Radiant Barrier versus Fiberglass Insulation Hot Box Test
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- เผยแพร่เมื่อ 3 พ.ย. 2010
- Are you interested in seeing the effectiveness of radiant barriers? Watch this short video from www.insulationstop.com, the leader in reflective foil insulation. This hour long hot box test is condensed down to a few minutes but clearly shows how a radiant barrier can control the amount of heat gain in an area. Watch the thermometers as the temperature in the side with just fiberglass insulation goes through the roof, literally!
- วิทยาศาสตร์และเทคโนโลยี
This is interesting, because it shows that you can create a small model and then test it. I would test this again with a few layers of realistic roofing materials between the lamp and the radiant barrier.
And then test over 6 to 8 hrs of simulated direct sunlight. The big question is, does it also slow the cooling of the house throughout the night causing another issue.
Stops radiant heat, not convection or conduction. Hot attic needing to cool would be convection. The sun is 100% radiant heat. Uses radiation to heat objects that can conduct, convect, and re-radiate. Still need to address conduction and convection in home design. Blocking radiant heat is huge and needs an air gap on both sides so the film doesn’t conduct.
@@VElitePV Yes, the problem is that if the light bulb is simulating the sun then this video does not show us a realistic house insulation model. The sun doesn't shine on your attic insulation -- it shines on the shingles.
@@davejoseph5615 whow
@@davejoseph5615 The heat lamp uses radiation, just as the sun does. They weren't trying to create a realistic model of an attic, they were just demonstrating the principle. In the real world, the sun doesn't radiate heat directly onto your insulation. The sun's radiation heats up your shingles and decking, which then radiate heat onto your insulation. The principle is the same, this experiment just exaggerates the process.
Thanks, this was the answer I was looking for on my garage project. Want to keep the heat retained in the winter and out in the summer. Some of the "Garage Kits" don't have the reflective foil to setup the radiant barrier.
Thanks! I just went around 3 of my upstairs rooms with radiant barrier and was wondering how much it might help. This video gave me my answer.
Thank you for the information.
what about test just the radian witout extra insulation versus pink?
So I could put battens of fiberglass insulation between the rafters and then attach a radiant barrier to the bottom side of the rafters?
Thanks so much 🥰
I think a chrome roof is best, and reflect it at your bad neighbors !!
What's better perforated radiant barrier or non perforated for metal roofing?
What about radiant barrier by itself?
Soundproof insulation
How long the Radiant Barrier will last?
Shouldn't the radiant barrier and fiberglass insulation have an air gap?
Would this also work in reverse? It does right? Radiant energy is radiant energy?
Like If I were to try and use this to keep heat in, instead of out, it would also perform better than fiber insulation?
It would work if you used it in place of shingles. There isn't any light to reflect in the attic??
you don,t need to reflect light you want to reflect light waves, some of which are out side of the visible spectrum. Ultraviolet and infrared mainly
I thought this was going to be a test of just radiant barrier by itself vs. just fiberglass insulation. No surprise the side with both would provide better insulation. I have radiant barrier on the roof joists in my attic in addition to insulation on the attic floor. I saw a video of someone who put radiant barrier on the walls of a shed instead of insulation. I didn't think it was an alternative to fiberglass insulation.
For r-value the foil would not be a suitable alternative. But to block radiant heat, the bubble foil is much better suited. There are many cases where fiberglass insulation is not an alternative to reflective insulation (the shed you referenced for example, areas with high moisture content, metal buildings, duct wrap insulation, etc). Ultimately the best thermal performance depends on the application and the product either stand alone or a system of products not necessarily one or the other.
I would like to see one with just radiant barrel without the fibreglass insulation
I too am confused about how closely the "hot box" experiment represents the real world.
(1) As mentioned in previous comments, the hot box experiment radiantly couples the top of the insulation to an IR source which is several hundred of degrees Centigrade. In the real world the top of the insulation would be radiantly coupled to the underside of the roof sheathing which I would expect to be less that a 100 degrees Centigrade (or 212 degrees Fahrenheit)
(2) In the real world it would be the heat energy flux measured in units like watts per unit area per second that would be important and not the equilibrium temperatures illustrated by the experiment. The heat flux into the system would be indicative of the air conditioning energy required to maintain the system at the desired temperature. The experiment would be more representative of the real world in my mind if they compared the energy required to cool each of the two sytems to the same temperature.
