INefficient windows (Rant)

[coolidge]

Doing a little "Mad scientist" experiment, i have come to the conclusion that installing new "energy efficient" windows gets you nowhere fast. I am in the process of rebuilding the kitchen area of my old shack and ordered two new Anderson 400 series windows. Lo e the whole nine yards. I bought four thermometers from Walmart(cheap) before i started to do this experiment, placed one in each window(2) and the other two around the area, took readings for two weeks and compared to set thermostat.Gutted the whole area, replace the R13 cellulose (2x4 walls) with 4" sprayfoam(R28) Installed windows,and found no increase in effeciency from old to new. Except for the sprayfoam, huge difference. Baught two more thermometers from Wamart(same kind) placed one on window sill one 5" below and i have an 8 degree difference in that 5". Should have sealed the whole Darn thing with the foam.

Sorry for the rant, kinda PO

 

[EatenByLimestone]

What were your windows before?

Unless they were leaky you probably will not notice a huge difference over decent window. If the windows were bad, going from R13 to R28 may have overshadowed the improvement in the window.

Since you gutted the kitchen I don't think you lost out by installing them.

Matt

 

[midwestcoast]

Yeah, even the newer high-quality (LoE, Argon filled, insulated frame...) windows are still pretty bad for insulation compared to an insulated wall. I bet that's why they only use the "U-factor" to rate them. If they listed the R-value then who would spend the money to got from R-2 to R-3 or whatever they'd come out at. IMO replacement windows are pretty low on the list of cost-effective efficiency upgrades unless the old ones are single pane, leaky, no or poor storm windows...
They are nice looking though. I'm (slowly) putting new sash-kits in & they sure are nicer than the sticky old single panes. Keeping & fixing up the aluminum storms for another layer.

 

[pyper]

How do you figure you are measuring "efficiency" with just thermometers? You have way too many unaccounted for variables.

 

[jharkin]

This is a very hotly discussed topic amongst old/historic house owners. The general consensus has been that adding storm windows andproper weatherstripping is as efficient as all but the most high end "energy efficient" modern windows. And older windows were made of much better materials (oak vs. pine or plastic, counterweights vs cheap aluminum track) and last so much longer than modern windows that the energy savings from the really high end low-e gas filled etc windowscant outweight the replacement cost.


Not to mention that even the best window has only a fraction of the insulation value of a well insulated wall as you discovered.

 

[DBoon]

No question about it, replacement windows are about the worst thing you can buy for energy efficiency improvements IF you currently have reasonably decent windows. The heavily advertised replacement windows are usually very cheaply made and will likely not last long enough to pay themselves back.

 

[ihookem]

I put windows in for a long time. The old single pane windows if glazed properly with storm windows work ok. It leaks some air on windy days but you will never have a fogged window with a seal break neither. Break a single pane glass and it's 5 bucks and an hour to replace, break a thermal pane and it's 50 bucks. All this hype about storms not helping is nonsense too. I have a 6 month old house with Andersons and some have storms and they have a lot less moisture on the windows. This means it has to help. A lot depends on how much you pay for the windows too. Some companies charge anal bucks for cheap inserts or vynle replacements. We used to be much cheaper with better windows but I bet it still took 10 years to get their money back. My friend told me it takes 18 yrs to get your money back with new windows. I believe him too. Unless your windows are really bad don't change them. Don't ever spend 15 k on windows for heat savings. 15k @ 6% on a home equity is 900 towards your heat bill. Take your casing off and foam between the windows and the stud. This means 3 bucks for a can of foam and an hour to re case the window and the whole room is updated with new casing. Re glaze the window and maybe new storms (50 bucks each) and the window is better than a new vynle for efficiency. New vynle replacement installers don't foam between the window and studs neither.

 

[madrone]

My old windows sucked. Even with storms. They were 100 years old, poorly constructed with huge gaps all around, some completely rotten, and the storms had lost their seals long ago. The curtains moved even with the storms closed. I replaced them myself with vinyl double-panes. After a manufacturer's rebate and the tax credit, it'll cost around $2500 for the whole house. Huge difference in noise and usability. Some difference in temperature. Totally worth it. If the frames had been any good, I'd simply have had them retrofitted with double-panes or replaced the storm windows, but there was no question they needed to go.

I'd agree that not everyone is going to see the full benefit of replacement windows, but it was night and day for me.

