Best Attic Ventalator for South Texas ?

Hi all,

I recently had a 120V attic ventilator fan fail, and was needing to replace it.

I was wondering what is the best on the market now a days.

The ones I have must be 20 years old, at least. And use lots of electric power.


I see that they have Solar Powered ones now a days.

Are these Solar powered ones any good, Or a waste of money ?


We normally have a breeze blowing so maybe a Turbine would work also.


My attic reaches about 120-125 Deg. on a 96 degree sunny day.


Any input would be great. Thank You.


Have a good day, and a Great weekend.


DonL

The 120F powered attic ventilators usually just depressurize the attic and cool it at least partially with air sucked up from the conditioned space. Studies done at Texas A & M in the 1980s showed that most of them INCREASE the cooling energy use. Later studies conducted by the Florida State Energy Center demonstrated about a 6% reduction in overall cooling energy use in homes with modestly insulated R19 attics. (At least it wasn't power-negative!) If the attic is bumped up to R30+ the benefits would surely be lower (and possibly negative, if the attic floor interface isn't super-air-tight to the conditioned space below.)

Turbine vents would run both day AND night probably increasing the latent loads of the house due to infiltration (unless your blower-door test comes in at under 1.5 ACH/50 or something.) Attic ventilation was originally & primarily a cool/cold climate strategy for purging moisture from attics, but in the humid gulf-coast states vented attics generally pull more moisture in than they purge. Solar powered fans at least run primarily during higher sensible-cooling hours, and don't suck air 24/365 the way a turbine vent would in a breezy location, increasing both your cooling and heating expenses.

You might ponder applying the ventilation fan dollars to adjusting your insulation vs. ventilation strategy. If you're at only R19 and have the space to accomodate another R12-R20 in blown cellulose is pretty cheap stuff, at which point it doesn't matter what temp your attic runs at, unless you have uninsulated & leaking ducts in the attic. Radiant barrier helps if you're only at R19, but not as much as bringing the R values up to current code (or higher.) See: http://www.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/RBFactSheet2010.pdf

Sealing off all attic venting and insulating the roof deck (and any gables, etc) with 3" or more of open cell foam is a more expensive solution than doubling down on R value with cellulose on the attic floor but that would put ductwork at least partially within the insulation boundary, and fully within the pressure boundary of the house, at which point leaks would drive far less infiltration than they would currently. (Assuming you have ducts in the attic, as do many/most south TX homes.)


If you ever decide to go the spray-foam on the roof deck route, don't let any contractor talk you into removing the existing insulation (an unfounded practice in the spray-foam biz. They charge you for it too!) Only let them move/remove the stuff they need to in order to be able to insulate right down to the soffits. The R-values add up, and in south TX there is ZERO moisture risk from sealing the attic venting, only moisture reduction, since the body of air in the attic is now at the same absolute moisture (dewpoint) of the air-conditioned interior air.

Thanks for the info Dana,

I have already installed more blow in insulation.

It has settled a lot, but I don't want to add to much more weight.

If I read your post correct, Having no ventilator may be better ?

I was really interested in knowing if the Solar powered ventilators are any good, Or just a joke and a waste of money ?


Have a good day.


DonL

Don,

I am no expert on the subject, but I did have a through the roof attic ventilator also, I think it was a Nutone, or Broan. It probably was similar in results to what you had fail. When mine failed after 10 years or so, I replaced it with another identical model. In fact, I left the shroud and dome in place and just replaced the guts from inside the attic. It brought the attic temp down as I remember, about 25 degrees from what it was if it were not on. In 2005, I had my roof redone, and I removed that ventilator because the roofer installed ridge venting by cutting the sheathing back on the ridge line an inch on each side and putting that plastic ridge vent material under the cap shingles. He made a few holes, but not enough, I guess, in the soffits for ouside air to enter under the soffits so the hot air could exit at the ridge. To tell you the truth, I think the power ventilator did a much better job. I have end gable vents that keep th eattic ventilated too. I cannot imagine a solar powered fan having anywhere near enough power to do a good job, especially where you live. Lots of sun, but very hot. There are showrooms that sell these solar powered fans. Maybe you can get a demo. I think a turbine would do a better job if you have breezes most of the time. I defer to Dana's expertise though. He souns like he knows what he's talking about. My experiance is just my experience. Your mileage may vary, as it is said.
I have R30 insulation in my attic with plastic insulation baffles so any air that enters the soffit vents can rise up between the rafters. My house gets pretty hot in a fairly short time if I shut off my AC.

These are Nutone and the motors are 120 Volt 3.15 Amp, 12 inch I do believe.

