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Reduce electric bill by installing radiant barrier in attic?
Old 07-08-2008, 02:42 PM   #1
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Reduce electric bill by installing radiant barrier in attic?

May's electric bill was +$200 and June's was +$300. While that comes with the territory in Texas, I am desperate for any cost-effective way to reduce the number of kilowatt hours we use (we're paying $0.15/kwh, ouch) and the biggest driver of that is the A/C. I came across the idea of installing a radiant barrier in the attic of our 2000 sq. ft. house. Bascially it is a big roll of shiny foil that reflects heat from the roof before it can come into the attic and down into the house. I like it because it is relatively inexpensive to buy the materials and I could install it myself by stapling it to the rafters.

Has anyone done this before and would you recommend it? Did you recover your investment? Curious if you can give any estimate of how much it reduced your energy consumption (granted, there will be big differences based on house layout, climate, etc.). Would it be a better use of my time and money to further augment the existing insulation that's in the attic?
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Old 07-08-2008, 02:45 PM   #2
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I am curious about this as well. Local radio station ads in Texas are hyping this up to the nth degree.

So if anyone could give concrete examples of before-and-after energy usage -- particularly in areas with long, hot summers -- it would be appreciated.

My electric bill went from $91 in May to $150 last month (1170 sq ft house set to 78 degrees and about 1300 kWh at about 11.5 cents per). It would be nice to know approximately how long it would take to pay for itself.
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Old 07-08-2008, 02:47 PM   #3
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Radiant Barrier?
Confused About Attic Fans versus Whole House......
Attic Insulation.............
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Old 07-08-2008, 03:48 PM   #4
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I've partially completed installing it in my attic. No data yet, since it's only been a month or so, but it seems to have reduced the max attic temperature by about ten degrees. Cost about $350 for materials; installation "free"...
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Old 07-08-2008, 03:53 PM   #5
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Don't know anything about this, but I'd think it would be a lot easier, cheaper, and more effective to paint the roof.

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Old 07-08-2008, 04:07 PM   #6
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Don't know anything about this, but I'd think it would be a lot easier, cheaper, and more effective to paint the roof.
Unfortunately we have an HOA that I'm sure prohibits any such radical action...
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Old 07-08-2008, 05:01 PM   #7
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How about a solar panel on the roof? Kill two birds with one stone. If your HOA prohibits it now, they may be more easily persuaded than before the bills went up.
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Old 07-08-2008, 05:42 PM   #8
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Do you have many/any south facing windows?
If so, do you have blinds on them?
If not, that would be the cheapest method to decrease your AC bill. Keep them closed when the sun is shining in.
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Old 07-08-2008, 06:18 PM   #9
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Re: blinds, I have four windows in the LR that face west, and catch the brunt of the afternoon infrared in the summer. I bought the screening material, frames, etc. at Lowe's, and made my own solar screens, which are outside, so they block the heat before it gets in, per Al.

As for the roof, ideally the barrier should go on the roof decking, under the shingles, but that requires a new roof...

I've got it in the back of my mind to investigate metal roofing when it's time for a new roof. Fifty year lifespan, built-in radiant barrier qualities, and, with the standing seam system, solar panel ready, should I decide to do that someday.
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Old 07-08-2008, 06:44 PM   #10
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Originally Posted by soupcxan View Post
May's electric bill was +$200 and June's was +$300. While that comes with the territory in Texas, I am desperate for any cost-effective way to reduce the number of kilowatt hours we use (we're paying $0.15/kwh, ouch) and the biggest driver of that is the A/C.
Our local utility just asked for a 5% raise on top of 25 cents/KWHr. The payback's pretty quick at those numbers.

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I like it because it is relatively inexpensive to buy the materials and I could install it myself by stapling it to the rafters.
Has anyone done this before and would you recommend it? Did you recover your investment? Curious if you can give any estimate of how much it reduced your energy consumption (granted, there will be big differences based on house layout, climate, etc.). Would it be a better use of my time and money to further augment the existing insulation that's in the attic?
As mentioned in the other threads we've put the foil in both our attics, the stud bays in several walls, and on the back of the garage door. It's one of the cheapest energy-saving improvements you can make and it has a quick payback.

But do it while you're young. You will replace every water molecule in your body, several times, even if you're doing the work at 4 AM.

As you put up the foil you can feel the attic cooling. Our west & south walls no longer heat up and in fact you can locate the studs by temperature.

A rooftop PV system will reduce the roof temperature by shading the roof while still letting cooling winds blow over it (assuming you or REWahoo have cooling winds in Texas). Reflective paint also works great, assuming the HOA approves it. The "ceramic reflective" powders have no measurable effect.

Anything that keeps the heat from getting into the attic will make the existing insulation that much more effective in keeping the house at whatever temperature you cool it off to.
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Old 07-08-2008, 07:04 PM   #11
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If you have an electric tank water heater, you can add one of these heat pumps to it for about $500. It will save about $250/year on average and pay for itself in 2 years. Airgenerate.com | Adaptive Energy Solutions
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Old 07-08-2008, 07:21 PM   #12
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Originally Posted by TromboneAl View Post
Don't know anything about this, but I'd think it would be a lot easier, cheaper, and more effective to paint the roof.

Roof Insulation, Roof Painting, Roof Restoration, Roof Products, Roof Materials and Roof Paint

Insulating Roof Paint

Kick those nasty photons in the butt before they get into your house.
Here's a test done by the Florida Solar Energy Center on different roof colors and coatings. They really seemed to like Kool-Seal, which is available at your local Home Depot or Lowes. FSEC-CR-670-00
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Old 07-08-2008, 07:25 PM   #13
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Here's a good Q&A on the radiant barrier: FSEC-EN-15
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Old 07-09-2008, 06:33 AM   #14
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...letting cooling winds blow over it
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...cooling winds in Texas...


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Old 07-09-2008, 08:19 AM   #15
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I went into the attic yesterday evening and it was about 120 while the outside temp was 96. As soon as I went up there I realized that all of the A/C has to pass through the attic, so having a hot attic is a double whammy - first you get hit by the heat that is conducted down into the house, then you get hit by the loss of A/C efficiency because the cold air warms up while it passes through the attic. I am trying to get my hands on the radiant barrier material ASAP.

I also noticed that I only have about 10 inches of rockwool insulation, which I think gives me a R-value of about 30-35, versus the recommended insulation of R-49 for my region. Depending on the impact of the radiant barrier, I may blow in some more insulation as well.
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Old 07-09-2008, 09:13 AM   #16
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I went into the attic yesterday evening and it was about 120 while the outside temp was 96. As soon as I went up there I realized that all of the A/C has to pass through the attic, so having a hot attic is a double whammy - first you get hit by the heat that is conducted down into the house, then you get hit by the loss of A/C efficiency because the cold air warms up while it passes through the attic. I am trying to get my hands on the radiant barrier material ASAP.

I also noticed that I only have about 10 inches of rockwool insulation, which I think gives me a R-value of about 30-35, versus the recommended insulation of R-49 for my region. Depending on the impact of the radiant barrier, I may blow in some more insulation as well.
In that case I'd do the insulation upgrade first. This typically gives you the most bang for the buck. Also, check the insulation on the ductwork to make sure it's tight and has a vapor barrier. You might want to increase the insulation around the ducts also. If you can get to the duct joints, make sure they are sealed with mastic to prevent leaks of conditioned air into the attic and the suction of superheated attic air into the air handler on the supply side.
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Old 07-09-2008, 10:00 AM   #17
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If you have an electric tank water heater, you can add one of these heat pumps to it for about $500. It will save about $250/year on average and pay for itself in 2 years. Airgenerate.com | Adaptive Energy Solutions
Great Link Patrick. I also noticed that they have an adaptor ($79) for the air side to dump the chilled air back into the house. So, now we have $579 plus S/H....say $600 +/-. Payback is just over 2 years, but you have to back out the power this thing uses. Their specs show it to use 660 watts. Assuming it actually runs about 50% of the time, that's $30/month ($360/year) at 12 cents per kwh. Payback just went to 5 plus years. ( I wonder what the expected life of this thing is?)

Someone shoot holes in my thinking or my math here.
Okay, If I knew how, we could also get some credit for the "free" cold air, but with the available data, I'm not sure how to turn that into $ savings. It's only going to give you "free" cold air when it's running. When it's not running, there is an opening that will allow a certain amount of "warmer" air to inflitrate the home.

I was intrigued by this thing when I first looked. After doing the math, I'm not sure it's worth the money for a retired couple with no teenage girls at home.

There is no free lunch.
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Old 07-09-2008, 07:54 PM   #18
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Great Link Patrick. I also noticed that they have an adaptor ($79) for the air side to dump the chilled air back into the house. So, now we have $579 plus S/H....say $600 +/-. Payback is just over 2 years, but you have to back out the power this thing uses. Their specs show it to use 660 watts. Assuming it actually runs about 50% of the time, that's $30/month ($360/year) at 12 cents per kwh. Payback just went to 5 plus years. ( I wonder what the expected life of this thing is?)

Someone shoot holes in my thinking or my math here.
Okay, If I knew how, we could also get some credit for the "free" cold air, but with the available data, I'm not sure how to turn that into $ savings. It's only going to give you "free" cold air when it's running. When it's not running, there is an opening that will allow a certain amount of "warmer" air to inflitrate the home.

I was intrigued by this thing when I first looked. After doing the math, I'm not sure it's worth the money for a retired couple with no teenage girls at home.

There is no free lunch.
Well, my numbers were based on the info on this page: Airgenerate.com | Adaptive Energy Solutions

They are using an "average" family's needs. Of course, YMMV if your conditions are different than the example.

Yes, the unit is using 660 watts, but at a COP of 2.6, you are getting 1700 watts worth of heat from the system. If it cost $30/month to run, you actually got $78 worth of heat from it, so you saved $48/month compared to just resistance heating (which has a COP of 1).
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Old 07-09-2008, 08:08 PM   #19
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In that case I'd do the insulation upgrade first. This typically gives you the most bang for the buck. Also, check the insulation on the ductwork to make sure it's tight and has a vapor barrier. You might want to increase the insulation around the ducts also. If you can get to the duct joints, make sure they are sealed with mastic to prevent leaks of conditioned air into the attic and the suction of superheated attic air into the air handler on the supply side.
Absolutely. If you've got easy access to the existing insulation, blowing in more is an easy job (easier than installing any kind of radiant barrier), and it pays off year round (not just in the summer). Also, if you live in a cold climate, both rock wool and fiberglass lose a LOT of their insulating value once temperatures dip below 5 deg F. This is because the relative buoyancy of the lower, warmer air is sufficient to drive it through the fibers of these insulations, and the convective heat loss is considerable. Blown-in cellulose insulation, on the other hand, packs down tighter and stops this convective heat loss. Thus, if you live in a cold climate you get not only the R- value of the insulation you blow in, but you'll increase the effectiveness of your already existing insulation by approx 30% on the very coldest days. Finally (after you've checked your ducts for leaks and properly repaired them with mastic and fiberglass mesh), if they are the kind that are just lying on the floor of the attic the very easiest way to insulate them is to just blow a mound of this cellulose right on top of them while you are doing the rest of the attic. It works great and it is faster than any other method.
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Old 07-09-2008, 08:39 PM   #20
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I would hesitate to put reflective material up there for the simple reason that the roofing material and underlayment may not tolerate so much heat on their underside. Check specs.
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