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Thanks for the reply. I thought about a rebuttal that would address issues point by point, but that would take more time than I wish to devote to this. So, I will simply make a few comments (in no particular order) that you can apply as you wish.
First, I don't see any difference, in principle, between hot air rising over cold air when using a fan to help it rise versus letting it rise simply because the hot air is lighter. The lighter objects are going to be the easiest to move as illustrated in my example in my previous post regarding the vacuum cleaner. The exhaust fan is simply expediting the process of the hot air rising faster.
Second, yes, the roof is hot and that's yet another reason why the air closest to the roof is the hottest air. The other reason being, as mentioned, is because the hot air is lighter than the colder air. This is yet another reason why the hottest air will be exhausted first which is our goal.
The only way that I can see that adding an exhaust fan would be detrimental to cooling the attic is if you simultaneously closed some of the intake soffit vents.
As to the claim that the exhaust fan would create turbulence and disrupt the flow of the hot air out of the attic, that would apply only if the fan were directing the airflow back INTO the attic. A properly installed exhaust fan is, of course, directing the airflow OUT of the attic which is what you want.
IF, and this is a big "if", you are convinced that the jumbo exhaust fan that you installed in the attic roof is drawing air IN from nearby roof exhaust vents instead of drawing it from the hot attic through the soffit vents, then the simple solution to that problem is to simply stuff some rags into any nearby exhaust vents. That fixes that problem and, in the meantime, greatly increases your cool airflow in from the soffit vents and thereby lowers the attic temperature which is the goal.
My response is to re-iterate what I suggested before. An efficient and cost effective way to achieve the desired goals is to increase the insulation in the ceiling.
You have air being heated in an attic. A roof vent allows that air to flow out. Instead (or in addition to), you purchase a solar powered vent to create a suction to pull hot air out. It does so.
Some of that air being sucked out comes from the soffits, some comes from the ridge vent. Do you see an issue there, as far as efficiency and cost? IMO, it is just a variation on various free energy schemes. The hot air is in the rhetoric, not the performance.
My response is to re-iterate what I suggested before. An efficient and cost effective way to achieve the desired goals is to increase the insulation in the ceiling.
You have air being heated in an attic. A roof vent allows that air to flow out. Instead (or in addition to), you purchase a solar powered vent to create a suction to pull hot air out. It does so.
Some of that air being sucked out comes from the soffits, some comes from the ridge vent. Do you see an issue there, as far as efficiency and cost? IMO, it is just a variation on various free energy schemes. The hot air is in the rhetoric, not the performance.
MY "desired goal" (in this situation) is to have a cooler attic. Increasing the insulation in the ceiling would have no effect on cooling the attic because the heat isn't coming from the living space.
As I mentioned above, if you think it's necessary, you can close off any nearby "static" vents. The main method of cooling the attic, as I see it, is to move more cooler air through the attic at a faster rate. Doing nothing doesn't help the situation.
Yes, installing an attic exhaust fan or two will cost some money, but it may be money well spent if it increases the life of the roof, makes the attic more useful for storage, AND makes it easier to cool your house.
MY "desired goal" (in this situation) is to have a cooler attic. Increasing the insulation in the ceiling would have no effect on cooling the attic because the heat isn't coming from the living space.
As I mentioned above, if you think it's necessary, you can close off any nearby "static" vents. The main method of cooling the attic, as I see it, is to move more cooler air through the attic at a faster rate. Doing nothing doesn't help the situation.
Yes, installing an attic exhaust fan or two will cost some money, but it may be money well spent if it increases the life of the roof, makes the attic more useful for storage, AND makes it easier to cool your house.
Went through the mental exercise years ago in Florida. Attic heat has about zero effect on the longevity of shingles and roof decking. ZERO. The major factor is the UV impact on the roof, particularly asphalt shingles.
Storage in an attic? Did that at one point. Live and learn. I'll leave it at that.
Your third point is what we are addressing. I won't say you are wrong, but I will suggest that you do more research - which may make you shift your stance.
Went through the mental exercise years ago in Florida. Attic heat has about zero effect on the longevity of shingles and roof decking. ZERO. The major factor is the UV impact on the roof, particularly asphalt shingles.
Storage in an attic? Did that at one point. Live and learn. I'll leave it at that.
Your third point is what we are addressing. I won't say you are wrong, but I will suggest that you do more research - which may make you shift your stance.
Here is what Owens Corning has to say about that.
"When it’s hot outside, the sun beating down on the roof can increase the temperature in the attic. Exposure to this excessive heat can warp the roof sheathing and distort and prematurely age the shingles. If the attic floor isn’t evenly and adequately insulated, that heat can radiate down into the finished living areas and make it more difficult and costly to keep the living space comfortable."
MY "desired goal" (in this situation) is to have a cooler attic. Increasing the insulation in the ceiling would have no effect on cooling the attic because the heat isn't coming from the living space.
As I mentioned above, if you think it's necessary, you can close off any nearby "static" vents. The main method of cooling the attic, as I see it, is to move more cooler air through the attic at a faster rate. Doing nothing doesn't help the situation.
Yes, installing an attic exhaust fan or two will cost some money, but it may be money well spent if it increases the life of the roof, makes the attic more useful for storage, AND makes it easier to cool your house.
Have you considered spray foam insulation under the roof?