Works out to about 378 watts each. With 2 of them running about 8-10 hours a day, cost can be a little expensive.

I just did not think that the Solar ones would be ably to move nearly enough air.

I should have went with the ridge vents when I put the new roof on my house.
All the new homes here use the ridge venting.

The House originally had wood cedar shingles, And venting was much better.

I may just try to find a more efficient motor, maybe they make better ones now a days.

Bob are your end gable vents electric powered or just open vents ?
I have thought about gable vents, but I don't know much about them.


Thanks, Have a good day.


DonL

Don, the end gable vents I have a just static unpowered louvers made out of vinyl. I put them in many years ago to keep the attic ventilated besides what the builder put in in 1971 0n the roof: 3 or 4 of those roof metal vents that just let the hot air escape similar to the second one down here: http://www.airvent.com/homeowner/products/staticVents-roofLouvers.shtml

Have a good day

Thanks for the web info.

Very interesting.

I put in some radiant barrier foil, stapled up to the bottom of the roof rafters...that alone lowered my attic temps probably 25-degrees. I know that before, at the end of a long sunny day, the ceiling was warm to the touch and radiated heat even with the 7" of cellulose and 6" of fiberglass on top of it - it all got heat soaked. Now, the ceiling is the same temps as the interior walls and much more comfortable. no on-going energy costs, simple, quick installation, not a lot of money. It comes in many forms, mine is double-sided, fiber reinforced with paper for strength. It's also perforated so it doesn't trap moisture, but I'm not sure how well that really works (I've not seen any detrimental effects). The stuff comes in 4' wide rolls, and various lengths on a roll. Since it is a little unweildy, it's easier to install with two people, but wrinkles won't affect the operation much, if any.

Jim, I would think that reflecting all that heat back up to the roof sheathing would cook your roof shingles and possibly damage the sheathing itself, but I need to look into it. Got a link to point me to that stuff?

It's been too long for me to remember what specific brand I used, but there are numerous manufacturers available. I happened to buy it on a close out at a big box store (they were changing to a different supplier). This is one http://www.ecofoil.com/Radiant-Barrier?gclid=COGhqdPt96kCFcdM4AodX1rBzA . Your roof has the whole world to reradiate the heat, and, since there is a gap, the air can circulate to help minimize the heat buildup.

I just wanted to install a new vent.

I already installed a foot of blow in.

May be it would be cheaper for me to build a new house.

But then they would just raise my taxes...

Again.


Thank You for the tips.


DonL

Radiant energy penetrates materials...even insulation gets hot. the radiant barrier stops that and makes your existing insulation work better, at least that's what happened in my home. The bedrooms before installation got hot from the re-radiation of the heat stored in the mass of the insulation (which only slows the transfer, not stops it like the radiant barrier). After, the bedrooms were MUCH more comfortable. I think it helps a little during the heating season, but not as much as a layer on top of the insulation might.

Is any of the radiant barrier paint worth using ?

The way my house is built it would be very difficult to install radiant barrier foil.


DonL

DonL said:

Thanks for the info Dana,

I have already installed more blow in insulation.

It has settled a lot, but I don't want to add to much more weight.

If I read your post correct, Having no ventilator may be better ?

I was really interested in knowing if the Solar powered ventilators are any good, Or just a joke and a waste of money ?


Have a good day.


DonL

Click to expand...

Yes, according to all available evidence from academic investigations over the past 3+ decades, having no ventilator is better than having a grid-powered ventilator. If you have low R (which apparently you don't), there may be single-digit savings on cooling power if you used a solar version (the FSEC R-19 attic investigation.)

If you look carefully at the ORNL radaint barrier fact sheet you'll note that the utility savings of adding radiant barrier to anything R30 or higher is miniscule. Spend the money on duct sealing & duct insulation instead. See the graphs on P5. Even with uninsulated ducts in Miami with code min on R value you might save as much as $100/year by adding radiant barrier. At code min with insulated ducts adding RB is buying you $50/year. If no ducts are in the attic, RB buys you maybe $15-20/year in power savings. The higher the R value in the attic (or ducts) the less RB is going to buy you.

When it's time to re-roof, using a CRRC "cool roof" shingle or coating is relatively cost-neutral, and is more effective than an interior radiant barrier. Better still would be to add 2-3" (R13-R19) of rigid polyisocyanurate above the roof deck and seal the attic. Holding the rigid foam in place with furring through-screwed to the trusses/rafters and adding an OSB nailer deck would allow the roof deck to be vented, extending shingle life a few years.

