Originally Posted by faithfulfrank
(Post 378774)
i find this a very interesting topic. I want to learn more about it myself. I have a good friend of mine who has a strong bias against radiant barriers, feeling that the payback is too long. I do not know if he is correct or not. He runs a blog, and i don't think he would mind me posting his views on it. He lives in a 55+ community not too far from the villages, so i'll post it here, just for another view, hopefully to spur discussion.
I do know i'm told that it is much easier to install it during construction....but it is a big money maker for the builder.
Here is my friend's viewpoint;
"this has come up again recently and rather than have you search through to find this i thought i'd post it and make it sticky.
First, the disclaimers -- this isn't to put down anyone who wants to buy an rb, or who already has bought one. What people want to do with their money is something i truly believe is none of anyone else's business. This is more to answer the honest questions posed by someone who isn't sure they want or need an rb. And, yes, this my the definitive answer.
A radiant barrier is just what it sounds like -- something placed in your house to act as a barrier to the radiant (sun) energy that is outside. They have been around a long time, and their effectiveness is still being debated. For most of the new construction they are offered as an option because they are a huge money maker for the builder (if you were to buy the barrier yourself and put it in yourself, a very simple job at the time of construction, you could do it for pennies on the dollar they will charge you). The sellers of the rbs absolutely love them for this very reason -- cost them $ and cost you $$$$.
The two big questions: Do they work, and are they worth it?
Oddly enough, even the answer to the first is not certain, despite the fact that studies have been ongoing for many decades now. While most studies show they can reduce energy costs, there are actually some small studies that show they are either completely ineffective or can even increase energy costs (more on this later). You can do the relevant research yourself on the web, but based upon all that i've read i tend to believe the studies (funded, mind you, by the radiant barrier association) that indicate costs are reduced, particularly in the florida area.
The second question is more significant and i'll cut to the bottom line: Based on the current pricing at most communities, rb's can not pay for themselves in less than 25 years. Let's talk about why specifically.
First of all, it helps to understand some basics. Ceiling heat gains account for about 15 to 25% of the total cooling load of your home. Secondly, the amount of insulation you have in your attic can dramatically reduce this figure: R19 or higher will put your home at the low end of this range, and r34 can place it even below 10%.
A radiant barrier can reduce this ceiling loss by 16 to 42% in studies, which sounds impressive until you realize it is only a percentage of a small percentage (we'll see how this adds up in a moment).
Cooling load of your home is not your total electrical bill: That bill depends a lot upon whether you use natural gas (because a water heater or clothes dryer or electric oven all use a lot more electricity than your air conditioner) as well as all your other electrical appliances. Here's a rundown of what various things use along with a pie chart of overall electrical use:
http://michaelbluejay.com/electricity/howmuch.html
in this chart, air conditioning for a year represents only about 12% of the total electrical usage for a home, but that home is an "average" home. For the sake of argument here let's assume that a home in florida would use more air conditioning than typical. Indeed, in that same breakdown it says air conditioning usage in the summer accounts for about 70% of the energy bill, and i think that's a number we can live with for the purposes of this discussion.
While we're on the subject of summer/winter, be aware that rds do not help in the winter at all. Indeed, here it is thought that they may actually hurt, cause the heating bill to rise (because the same mechanics are at work -- you prevent the heat of the sun from heating the house in either case). This is why some studies show an rb as not providing any benefits, when annual costs are taken into consideration.
Given that "summer" (or air conditioning use) in florida runs from around april through october, this isn't as bad as it might sound for rbs. But it still limits their effectiveness to only seven months or so out of the year.
Finally, we need to consider what a "typical" monthly electrical bill might be in florida: There is a lot of controversy about this (with some claiming as low as $75) but i'd like to think that $125 during the summer is more than generous based on the talks i've had with residents in legacy in a home of around 1900 square feet. Obviously what electrical company and the size of your home will determine what you will pay yourself.
So if you know what the builder is charging for rbs you have all the information you need in order to determine whether they are right for you. This will vary from builder to builder.
Some developers charge $2k for an rb. If your electrical bill during the summer months for a year totals $875, your air conditioning portion of that bill is $612 (70% of that). The ceiling heat flow loss is between 15 and 25% of that and with r19 probably closer to 15 but we'll be generous to the rb and give it a whopping 25% and so we have $153 or so that is lost through the ceiling each summer. (but remember -- if you have r19 or higher then that $153 figure will be lower, probably more like half or only $80).
Now, if take the percentage of this that can be saved by an rb, we get anywhere from $25 to $64 (16 to 42%) each year. We'll be more than generous here and say that we save $60 every year (once again, this figure is much more likely to be much lower -- a realistic number would be around $25 or less).
So a radiant barrier which cost $2k will be paid for in... Oh, about 33 years or so. Great for your grandkids, i suppose -- not so hot for us.
But wait, you say. What about rising energy costs? Won't that, eventually, make the barrier pay for itself sooner?
Very obviously if energy costs double in the next few years such a barrier would pay for itself sooner, say in 16 or 17 years. But remember -- putting that $2k in a bank account that earns even 3% interest will more than match that.
Also remember we've been more than generous on the side of the rb, taking the very best figures even the radiant barrier association has provided. If your attic has r19 or better you will probably see a much smaller savings with an rb. And we haven't even touched on what happens in the winter (when it could cost you money) or if it gets dusty (and loses effectiveness) or the humidity issues (there are problems with rbs that go far above saving money).
Now, i haven't addressed those who might be earth-first type folks who feel like any energy savings is a good idea, no matter how much it costs you. If you feel like this: Well, more power (so to speak) to you. Truth be told, the energy used in making rbs probably offsets what little savings are had in this area but i am all about living and let living.
To be positive here, the absolute best thing you can do for both your and the global economy is make sure you have r34 insulation in your ceiling. This should reduce your heat loss to 10% or less, and is cheap to do (you can even do it yourself after the fact). Now at this point you'll be spending about $60 per year in heat loss through your ceiling. You *could* save about $20 more each year with an rb, but i think you'll see it ain't worth it.
Some people have raised the point that an rb makes their garage feel cooler than their neighbors. Even if this were true (and it's extremely unlikely it is -- unfortunately most of the folks who are claiming this also have an insulated garage door, which is far more likely in providing this kind of difference than even the slight difference an rb could provide) remember that the opposite is true in winter -- that is to say, any improvement in coolness will also result in a garage that's colder than you might want in the wintertime.
If you want a cooler garage, by all means get an insulated garage door. Combined with r34 in your ceiling that ought to get you about as cool as you can go without air conditioning (once again, an rb *might* cool it off 1/10 of a degree more perhaps, but studies have shown humans cannot feel temp changes as small as that)."
i guess the bottom line is that folks will need to do their own number crunching. Another factor is perhaps it might be worth it just for comfort, or the perceived value if you plan on selling down the road.
Well, hopefully this helps. Mind you, i myself do not know enough yet about the subject to have an opinion...i just posted this to hopefully help spur discussion and to bring another point of view to the discussion.
Respectfully, frank
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