The hot box although imperfect gives you an idea of what the reflective material does to mitigate heat. For example if you put a piece of paper above the fiberglass insulation the final temperature difference would not change at all. You can experiment with different materials. Whatever test you run, it is important to run for a length of time. Any material can initially block heat but as the material heats up it eventually reaches its "saturation point" and the heat radiates through the material. Reflective aluminum is unique in that it will reflect this radiant heat and not absorb it. (Gold and silver have the same properties)
@@InsulationstopRadiantBarrier Not really. Sorry. From a materials and engineering perspective, you would then have to show how any real-world installation matches both the exposure and the construction of your experiment. Approximations which are highly divergent from real-world applications tell us very little. Here's a little experiment: Take the exact same setup, except replace the radiant barrier with a 1/4" thick piece of bright white Coroplast, or maybe even just with a thick piece of cardboard painted that color. The "protection" afforded is likely to be similar even though the material has little relation to your radiant barrier, and those could be expected to perform quite poorly in any attic application. The radiant-barrier industry has taken some hard hits from the building-science community in recent years and federal regulation has followed. More exaggerated claims, including from the RV industry which loves the stuff and makes the silliest claims on the planet about its R-value (it doesn't have any above about 1), are likely to result in stricter regulations and enforcement.
@@ReflectedMilesI guess we should tear off all the white cool roofs in California and remove the standard radiant barrier packages for all homes built in sun belt states. I guess Louisiana Pacific and Owens Corning should stop making their foil faced products, both radiant barrier sheathing and foil faced insulation. Take the stuff out of all the appliances, textiles, and packaging industries too. The exaggerated claims are just that exaggerated by mostly sellers and installers who would sell and install anything just to make money no different than any other example anywhere on the planet, since time began.
@@InsulationstopRadiantBarrier There's a big difference between scientifically valid uses, and most uses sold to consumers which are not scientifically valid. A white roof is a perfectly valid reflector, as is short-term temperature reduction that a foil facing can create between a very hot surface and surrounding air (in kiln and crematory use, for example), and that is also how it is used in many appliances, especially industrial. _What it doesn't do is insulate_ , that is the kicker, and that's where everybody from foil installers to a manufacturer as big as Owens-Corning--if they make false claims for that facing--created enough blowback from the scientific community and unhappy customers that they now have a federal law to deal with, 16 CFR Part 460, and will likely see more enforcement actions as many of the same old claims have been ramping up again in the last few years. You might want to review the FTC's action against one such home-sales company in 2013, the court ordering a fine of $350,000. www.greenbuildingadvisor.com/article/stay-away-from-foil-faced-bubble-wrap
Thanks for the information. I guess, for me, there is nothing novel about the idea of a company being punished for misrepresenting products to consumers. Look at the concept of planned obsolescence, how's that for scamming consumers. If you have sold something long enough, even the most idealistic and noble of buyers will be enticed by a lower price. Science is no better by the way, there are countless cases in human history of the masses being purposely misled. And, that's the rat race, there is nothing new about it. All people, all industries, all the time. I did see the article and have read it before. Interesting when you get down into the comment section however where the real users of the products are, not the science and marketers and there are real people saying the product worked for them, all in an article that says it doesn't. Do you believe them? I do. Then there are those readers who feel shame because of the article and say they got screwed having no scientific basis to make the statement just because an article states something. Incredulous yes, but again nothing new.
What is better for HVAC duct insulation? Fiberglass or reflectix. All reviews I've read have been great.
While I agree both insulations will become hot, I think we have to look at how much heat will be transferred through the insulation and the ceiling to the roof below.
Still needs an air space between the surface of the ductwork and the material to be effective.
You showed the barrier between the heat load (Sun) and the insulation, will you get similar results should you use fiberglass against the roof sheathing in your attic then add the thermal barrier? I'm thinking of using fiberglass then the barrier in my garage which has exposed rafters and sheathing with no soffit vents.
If we understand you correctly, when you stand in your garage you will see the foil insulation (the FG will be installed above that)? Yes, this will work fine. As reflective aluminum is 94-96% reflective that means it only emits the inverse, 4-6% of radiant heat.
Good scientific study because it can easily be replicated to prove or disprove the results, which are dramatic.
Thank you for the video. In the example the radiant barrier was placed on top of and touching the insulation. Do gaps between the barrier and the insulation help, hurt or not matter? Would it have been more effective to place the barrier on the eaves under the roof instead of across the insulation on the ceiling? I assume air permeable barrier should be used in both cases - is this true? Thanks.
An air space is always best with reflective barriers.
The ideal radiant barrier is stapled to the bottom of the trusses, so you have an air gap on both sides of the radiant barrier. This gives you the benefit of the radiant barrier being a poor absorbing of radiant heat, as well as a poor emitter of radiant heat.
The example in this video shows the impact of radiant barriers inability to absorb radiant heat. The newer roof decking has a radiant barrier glued to the bottom of the OSB. That radiant barrier will absorb heat through conduction, but it will still have the benefit of not being an effective emitter of radiant heat.
An air permeable radiant barrier isn't necessary as long as you leave a 12-18 inch gap at the bottom and top of the radiant barrier to allow for the area behind the radiant barrier to vent.