 

[jebatty]

Replacing old windows in our house with very high end R-8 windows 15 years ago were the single most important factor in my wife agreeing to move to our lake home in northern MN. Only 8 foot walls, but with 30' of 5' high glass across the front and lots of other windows, the cold air wash flowing from the old windows made it almost impossible to sit by the windows, and even made the house uncomfortable, during our very cold winters. Now even on a -30F day and colder (into the -40's not uncommon) with howling winds blowing towards the house we can sit right next to a window and the glass is warm to the touch. Also, no fogging, condensation at all.

We certainly saved energy, but that was not the reason for the new windows. Comfort and preserving great views with lots of glass were the factors that made very dollar of a very expensive window replacement worth every penny spent. I wouldn't consider this route though unless a person planned on enjoying the results for many years, as we will never recover our $ investment on sale of the house. At the same time, although energy saving was not the reason, I know the windows have saved on heating energy use, as we are able to comfortably heat the entire house with a single wood stove in the living room area, and this keeps our annual heating cost from backup electric baseboard usually less than $200/year.

 

[ihookem]

Well, ok if the windows are 100 years old that's a little different.

 

[pyper]

I work in a building that was made in about 1930. It's got huge single pane windows. They're really tight windows, but you can feel the draft rolling off them in the winter.

There were storm windows on our house when we moved in. Condensation dripping down the inside of the storm windows in the winter had rotted out 90% of the sills.

I don't know if double-glazed windows ever pay back from an efficiency standpoint, but they're more comfortable and they aren't nearly as likely to cause structural damage as storm windows.

But yeah, compared to even a modestly insulated wall, a window is just a big hole. Single pane is usually R1; double pane is usually R2. The math is pretty simple -- R2 is twice as good a R1, but not very good compared to R14 (R11 batts in a typical wall system).

 

[Jim K in PA]

Multi-layer glazing must be looked at as a system. Condensation inside the storm window is a clear indication that the primary window is not sealed well at all. Warm, moist air is flowing freely past the sashes and condensing on the colder outer storm window glazing. Keep the warm, moist air inside, and the condensation is prevented. Keep the outer sills painted, and exposure to moisture won't rot them. Google spring bronze for an inexpensive, durable way to seal inner sashes and storms.


Properly maintained, fit, and sealed double hung windows combined with a properly maintained, fit, and mostly sealed storm window will provide as high or higher an R-value as a replacement double pane window with a miniscule 5-10mm air gap. The larger the static air gap, the greater the insulating value of the window system. Look at a Pella window and compare the air gap, and slow rate venting, with a sealed Anderson or equivalent double pane window. Fancy gas between the pane does nothing to improve efficiency, but might delay mold growth when the seals fail.

I am restoring a c.1815 farmhouse, and am installing salvaged 19th century 6 over 6 sashes, along with wooden framed storm windows with lexan glazing. 100+ year old houses require some maintenance and effort to keep them in good shape. Most old windows getting replaced have not seen a paint brush or glaziers knife in many a decade. With the replacement of the original true divided light windows, an important part of the character of the house is lost, probably forever.

Yep - I'm a sucker for nicely built, and maintained, old houses. I guess I am an anachronism in an age where most folks equate maintenance with evil, plan to move every 4-6 years, and prefer to watch TV than invest time in their home.

 

[pyper]

Properly maintained, fit, and sealed double hung windows combined with a properly maintained, fit, and mostly sealed storm window will provide as high or higher an R-value as a replacement double pane window with a miniscule 5-10mm air gap. The larger the static air gap, the greater the insulating value of the window system.

That is a false statement. Once the air gap is more than 3/4 inch you get convection between the glazing, which is counter-productive.

And a 5mm gap of argon beats a 5mm gap of plain air.

I agree that the rotting sills were a symptom of way-loose sashes. They weren't well installed, or even well made, from the start. There's no way any kind of weather stripping would have fixed them. And they're probably not unique -- storm windows aren't necessarily a good, long-term solution. They don't look good, either.

 

[Jim K in PA]

That is a false statement. Once the air gap is more than 3/4 inch you get convection between the glazing, which is counter-productive.

No, it's not, and yours is a misleading statement. The smaller the air gap, the greater the radiant loss. The amount/rate of convection is dependant on a number of variables, and the "break even point" between the improvement in radiant loss vs. convection loss is dependent on those variables. The greater reduction in radiant loss with an air gap of 1-2" can be substantially more than the heat losses due to increased convection. Again, design and implementation is key.

I doubt either of us will convince the other on this point.

And a 5mm gap of argon beats a 5mm gap of plain air.

