double bubble foil insulation or not?
timestamps
| Posted in Energy, Heating & Insulation on
I have gotten many conflicting reports on the effectiveness of this double bubble foil blanket product. The manufacturer claims upto R-10 but govn’t resources say it has not been proven and discounts it’s use as an appropriate insulation. If trapped air is a good insulator, then why is two layers of entrapped air ( bubble wrap ) with a reflective coating of aluminum foil considered a practically useless insulation material? Thoughts? Opinions? Experience…
Replies
Can't agree with the term 'useless' but for the money and time involved foamboard insulation products fare much better.
sobriety is the root cause of dementia.
Reflective materials do not have an R rating. Reflective aluminum is a very good heat *conductor*. It works well to stop radiant heat, but that is a shadow effect. If you touch it, it will be hotter than something a few inches from it.
A better measure of "Radiant Barriers" is Emissivity/Reflectance. good example of how reflectance prevents the transfer of heat is to stand between a black car and a white one parked in the sun. Put your hands on the hood of each and see which is warmer. The black hood doesn't reflect as much sunlight so it gets hotter.
Emissivity is a measure of how well a material emits, (Radiates,) heat. Hold your hand an inch away from a shiny stainless steel coffee pot. Try that with a light bulb. Notice how much hotter your hand gets near the light bulb.
The bubbles in bubble wrap are big enough to let the air in them to develop convective currents which carry heat from the hot surface around to the cool surface greatly reducing its' R compared to an equal thickness of foam with its' much smaller bubbles.
SamT
http://www.healthyheating.com/Page%2055/Page_55_o_bldg_sys.htm
The number of studies proving that the R10 claim is an outright lie is large and growing all the time.
If they claimed that to you in writing, report them to the FTC.
If they did not... ask them to, then report them to the FTC.
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks to all for the advise! What then, would you use as a reflector in an under floor joist staple-up application below the heat transfer plates to direct the heat up to thru the floor? Just regular Roxul like an r-14.5?
IMO?#1. Spray foam.
#2. Foil side up foam board, 1" from fins.
#3. Foam board.
#4. Cellulose.
#5. Rock wool
#6. Foil side up Fiberglass. keep foil 1" from fins.
#7. FG.
#8. Radiant barrier.
#9. DW under the joist
#10. Fine Italian Leather.Some argument could be made that #2 is a better choice than #1 in your particular application, but without knowing the numbers, it's just an argument and not a debate.SamT
Personally, 10 is better than 1 when the customer has hardwood installed and forgets to tell the installer.
Money don't fix stupid.
So I should return the rock wool i was going to use and replace it with foil faced rigid board and then drywall? If R value is not in the equation for this application then why is sprayed foam at the top of your list?
"why is sprayed foam at the top of your list?"Because having a certain resistance to the flow of heat is the most important thing in the equation. That's why the list was from most insulative to least, until you get down to Fine Corinthian Leather, which, under the right circumstance, can generate a certain type of heat.SamT
Doesn't really matter. The plates are there to conduct into the subfloor. That's the primary heat transfer mechanism.If you use a reflective layer in addition to actual R-value, it'll help for awhile at least, though it's a small effect. I don't trust upward facing reflectivity long term, personally, and would not spend an extra penny for it, but if you want to eke out maximum performance it can help a little at least, for awhile at least. Maybe longer... that's controversial. I just prefer to spend money on known benefit. You DO need downward R value though. there is some radiation downwards; however, keep it from conducting out, and you won't lose much downwards.Make sure those rim joists and edge joists are well insulated too.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Thanks again! It's guy's like you, the real pros that make BT what it is...among other things, a place of great knowledge, field experience and sound advice...and some pretty funny #### too! We have in-slab ( too late, I've already poured over the double bubble foil #### ) and baseboard radiation in the rest of the space below ( the basement )and i'm hoping to get enough BTUs out of 17' of cores. If not I'll have to add more cores in tandem ( sort of like the high output rads ) so i can run lower temps and get that Baxi condensing. This was a new install but the first two contractors didn't know jack so I'm trying to make it work. I was going to use the left over bubble wrap (170.00 worth) as a "reflector" below the transfer plates but will return it and get my wife some fine Italian leather as SamT suggested...that should keep me warm at least till i screw up the next project anyway.
Edited 9/19/2007 9:04 pm ET by timestamps
timestamps
The aliminum foil on the buble wrap is unlikely to survive long in the alkaline environment under a concrete slab anyway.
Ron
NRTRob,
a couple of comments.. Instead of aluminum plates I used rolls of aluminum flashing . I ran it thru my bead roller to the size of the tubing and then nailed it up in place with a roofing nailer
sure was fast!
