Window heat loss

Posted By chuck172, Jul 10, 2010 at 1:24 PM

1. #26

begreen Mooderator 2. ```NULL ``` Staff Member

Nov 18, 2005
64,792
8,585
Loc:
South Puget Sound, WA
For an option that is easy to use daily and easy on the eyes, I like honeycomb cellular shades. The double-cell variety can offer a gain of almost R 4. Levelor has a sheer efficiency version of the Accordia that we are looking into: http://www.levolor.com/products/cellular-shades/energy-savings.php. Single cell, but more transparent with R 3.33 rating. Hunter Douglas has the Duette Architella which has an insulating cell within the cell. But I haven't been able to find the R value for this series yet, but their energy guide appear to indicate R =4.0. If so, that would be a 300% efficiency gain over an R 2 storm window according to their docs.

Total R-value ÷ Window R-value = Energy Efficiency Increase
(4.0 + 2.0) ÷ 2.0 = 6.0 ÷ 2.0 = 3
Energy efficiency is tripled (300%).

The U-factor of an R-2.0 window is 0.5 (R = 1/U; U = 1/R). To
calculate the heat flow through this window if its size is 48" x 60"
(20 sq. ft.) and the temperature is 70° inside and 0° outside:
Heat Flow = U-factor x Area (sq. ft.) x Temperature Difference
Heat Flow = U x Asf x ΔT = 0.5 x 20 x 70 = 700 BTU/hour
Over a 24-hour period, heat loss would total 16,800 BTU.

To calculate heat loss with an R-4.0 shade over the R-2.0 window:
R-value = 4.0 + 2.0 = 6.0; U-factor = 1 ÷ 6.0 = 0.167
Heat Flow = U x Asf x ΔT = 0.167 x 20 x 70 = 234 BTU/hour
Over a 24-hour period, heat loss would total 5,616 BTU.
The R-4.0 shade cuts heat loss by two-thirds (67%).

2. #27

benjamin Minister of Fire 2. ```NULL ```

Nov 7, 2009
693
5
Loc:
SW WI
+2 on builditsolar.com

Floydian brings up a good point that wood windows may suffer from the condensation caused by making the windows colder with curtians etc.

low e will reduce solar heat gain during the day and reduce heat loss all day and night, so it will usually still reduce total heat loss even on south windows (it would be great if you could find "high heat gain low e" but I haven't found it in my price range). For all other windows, especially west facing in the summer, low e is "the bomb".

I'd love a good solution but it seems like all of the options have been tried and discarded. To me, there are easier places to save energy (air sealing, insulation, DHW tempering tank) and it's easier to cut a little more wood than improve on decent windows.

Maybe some day I'll have a bead blower or bubble windows...

3. #28

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,119
490
Loc:
SW Virginia
The cellular shades I mentioned earlier in this thread are also eligible for federal energy tax credits.
http://www.comfortex.com/comfortrackproduct.html

4. #29

begreen Mooderator 2. ```NULL ``` Staff Member

Nov 18, 2005
64,792
8,585
Loc:
South Puget Sound, WA
I like the design. How long have you had them installed? Any issues so far?

5. #30

GaryGary Feeling the Heat 2. ```NULL ```

Jul 12, 2010
291
18
Loc:
SW Montana
Hi,

We have the insulated shades with the side tracks on some our windows, and I agree they are a good product. The ones we have add R4 to the window, so they cut the heat loss to less than half when they are down.

We use triple wall polycarbonate inside storm windows on some windows -- they let plenty of light in but cut the window heat loss in half. The dual wall version of this stuff is what most greenhouses use today. They are easy to cut to shape with ordinary wood working tools lightweight to handle. They do distort the view out the window.

For example, if you take 100 sqft of double glazed window (R2) and add a good thermal shade like the ones mentioned above (R4), for our cold climate (Montana), and heating with \$2.10 a gallon propane -- the saving is \$183 a year. The 10 year saving with 10% a year inflation in fuel prices is \$2910.

Gary

6. #31

midwestcoast Minister of Fire 2. ```NULL ```

Oct 9, 2009
1,745
322
Loc:
NW Indiana
Hi Gary, welcome to Hearth.com. I just wanted to say that I've spent many hours on builditsolar and have learned a ton. Thanks for collecting & spreadinng so much great info!

7. #32

BucksCoBernie New Member 2. ```NULL ```

Oct 8, 2008
450
1
We have a big picture window in the living room that is original to the house (about 55 yrs), all the other windows were replaced by the previous owner. Our solution was to use the frost king window insulation film in addition to hanging insulated curtains. The combo of the 2 did a nice job this past winter and was relatively inexpensive.

8. #33

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,119
490
Loc:
SW Virginia
We've had them in for only 6 months so I can't speak to durability. They are real well made and seem to work as advertised. We have about 12 large unsealed, double layer cellular shades in another room and you can really feel the cold air leaking out around them. I find that frustrating. They do keep the room warmer when closed though.