Feel free to support this statement with some data. By how much, in what manner, and at what cost? A gas, any gas, used as a thermal break is the advantage in the window system. The advantage of a any gas over a solid as an insulating material (other than the fact you can see through it) is the low molecular density of the gas, which inhibits radiant energy transfer. "Plain air" is 78% nitrogen, an inert gas like Argon. Replacing 22% of the volume of the thermal break gas with another inert gas is an unnecessary and unproductive exercise. If you have some insight into the thermodynamic efficiency differences between nitrogen and argon, please enlighten me.

I agree that the rotting sills were a symptom of way-loose sashes. They weren't well installed, or even well made, from the start. There's no way any kind of weather stripping would have fixed them. And they're probably not unique -- storm windows aren't necessarily a good, long-term solution. They don't look good, either.

And I agree that ALL old double hung sashes are not good, or well made/installed. Sometimes it is prefectly logical and justified to replace a poor window system entirely. However, many older window systems that only needed maintenance get replaced based on puffed up claims by window sales reps and "warm & fuzzy" commercials on TV.

The subjectivity of the appearance of the storm windows is apparent, and dependent on not only the person looking at them, but the design, construction and implementation of the storm windows. I personally dislike protruding, aluminum framed storm windows (which were popular in the 60's and 70's). However, divided lite wooden-framed storms that sit within the casement moldings and have some architectural detail can enhance the appearance of the window, IMO.

There is much information to be found regarding this issue. Just one example for reference: (broken link removed to http://www.presnc.org/Preservation-Answers/Historic-Windows-Resource-Page)

 

[dvellone]

I installed 100+ year-old salvaged windows in my home because my low budget. They're leaky, a pain in the neck opening and closing and winterizing, and I spent hours refinishing them, and installing them. That said, once I seal them with rope caulk and install the home-made winter storms they are as efficient if not more so than the pella windows that I installed. In double-digit below zero temps I'll get a little icing on the edges of the glass on the pellas, but none on my old windows, and i have to say that to real panes look great compared to those ridiculous fake panes they install in the modern windows. But...the new windows are a joy to install, a pure joy to open, close and clean, and the warranty is pretty darn good.

I have to add to the rant though: The cost of these assembly-line fabricated windows is grossly more than it should be. There is no reason that the budget for windows in new construction should be as high as it is. They're priced as a luxury item and unless you can afford ultra efficient triple glazed high-r widows (which most can't), the efficiency of good quality standard windows doesn't jibe with the price. I'm starting construction on our new home and I'll be installing as many built-in (non-opening) insulated glass units as I can and carefully selecting where I'll most utilize the double-hungs that we'll need to open, otherwise the windows will break the budget.

 

[Gooserider]

I don't see why people are in love with double-hungs... At least according to some sites that I've seen, including the (broken link removed to http://www.efficientwindows.org/index.cfm), they have an inherent problem with sealing because all the sealing surfaces are sliding joints, and you have this big, mostly unsupported seam in the middle.

Going to a pivoting window, be it casement, awning or hopper style, as opposed to a double hung or slider is supposed to give an improved performance because the sash seats into the frame and seals with a gasket, which gives much lower air leakage, and holds up better under frequent opening / closing use...

Gooserider

 

[dvellone]

I think that considering casement windows you have to be a bit particular about not keeping the windows opened to the point where their edges are exposed during rainy weather (unless you have really deep overhangs.) Architecturally they have a lot more limitations where they can be used when compared to double-hungs, and they can't be used where they'll open out into traffic areas like a deck or first floor level low enough to pose a danger of collision. They do seal well though.

 

[pyper]

That is a false statement. Once the air gap is more than 3/4 inch you get convection between the glazing, which is counter-productive.

No, it's not, and yours is a misleading statement. The smaller the air gap, the greater the radiant loss. The amount/rate of convection is dependant on a number of variables, and the "break even point" between the improvement in radiant loss vs. convection loss is dependent on those variables. The greater reduction in radiant loss with an air gap of 1-2" can be substantially more than the heat losses due to increased convection. Again, design and implementation is key.

I doubt either of us will convince the other on this point.

And a 5mm gap of argon beats a 5mm gap of plain air.

Feel free to support this statement with some data. By how much, in what manner, and at what cost? A gas, any gas, used as a thermal break is the advantage in the window system. The advantage of a any gas over a solid as an insulating material (other than the fact you can see through it) is the low molecular density of the gas, which inhibits radiant energy transfer. "Plain air" is 78% nitrogen, an inert gas like Argon. Replacing 22% of the volume of the thermal break gas with another inert gas is an unnecessary and unproductive exercise. If you have some insight into the thermodynamic efficiency differences between nitrogen and argon, please enlighten me.