Oh by the way, doesn't everybody use two inch thick hardwood subflooring?
I digress,.... ;-) then I used the foil faced Isocianurate foam and sealed the edges with spray foam..
Anyway as long as heat rises won't the heat trapped inside the building envelope remain there and eventually warm the floors above? (minus what's lost thru windows of course)..
Another words if you pump x number of BTU's in a building won't each floor above get warmer as a result? (minus losses of course) ..
Hot air rises
Heat goes from hot to cold and is not affected by gravity.
If you are heating by forced air, the heat carried by the air will rise.
Eventually the BTUs will get somewhere where they do some good, minus additional losses from the joist cavity's elevated temperature, either through the rim or downward to cold space. So there is loss of efficiency there.The other thing to consider is that while BTUs will eventually migrate through the floor, they may not do it FAST enough to meet the load. Heat transfer is units per unit time... BTUs/square foot per HOUR, for example. So if you can't push them through the floor fast enough, you have to raise the water temperature to drive them faster.and if you didn't insulate, heat doesn't rise, as another poster said. hot air rises. you'll radiate heat to the ceiling below and into whatever space is there, without control, if you don't insulate underneath.
-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
Aren't we just splitting hairs? True heat radiates but as you say when it reaches something where it does some good, say an air molecule and raises the temp of that air molecule, then that air molecule rises..
It's understandable that losses could easily exceed the ability to generate heat.. If they didn't we could heat our homes with litebulbs (terrible wasters of energy) thus real world efficiency becomes more and more critical. For example my walls have a real world rating of about R35 but I have a strange preference for windows which for all practical purposes have no insulation.
I'm not sure what you mean.If you elevate the joist cavity temperature and you aren't using plates to conduct heat into the subfloor directly, you slow down heat transfer; quite often, to the point where the system can't keep up when it's very cold out. That's also more heat going back to the boiler, raising its temperature faster, more going out the flue. You're maximizing expansion stresses through the system. You're maximizing heat loss through the joists. If you're not heated below the floor you're heating now, that can be quite significant! Sure, you might slightly elevate the basement temperature, slightly slowing down the downward loss, but if you want a heated basement, heat the basement; uncontrolled downward losses is no way to heat a space you want to occupy. If you don't, that is heat loss, you're heating space you don't want to heat.So there is a lot more to that than just dumping BTUs into a joist bay and waiting for them to rise.Plus, only about 35% or so of radiant output ends up being convective in nature. air molecules are small. Heat can beam right through to an object somewhere else, which will warm up but eventually the goal is to balance the mean radiant temperature of the surfaces, not elevate them all so they all become convective radiators! Unless you are raising a mass of air to higher energy levels, you won't get much additional convection. I keep getting asked if we can skip heat on the 2nd floor, because "heat rises". In radiant, it doesn't rise that well. Some, yes, but not that much. This is not a forced air system. The answer is usually "no" (excepting lofts that are not too deep).So that's a very important distinction. You can't count on all that heat rising. Only a portion of it will. That is definitely not hair splitting!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
NRTRob,
I'm not sure what you are answering, I'll review briefly.
I Installed radiant tubing by taking aluminum flashing running it thru my bread roller and nailing it and the tube to my sub floor with a roofing nailer.. Extremely fast way to install. I then put some foil faced insulation (R13) into the joist cavity and sealed it with spray foam.
The flashing transfers heat to the sub floor and the foil facing radiates lost heat back up.. While the thickness of my subfloor slows heat transfer down a bit it's pretty much kept into the joist cavity untill it can migrate upward since doing so is easier than getting thru the foam..
Once there it does the important job of warming toes.. it loses heat thru the air and the room above. (warming the rest of me) With the excellant insulation in my walls my only real losses are thru the windows.
"True heat radiates "I don't know what the difference between "true" heat and "faux" heat. But heat energy is transfered by 3 different means, conductio, convection, and radiation.Lets run a little test.You hold a solid copper rod in your hand. But hold it upright with the free end up. Then we will take a radiant barrier and put a hold through it so that no radiant energy can pass.Then I will put a propane torch on it. With the radiant barrier you wan't get an radiant heat.And since the torch is ABOVE your hand and as you say "heat riase" you won't get any heat at all.Lets see how long you will hold that rod. .
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
BillHartmann,
I failed to put a comma there. I should have said True, heat radiates.
the rest of your explanation was uneeded..
,
seems that the little details really are important. :)
Missing punctuation? It reminds me of the story of a sentence written on a board:
"Woman without her man is nothing."Someone came along and added punctuation:"Woman! Without her, man is nothing!"(Of course, this hardly adds to the thread. Sorry)
"Eats, shoots, and leaves" is the one I think of.