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I am a mechanical and environmental engineer, and I help companies pollute less by making a more efficient use of energy, water, materials and chemicals in their operations. When I started doing this, 15+ years ago, it was called pollution prevention or cleaner production, but now it has been rebranded as sustainability. Whatever the name of the practice, it is a pretty good idea to tread lightly on our resources by doing more with less.

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  • Insulating curtains that cut heat losses through windows by 50%

    I am so impressed by your drive to find a way to make these curtains work optimally in your home.My experience with the curtains that I installed in my house is that, as long as they are tucked in properly into the window opening, the amount of condensation is minimal. However, as I have mentioned before, I live in an area where nighttime temperatures seldom drop below 20F, and this certainly contributes to reducing the buildup of condensation behindthe curtain.Over the past few days I have researched various sites that talk about thermal curtains and even contacted a few manufacturers of commercial insulating shades. They nearly all agree that, in very cold climates, condensation on the cold glass is nearly inevitable, and that it is the price you need to pay to keep your rooms warmer ...see more »I am so impressed by your drive to find a way to make these curtains work optimally in your home.My experience with the curtains that I installed in my house is that, as long as they are tucked in properly into the window opening, the amount of condensation is minimal. However, as I have mentioned before, I live in an area where nighttime temperatures seldom drop below 20F, and this certainly contributes to reducing the buildup of condensation behindthe curtain.Over the past few days I have researched various sites that talk about thermal curtains and even contacted a few manufacturers of commercial insulating shades. They nearly all agree that, in very cold climates, condensation on the cold glass is nearly inevitable, and that it is the price you need to pay to keep your rooms warmer and your heating bills down. Many mention that they keep a squeegee or a towel handy to clear the condensation when they open the curtains in the morning.There is no question though that the tighter the fit of the vapor barrier in the window opening, the lower the infiltration of moist air behind the curtain and, as a consequence, the lower the condensation on the window pane. Therefore, my recommendation would be that you adopt in other parts of your house what you did in the laundry -- that is, make the vapor barrier wider so that it completely fills the window opening … and find a way to deal in the morning with the reasonable amount of condensation that forms overnight.The solution you applied in the bathroom (i.e., removing the back panel of fleece) is not optimal because it reduces notable the insulating performance of the curtain. In fact, the reason why you had less condensation after making this modification is that without the back panel the curtain let more heat reach the window and flow outdoors, and by keeping the glass warmer this heat hindered the formation of condensation.Good luck with your curtains … and please do let us know if you come up with the optimal solution.

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  • Insulating curtains that cut heat losses through windows by 50%

    Hello GEGJ11) I am sure that a thick piece of corrugated cardboardshould be a better thermal insulator than a layer of polar fleece. However, Iwould be a bit concerned about humidity, especially if you are planning toleave this panel up for long periods of time. Unless your assembly is extremelytight and prevents the passage of even a minimum amount of humidity, you willend up with some condensation on the glass. In the case of the curtain, this isnot much of a problem because the condensation either evaporates or is wipedoff when the curtain is rolled up in the morning. However, in your case, itwill probably accumulate over time and soak into your cardboard. I may be wrong, so please give it a try.If you do end up with a problem with condensation, I wouldtry a water resistant insulatio...see more »Hello GEGJ11) I am sure that a thick piece of corrugated cardboardshould be a better thermal insulator than a layer of polar fleece. However, Iwould be a bit concerned about humidity, especially if you are planning toleave this panel up for long periods of time. Unless your assembly is extremelytight and prevents the passage of even a minimum amount of humidity, you willend up with some condensation on the glass. In the case of the curtain, this isnot much of a problem because the condensation either evaporates or is wipedoff when the curtain is rolled up in the morning. However, in your case, itwill probably accumulate over time and soak into your cardboard. I may be wrong, so please give it a try.If you do end up with a problem with condensation, I wouldtry a water resistant insulation material such as an extruded polystyreneboard. They are not very expensive, have a very high R-value, and are notaffected by humidity.2) In my case, I use the extra width of the curtain fabric topress against the sides of the window opening and prevent the passage of air.This is a good solution for a curtain that needs to be rolled up every morningand rolled down every night, but if you have a more permanent installation youcould use other materials to seal the perimeter of your insulating board (e.g.,rubber foam strip).3) Please see my answer to Brandon’s post.Also, if aesthetics are not a problem (and they should notreally be if you were planning to put a shiny mylar facing the window), youcould consider spray painting the glass white. The paint has to be on theoutside pane of your window and block nearly all of the solar radiation. Ifthis is not an option and you are very worried about cracking your windows(which I assume are double pane), you should try to find another option toshade your windows/doors from the outside.4) The function of the plastic in my curtains is to act as avapor barrier. A vapor barrier should be placed closer to the “warm” side ofthe insulated assembly (i.e., closer to the side which faces your indoorspace). Since you are planning to have a layer of mylar facing indoor, thiswould act as the vapor barrier on the warm side of the assembly (i.e., you don’tneed to add an additional plastic sheet).Please note that for insulation purpose, it is generallyrecommended to have an air gap that is between 0.5 to slightly less than 1 inch(your 2” gaps are too big).5) Sure, a radiant barrier facing the inside of the roomwould be useful from a thermal standpoint. On top of that, it will act as a vaporbarrier and prevent moisture from penetrating into your cardboard andcondensing once it reaches the cold side of your assembly.Good luck!

