Thread: solar attic vent

Any words of wisdom/experience regarding these solar powered roof vents? It was not accessible from the inside.

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As far as usefulness goes, worthless.

Oh yeah, from what I can see (actual cannot see) it's not installed correctly. I do not see flashing on the lower side of roof.

Just an attic fan which depressurizes the attic, sucking conditioned air out from the house, except that this one does it by using the sun to run the fan.

Same bad end result, though.

If adequate soffit vents are installed or gable vents the likely chances of depressurization are slim.

These units are not cheap to purchase. At night they still act as static vents.

Originally Posted by Raymond Wand

If adequate soffit vents are installed or gable vents the likely chances of depressurization are slim.

Only if that fan has almost no useful air movement. If that fan is actually "venting the attic by drawing air out" then that fan can depressurize the attic.

Yes true, but then again I would ensure adequate soffit venting and would ensure any penetrations into attic by plumbing vents, ceiling light boxes are sealed as well as attic.

I am also curious as to Cfm of air these units draw?

As homes are typically at negative pressure with respect to the outdoors (attic included), I would think that one of these would have an incredibly difficult time negatively pressurizing an entire attic space. If you give me fan CFM and attic volume we can see how 'close' it may come in theory. No info was given as to low ventilation points or any other static vents present.

Homes are generally under a 'stack effect', air entering at lower points of building and being pulled up through the house due to solar loading and winds.

Almost every home I see has more square footage in eve/soffit vents than it does roof top vents. These solar vents are no where near the same volume of air an electric roof vents does. I am not sure that I have seen 20% of homes where the roof top vents was equal to the eve vents.

I have found that the solar vents are a great product and the impact to a home in the depressurization is way, way over blown. I recommend to countless clients that they add a solar vent were a turbine vent is.

The wind blowing against the outside of a home, no matter how slight, will keep the AC pounding away all day. As soon as the wind stops the homes (even new homes) AC just comes off and on occasionally. I have seen the solar vents pumping away sucking air out of an attic and it does not appear to keep the AC pumping all day as wind blowing against the side of the home. Along with the air being slightly drawn through the attic and out the roof the attic it far, far cooler which has a much greater positive impact to the homes AC bill. You have to think of all those ducts (in the southern half of the country and many states up north,) and the air handler that is in the attic that has much higher air temperatures around it sucking the energy right out of the ducts and equipment. This has the similar affect to radiant barrier keeping the attic temps much cooler.

In short, and that is how I should have left it, In my opinion solar vents are a wonderful product.

Originally Posted by Raymond Wand

Homes are generally under a 'stack effect', air entering at lower points of building and being pulled up through the house due to solar loading and winds.

The stack effect is relative to difference in indoor temps vs outdoor temp. In the winter when it is cold out the indoor air is being heated. This does 2 things. It expands its volume and it makes the warm air buoyant. So the air flows from the leaks at the top of the house into the attic. Pluse hot is going to cold.

In the sumer the air in the house is being cooled. It is becoming denser and its volume is shrinking. The air from the upper level is falling and thus pulls air into the house from the attic.

Mechanical forces, winds etc can disrupt this pattern so it is not always constant.

You may not think that powered roof vent would not create enough pressure but it will. Air pressure can be measured in pascals or inch of water column. A pascal is 1/250 of in of WC. Blower door testing can be done at 25 or 50 pa. Differences in 1 or 2 pa can determine leaks in a room or area.

Powered attic fans have been shown to draw air out of a house thus costing the homeowner money and not savings it.

It you want to educate homeowners on improving their homes learn that air sealing the attic floor is the best thing they can do. It is all the tiny leaks that add up along with a few not so tiny leaks. Things like the seams along the top plates of interior and exterior walls, holes through top plates for wiring, outlet boxes for light fixtures, can lights, etc. They all add up. Its the small details that matter. Then add cellulose (much better in an attic than fiberglass) so that it exceeds code. You should be looking at R50-60 in most areas. If all that is done it lessens the need for attic venting, I didn't say eliminates the need. Then the 1/300 rule will suffice.

