Double Sided Radiant Barrier?


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Old 01-05-12, 12:05 PM
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Double Sided Radiant Barrier?

I have some questions about the physics of radiant barriers before I start making some for a couple of windows and doors in my home.

Background: I rent a 2-story brick row home in the center of the lot that was built in 1915. It has hot water radiators in most rooms of the house. There is one thermostat on the first level that controls all of the radiators and there are not valves to control the temperature of the radiators in each room individually.

Please assume: We have patched up drafty windows and doors to the best of our ability. Since we're renting, we are interested in a short-term, easy, fast, and CHEAP solution for this winter only that ideally can be implemented this weekend or earlier. The landlord is not willing to contribute further to our dilemma. In addition to what I mention below, we are taking other measures to increase the temperature on the first floor.

Dilemma: All of the heat on the first level (where the thermostat is) escapes upstairs, leaving the downstairs freezing and the upstairs unbearable when the thermostat is set at 63F. There was an addition made at the back of the first level with a backdoor that exits to a patio and alley. We hung a curtain separating the addition from the rest of the house and that has made a world of difference. However, 1) It's now freezing in the addition because there is no radiator in that room. 2) The curtain was a huge improvement, but not a perfect solution and we'd still like the rest of the first floor a little warmer.

Questions: Would there be a noticeable difference in the temperature of the addition if I put grocery store tinfoil on all of the windows and the backdoor? Would there be more of a difference if I put tinfoil AND bubble wrap on the windows and back door.

How effective would a double-sided radiant barrier be between the addition and the rest of the house? Let me explain... The curtain that I am using to separate the addition from the rest of the house is in a doorway directly across from the backdoor. What would happen in the addition, and the rest of the downstairs, if I put radiant barriers on the windows and doors at the back of the house in the addition and ALSO across the room, put a double-sided radiant barrier on the curtain. I'm imagining a layer of tin foil - shiny side facing into the addition - separated by bubblewrap with another layer of tin foil shiny side facing the curtain that leads into the rest of the house. The hope would be to keep some heat in the addition but also to keep most in the rest of the house. Thoughts?

Are radiant barriers any more effective if there are two or more radiant barriers across a room from each other facing and reflecting off of each other?
 

Last edited by brunoblt; 01-05-12 at 01:42 PM.
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Old 01-05-12, 02:27 PM
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Come back in a few months and I might have a better answer LOL. RBs are one of the most misunderstood tools for use in heat management. The most common response is "scam", but radiant heat transfer is still one of the three main transport methods and once conduction is eliminated, like inside a room, you are down to convection (slow) and radiation (the speed of light). So, in my opinion, we need to know more about it.

I'll just list some of the bits we currently have to work with, not all proven.
1. RBs on the inside of a window can cause problems with low e coatings, as heat can built up and damage the window. Plain glass windows would be less of an issue.
2. Windows work in two directions, allowing in solar heat and, if not covered, allowing radiant energy to go right back out. Since these are different frequencies, that low e can be tuned to our advantage. But what we need for tuning up north is opposite what they need down south and often the same windows go to both places.
3. All surfaces above absolute zero radiate energy. Inside a home at 70, everything (almost) is radiating 460 watts and receiving 460 watts per sq meter. This number changes with the reflectivity of the surface which is what we are talking about. Because all surfaces receive essentially what they lose, little change. Add a layer of foil and now that surface will neither receive nor transmit that energy, so the question becomes, what did you gain?

I can go on with many more bits of information, but space is limited, so here is my conclusion to date for cold country. A curtain or one inch of rigid foam board would be better than foil for the windows. Since foam is supposed to have a fire rated barrier, the foil covered polyisocyanurate commonly sold at the big stores would give you some insulation and the reflective surface for whatever it is worth.

The same approach can be applied to any wall. The colder the wall, the more benefit, but the insulation is the major contributor.

As for the addition, if there is no heat source in there, you can't keep the heat in and you simply move the barrier to the curtain you have installed and it has little value, other than as an air barrier.

Bottom line, cover walls and windows with something that insulates and solve the RB issue on your next home.

Bud
 
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Old 01-05-12, 02:37 PM
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Are the windows still an issue? If so, I'd cover them with 3M plastic on the inside.
 
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Old 01-05-12, 06:24 PM
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I understand that the advertized savings on your energy bill from radiant barriers are a scam, but I thought that it might actually help with the comfort level in the house and be worth the cost if we were just buying regular tin foil and bubble wrap from walmart. You think that the claims about temperature control are also a scam?
 
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Old 01-05-12, 06:31 PM
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I think the primary source of your problem is air infiltration. I think the radiant barrier will not get your the results your are looking for. You need to reduce air flow from the the outside to the inside. Given your situation, probably not worth your money.
 
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Old 01-06-12, 07:10 AM
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I'm sorry but I have to ask - how do you think tin foil and bubble wrap are going to help?
 
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Old 01-06-12, 08:34 PM
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One thing you might do is try and reduce drafts from the poorly sealed windows by installing some poly based window insulator seal kits over them and at least move toward reducing some of the air flow you are having. Not sure how many companies make them but the guys who make scotch tape I know do. Their might even be a cost saving payback in just once season. Other than this idea, without spend you won't get much more than you already have.
 
 

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