I recently insulated my detached garage flat roof by putting 150mm of rockwool insulation sandwiched between the roof and 12mm plasterboard. I dont want to take that all down to apply this as the forst layer. So my question is, can i add this as a layer after the plasterboard? Will it still be effective?
If understanding correctly you want to add a radiant barrier to the face (exposed side) of the plasterboard. This will reduce radiant heat gain in the garage if there is any that makes it through the roof system. Critical to not cover the radiant barrier, the exposed side needs to have an airspace of 3/4" or greater to be effective in this assembly. Radiant barriers have high reflectivity and low emissivity. In terms of insulation, a material with low emissivity would tend to hold onto heat more effectively because it emits less thermal radiation.
I could be wrong but I don't think this was a valid test. Sure... it would reflect the heat (from the lamp) due to a transparent object (the glass) and provide the protection. Now... if you did the same test and put something in-between (maybe shingles, plywood on top of both boxes) and repeated the test, then... I think you would have something. This isn't a good test but it did give me an idea to perform my own test.
How did your test work? I think the idea is that the shingles would get hotter and radiate extra heat back out into the air.
The principles are the same. The heat lamp radiating heat directly onto the insulation is no different than the heat lamp heating up shingles, which then radiate heat onto the insulation. Radiated heat is radiated heat.
is it intended to use on out side of exiting walls w/o any insulation in the wall?
No. If you were to "wrap" the exterior structure, you would still need to insulate. The reflective benefit of the barrier needs air space to be effective.
if foil is under the roof shingles and plywood then it can not reflect radiant heat since it is not directly exposed to the light. experiment makes sense as you can see when there is direct light hitting and getting reflected by foil.
It doesn't need direct exposure to the light it needs an airspace to be effective.
Excellent job! You rock :-)
I would love to see this same test but with the heat source coming from the bottom (to represent heat rising in the winter) also would love to see this test with cellulose (including the heat coming from the bottom)
It would not matter. We don't care which side of the insulation gets hot, we just care that overall it slows down the thermal transfer process which in any case saves you money. There are no if ands or buts about it.
If I have galvalume metal siding on the outside of my house, wouldn't that act as a radiant barrier the same as the aluminum barrier you sell. They're both metal. Whats the difference???
The difference is in the reflectivity. All materials absorb radiant heat, the question is how much. A radiant barrier only absorbs approx 5-7%. What is the reflectivity of the galvalume panel. The manufacturer may be able to answer.
I have a patio cover of white galvalume, uninsulated. Summer temperatures heat the metal, which reflects some of the heat, but also radiates some. On the hottest days it is not comfortable sitting under the metal roof. When it is cold, depending on moisture in the air, condensation forms underneath and it "rains" under the patio. Seams are sealed. The discolored redwood joists tell that story. I inspect homes professionally and have been under patio roofs made of reflective metal roofing over sealed foam insulation with textured FRP bottom. In this type patio roof radiated heat is minimal and no evidence of condensation.
This test represents an attic without a roof? How much infared penatrates a roof?
Unsure about the infrared but a practical explanation for heat transfer would be comparing the roof to a sponge. The sponge will continue to heat up and then pass this heat (via radiation and/or conduction) to the cooler interior surfaces below the roof line until the heat source subsides (typically night fall) and equilibrium is met. The cycle repeats the next day.
Unsure about the infrared but a practical explanation for heat transfer would be comparing the roof to a sponge. The sponge will continue to heat up and then pass this heat (via radiation and/or conduction) to the cooler interior surfaces below the roof line until the heat source subsides (typically night fall) and equilibrium is met. The cycle repeats the next day.
Thank you for this well explained video which explains a difficult concept in very clear terms. What a difference...radiant barriers need to be part of the building code.
See that huge air gap between the radiant Barrier and the insulation? Therein lies the problem. It doesn’t work without that air gap. Like works 0 without it.
@@cygnus1965 NOT TRUE! There is air in that fiberglass insulation. Thats the air gap and thats why you never compress insulation! Use some common sense. geesh! Boy there are some real dim wits on here.
Just an observation. The left side thermometer on the bottom went up 11 degrees in an hour.
Now extend that over the afternoon... 6 hours X 11 degrees per hour equals 66 +69 degrees = 135 degrees. It seems that eventually the insulation would become almost as hot as the
non covered insulation, by the time the sun went down. Now after the sun
went down the non covered insulation would "bleed off the excess heat"
(at what rate I'm not sure) where as the insulation with radiant barrier
would hold the heat in longer due to the radiant coverings properties.
Consequently I'm not sure if radiant barrier on the insulation is the
way to go at least in hotter climates. Maybe roll it up and store it out
of the way in the summer and unroll it in the winter. Just an
observation.