We have all felt the air flow from around a electrical plug in a wall insualted with fiberglass. Fiberglass does not stop air flow. It will not stop the leaks at the top plates and it will not stop the air currents in the attic from degrading its insulation properties when exposed in the attic.

Typically the attic fan is trying to compensate for bad insulation and air leaks but it doesn't work. Tackle the root of the problem for comfort, energy eficiency, moisture source, etc.

What you should know about fiberglass insulation is that it needs to be in a sealed box to perform near its stated R value. In an attic it is open on the top plus it has air leaks from the ceiling below cutting the R value significantly maybe by 50% or more. When you see a skylight chase or a knee wall with an exposed batt its effective R value is around and R3.

Adding 8 inches of cellulose over fiberglass will help the fiberglass perform better plus adding superior radiant heat blocking properties and adding an additional R30. The additional insulation will stop thermal bridging through the joists.

Building Science Digests


BSD-014: Air Flow Control in Buildings

By John Straube
Created: 2008/05/09
Stack Effect

BSD-014: Air Flow Control in Buildings — Building Science Information

Originally Posted by Raymond Wand

Building Science Digests


BSD-014: Air Flow Control in Buildings

By John Straube
Created: 2008/05/09
Stack Effect

BSD-014: Air Flow Control in Buildings — Building Science Information

I have heard both John and Joe talk, more Joe. Joe talks of the limits of attic venting. He has stated is has a limited and minor effect on temperature. I have heard him say that it doesn't do a good job of greatly reducing temps and that attic venting relieves excess heat and helps control moisture buildup but is not great at either. They have done studies and shown only a couple of degree difference in shingle temps between hot and cold roofs so keeping the shingles cooler is not a major function of a vented attic.

Most of the heat gain to the interior of the home is from radiant heat. Air sealing and providing more insulation is a better investment when compared to an attic fan. Air sealing and insulation will do more for durability, comfort, and energy efficiency. He favors cellulose over fiberglass as cellulose does more to block radiant heat and does a better job of trapping air/stopping convective currents.

Joe talks about commercial buildings and why they have revolving doors. In the winter the air will flow in and up but in the summer it will flow down and out. Hot goes to cold and high pressure to low pressure. Bigger effect in taller buildings. In homes in the summer the heat in in the attic and the cold is in the house- relative. In the house the higher pressure is where the colder air is that is the basement. Lower pressure is outside and the air leaks from the basement to the outside drawing air in from above.

In the summer moisture drive will be from outside in. Dryer indoor air from ac. In the winter it will be from inside out.

Originally Posted by Ted Menelly

Almost every home I see has more square footage in eve/soffit vents than it does roof top vents. These solar vents are no where near the same volume of air an electric roof vents does. I am not sure that I have seen 20% of homes where the roof top vents was equal to the eve vents.

Ted

I looked into net free openings of soffit vents and popup vents a while back. I found that soffit vents have a net free opening of about 35-40%. So those 8 x16 vents have a net opening about 1/3 of their actual size, they are not as big as they look. Popup vents had a free area much closer to the their actual size.

Thus you will need about 2 times as many soffit vents as popup vents. I also think that spreading them out helps ensure more uniform air flow even if you end up with a slight inbalance between high and low.

The only problem with BS and their research is that most homes do not seal penetrations into the attic, thus venting is a necessity in my view.

If one really wants to go crazy, all wall floor junctures, outlets and switches should be sealed as air will can be pulled up via baseboard gaps etc.

Originally Posted by Raymond Wand

The only problem with BS and their research is that most homes do not seal penetrations into the attic, thus venting is a necessity in my view.

If one really wants to go crazy, all wall floor junctures, outlets and switches should be sealed as air will can be pulled up via baseboard gaps etc.

Exactly all the small leaks, and larger leaks too, should be sealed. Then the insulation should be upgraded to above code. This is far more beneficial to the home owner.


CE News Release: HOW IMPORTANT IS ATTIC VENTILATION? - April, 2000

The final argument for ventilation is that it keeps a house cooler in summer. However, the research that Ten Wolde and Rose reviewed make it clear that such ventilation does not have much impact on the temperature of the house below, particularly if the attic floor is well insulated. In one study that compared cooling costs for houses with various types of ventilation, a house with a powered attic vent fan actually cost more to cool.