Ideally if your home already has a ridge vent and unobstructed soffits then adding an exhaust fan is redundant and not cost effective. If your home doesn’t have ridge vents but instead has a wind driven fan or an electric fan then changing to a larger capacity fan or adding another small fan would increase the air flow. I’ve seen some homes with vents at the sides of the house at the gable and some include an electric fan. All depends on climate, building codes, and original home design. Natural convection is preferred over forced air for attic ventilation. Properly engineered home with forced air will have the right size fans for the attic size. Going too large in forced air will create a negative pressure in the attic greater than normal. Potential issues depend on climate. I live where it is very humid so it could cause more moisture being drawn into the attic, especially during and after major storms. Gable and ridge vents are usually best because they release the air where it is hottest. Exhaust fans mounded on the roof are usually well below the ridge line leaving hot air somewhat trapped at the highest points. A ridge vent and clear soffits will draw air in from under the overhang, up across the length of the roof, and out the top at the ridge. Making the attic a finished space with ventilation is the only other way to keep the attic cool.
I was trying to keep it in as simple terms as possible- I was avoiding the one discipline that explains most of this- Fluid Dynamics.
Then again, maybe I was just trying to convince a H/O that less is more when it comes to systems of a house- a passive system requires no upkeep, maintenance, or replacement.
There was one statement that apparently missed the mark- and will not warrant any further comment.
“…cooling the attic”. Why would there be a purpose to “cool the attic”? It’s to reduce the radiant heat entering the conditioned space. You don’t “cool an attic” for the sake of “cooling an attic”. Insulation has more benefits!
Last edited by K'ledgeBldr; 05-04-2023 at 08:27 AM..
I was trying to keep it in as simple terms as possible- I was avoiding the one discipline that explains most of this- Fluid Dynamics.
Then again, maybe I was just trying to convince a H/O that less is more when it comes to systems of a house- a passive system requires no upkeep, maintenance, or replacement.
There was one statement that apparently missed the mark- and will not warrant any further comment.
“…cooling the attic”. Why would there be a purpose to “cool the attic”? It’s to reduce the radiant heat entering the conditioned space. You don’t “cool an attic” for the sake of “cooling an attic”. Insulation has more benefits!
I think you missed the part about cooling the attic is also to prevent excessive attic heat from damaging the roof itself. This is a real possibility, especially in the southern part of the country where the sun's rays and the heat are more intense. Also, many people use the attic to store things that they don't want cluttering up the house or garage. Excessive heat can damage items you may store in the attic.
From my perspective as a resident of central Florida, the cooler the attic is, the better. Even in the winter, it doesn't get cold enough here for a "cold" attic to do any harm. It's not like we have to worry about ice dams on the roof or anything like that. I haven't seen a snow flurry in 20+ years and the only ice I see is in my drinks.
In my situation, and others like mine, I don't think there is such a thing as "too much ventilation" for an attic. Granted, you may reach a point where it is no longer cost effective to spend more money to provide additional ventilation for the attic, but as long as the rain doesn't intrude into the attic, then the more attic ventilation the better.
In central FL? If I remember correctly, there has been some discussion about roof ventilation and their “susceptibility” in hurricane conditions(?).
Seems I recall a “white paper” on the elimination of “venting” of attic space- pressure differentials, hip roof size (hgt) and pitch, blah, blah, blah; yada, yada, yada. All to reduce damage- which in-turn decreases payouts on insurance, and keep premiums in-check. Then again, maybe it was all hogwash- or in your case, orange juice!
In central FL? If I remember correctly, there has been some discussion about roof ventilation and their “susceptibility” in hurricane conditions(?).
Seems I recall a “white paper” on the elimination of “venting” of attic space- pressure differentials, hip roof size (hgt) and pitch, blah, blah, blah; yada, yada, yada. All to reduce damage- which in-turn decreases payouts on insurance, and keep premiums in-check. Then again, maybe it was all hogwash- or in your case, orange juice!
Obviously, any "venting" that is done to the roof/attic must keep in mind that rain often times doesn't fall straight down. It is sometimes windblown, and therefore the design of the vent is very important, hence my qualifying clause in my last post "as long as the rain doesn't intrude into the attic".
So, with that in mind, do you see anything wrong with my statement in my previous post to wit: "Granted, you may reach a point where it is no longer cost effective to spend more money to provide additional ventilation for the attic, but as long as the rain doesn't intrude into the attic, then the more attic ventilation the better"?
"When it’s hot outside, the sun beating down on the roof can increase the temperature in the attic. Exposure to this excessive heat can warp the roof sheathing and distort and prematurely age the shingles. If the attic floor isn’t evenly and adequately insulated, that heat can radiate down into the finished living areas and make it more difficult and costly to keep the living space comfortable."
Why do I think a lawyer got involved and inserted BS? Roof sheathing is also known as decking. How exactly is excess heat going to warp the decking??? There is a normal thermal expansion and contraction that goes on every day in Florida, but warping? Maybe with wet thin OSB, but code requires plywood in Florida. Distorting shingles? Really? If you have been around asphalt shingles at all, you know they get floppy in heat when new. After the asphalt ages out and dries, they don't. They crack instead. They can curl with age, but I can't recall ever seeing heat "distorted" shingles.
I lived in south Florida for 20 years, not only having my roof replaced, but having regular contact with commercial roofers fixing flat theatre roofs. Every one of them pointed to UV radiation and direct sunlight as being the primary problem with aging roofs.
Attic heat cannot get above the temperature of the roof decking. There is no furnace supplying excess heat. The heat in an attic primarily comes from radiated heat from decking supporting the shingles in the sun, as well as convection heat from the air getting heated by that same decking.
The inference in the quote is that the attic gets hotter than the deck, and that excess heat damages shingles. It is as incorrect as saying that the temperature of your bath water will get hotter than the water in your water heater if you let the water sit in the tub.
At this point, this is devolving into arguing for arguing sake. You want to buy and install solar powered vents? Knock yerself out. You want to think that attic heat will shorten the life of your roof by any significant amount? Go ahead. It won't, but to argue is pointless.
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