9. #34

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,119
490
Loc:
SW Virginia
There was a pretty good discussion of sealing windows this way here some time ago. http://www.hearth.com/econtent/index.php/forums/viewthread/29984/ If I remember right you can buy that film in bulk from one of the industrial supplies like MSC or Grainger.

10. #35

GaryGary Feeling the Heat 2. ```NULL ```

Jul 12, 2010
291
18
Loc:
SW Montana
Thanks! That's great to hear.

11. #36

horrocksd Member 2. ```NULL ```

Mar 2, 2010
42
0
Loc:
Finger lakes, NY
We have a lot of 25 year old double pane, double hung Anderson windows. They are in decent shape and don't leak much, but in winter you notice the chill off of the glass. For the inside my wife and I have made our own insulated fabric window coverings for the winter. She buys "quilted fabric" by the yard. Each window requires about one yard of material and is about 26" wide and 30" long. My wife cuts the fabric and hems the bottom normally, but sews a "flap" as a hem across the top. Each window covering is over-sized in each dimension by about one inch. The coverings are held in place in each window by a spring loaded curtain rod that goes through the flap and holds up the fabric by wedging the curtain rod in the casement of the window. We tuck the fabric in at the bottom and sides of the window. Between the fabric cost and the curtain rod we have about a \$7 cost per window. The difference in the cold coming off of the windows is very noticeable. On sunny days we roll the fabric up from the bottom, without removing the curtain rod, and place this half-window roll-up on the ledge of the top of the lower double-hung window and it stays in place. To put them back down we just nudge this roll and it drops to the bottom of the window and we tuck it back in and we're good to go. This has worked very well for us on the 28 large windows we have in the house. We have made a similar window covering for a large bay window off of our kitchen.

Additonally, every fall I buy several "12 window plastic kits" and apply the plastic to our screens and put the plasticed-over screens back in place for the winter. This acts as a triple-glass window and makes a surprising difference. It only costs about \$28 to do all of our windows, including 6 casement units. I have learned to apply this shrink-to-fit plastic to the inside so the high winds we sometimes get doesn't shred it. In the spring I peel the plastic off, then the tape that held it, then clean the screen frame with Goo-Gone to get rid of any adhesive residue.These two things--the "window quilts" and the "screen storm windows" have made a very big difference in the comfort level of the house. This winter the econoburn should make an even bigger difference!

12. #37

chuck172 Minister of Fire 2. ```NULL ```

Apr 24, 2008
1,038
5
Loc:
Sussex County, NJ
horrocksd, I like your approach to this problem. I especially like the idea of covering the screens.

13. #38

tlc1976 Member 2. ```NULL ```

Oct 7, 2012
119
19
Loc:
Michigan
I know old thread but I was reading and really like the idea of the fabric enclosures for the windows. And I was wondering if anyone else did what I do.

My house is nothing spectacular so I do what I learned from my grandparents. For the winter and late fall/early spring, I use old comforters, fold them to size, and nail them in place so they overlap the window trim. It makes a HUGE difference. I have double pane wooden casements that are likely as old as the house which is 30 years, and new windows are out of the question. I do leave the slider door uncovered since I use it sometimes, it's the only window the sun sees, and besides the only window I'd miss looking out of. If something happened like a fire, the blankets would be easy enough to rip down and get out the window.

14. #39

Ehouse Minister of Fire 2. ```NULL ```

Jul 22, 2011
906
256
Loc:
Upstate NY
Another approach is to cordon off the space creating a small sun room. This allows you to use other, perhaps more sightly and easier to manipulate insulating strategies such as tambor, bifold, or pocket doors, or a curtain on a track.

Ehouse

15. #40

WES999 Minister of Fire 2. ```NULL ```

Jan 12, 2008
1,001
272
Loc:
Mass north of Boston
I think I will try to make a few of this type of DIY "storm windows" and see how they work.
Quite simple and and cheap.

16. #41

SmokeyTheBear Minister of Fire 2. ```NULL ```

Nov 10, 2008
13,363
1,662
Loc:
Standish, ME

I made 16 of them following another written set of instructions, have two left to install after the holidays. Wife does special decorations in one of the double windows.

17. #42

GaryGary Feeling the Heat 2. ```NULL ```

Jul 12, 2010
291
18
Loc:
SW Montana

Not trying to talk you out of doing these storm windows, which look good and effective, but one alternative that I kind of like is to get a sheet of Acrylic (Plexiglass) that is about 1/8 to 3/16ths thick, and just cut to match the size of the window frame opening. You can just push them into the opening and secure with a couple of small screws that go into the window frame (or more screws for large windows). They are very little work to make (no frame) and essentially invisible. Last many years.
The downside compared to the windows in the video is that they don't provide double glazing.

Example: http://www.builditsolar.com/Projects/Conservation/acrylicstormwindow.htm
The example uses velcro to hold the window in place, but I've since gone to the two small screws, which are so small they don't really show at all.

Gary

18. #43

TradEddie Minister of Fire 2. ```NULL ```

Jan 24, 2012
823
226
Loc:
SE PA
Early this year my son kicked a soccer ball though one of our small basement windows, a 35 year old single pane Anderson, I couldn't replace just the glass and frame, and replacing the whole window assembly would mean a huge demolition inside and out. I pulled the frame apart with only minor damage, used a Lexan sheet to replace the glass, and then glued another sheet where the insect screen would go. Now I have a bulletproof window, and the difference in temperature inside is remarkable.

I have now replaced almost all of my original Anderson double hung window sashes. The original wood sashes were beginning to rot and separate at the joints, but the vinyl clad frames were still perfect. Sashes cost perhaps a quarter of the cost of entire window replacements, never mind labor, and each window takes barely 10 minutes to replace both sashes. The resulting air sealing improvement is very noticeable, and I suppose the "Low E High Perf" will be worth something too in the long run. I called Anderson for the part numbers then went to Home Depot to order, HD start out with the same price but for my first few orders when they total up and apply a HD discount, the actual price was 30-40% less than direct from Anderson. Unfortunately, on my last order that deal with Anderson was gone, so I paid full price, but still a huge saving over entire windows, and I don't think that difference would ever have paid itslef back.

TE

19. #44

GaryGary Feeling the Heat 2. ```NULL ```

Jul 12, 2010
291
18
Loc:
SW Montana
Very nice.

Can you give us a rough idea what the cost of one replacement sash is?

Gary

20. #45

TradEddie Minister of Fire 2. ```NULL ```

Jan 24, 2012
823
226
Loc:
SE PA
I'll have to check tonight, but IIRC, about \$100 per sash originally, depending on sizes, and whether upper or lower. Narroline windows. Last set were significantly higher. I wouldn't have replaced them just to get the energy savings, but many were beginning to rot, and on some, the spring-loaded sash cords were literally pulling the frame joints apart. When we moved in, the top of one lower sash was bowed up so far in a U shape that there was an air gap between the glass and frame! I still have one or two of the originals that are in good enough shape not to be on my priority list. For 35 year old windows, not bad. A few years earlier they'd have lead paint on them and probably none of them would be rotten yet.

I do regret that on my first round, I bought direct replacements, not High Perf Low E, bad salesperson didn't even offer me the option. Second time around they mentioned the High Perf option, and better yet, prefinished white painted interior for only \$10 extra per sash.

TE

21. #46

johnny1720 Burning Hunk 2. ```NULL ```

Mar 6, 2007
235
30
Loc:
The Great North East
Here is a little hint, Anderson Windows are warrantied for life. Each window has a serial number on it somewhere. I had some issues at work with a few Anderson Windows (we have thousands of them) and they sent me replacements for the cost of the shipping.

22. #47

TradEddie Minister of Fire 2. ```NULL ```

Jan 24, 2012
823
226
Loc:
SE PA
Not according to their website, maybe it depends on the type. 20 years limited on glass and 10 on frames for Narroline, mine are 35 years old, and the ones I haven't replaced are still in almost perfect condition. I've even kept the best of each size that I took out, as a temporary fix for another soccer ball accident.

To the question about price, my most recent replacement sashes (Feb 2012) varied from \$128 to \$167 per sash depending on size, for Narroline Low E High Perf with a prefinished interior. Earlier replacements were about 30% less. That's cheap compared to installing all new windows, but even still would take a long time for payback if they didn't need to be replaced anyway.

TE

23. #48

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,119
490
Loc:
SW Virginia
I really wish this was true.
The vinyl cladding on our 25 year old double-glazed Andersen casements is cracking and allowing water in which rots the frame.

24. #49

TradEddie Minister of Fire 2. ```NULL ```

Jan 24, 2012
823
226
Loc:
SE PA
If you only mean the frame around the glass, and if the actual frame (head, jamb, sills) is in good enough condition, then you may be able to get replacement casements without having to replace the entire window. I expect that replacing the casement would be even easier than replacing sashes. Call Andersen, their support were very knowledgeable and helpful for me. Before you call, measure the visible glass sizes, and write down anything you can read from the etching on one corner of the glass. Work with them to get part numbers, and prices (they also charge shipping), then go to Home Depot and compare prices.
I have no affiliation with Andersen, just a good experience.

TE

25. #50

semipro Minister of Fire 2. ```NULL ```

Jan 12, 2009
3,119
490
Loc:
SW Virginia
The casement windows are relatively easy to replace. I have done one under warranty, another purchased, a victim of a soccer ball (kicked poorly by me). Andersen was good to work with but when I called recently they told me the windows were only covered for 20 years.

I may take your advice and call anyway and maybe supply a few photos. We have something like 45 Andersen fenestrations in this house in the way of windows, doors, skylights.