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  • Insulating curtains that cut heat losses through windows by 50%

    You are spot on. The best way to reduce the solar heat gain through a window is by shading it from the outside.

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  • Insulating curtains that cut heat losses through windows by 50%

    Thank you for your comment. I am glad to see that the curtains have made a noticeable difference in keeping the rooms warmer, but I am surprised to hear that you have problems of heavy condensation on the glass when the curtains are closed.My experience with the curtains installed in my house and in the houses of friends and relatives is that when the curtains are closed there should be no (or a minimum amount) of condensation on the windows as long as the following conditions are met:1) The vapor barrier panel and the fleece/cloth panels are cut to the correct size. There should be only a small gap (approx. 3/8”) between the sides of the plastic sheet and the sides of the window opening, and when the curtain is closed this gap should be totally filled by the excess width of the f...see more »Thank you for your comment. I am glad to see that the curtains have made a noticeable difference in keeping the rooms warmer, but I am surprised to hear that you have problems of heavy condensation on the glass when the curtains are closed.My experience with the curtains installed in my house and in the houses of friends and relatives is that when the curtains are closed there should be no (or a minimum amount) of condensation on the windows as long as the following conditions are met:1) The vapor barrier panel and the fleece/cloth panels are cut to the correct size. There should be only a small gap (approx. 3/8”) between the sides of the plastic sheet and the sides of the window opening, and when the curtain is closed this gap should be totally filled by the excess width of the fleece panels which is pressed and folded against the sides of the window opening.2) There is no large hole or tear in the vapor barrier. Even a very thin sheet of plastic (e.g., saran wrap) is enough to stop the movement of vapor through the curtain. The reason why I recommend using a 4 mil plastic sheet is that, according to my experience, it is more resistant and can handle the frequent rolling/unrolling of the curtain without tearing. 3) The curtain really “plugs” the window opening when closed. The curtains needs to seal extremely well the complete perimeter of the window opening. You can check this by closing the curtain during the day and turning the lights off in the room. You should see no daylight seeping through the perimeter of the curtain (a very thin sliver of light here and there is ok, but no more than that). If that is not the case, then you will have a trickle of moist flowing through the gap and bringing condensation to the glass panes.I am not sure what the problem might be in your case. Could you please post pictures of your curtains (including details showing how the curtain fits against the top, bottom and sides of the window frame), of the windows on which they are installed, and of the condensation? Could you also provide more information on your particular installation? 1) Where are you located?2) What are the typical nighttime temperatures during the winter? 3) Are these curtains installed in a room with a very high level of humidity (e.g., kitchen, laundry room)?4) When you close the curtain, after how much time do you start seeing condensation on the glass?5) Are your windows very drafty? If so, could it be that the moist air is coming in from outside?Looking forward to your input.PS: If you have condensation on your windows it is not surprisingat all that it will freeze during a cold night. You have to keep in mind that the closed curtains prevent the heat of the room from reaching the window. Therefore, on a cold night, the temperature of the inner pane of the window can drop to below freezing and any condensation on it will turn to ice.

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