Replies

1. 
   onslow | Dec 23, 2018 05:00pm | #1

   Mr. Donahue,

   Before getting too deep into committing to insulated shades, it would be best to consider your climate zone and anticipated humidity levels in the house. The idea of saving energy with shades doesn't always work the way one might expect.

   My second home, located in the upper midwest, which had new argon double pane windows, always had condensation issues. It was very common during the winter to have wet edges at the perimeter of the glass due to a flawed combination of old tech window spacers and aluminum cladding that physically touched the glass. I installed fairly expensive honeycomb cell shades with the aluminum barrier layer on the outside cell thinking I would get a two-fer boost in beating loss of heat in the winter and excessive sunload in the summer.

   Unfortunately, this was all pre-GBA reading and learning. The summer sun load was somewhat reduced at the expense of creating a tomb-like ambience during the day. The winter heat savings were never of much value given that the condensation was aggravated to the point of icing at the perimeter. Mold and paint damage prevailed.

   As we all experience on our glasses of ice tea , humid air condenses on colder surfaces. The insulated shades I had installed did reduce heat flow out the windows, but they also lowered the interior glass surface even more than normal, which caused condensation despite relatively low interior humidity levels. The shades that fit the opening the tightest were the worst offenders. The side tracks, which corral the shade edge for a tighter seal yet, might have helped, but I suspect that negative pressure from window leakage would most likely suck humid room air into the gap between cold glass surfaces and the shade.

   My fourth home now has Alpen triple pane with argon windows and fiberglass frames as well as more advanced spacer technology. At zero degrees and below, I am comfortable sitting next to them (even now with less hair than 20 years ago). The only condensation we have on the inside of the windows occurs in the bathroom during showers and the kitchen on pasta night. This is not an issue with the fiberglass frames and mold has not appeared after 3 years. We do have sunblocking shades in some windows to keep our computer screens clear, but the SHGC I chose allowed us to forego installing air conditioning thanks to our climate's 30-plus degree swings from day to night.

   I would urge you to expend more on windows that control heat loss and gain over trying to patch up any deficiencies after the fact. Reflecting shades that are meant to reduce heat gain are also only partially successful, as the solar heat gain has already been introduced into the house by the time it encounters a shiny shade. Yes, some energy will be reflected back, but much of the energy will be busy warming the window glass, frame, trim, etc.

   Shades or curtains may be absolutely necessary where you are for sunlight control or privacy. If you are located in a very mild climate, interior glass surfaces may not fall to a point where the humidity can condense. The closer you are to a New England level of winter, the more likely you will have cold interior glass to contend with. If double pane units are currently what you are working with, perhaps experiment with hanging a blanket over an opening. You will see if interrupting the warming effect of room heat on the inside glass causes the interior surface to hit the dew point for your conditions.

2. 
   BrianPontolilo | Dec 23, 2018 06:22pm | #2

   Bill,

   If you do a search for insulated window shades on this site, you'll find a bunch of articles. Not sure if there is some state-of-the-art technology newer than our most recent article, but here are a few places to start:

   https://www.greenbuildingadvisor.com/article/insulating-window-shades
   https://www.greenbuildingadvisor.com/article/do-window-shades-save-energy
   https://www.greenbuildingadvisor.com/article/window-shades-blinds-and-awnings

3. 
   rockies63 | Dec 23, 2018 06:33pm | #3

   These window quilts help eliminate the problem of cold air getting past the edges of the window shade (which is a common problem with honeycomb designs) and can help prevent condensation on the window.

   https://www.windowquilt.com/index.htm

   https://www.windowquilt.com/products/full_broch.htm

4. 
   davidsmartin | Jan 08, 2019 12:08am | #4

   A honecomb shade product that avoids the problem of condensation is ComforTrack Cell Shades. They include a track down the sides of the shades that prevents air from circulating behind the shades. I have used them for years in Vermont and have not had condensation.