However, a study by Rose found that ventilation had minimum impact on shingle temperature. In ventilated attics, the temperature of the sheathing directly beneath the shingles was roughly 10 degrees Fahrenheit lower than it was for the sheathing above unventilated attics. Sunlight and wind were the primary predictors of shingle temperature.

The research review by Ten Wolde and Rose shows that ice dams are unlikely with or without ventilation unless there is significant leakage of heat into the attic from below, either because of inadequate insulation or air leakage. Sources of heat leakage could include warm chimneys, poorly insulated duct work, leaky exhaust fans and ducts, plumbing stacks and poorly sealed and insulated attic hatches.

I just don't know what to tell you folks about poorly vented attics.

You can read all the studies by this guy and that and Elmer Fud and it is still go to come out the same with serious practical experience.

Poroper attic ventilation is an extreme key to the efficiency of any homes heating and cooling system. Mo0st home have very poor roof top ventilation and the vast majority do not have adequate eve ventilation. You folks or others may not notice a bib difference in Ice Cube land but in the south it is a very heavy key player in the home economy of heating and cooling. In the north it is also an extreme need for proper ventilation as to moving any moisture out of the attic in the winter and by all means that hot moist air in the summer. Yes it gets very hot and humid in northern climates and it must be moved from the attic.

Back to the attic solar vents. They have no where near the pull that a electric powered fan does. They just supply a lighter even pull of air up thru the eve vents (and the eve vents must be adequate) thru the roof and by the way, not using any electricity. Duct work in the attic. Air handlers in the attic. All being attacked by the hot air in the summer and with the stagnant, having to rely souley on physics to draft up- through the roof vents just does not cut it. For every ten degrees you remove from around the duct work and equipment you are saving serious money. As far as leaky homes? If there is adequate eve venting with solar vents the pull from the home by depressurization is going to be extremely minimal.

I hate to disagree with said learned authors but I am not sure where they spend there time analyzing this stuff with out putting everything into play. I think they are thinking all this stuff to death.

All the studies on crawl spaces and ventilation. Closing them off or not closing them off. Way to many factors that are different on every home to give such a broad scope of "Seal em all up". You can do what ever you wish to older homes but unless you about rehab the entire home sealing crawl spaces off is not a great idea at all. The cost factor alone would kill the benefits all together. Those old homes have far to many leaks just up thru the floor boards to even conciser it it most cases. Then you have the entire fact that there is gong to be a leak down there some day. Most likely the home owners will never venture in there again until they are stepping thru a rotted floor from plumbing leaking in the crawl and the moisture being at such high levels for such a long time before being discovered. Conditioning the space???? Yeah, that works. And where is that air getting drawn back to? Not into my home, no matter how well you thought you sealed it up. Those old omes where treated with some pretty serious pesticides that I would not even concider drawing through my ventilation system. You just cannot seal it up enough.

Sorry for the run off but that was an example that sometimes way to much thinking goes into all of this and one tricks himself up by over analyzing.

Decent or should I say adequate eve vents for the application and you just cannot beet no power power vents for removing heat and or moisture from an attic. Sun shine or just day light and they keep on turning. You would never put a power vent, electric or solar, on a roof with out sizing up the rest of the ventilation and of course .... seal up those leaks to the inside of the home as you should anyway.

Enough said. Just my humble, built and remodeled all my life as well as inspected all my life as well, opinion. Over 3 1/2 decades of experience must of taught me something. Books and studies are nice .... sometimes! I have and have done my own.

Now, if you want to talk structural insulated panels? Totaly different story. You can make those so tight with out trying that you have to bring outside air in to compensate. Dne right and you could cool with ice cubes and heat with candles. And maybe not much more at all than the standard home to build.

I agree with Ted about the solar fans having less draw then the electric fans. I had one installed last year below the ridge peak on a hip roof. I took the 30% tax deduction. They apparently have gone up in price this year. This is the one I purchased from Costco: Solar Powered Attic Fan #1010TR from U.S. Sunlight Corp

It comes on when the temperature reaches 79 degrees. It is pleasingly quiet and sufficiently lowers my attic & upper level temps.