Both radiant barrier or insulating the roof deck (between the rafters or above the roof deck) do shorten shingle life somewhat on low-angle roofs (your 25 year shingle is toast at year 22), but every careful lifecycle cost analysis of an insulated roof deck I've seen is strongly cash-positive going with an insulated roof deck- the energy savings far outstrip the loss in shingle life. Shingle color (the "cool roof" solution) has a greater effect on shingle life than insulated vs. vented roof deck though. The hit in shingle life is primarily at roof pitches lower than ~3:12- at steeper pitches the extra inherent convective cooling on the exterior makes color the predominating factor (and in many instances the average shingle temps are lower with the insulated roof deck, even when the peak temps are somewhat higher.)

Powered attic ventilators DO cool the attic- but they do so by sucking air-conditioned air up into the attic, unless you've made that boundary a very SEVERELY air tight ceiling. A blower door test on the whole house would give you a good idea whether that's the case, but unless that house was built to a very stringent test, attic ventilators will be a money losing proposition every time it turns on. It uses power to turn the fan, and the fan is robbing the conditioned space of compressor-cooled air. (There are ample references to the underlying studies in the footnotes of the FSEC solar-ventilator reference, if you need more proof.)

The whole argument for attic ventilation in the hot humid south is misplaced. The history behind the drafting of those standards is outlined as well as some of the shingle lifespan issues here.

When I did my first floor remodeling, I used www.insuladd.com in the paint. It does change the texture of the paint, but does seem to help a little bit. I need to check with one of my neighbors and use my (relatively) new IR thermostat and compare the interior wall temp between theirs and mine to see if the wall is actually any cooler. I plan to remove the popcorn on the upstairs when I get around to remodeling there, and will paint the ceiling and walls there with the stuff to see. At least, the stuff isn't very expensive. If you haven't looked at this stuff, it is micro-spheres of hollow ceramic material - very similar to the heat shield material on the space shuttles. Other companies sell paint with the stuff mixed in for a premium - this company sells the 'raw' stuff, and you can mix it into any paint you desire. You'll need a big bucket to mix it, as it doesn't disolve, it adds to the volume, and you need a bigger bucket than the typical gallon to mix it (it adds about a quart to the gallon). It works best on the hot side, so the benefits to me are more in the winter verses the summer. For exterior heat, you'd want it in the exterior paint.

jadnashua said:

When I did my first floor remodeling, I used www.insuladd.com in the paint. It does change the texture of the paint, but does seem to help a little bit. I need to check with one of my neighbors and use my (relatively) new IR thermostat and compare the interior wall temp between theirs and mine to see if the wall is actually any cooler. I plan to remove the popcorn on the upstairs when I get around to remodeling there, and will paint the ceiling and walls there with the stuff to see. At least, the stuff isn't very expensive. If you haven't looked at this stuff, it is micro-spheres of hollow ceramic material - very similar to the heat shield material on the space shuttles. Other companies sell paint with the stuff mixed in for a premium - this company sells the 'raw' stuff, and you can mix it into any paint you desire. You'll need a big bucket to mix it, as it doesn't disolve, it adds to the volume, and you need a bigger bucket than the typical gallon to mix it (it adds about a quart to the gallon). It works best on the hot side, so the benefits to me are more in the winter verses the summer. For exterior heat, you'd want it in the exterior paint.

Click to expand...

The value of ceramic nanosphere technology has come up woefully short in the macroscopic world, as interesting as these materials might be when applied to 1- micron or smaller structures micromachined into silicon. They're essentially useless. There are other "insulating paints" out there (Nansulate, Supertherm, etc) with outlandish performance claims that DO NOT PERFORM in the real world, despite the fervent faith of the true believers.

The true believer was an idiot taken in by his own hype,mis-applying something that actually works OK as a solar heat rejection exterior paint/coating, but is by no means an insulation. The stuff is highly reflective of visible light but also highly emissive in the infra-red, and radiates heat across stud cavities quite well. In applications where limiting the heat absorbed across the solar spectrum and being able to radiate the portion absorbed quickly is of benefit, there are worse products than SuperTherm, but I wouldn't pay extra for it. (And the marketing arm of that company is so abominably misleading I'd personally pay extra not to reward them. YMMV. ;-) )

If ceramic insulation came in sheets or tiles and wasn't held together with a matrix if fairly heat-conductive paint it would likely have more benefit. Side by side comparisons in any type of ASTM insulation tests do not show differences greater than the inherent measurement error.