Just one problem: reflective barriers are usually not installed as the roof surface. Add some plywood and asphalt shingles on top with radiant barrier under one and not under the other and get those same results and THEN I will be impressed.
thank you BDB! This would give us the real data
In order for pink insulation to work as designed it needs 6 sides, you only had 5. A better test would be a piece of dry wall on both over the insulation and then put your material over the the drywall.
of course one side is gonna be hotter than the other one since one has double proteccion
Ok genuis,,,,,, do I put the reflective shield over my singles?
*genius
um... so how much sunlight am i getting in my attic or walls? none? so should i put reflective barrier on the roof?
edit: try putting a lid on it...
You forgot that there's a roof between the insulation and the sun. 🤦♂️
Those materials still absorb and transfer heat.
@@kcmaldonado3948 dont radiant barriers reflect radiant heat which is in the form of light? And the roof takes the grunt of this radiant heat, heats itself up and also the air underneath it, converting the radiant heat of the sun to convection with the air touching the other side of the roof. This is why most insulation is focused on air pockets. The concern then is whether or not such a reflective insulation adds any value given that the roof already takes most of the radiant heat and transforms that heat to convection (heating thru air not light).
@@PablocitoSantino What you're missing is that thermal radiation isn't just from light. All matter that has a temperature greater than absolute zero will radiate heat. The roof is radiating heat onto the insulation. It's not using convection to heat the insulation in a home. If convection were the primary form of heat in attics, then venting would solve all our problems with attic heat. Instead, we use venting to cool the roof deck so that its not radiating as much heat.
Some of these comments shows that lots of people dont need a science class, they were not born with any common sense.
Should have been an air gap between rhe radiant barrier and insulation.
The test is bogus. Note the placement of the heat lamps above the box allowing the free movement of air in this region. Of course the radiant barrier will be effective in this instance (the air below the insulation never becomes heated). The correct way to preform this test is to measure the AIR temperature both above and below the two insulations; doing so will return very different results.
To prove the point, you could have repeated the experiment with two setups: one with the fiberglass insulation alone and one with just a SINGLE layer of aluminum foil and NO FIBERGLASS; you'd get virtually the same results.
This simulates a reflective roof…
Eventually the fiberglass will become the same temp with it without barrier over a full day. Just really not worth the money or time.
Not true with proper ventilation.
This test is bunk: The test ignores heat transfer along the glass sides. The radiant energy is not going through 6 inches of insulation it stops at the top of it. Of course black body radiation will heat the top layer of insulation greater without a radiant barrier but that heat doesn't transfer through the insulation(that's the concept of insulation), it will transfer down the glass sides.
Both boxes were plexiglass though. If the effect you're describing were meaningful, then we would expect to observe less of the benefit from radiant barriers in this experiment than occurs in real world applications.
Total nonsense. What is the wattage of the heat lamp? 300 watts - maybe more across a 5 inch diameter bulb.
If the temperature of your roof sheathing is 150 deg F then a 5” round piece of your sheathing (same as your bulb) is radiating less than 10 watts @ 150 degrees F.
Put a 10 watt incandescent bulb in your heat box and redo your one hour test.
So many misconceptions in the comments, it is not really worth the time to clear them up...…...people will believe whatever they want, no matter if it is fact or fiction. ……..Have fun with high utility bills and your air leaking houses that need to breath....lol
I too Question the test because it does not take into account conductive and convection heat transfer, In real life the radiant Barrier is on the underside of the roof material. which will then get heated from above and below, Ultra violet waves from above and infrared waves from below. How ever radiant barrier does nothing to stop heat transfer through conductivity from roofing members. the insulation between framing members, when the foil absorbs heat it will emit heat through conductivity into the air drivin by convection. I would like to see a test with a real life structure simulated in you lab. thanks
@@mydreamhouse1 There are a bunch of videos on TH-cam showing the impact of radiant barriers. We have cheap Flir cameras now, so everyone with $200 can test this out. The radiant barrier has two purposes. Its a poor absorber of radiated heat, so most of it is reflected back. It's also a poor emitter of radiated heat, so the heat it does absorb isn't effectively emitted. An air barrier on both sides of the radiant barrier would take advantage of both of those traits.
exactly this is a poor example.
Lets go for the age old question: Why?
@@tollav Follow the money. The tester is motivated by money and designed a bogus test that would exaggerate the benefits of the material he is trying to sell.
@@skipondowntheroad5833 say what you want, these cut down on heat transfer
this is the dumbest test ever ,, we need to see the radiant alone vs the fiberglass alone ...this is like saying tiger and a lion vs a lion who will win..lol i cant believe is no one mention it. failed
Actually in residential home application you would want to see them both. As fiberglass is part of the building code its already there, the foil is in addition. The radiant barrier versus the fiberglass would be good for metal buildings and pole barrns.
A better test would recreate a real roof
Tin foil on top of insulation would have the same results
This test is meaningless