...Low E windows cannot have exterior storm window??
I did not know that. So you are stating that anyone that buys a Low E window cannot have storm windows....and if they already have them they must be removed?? I searched for more info on that but could not find it. Where did you get that info.
Thanks
Key1

The issue with Storm Windows and Low E Coating is not an issue with just Storm Windows as they are on the exterior. The only issue would be if you had a Low E Storm window and a Low E regular window

Thanks millworkman for that feedback. My situation treats the existing exterior windows as nicely sealed expensive storm windows. They do not have low E or Argon. However the new internal window will be 9500-impact windows with laminated glass, loE and Argon.

Skydaggy both windows will still function so to clean between the two all I need to do is open the interior window.

right now I am thinking of buying a few on the north facing wall and try them out first...

Key1

Local township inspector was just here to approve permit for another item. While in the basement I asked him about having the secondary internal window. He indicated as long as I do not reduce the overall opening size, and the internal window is operable without any special tools or keys..... I can do it and no permit is needed....

I spoke with someone at Larson Doors.

The link below shows an airtight inside storm window that is available with or without low E. I would think they would have the same problems being mentioned here....but I am told they do not. They however did indicate that if the outer window is not properlly sealed, some condensation could develop.
Anyone ever try an inside storm window?

http://www.larsondoors.com/storm_windows/products/insider_windows/
Key

Well here I am just about a year later to report in. I put 3 of the 9500 windows in without removing the existing windows. I have been monitoring them closely and to date have seen no condensation issues. I rarely need to open these windows but I could (and I have on occaision) if needed. The insulation value is outstanding. Standing right next to these 3 windows (like 1 inch away) is like standing next to a wall. I feel no cold air at all. For the windows that I have not doubled yet it is clearly a huge difference as I do feel the cold when I stand that close. Next I plan to install a couple more and continue my evaluation. The impact windows in this configuration give me added security as well as added efficiency and sound reduction. The impact windows themselves have a U-value of 0.31 and are low E. The original windows that were left in place have a U Value of 0.49 (clear glass double pane). Does anyone know how to calculate my new U-value of the combination?

Key1

I'd like to see a picture of this.

As far as calculating the U. Value, I have no idea.

GulfBreeze,
I will post pictures when I get home this evening.
I took a look at your website.
What do you think about the 9500 Silverline Impact Window?

It has 0.09 laminate. Are their windows with thicker laminate for residential application? I know .09 is the highest silverline sells, and I know they have a lower cost 0.06 laminate version. I am just curious if higher laminate thicknesses are available.
Key1

There is no real formula for calculating the U-Factor in this case but assuming there is no leakage of air between the untis and that air space is static, you could somewhat assume that the addition of the R-Value (R-3.33 + R-2) would equal out (assuming some loss of R-Value) to a window near a U-Factor of 0.20.

Thanks windowsonwashington,
Now that you mention it, that makes a lot of sense.
My U value of .31 = 3.23 R value and my u value of .49 = 2.04 R value for a total of 5.27. 1/5.27 gives me a new U value of 0.19. Sweet!!! I'll take it as a nice side benefit eventhough my primary reason for doing this is security.
Key

Yes there are laminates that are thicker than .09 but you won't typically see them used.

What you will see are different types of material. Normally PVB or Sentry.

When companies want to make the glass stronger, they start stacking glass. It increases the strength and decrease possible visual failures with the inter layer.

As far as the 9500 goes, ehh I know some people that are hard core believers of them, but I have seen them with gaps in them that you could slip a few business cards through them.

Used as a double window setup? I have no idea.

You really don't need .06 laminate, especially if you are going to continue going with a double window. That's 5 peices of glass they have to get through. Most criminals will just move on, unless your storing gold, then they will probably just go through a wall.

I'd like to see a pic as well... Have you thought about resale with such an unconventional setup?

Excuse me, I meant, you don't really need .09 laminate.

I have not considered resale. Hopefully I will not have to for another 10 or 20 years. But the windows are simply sitting on the sill and screwed in on each side and caulked around the edges. The caulk can be cut and the screws can be removed if someone objects. But I could not imagine anyone objecting given the benefits. I have some pics.
Can someone please let me know how to post them..
key1

Here are 3 pics of a window before I convert it to double with the large window-sill. .

Now here are 3 pics of a different window that I already converted to the double. It was identical to the previous pics before I converted it.

Looks pretty slick.

Good job.

Thanks windowsonwahington.
The wife was concerned in the begining but is happy with the final look.
I do however need to discuss a problem I encountered on the last window installed. The next day it had quite a bit of condensation between the windows for that one install. The strange thing is there was none between the 3 that were installed for almost a year and more suprising there was none between the one I installed a day earlier which is on the same wall a few feet away. I opened the interior window and let the moisture escape all day then I locked it tight. The next day (today) there was no condensation. The only thing I can think of is I used quite a bit of caulk around the edges and above and maybe the moisture from the caulk drying was trapped between the windows?
Key1

key, while I'll agree with WoW that you have actually made a really weird setup look decent, it does not change the fact that it is not a recommended installation for about 100+reasons. The condensation between the windows is something that was warned about above. I suspect that the quality of the installation along with the mediocre(or less) quality of both "layers" of window are responsible for the issues that you are seeing.
The inner window is keeping the temperature of the outer window colder. If the inner window leaks enough of the interior moisture through it, it will just condensate on the outer unit. I expect that this and other issues will only get worse with time. I appreciate your ingenuity here, but it is what it is... and that is : a terrible idea.