If it's not listed with the Cool Roof Rating Council all performance claims need to be taken with a pound of salt, not a mere grain. See: http://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-paint-merchants-dupe-gullible-homeowners While some high-solar-reflectivity high-IR-emissivity coatings can be useful for reducing peak cooling loads (when properly applied== on the exterior layer of the building) none have any demonstrable efficacy for reducing heating loads. The goods listed here at least have had a first-blush of 3rd party standardized testing to support their performance claims rather than a list of "gee whiz" testimonials and cherry-picked field studies of the type that Nansulate & Insuladd are fond of. These ceramic sphere coatings (in general) have more use as harsh-environment protective coatings than as insulation value that would show up reliably on a utility bill.

The initial solar reflectivity of exterior latex was improve only very modestly improved with the addition of Insuladd, but by their own test company's data it reduced the IR emissivity by an even greater amount, making it not very useful as an exterior radiant barrier or "cool roof" coating:
http://www.insuladd.com/energy.html#energypdf
They use the CRRC logo & link on the bottom of their web page, but could not find any of their actual products listed on the CRRC site. There are plenty of coatings with 3 year aged reflectivity & emissivity higher than the initial number listed on the Insuladd page:

http://www.coolroofs.org/products/results.php?pageStart=1&type[0]=Field-Applied%20Coating&type[1]=Other&ob=solar_reflect_3yr&od=down

If a roofing product has a California Tile 24 compliance listed, it's probably going to be on the CRRC site, and actually have meaningful, measurable results.

Any IR testing on paints or reflective materials needs to be calibrated to the actual IR emissivity of the material. The emissivity of bright aluminum or chromium is low enough that they can read 10s of degrees lower than reality if the higher default emissivity is used in the instrumentation. Any attribution to temperature differences between your neighbors' place and yours will have error-bars larger than the delta-T. To be any use of all the temperature measurement needs to be on the same wall, same insulation, same orientation and same shading factors. To the extent that interior walls with lo-E paints on them are insulated with something that passes muster in an ASTM C 518 test, any benefit from lo-e additives or paints go from pretty small to nano-scale small. It might be working, but it's at an immeasurably low level.

Since I live in a row of townhouses, my neighbor's place is in the same plane and orientation. I'll see if the IR thermometer reads anything different. It does have an adjustable emissivity, so I can adjust it for the material. Anyway, since it makes the paint film thicker and have some texture, it hides surface imperfections, so is not a total loss, regardless!? the quality of the drywalling in the place is not totally up to best practices, and it does hide that pretty well.

To make a reasonable apples-to-apples comparison for the performance of cool-roof heat rejecting paints from the raw solar reflectivity & IR emissivity of the product as listed in the CRRC, you can use this handy li'l Solar Rejection Index calulator cooked up by the good folks at the Lawrence Berkeley National Labs.

http://coolcolors.lbl.gov/assets/docs/SRI%20Calculator/SRI-calc10.xls

Applying that to the Insuladd test data listed, the unmodified paint had an SRI of 92, (very good) and would result in a peak roof temp of 47.7C, (under ASTM E 1980 standard conditions) whereas the Insuladd-modified latex has an SRI of 99 (even better), with a peak roof temp of 45.1C, a difference of less than 5F. Methinks you get that much between light tan and medium green on the shingle colors.

If you plug in SuperTherm's 3-year aged numbers you get an SRI of 93 and a roof temp of 47.2, which means it's about as good as the (probably white) latex used in Insuladd's test.

Since Insuladd seems to only decrease the emissivity of latex paints modestly according to their test data, it's probably not the right thing to put on an interior wall in any climate, since it emits the heat from the wall to the human slightly more efficiently during the cooling season, and absorbs rather than reflects the IR emitted by the adjacent humans in winter. A low-E coating<<0.2 would be more comfortable on the interior, not something in excess of 0.70.

Insuladd's energy transfer estimates also make the ridiculous presumption that the predominant heat transfer mechanism on the interior is radiation, rather than convection & conduction, which is a dubious assertion at best, given the relatively low delta-Ts between wall surfaces and interior objects in an insulated house. (The exterior radiation temperature differences are an order of magnitude or more higher.)

Apologies to Don for taking this to the techno-nerd extremes. But when re-roofing it really pays to consider this:

http://coolcolors.lbl.gov/assets/docs/fact-sheets/Cool-roof-Q%2BA.pdf

Cool-roof shingles will run cooler, last longer, and leave your attic cooler no matter what you decide to do about vented/unvented/power-vented

That is fine Dana.

I did use light colored shingles.

It is interesting all that it takes to replace a bad Ventilator.


Have a great day.


DonL