(broken link removed to http://gaia.lbl.gov/btech/papers/12486.pdf)

Page 6. It says that Argon has a thermal conductivity factor of 1.78 and Air is 2.5 -- so that makes Argon 140% better than air at slowing heat loss through the gap. This probably explains why every low-e window seems to have something other than air in the gap.

On page 8 it shows what happens to the U value as air gap is increased from 0 to 5 cm, with zero, one, and two plastic films between. It shows that with double glazing the performance increases dramatically up to about 15mm, and after 2mm holds constant. This probably explains why there are no double glazed windows on the market with 2" air gaps.

Personally, I don't care if they put pixie dust in them, if it results in better U-values. :lol:

 

[Jim K in PA]

(broken link removed to http://gaia.lbl.gov/btech/papers/12486.pdf)

Excellent! Thank you for locating that. :coolsmile:

Page 6. It says that Argon has a thermal conductivity factor of 1.78 and Air is 2.5 -- so that makes Argon 140% better than air at slowing heat loss through the gap. This probably explains why every low-e window seems to have something other than air in the gap.

Math issue: The difference in thermal conductivity between air and argon = 2.5-1.78 = .72. The proportional reduction in thermal conductivity by going from air to argon = .72/2.5 = 0.288. Argon represents a reduction in thermal conductivitiy of 28.8% over air. Not too shabby, but not 140%.

But, more importantly, keep in mind the following from the paragraph at the end of page 5, before the table:

Table II gives some of the physical properties of gases that may be used in an architectural window. The variation in these properties over the range of ambient temperatures should be considered when doing detailed calculations. All of the gases listed have a lower thermal conductivity than air, which means they will perform better at small gap spacings where conduction is the dominant mode of heat transfer. Low conductivity is a necessary but not sufficient condition for their use; cost, chemical reactions with other window components and toxicity must also be considered.

I think we are coming to an interesting crossroad here. The small gap spacing typical of most multi-pane windows is clearly the best application for the low conductivity gas in the interstitial space, because such a small space provides very little resistance to thermal conductivity! Continued with the next point . . .

On page 8 it shows what happens to the U value as air gap is increased from 0 to 5 cm, with zero, one, and two plastic films between. It shows that with double glazing the performance increases dramatically up to about 15mm, and after 2mm holds constant. This probably explains why there are no double glazed windows on the market with 2" air gaps.

Other than the typo above (after 20mm, not 2mm), you are highlighting exactly where I think this debate is going. A 5mm gap is only marginally effective compared to going with a 15mm+ air gap. A 20mm air gap is just over 3/4 of an inch, which is just about what the spacing was on my c.1990 Pella thermopane windows I installed in my newly constructed house that year. Over 1" is clearly a situation of diminishing returns. I think the data in that (old) paper shows that utilizing Ar or Kr is CRITICAL when choosing a small gap thermopane window. When a larger air gap is utilized, the efficacy of the reduced conductivity becomes a much smaller proportion of the overall efficiency of the window system. I also suspect the cost for the higher volume of gas becomes a substantial consideration. Combine the additional cost of the gas, with the architectural challenges of making a thermo-pane window with a gap larger than 3/4-1" and you have the reason why such windows are not offered in the mass market.

It appears to me that the choice between a low-e thermopane window with a small gap and argon, or a single pane and storm window, is going to depend on personal preference, good application practices with the old system, and condition of the existing window system.

Personally, I don't care if they put pixie dust in them, if it results in better U-values. :lol:

LOL - agreed. I was intrigued to see that CO2 actually has a BETTER (lower) thermal conductivity quotient than Argon! Maybe we have a newfound use for all the excess CO2 we are frittering away into the atmosphere . . . ;-)

There is another article with good data calculating U-factors for single pane sash & storm stash combinations and comparing the data to that for thermopane windows. I had downloaded it to my computer, but it was several years ago and cannot find it. If I do I will post it somewhere.

Thanks for an invigorating discussion!

 

[semipro]

I don't see why people are in love with double-hungs... At least according to some sites that I've seen, including the (broken link removed to http://www.efficientwindows.org/index.cfm), they have an inherent problem with sealing because all the sealing surfaces are sliding joints, and you have this big, mostly unsupported seam in the middle.