Take a look here:

The Unplanned Impact on Houses by Powered Attic Ventilators

Many of the houses I inspect have relatively small and/or under-ventilated unconditioned attic spaces, and when PAV's are installed the resulting negative pressurization problems are made worse by the fact that both contractors and homeowners often think "bigger is better" when purchasing a PAV, an attitude which is reinforced by the fact that big-box stores often stock only the manufacturers' larger or largest capacity ventilators.

From this perspective the lower capacities of the solar powered units may actually be a significant advantage compared their higher capacity AC powered counterparts.

Originally Posted by Michael Thomas

From this perspective the lower capacities of the solar powered units may actually be a significant advantage compared their higher capacity AC powered counterparts.

True.

Likewise, shooting oneself in the foot with a .22 caliber is an advantage over shooting oneself in the foot with a .44 magnum.

However, wouldn't it be better to not shoot oneself in the foot to start with?

My opinion based on inspection and maintenance experience follows. Although it's not wrong, I don't recommend anything with a motor be installed in an attic. Home owners don't periodically visit the attic to check their equipment. Therefore, motors fail and are never detected or repaired. JMO.

Darrel Hood
DILIGENT PROPERTY SERVICES

I have to agree with Darrel. Any power vent in a Texas attic won't last long since it will be running just about all day long for 8 months or more out of the year. 90% of the power vents I see either no longer work or never worked because the roofers install them and the owner doesn't get an electrician to hook them up..........as in the 160 degree attic I inspected Friday afternoon.

Originally Posted by Gary Burnett

as in the 160 degree attic I inspected Friday afternoon.

NM-B cable run in that attic, for that matter - ANY 90 degree C insulation wiring, would need to be run TWO sizes larger just to account for ambient temperature derating.

The ambient derating factor for 159 to 176 degrees F is 0.41.

#14 90 degree C insulation has an ampacity rating of 25 amps for derating: 25 x 0.41 = 10.25 amps *and that does NOT include any derating for multiple conductors without maintaining spacing*.

#12 90 degree C insulation has an ampacity rating of 30 amps for derating: 30 x 0.41 = 12.3 amps *and that does NOT include any derating for multiple conductors without maintaining spacing*.

#12 NM-B would NOT EVEN BE SUITABLE FOR A 15 amp breaker - you would need to use #10 NB-B for a 15 amp circuit if the cable is run through that attic.

Jerry, that all makes sense, but I missed your point.

Darrel Hood
DILIGENT PROPERTY SERVICES

Originally Posted by Darrel Hood

Jerry, that all makes sense, but I missed your point.

Darrel,

The point was that in attics which are 160 degrees F - you should write up #14 AWG and #12 AWG NM-B (especially the older NM) as being undersized for the circuit overcurrent protection.

As shown previously, in attics which are 160 degrees F you should see #10 AWG on 15 amp breakers (40 amp rated x 0.41 = 16.4 amps derated) and #8 AWG on 20 amp breakers (55 amp rated x 0.41 = 22.55 amps derated).

I know that sound a bit ridiculous and like overkill, but when you do the derating for 160 degree F ambient that is what it is.

And if you were to also have to derated for lack of maintaining spacing/bundling ... that would kill those two sizes and require even larger size conductors.

The unstated point would be that in climates with those temperatures ... KEEP THE CONDUCTORS *OUT OF THE ATTIC* and in the thermal envelope of the house, you will be okay that way.

Thanks, now I get the point.

Darrel Hood
DILIGENT PROPERTY SERVICES

Did I mention I believe solar vents are extremely well worth the cost. I also, by experience and output from a multitude of folks, have a wonderful outlook on no detrimental affects as far as increased cost but actually a lowering of operating costs.

Depressurization? Whether it is or is not is entirely beside the point. They lower operating cost is what one is after. That appears to be the desired affect, no?

Dang Turbine vents and Ridge vents don't cost a dime!
The heat in Texas attics will burn out just about anything including me!