtering dust out the air as it got sucked past the floor molding and into the wall cavities leading to the attic. My attic had a lot of soffit vents and a large gable vent - perhaps more were needed - hard to say - the only thing I know for sure was that there was air motion into the wall cavities. Also, the attic was still plenty warm - I regret never putting a thermometer up there.

In my new house we have a sealed (non-ventilated attic) - it is quite comfortable up there in the middle of the day.

[smp7015]

Ok!!

All this argueing over ventilation an Pv's. All I want to know is giving the pic I posted, are three of theses enough to keep a 1500-1700 foot attic cool with sofet vent's all the way around:

http://www.geocities.com/sp7015/vent.JPG

[dash]

Sure ,







if they pull enough air from the home.LOL

Seriously,what you have been told is worth checking,if the walls ,etc. aren't tightly sealed,and/or the soffit vents are too small,it's more of a problem then not.

[tuccillo]

Originally posted by smp7015
Ok!!

All this argueing over ventilation an Pv's. All I want to know is giving the pic I posted, are three of theses enough to keep a 1500-1700 foot attic cool with sofet vent's all the way around:

http://www.geocities.com/sp7015/vent.JPG

Define what you mean by cool.

[ps]

smp - unfortunately, there is no way anyone here can give you the thumbs up or down. There are too many factors to consider and in the end, the only way to know for sure is via actual measurements over an extended period of time taking into account all the contributing (and varying) influences on your measurements.

I don't know your situation - but I would suggest that you have the installer "prove" to YOU that it is sufficient, along with the criteria he is using as the basis for his installation/design. Good luck.

[whos on call]

Tuccillo
I am not assuming. Everything in nature always attempts to take the easiest route in order to accomplish it's task.
In the case of replacing exhausted air, the air will be replaced by air that is closest in proximity, and in this case it will come from the nearest vent opening. Like I said , this is not my opinion, but it is a fact. Your not going to get negative pressure in a room that has equal inlet and outlet pressures, nor is the space under the attic going to try to compensate for exhausted air that is being replaced on a countinuous basis, by inlet air that is readily available close by.

[uktra]

Whos on call--we are not talking about nature, we are talking about pressure differentials. If you pull air from an attic you will have a pressure differential on all holes no matter where they lead. If it is a 100 cfm fan, 100 cfm is not coming from one hole if there is more than one hole. You get a whole house fan in the old days and you can feel wind from many rooms if the windows are open. Again--buy a smoke pencil, and put it up to a non-sealed canned light and see what the smoke does when the pav is on vs when its off.

[tuccillo]

Originally posted by whos on call
Tuccillo
I am not assuming. Everything in nature always attempts to take the easiest route in order to accomplish it's task.
In the case of replacing exhausted air, the air will be replaced by air that is closest in proximity, and in this case it will come from the nearest vent opening. Like I said , this is not my opinion, but it is a fact. Your not going to get negative pressure in a room that has equal inlet and outlet pressures, nor is the space under the attic going to try to compensate for exhausted air that is being replaced on a countinuous basis, by inlet air that is readily available close by.

Sorry sport, the attic will always have negative pressure with the PV running otherwise you could not have a pressure gradient that forces air movement. The pressure gradient is a 3 dimensional field that will vary throughout the attic. While the mass flux entering and leaving the attic may be the same, this only happens with a pressure gradient. You are making assumptions about the geometry of the attic and where air will come from. Without modeling it, you dont know where is coming from. I dont believe you know more than the people who study this stuff for a living. You are are in over your head - I suggest you give it up.

[smp7015]

Well I was doing some research and the vents I have in the attic are suppose to vent a 104 sq feet of attic space.

There are only three of these vents. So 3 times 104 is 312 sq feet of attic. The attic itself with the attatched garage is like 1800 sq feet. Look's like me an the builder are going to get into it again!!

[uktra]

Smp7015--Venting codes in attics are to prevent ice dams. In the 70's people started turning this into the "get the hot air out" reason for having vents. If you are concerned about cooling your house properly, the most important areas of consideration are; leaky ducts-air handlers if in the attic, holes between the attic and rooms below, and the insulation levels. Those are things that will save much more energy than a slight decrease in attic temps. Not only that but they will save in cold weather also.

[whos on call]

tuccillo
o.k thats all I wanted to hear. I couldn't care less about being wrong about the absence of negative pressure "Sport". I did notice, however subtle you were trying to be, that you admit that you are not going to get makeup air from the living space when you already have enough in the attic. I do not know who you think you are talking to, but I am not the type to ball my ass off when I am wrong about something, however you on the other hand sound like many others I've encountered before. Here's a tissue.

[old yeller]

Uktra- I gave you the last laugh on the PAV- they do draw too much from the house.

BUT- I find it hard to believe that you would say lower attic temps are not a good thing no matter how you get them. PAV, radiant, sprayfoam, whatever.

To the original poster- I will answer a very confident and qualified:

NO - you do NOT have enough venting for your attic. PAV is the riskiest method and uktra will probably find out where you live in break it in the night.

You need more ventilation- period. get it however you can.

AC units are NOT designed to be run in attics that are rediculously hot. Yes, they can do it, but they are NOT made to do it with any kind of efficiency.

Tucillo has, BY FAR, the best setup with the sealed attic and spray foam, but I am afraid it is too late for you.

I am not saying PAV is the way to go- you should at least look into replacing two of those vents with whilry birds and having the third covered up- yes, covered up- it will do more harm than good if you don't. Also make sure you have lots of UNBLOCKED soffit vents. Check them- the builder may have skimped. The are often blocked with insulation.

[uktra]

Old Yeller--I never said lowering attic temps is not a good thing. What I have said time after time is that spending money to lower temps in the attic to try to lower cooling bills or increase comfort is NOT the best return on investment due to the fact that hot air doesn't tranfer as much heat to the attic floor through the insulation as the radiant transfer. What is a better return on investment is to seal ducts and the air handler (you can lose 30% of the cooling power with leaky ducts). Sealing the holes between the attic and rooms below (this can be a do it your self project with a high cost/benefit ratio). and last make sure there is enough insulation. These things pay back both summer and winter.

[old yeller]

I completely agree with that.

If I were to seal everything- walls, ducts, etc.. and my AC still works too hard or can't handle the job, I should then look into taking steps too bring attic temps down- that heat WILL find its way to the ceiling through the insulation- no matter how thick. OFten the excessively thicker insulation will actually hold MORE heat in the summer- even if it is beneficial in winter. That is proven.

I admit you didn't SAY that- you seemed to make the point by discounting any arguments for lower attic temperatures.

At SOME point ludicrous attic temperatures WILL have an effect on heat load.

[tuccillo]

Originally posted by whos on call
tuccillo
o.k thats all I wanted to hear. I couldn't care less about being wrong about the absence of negative pressure "Sport". I did notice, however subtle you were trying to be, that you admit that you are not going to get makeup air from the living space when you already have enough in the attic. I do not know who you think you are talking to, but I am not the type to ball my ass off when I am wrong about something, however you on the other hand sound like many others I've encountered before. Here's a tissue.

I am not trying to be subtle. You dont know where the air is coming from and you dont have a clue about the physics of the situation. Since you dont know what you are talking about I suggest you shutup. Is that nasty enough for you, sport?

[old yeller]

Hows about you two take this outside to the parking lot...

[uktra]

Old yeller--insulation does't hold heat. Insulation slows heat tramsfer by making heat change its means of transfer. hot air transfers heat to the rooms below by two methods through insulation. conduction and convection. conduction is where the hot air meets the top of the insulation surface. convection is where the hot air blows through or around the insulation. Many times there is more heat transfer from convection than conduction. That is why sealing all the holes is important and cost effective if you do it yourself. Just sealing the holes (beneficial in both summer and winter) will save more energy than any pav.

[Black Adder]

How about a power venter in the roof and a matched fan supplying outside air into the attic? Makes sense to me. I am not too concerned with saving money on this guys power bill but I am concerned with seeing his A/C unit achieve the proper level of temperature he is looking for in his home. Now I suppose I am going to be told that putting a dedicated fan to introduce outdoor air to the attic will only add warm outdoor air into the house via infiltration. I would think some good gable vents and a couple of decent whirly birds would also do the trick. Cross ventilation is the key. If you put a pile of roof vents in there they are only going to vent as much air as they can pull into the attic at a lower point do to the nature of convection a(hot air rises).

[uktra]

Black Adder--what you suggest would lower the amount of conditioned air coming from the rooms below. The point I am trying to make is that the best things to do to lower the load and let his unit reach set point are the three things i suggested before.

[Edited by uktra on 07-02-2005 at 11:01 AM]

[docholiday]

OK, IM lost....

How hot is your attic on say an 85 or 90 degree day? So far we dont know that, at least I dont. If it is above 120 degrees, then you got an attic issue. You also need to know what kind of temperautre rise your ducts are experiencing from start to end. You can run your fan only and read return temp and supply air temp at the grilles. This is not always a true measure though. Then you need to run the machine (increases temperature difference and read your supply air at the plenum and the register as well as the return plenum and return air grille. Add the two differences. You can actually figure the lost btuhs if you know the actual CFM.

I dont have any holes in my ceiling and my ducts are sealed and insulated so an attic fan will simply not pull from the house, especially if you have ample opportunity for it to come in either through soffits or gables. I'm afraid the air would take the path of least resistnace. It would be a good idea not to have the fan close to the gable ends or the work is usless. The greater the temperature differecne, the faster and greater the heat transfer. So if you ceiling is hot you will absorb heat into the room (hot goes to cold). If you can keep your ceiling cooler by not exposing it to such extremes the heat transfer amount and rate are much less. This also goes for the ductwork. It needs to be well sealed and insulated to slow the transfer of heat..

As far as pressure differences go, yes ther has to be a difference or air will not move. However, it does not need to be great provided you have plenty of opening. A leaky return is a perfect example. The atmospheric pressure around the return is much higher than the return's negative pressure.

[pstu]

Several different points:

1) I have also been told that attic insulation *can* store BTUs, by no means do I consider that I know enough on this topic. Since it is a solid material, it seems clear to me insulation must be able to store *some* heat. Perhaps if I had some idea of how the specific heat or other qualities of that insulation (how many BTUs to raise its temperature 1 degree) that would make the truth clearer.

2) On whether a power ventilator sucks interior air from the house, it seems to me probable that is unavoidable unless you have *no* leakage between the attic and the ceiling. For example if you have 50 sq.in. leak at the ceiling (easily obtainable) and 450 sq.in. soffit vents, then one would expect the leakage to be 90% from outside air, and 10% from the house interior. Does that make sense?

3) Has anyone referred to standards of ventilation area for attic soffit and attic ridge? I tried to follow this thread but don't remember that. I have seen a recommendation of 1 sq.ft. of "net free area" per 100 sq.ft. of ceiling area, along with the idea that oversizing that vent area is a good thing (assuming you won't go with the conditioned attic design).

Best wishes -- P.Student

[deejoe]

Rule of thumb;A minimum of 1 sq ft of vent for every 300 sq ft of attic floor area .This total is split 50/50 between the (low vents) soffit, and the (high near peak vents)or ridge vents. In your case; based on 1800 sq ft= 6 sq ft= 3 sq ft for low vents and 3 sq ft for high vents.
Remember this is " free" area. Some vents may have an opening of 144 sq inches (1 sq ft), but with the screen attached to it may only be approx 72 sq inches (1/2 sq ft.

[bluetooth751]

I used to believe in attic fans also. but know after going to an e-star school I have to agree with ulkra.

Putting a fan in an attic is just an easy way to suck conditioned air from the living space.

I would prefer to you install a radiant barrier on your roof rafters or have it sprayed with foam.

If you still want to use the fan setup make sure your attic is sealed like previously stated.

Attic temperatures that are too high will also lead to condensation problems and lose of capacity on your a/c equipment.

I recently installed a 2-speed variable speed fan setup in a customers home with a metal roof. His attic reaches temps of 130 degrees plus. He also likes his a/c set on 70 in the middle of the day. Add all that up and you have serious condensation issues. Even with a trunk and branch system rated at R-8.

Less heat in the attic is a benefit...

[old yeller]

Good points-

Uktra- I am agreeing with you again, but you have put your blinders back on and are refusing to see outside the box.

After reading the material at the links you provided, I read that it has been proven the insulation can and does store heat. If it can slow down the convection in or through it, it will also slow down the convection OUT of it. More insulation is not ALWAYS better.

You are correct, and I agree, sealing obvious holes and keeping the cool air you have is the MOST cost effective way of saving money.

ALSO- once that has reached it's peak benefit, and more steps ARE necessary to ensure comfort (NOT cost efficiency), there is no other option but to bring attic temperatures down someway, somehow. Radiant, vents, anything.

You still have not denied that you are arguing to ignore attic temperatures completely. I am not putting words in your post, it's just that is your obvious point, unless you clarify otherwise, please.

[uktra]

Doc holiday--I have been involved in sealing many attics on the homes I help build and I have never been able to get one air tight yet. I can tell you for sure yours is not either. But even if it was, you are only eliminating convective heat transfer to the rooms below. The pav still uses electricity, and the majority of heat tranfer to the rooms below is still radiant not conductive. You are only lowering the conductive transfer (from 120 to 130 to outside temp.)not eliminating it. Pavs have no effect on radiant.

P student--You have been told wrong. Heat always flows from hot to cold, while insulation slows this process, the flow contiues.