Going to a pivoting window, be it casement, awning or hopper style, as opposed to a double hung or slider is supposed to give an improved performance because the sash seats into the frame and seals with a gasket, which gives much lower air leakage, and holds up better under frequent opening / closing use...

Gooserider

Yep. Casements seal better which helps minimize infiltration. Air infiltration is why replacing old windows with new ones usually makes sense, not because of an increase in the conduction/radiant R factor.

We have 40 plus casement windows in our house that seem to seal very well after 20 years of use. We installed double layer cellular shades that do a great job helping with energy loss through the windows, especially at night. Unfortunately, we trusted a big box with the order and ended up with significant side gaps. You literally feel cold air convectively flowing out of these gaps when the blinds are closed, very disappointing. I think we'll try these next time:
http://www.blindsonline.com/pc/viewPrd.asp?idproduct=85 They have a sealing channel along the side of the blinds.

 

[pyper]

LOL - agreed. I was intrigued to see that CO2 actually has a BETTER (lower) thermal conductivity quotient than Argon! Maybe we have a newfound use for all the excess CO2 we are frittering away into the atmosphere . . . ;-)

Doesn't he say that CO2 will absorb solar radiation though. That wouldn't be a good choice around here! We're generally more concerned with keeping heat out than in. Our house has a pretty big window and the front door facing west, and they were both getting really hot in the summer. I put some of that reflective solar film on them and it made a huge difference. Supposedly it does the same job in the winter at keeping heat in. I'd love to get a hold of one of those infrared cameras to compare.

I have a friend with a historic house and he's been complaing about loosing heat through the windows, but he doesn't like the idea of replacement windows due to the cost. Where would he look to find out about wooded divided-lite storm windows?

Regarding casement windows. I love them. We have two in our bathroom and they're great at catching a breeze. We had to remove them when we did some renovations and put them back in, so they don't close as tight as they used to unless you use the locks.

I think our new double hung windows seal reasonably well. They have two sash locks on them, and the locks are kind of spiral wedges so they help draw the two sashes together. If you turn them!

There's another factor to consider in the replacement window decision. Cleaning. If you have standard windows, especially on the second floor, and put storm windows on them, then they can be really hard to clean. Tilt in windows are pretty easy to clean, which seems to make my wife really happy. Although another way to think about that is I gave myself a new job. :-S

 

[Jim K in PA]

Doesn't he say that CO2 will absorb solar radiation though. That wouldn't be a good choice around here! We're generally more concerned with keeping heat out than in. Our house has a pretty big window and the front door facing west, and they were both getting really hot in the summer. I put some of that reflective solar film on them and it made a huge difference. Supposedly it does the same job in the winter at keeping heat in. I'd love to get a hold of one of those infrared cameras to compare.

Yes. CO2 has a strong absorption band in the infra-red wavelengths. Good for cold climes, but not warm.

And that is an excellent distinction to make when shopping for windows. If you optimize for cold weather, you compromise warm weather performance, and vice versa.

I have a friend with a historic house and he's been complaing about loosing heat through the windows, but he doesn't like the idea of replacement windows due to the cost. Where would he look to find out about wooded divided-lite storm windows?

Depends on what he wants to do. There are some very good millwrights that can reproduce his sashes, or make completely new ones. www.oldhouseweb.com has lots of forums with plenty of posts regarding wood window repair and restoration. A good book that is a primer for old house owners and their windows is called "Working Windows" by Terence Meany. Available through Amazon. It's a good one to start with.

Regarding casement windows. I love them. We have two in our bathroom and they're great at catching a breeze. We had to remove them when we did some renovations and put them back in, so they don't close as tight as they used to unless you use the locks.

I think our new double hung windows seal reasonably well. They have two sash locks on them, and the locks are kind of spiral wedges so they help draw the two sashes together. If you turn them!

Ditto! I only have a few casements, and they generally seal well on all sides except the hinge side. But unless you latch them they do not seal well at all. I removed the casements that opened out onto my kitchen porch.

There's another factor to consider in the replacement window decision. Cleaning. If you have standard windows, especially on the second floor, and put storm windows on them, then they can be really hard to clean. Tilt in windows are pretty easy to clean, which seems to make my wife really happy. Although another way to think about that is I gave myself a new job. :-S

LOL - agreed 100%. Divided lite windows are a PITA to clean. But they are worth it to me. We had Pella tilt in windows in our first hhouse, and I can tell you with confidence that less than 10% of the windows ever got tilted in for cleaning. They were not a priority with two small children to chase after. :bug: