Reduce electric bill by installing radiant barrier in attic?

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soupcxan

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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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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.
 
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"...
 
TromboneAl said:
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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Unfortunately we have an HOA that I'm sure prohibits any such radical action...
 
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.
 
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.
 
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.
 
soupcxan said:
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.
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Our local utility just asked for a 5% raise on top of 25 cents/KWHr. The payback's pretty quick at those numbers.

soupcxan said:
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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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.
 
TromboneAl said:
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.
Click to expand...

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
 
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.
 
soupcxan said:
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.
Click to expand...

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.
 
Patrick said:
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
Click to expand...

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.
 
bentley said:
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.
Click to expand...

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).
 
Patrick said:
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.
Click to expand...

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.
 
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.
 
Well I plunked down $250 for 2000 sq ft of the stuff and just for kicks started to put a few pieces up in the attic. I swear by the Hammer of Thor, that is tough work! The ambient temp was 116 when I started around 6PM, and working with the material by yourself is definitely not the quickest way to do it. Hopefully as I get more up this weekend I'll notice some improvement.

The hardest part of the job is just getting around the attic without stepping through the ceiling, tripping over the A/C ducts, running into the trusses, or hitting your head on roofing nails.

Upon searching other home improvement forums, the usefulness of the radiant barrier material seems to be hotly debated. I am hoping that this project is not an exercise in snake oil installation...
 
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IMHO a couple of wind driven turbines on the roof coupled with another 10 or 12 inches of blown in insulation would be a better investment. Turbines evacuate the hot air and added insulation restricts migration of the heat downward. This is what I did several years ago in Northern Virginia. Enlisted a friend to feed the hopper, use provided by HD with the purchase of the insulation and two turbines professionally installed (today it would have been a DIY deal). The reduction in electric bill was, as I remember, not that great but the home was quieter and the work added, in some small part, to resale value. I believe the radiant barrier will actually raise the temperature of the roof material and the impact is not going to be positive on the life of the roofing material. BTW IMO the time to be doing attic work is winter or EARLY in the morning (before the Sun rises).
 
OAG said:
I believe the radiant barrier will actually raise the temperature of the roof material and the impact is not going to be positive on the life of the roofing material.
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This is what the Florida Solar Energy Center has to say on this topic:

"Will heat build up in the roof and damage my shingles?

It's extremely unlikely. The Florida Solar Energy Center has measured the temperatures of roof shingles above attic radiant barriers on hot, sunny summer days. Depending on the color of the shingles, their peak temperatures are only 2-5° F higher than the temperature of shingles under the same conditions without a radiant barrier.

Roofing materials are manufactured to withstand the high temperatures to which they are frequently exposed. A 2-5° F increase in peak temperatures that normally reach 160-190° F should have no adverse affect."

Reference: FSEC-EN-15
 
soupcxan said:
I am hoping that this project is not an exercise in snake oil installation...
Click to expand...

From FSEC: FSEC-EN-15

"When will I see a payback from an attic radiant barrier?

Two things affect the performance of a radiant barrier system – the level of insulation in the attic, and the geographic location of the home. A simple answer to the question is that a radiant barrier system reduces the heat flow into the house from the attic by approximately 40 percent. Attic insulation levels have a large effect on the amount of heat flow that is reduced, in other words, if you have little or no insulation in your attic, a 40 percent reduction is very significant, but if your attic is insulated to R-30 or better, there is very little heat flow to reduce. The more of your energy bill that is concerned with heating, the less desirable having a radiant barrier becomes. When you are using your heater, any heat gain from the attic is desirable. There may be a reduction of heat loss through the roof during winter nights, but the climates where testing has been performed do not lend themselves to demonstrating this, as there is very often a brief or non-existent winter. A very helpful website for guidance to the cost effectiveness of installing a radiant barrier is found on Oak Ridge National Laboratory's Web site, http://www.ornl.gov/sci/roofs+walls/radiant/rb_02.html.
In Florida, computer studies conducted in the development of the Florida Model Energy Code indicate that a typical attic radiant barrier installed in a Florida home will offer a six to seven year simple payback and a 15 percent to 19 percent return on investment."
 
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