Bluetooth751--I would be surprised to see condensation on R-8 ducts if there is no leakage. Generally the surface of the duct is above the dew point.

[uktra]

I don't have any blinders on. I never said conductive heat transfer from the attic to rooms below doesn't matter. If one has invested his money in all the other ways to lower heat transfer that I have mentioned, and stll has not been able to reach set point, then adding additional PASSIVE ventilation will help. Adding a pav not only will not help, but will probably increase load due to higher infiltration rates.

[old yeller]

Originally posted by uktra
I don't have any blinders on. I never said conductive heat transfer from the attic to rooms below doesn't matter. If one has invested his money in all the other ways to lower heat transfer that I have mentioned, and stll has not been able to reach set point, then adding additional PASSIVE ventilation will help. Adding a pav not only will not help, but will probably increase load due to higher infiltration rates.

OK- we're cool. Thank you.

[uktra]

You are most welcome--have a great 4th.

[Carnak]

I always thought that venting the attics was first off a northern thing, to stop condensation in the winter.

I can see a house in the summer, with poor ceiling insualtion benefitting from a power venter, however sometimes they can depressurize the whole home.

I do not have to worry about the cold weather where I am now, and I think it is better not to vent the attic as it just allows more humidity in.

We had a guy from some icynene (sp?) down here a while back and they promote insulating the whole pitch of the roof and sealing the top of the walls to the roof. May only end up with a 100 degree attic this way. It also seems to rely on leaky supply ducts for additional cooling in the attic.

Seems like a good way to go in the hot humid environment, insulate the pitch with something that does not trap moisture and keep the humid air out.

[uktra]

Carnak--you are correct about vented attic due to prevention of ice dams. Vented roofs for cooling climates are fine as LONG AS THE DUCTS & AIRHANDLER are NOT IN THE ATTIC. Then like you say insulating the roof inder the sheathing is the way to go.

[Carnak]

It is unfortunate that you get forced to put air handlers and duct work in humid attics in order to maximize floor space and ceiling heights.

Then everyone gets dissapointed when these cold systems inevitably do what comes natural to them and they sweat.

[uktra]

One of the ways I get around the codes is to put foam chutes between the roof rafters and then net and dense pack cellulose. This turns the attic into conditioned space and yet still meets codes.

[mdman]

Originally posted by whos on call
uktra.
This is my first reply. Uktra your not making sense. Are you saying that a 100 cfm fan pulls more than what it is rated for? If so then I need to go back to school and complain to my teachers that I was taught incorrectly. I want my money back!! The fan will pull the air that is closest to it, and if that vent allows for 100 cfm or greater, then thats where the fan is going to pull the air..period. Thats not my opinion, thats the laws of physics. You can't argue with reality.

"go back to schoo", yes that's a good idea. As if there are any scool in HVAC worth more than the price of the text book.

uktra is the only one not talking trash in this thread. I could direct you to some good reading that I'm sure uktra is well aware of, but I'd be wasting my time.

md

[tuccillo]

Originally posted by Carnak
I always thought that venting the attics was first off a northern thing, to stop condensation in the winter.

I can see a house in the summer, with poor ceiling insualtion benefitting from a power venter, however sometimes they can depressurize the whole home.

I do not have to worry about the cold weather where I am now, and I think it is better not to vent the attic as it just allows more humidity in.

We had a guy from some icynene (sp?) down here a while back and they promote insulating the whole pitch of the roof and sealing the top of the walls to the roof. May only end up with a 100 degree attic this way. It also seems to rely on leaky supply ducts for additional cooling in the attic.

Seems like a good way to go in the hot humid environment, insulate the pitch with something that does not trap moisture and keep the humid air out.


I see 80-90F in the summer in south GA with an unventilated attic.

[mdman]

Originally posted by tuccillo

Originally posted by Carnak
I always thought that venting the attics was first off a northern thing, to stop condensation in the winter.

I can see a house in the summer, with poor ceiling insualtion benefitting from a power venter, however sometimes they can depressurize the whole home.

I do not have to worry about the cold weather where I am now, and I think it is better not to vent the attic as it just allows more humidity in.

We had a guy from some icynene (sp?) down here a while back and they promote insulating the whole pitch of the roof and sealing the top of the walls to the roof. May only end up with a 100 degree attic this way. It also seems to rely on leaky supply ducts for additional cooling in the attic.

Seems like a good way to go in the hot humid environment, insulate the pitch with something that does not trap moisture and keep the humid air out.


I see 80-90F in the summer in south GA with an unventilated attic.

Do you read Joe Lstiburek's work or HE mag?