Or does it even really matter?

Suppose I'm looking to upgrade my north-facing windows from a double pane to a triple with low-e coating. My double pane window is a bit too cold and it bothers me because it's in my bedroom. I have my house well air sealed, so as far as I can tell the only way to improve the comfort of having to be next to that window on a cold winter night is to replace it. What factors should I be considering?

Re-siding the house is down the road a ways. I might like to replace my two north-facing windows first.

Posted By strategery on 29 Jun 2012 03:55 AM
Or does it even really matter?

Suppose I'm looking to upgrade my north-facing windows from a double pane to a triple with low-e coating. My double pane window is a bit too cold and it bothers me because it's in my bedroom. I have my house well air sealed, so as far as I can tell the only way to improve the comfort of having to be next to that window on a cold winter night is to replace it. What factors should I be considering?

Re-siding the house is down the road a ways. I might like to replace my two north-facing windows first.

On cold days/nights, poorly insulated windows basically suck the warm air out of the room and create that cold spot near the window.

Most residential windows in the USA are probably around an R-1. Good windows would have a R-5 or higher. > R-5 should be what to look for.

Also make sure the window is air tight as not to create cold drafts. Avoid sliders or single or double hungs. Casements are better in sealing air.

According to DOE:

"Common ENERGY STAR windows only have an R-value of 3. Increasing the R-value from 3 to 5 reduces average heat loss through the windows by 40% and saves consumer money on energy bills.”

strategery-

If there is room inside the windows, you might consider adding double-cell cellular shades with side seals to your exiisting windows as a less expensive fix for the bedroom chill compared to replacing the windows with triple-pane windows.  If your windows are not low-e, then the R-value for double panes is about R-2, and the double-cell, light-blocking, cellular shades with side seals have an R-value of around 2.0 or greater (http://www.residentialenergylaborat...hades.html), so the combined R-value would be about 4 (or U=0.25).  These shades for a 40"x60" window cost about $130 if you install them yourself, which should be much cheaper than a good-quality, triple-pane window.

These shades also dramatically reduce the convective air flow that is downward across the windows, and can be improved further by using something like Permagum to seal any openings around the enda of the side seals.
 
I have these shades throughout the house, and I can sleep comfortably next to the windows with it at -15 F (-26 C) outside, although my windows are triple-pane and low-e.

Some more questions-

So a triple pane window argon filled is *probably* and R-5?

Given that the wall around that window is about R-12 - R-15, that glass is ALWAYS going to be a weak spot where the conductive heat loss occurs, correct?

I know in passive solar designs, they try to limit windows on the north side for 2 reasons: 1) glass on the north side receives little to no direct sunlight and therefore no beneficial solar gain during the winter 2) the glass is a weak spot of the wall and is susceptible to greater conductive energy loss

I really only will have one opportunity to get these two windows right when making this replacement. Should I go for the very best window I can afford for these two north-facers? or is it not that big of a deal as long as it's a double pane low-e with good air-sealing?

Posted By strategery on 02 Jul 2012 03:15 AM
Some more questions-

So a triple pane window argon filled is *probably* and R-5?

Given that the wall around that window is about R-12 - R-15, that glass is ALWAYS going to be a weak spot where the conductive heat loss occurs, correct?

I know in passive solar designs, they try to limit windows on the north side for 2 reasons: 1) glass on the north side receives little to no direct sunlight and therefore no beneficial solar gain during the winter 2) the glass is a weak spot of the wall and is susceptible to greater conductive energy loss

I really only will have one opportunity to get these two windows right when making this replacement. Should I go for the very best window I can afford for these two north-facers? or is it not that big of a deal as long as it's a double pane low-e with good air-sealing?

Most good triple pane windows will be in the R-5 through R-7 range, although Serious Windows makes a dual pane window with R-5 through R-9 (very expensive). They way they get these values with dual pane is by utilizing heat mirror technology. Some people question the longevity of this technology but from what I read it is reliable. Although European manufacturers find this technology flawed and don't use it, they stick with triple pane.

R-Value is only ONE part of the equation. Windows must also be AIR TIGHT. A leaky window in winter will let in the cold and let out the warm interior air. The reverse is true in summer. The other part of the equation is SOLAR GAIN. If you are in a heating dominated climate, having a lot of south facing windows that have a high SHGC will help heat your home during winter. Even though at night the windows have a negative impact on the home, the overall SHG makes up for it as it cuts your heating costs during the day.

Windows also serve the function of letting in natural daylight and venting the home (if operable). North windows SHOULD be minimized but not eliminated as they provide indirect light during the daytime. Nobody wants to live in a cave, let me clarify that, most people don't want to live in dark caves.

Your question has a lot of factors. How long do you plan on living in the home? I would get pricing for each design (dual and triple pane), check the air sealing ratings, and then make a choice based on your budget and goals. Either way, you are looking at a long term ROI.

This is a bit off the wall but a friend of mine, 20+ years ago, made his south windows about 3" apart and used a Beam vac to fill them up with styrofoam beads at night or when it got too hot in the house. His heating bills were quite low, cooling was almost non existent and the system could be automatic or manual plus the beads could be replaced if they yellowed too much.

The interesting part of it was that the light was very nice in the day with the beads in the windows.  I don't know what the R value would be as he had single pane glass. Double would be quite something.

Mike; Insulated glass is used for bothe heating and cooling conditions, once you get past 1" the space invites solar gain and may be good for heating, but bad for cooling

Posted By strategery on 02 Jul 2012 03:15 AM
Some more questions-

...snip...

I really only will have one opportunity to get these two windows right when making this replacement. Should I go for the very best window I can afford for these two north-facers? or is it not that big of a deal as long as it's a double pane low-e with good air-sealing?

If you really want "to get these two windows right," download a free copy of RESFEN at http://windows.lbl.gov/software/resfen/resfen.html and do your homework by computing heat losses with your old windows and different proposed new windows.  You could also use BEopt available for free at http://beopt.nrel.gov/ which will also do the optimization for you, but I would judge it a little more difficult to use.  I would expect that this analysis will tell you that, as you said, it is not that big of a deal as long as it's a double pane low-e with good air-sealing, but why not get the real answer by doing the calculations?  I would guess that the break-point might be $20 to $30 per square foot of window, or for sleeping comfort, you could get there much cheaper with window coverings.  

You might also check out the calculations included in the earlier discussion in this same section titled "Going from a U .20 to .24 Worth the extra cost."  peteinny was asking a question very similar to your question. 

I have been pondering thoughts along this line as i live in ohio where attick insulation recomended is R 60. so 20 inches of pink stuff or in some cases 10 inches of foam board where needed (R50). my problem is i thought for sure in this day and age with all the concern about being green, ithoughtfor sure there would be R 60 windows aswell. so toss in the towel. no such animal exists. not even R20 so then i pondered storm windows, glass block, triple pane, my final thought i cannot get a bead on by thissiteor any site is why not install two windows or three triple paned windows in the same window hole in the wall.. doors too? i see walls on the internet that are R60, but no doors or windows. so anyway, i know there are problems with condensation, but just use materials that can withstand that for periods of time? thisis the 21st century and i am new to this wanting to do this and i'm amazed at what is not available for windows and doors. the DOE can suggest all they want. i think common sense says if your gonna put R60 in your attick, there needs to be products that convert existing homes into R60 walls, doors windows. sadly, there does not... but hopefully soon. i am contemplating adding 2x6 to the outer walls on the inside, moving electric and some registers panels in more on the floors and creating that warmer insulated houseon the main, existing , and upper basement.. aswell as the garage walls that touch the house.. instead of taking house interior space on those walls, ill take garage space. i don't see suggestions like that on my google searches either.. barriers, etc..moisture..etc. concernsall taken into account as well. take care good luck, I am still pondering. : ) Intus out of west virginia a lithuanian based window company triple panes for an economically good price so i've googled thus far.R10 if you have access to a thermal camera, by all means see. there are probably some photos online to show as well. very informative as we have taken photos of ourhome. losses thru garage, windows and upper basement if thatbit of 2x10 is not insulated from behind.. sitting on the cinderblock.

most sites have said, keep what you have. paint it, caulk it, add storm windows on the inside or outside depending on the look of the house and yourpreference.. trapping more air between outside and inside. that is the best there is to offer economically, etc. in 2016 as far as i can tell. i've checked into indoor insulated shutters for the night for security, sound, insulation on cold nights . ohio has half it's days sunny so a lot of these windows have sun factor of measuring the heat they get into them from the sun.. half my house is in the shade and it's ohio, so i hope the unit of measure definition of R value remains a constant. sometimes i wonder if some of the people talking about insulation of windows confuse this sun heat, passive stuff with straight up R value. that's all i've been able to find.

oh, i was also looking into plexi glass.1.75 inch thick perhaps or very thick glass , perhaps several panes of it for an R value. some of the zoos have 5 layers of very thick plexiglass~ cost is a factor.. i'm not sure of possibilites and cost is definitely a factor, of course. take care.

http://www.litezone.ca/complements-wall-r-values.html

http://www.naturalhandyman.com/iip/infenergysavers/infthickenwalls.html exterior wall thickening home depot responded to my request!

For a US climate zone 5 northern OH reasonable targets for R values are:

R4 windows (U0.25)

R8 slab (2" of sub-slab EPS foam)

R15 foundation walls (construction varies by foundation type. Full basement?)

R28-30 walls (whole-wall, not center cavity, eg: A 2x6/R20 stud wall with 2.5-3" of continuous polyiso)

R65 attic (20-22" of fluff)

Over a 50 year lifecycle the energy savings of going much beyond that ends up being quite a bit more expensive than the lifecycle cost of $3/watt rooftop solar leveraged by better efficiency air source heat pumps.

In zone 4 southern OH drop that to 2" of exterior polyiso on the walls, and R3.5 (U0.28) windows and may be R55-60 in the attic- leave the rest as-is.

The reason R60 is specifed for an attic and not a window is because the additional performance of taking it up to R60 is still pretty cheap, whereas even and R10 window (and they do exist) is extremely expensive.

From a bang per buck energy savings point of view you get a lot more out of bumping an attic from R13 to R50 than you do from taking clear-glass double-pane from R2 (U0.50) to R8(U0.13).

If you're having an issue getting line and paragraph breaks to show up, try a different browser. Chrome and FireFox both seem to work OK on this site.

Jollygrgiant,

Best practice is to get quotes from different window manufacturers and see where it lands. Sometimes the double pane windows will cost more than a triple pane window like Intus PVC windows. The most economical window frame will always be PVC. Just like in business operations where they will get at least 3 different bids for a particular job. Once you get those bids then sit down and do a fair comparison and see where it lands.

The Zola Windows I'm getting are an R-7 (U=0.14) (Thermo uPVC line)

However, if you want to go that route, definitely call and talk to them, but normally they have a minimum purchase order of $25k. The shipping is the other factor. any of the European made windows will take a while to be made and shipped, and the cost of shipping can make it a non-starter. Sometimes they'll combine crates and such, so you'd have to see if they could do anything like that. Companies like Intus will likely have the same problems.

I am of the opinion that the installation of the window is much more important than the quality of the window itself. as long as you get a decent window with very little air leakage, you're going to be much better off.