HomeSealed, I appreciate you opinion and your honest feedback. I welcome it and please do not take my response as defensive as I just want to lay out my perspective. I would love to know about some of the 100+ reasons why it is a bad idea. I still have two more to order so I am open to hear reasons why I should cut my loses now. From my limited persepctive I only see benefits. Keep in mind I have installed 5 windows and only saw the condensation issue on the one (the day after it was installed). Once I opened it and let it dry out the condensation has not returned. This supports my theory that the cause may have been due to the Caulk drying and releasing the moisture between the 2 windows that I mentioned above. Since then I have had no condensation issues and I look for it every morning. 3 of these windows have been in place for almost a year without issue.

The benefits I see are increased security, increased efficiency, and increased sound proofing. I agree all 3 of those could be obtained by simply replacing my original 0.49 U value clear glass windows with the new 0.3 u value low E windows....but I do not have the skill set to remove the siding and all the nails from the fins and put in a new window and replace the siding and J-channels etc. Nor did I see a need since I have such large window sills.
Please elaborate on the negatives (other than inconvenience of having to open two windows instead of one to let air in or of looks since the retrofit is not bad looking).
Key1

Condensation and trapped heat are the biggest of the reasons in this case.

Condensation can be a big issue if the inner window is the leakier of the two units as it will allow moisture to leave to the out surface and create a problem.

This may not be the case here because the interior window is the better of the two but it should be noted as a potential.

The other issue is the reflectance of the heat from the Low-e equip window and its inability to be vented to the exterior. This is the issue that would be more concerning to me and only time will really tell if it is a problem.

Keep and eye on them and post back.

key, obviously what's done is done. Please don't take my comments as lecturing or any attempt to make you feel bad, they are more for the benefit of other consumers who view this thread and think that this may be a good idea. That said, here are some potential issues, some of which have already been discussed-- I understand that you may or may not be experiencing these, but that does not mean that you will not at some point, or that somebody else who tries this will not.
-Condensation. This is a biggie. You mentioned earlier that you view the "exterior" unit as a "nicely sealed expensive storm window", however there are major differences. Storm windows are designed to let moisture escape as they have weep notches on the bottom. A storm would also be set on a sloped sill, so that any moisture that does accumulate can escape. In your case, you have an exterior window that will trap that moisture in, which will then just run down and sit on that flat wood sill.
-Warranty. If you ever need parts replaced for either of these units, I can almost guarantee that if a manufacturer rep would visit your home, he would say that your warranty is void.
-Resale. This is an unconventional and weird setup. Even IF it did not pose potential problems (which it does), a potential buyer (9 out of 10 anyway) would come into your home and be turned off by this. The first thought in my mind is that this guy does not know what he is doing. Not only did he put these windows in wrong, but who knows what other crazy stuff he did around the place, stuff that could be potentially dangerous like messing with electrical, or something along those lines... This would be red-flagged by a home inspector.
-Low e. I know that it was mentioned above that the low-e would have to be switched around to cause issues, but again, this is no ordinary storm window. There have been cases where the reflection off of a low e coating has melted or distorted vinyl siding and other materials under the right circumstances. Do you not think that could easily happen to the outer vinyl window?
My "100+ reasons" was clearly hyperbole, but I could go on further. That said, do you need any more reasons than what has been listed so far?... and let me reiterate, I am not saying that ALL of these problems are imminent, however the likelihood is substantially increased and that's why this is not a recommended installation.

Fair enough.
I know this is unconventional and I would not advocate others try it. But at the end of the day if it works for me without negatives then I am ahead of the game, considering the benefits I am getting. If I see issues developing I can always have the outside cheaper window (that came with the house) removed and have the nicer window stand on it's own (moving it back and sealing the outside of course). But for now I will keep you posted on how it goes (if I see any problems). Concerning re-sale I am not one to compromise safety or comfort for how a future home buyer may feel when I sale 20 years from now particularly when it can be easily restored to the original condition. Twenty years from now (or so) when I am ready to sell, I will likely meet with the real estate agent at that time and discuss what improvements I need to make to my home to get the best price.....and implement them at that time.

I find tremendous value in the advice I am receiving and I will likely delay the install of the final 2 windows because of it....maybe ;).

It sounds like my two biggest watchouts are condensation and heat build-up. I have a few digital thermometers so I will place one between the screen and the outside window to monitor the outside temp, one between the two windows to monitor that temp, and one on the sill in the house to see how the temp varies on the coldest and on the hottest days. If someone is interested in that info I can post it,
My digital thermometers memorize the highest and lowest temperatures achieved so I will know that as well as how well the double window set up is working.
Key1cc

Fair enough.:) Since these are already done, I do genuinely hope that you don't experience any of those issues.

Just to be clear one more point,
I believe at least two posters indicated if the inner window leaks I could have condensation issues. However as I stated in one of my very early posts the Larson interior storm window manufacturer told me that condensation issues can arise if the exterior windows leak. Can someone please clarify if it is the exterior or interior window leaking that causes condensation between the two?
Thanks
Key1

You have given me reason to be concerned about my unconventional install. So I will track the temperature differences of my system. I have placed 3 digital thermometers in one of my double window set ups as the pictures show. Each thermometer has two read-outs but I am only using the bottom read-out because that one is from the thermometer's probe and I have it suspended in air space without touching anything.
One picture shows the thermometer sitting on the window in the house and it reads 66.5 degrees. The 2nd one shows the entire window set-up where you have to look closely to see all 3 thermometers. The 3rd pic shows a close up of the two thermometers where one is between the two windows and reads 50 degrees and the other is outside between the sceen and the outdoors reading 37 degrees.
I have no need to open this window so I will leave them in place and monitor the temperature differences.
Should be interesting....
Key1

Temperature update. I decided to move my temperature probes out of the new double window located on the north side of the house because it just was not getting enough sun and I want to see the worst case scenario. So I placed my probes in one of the double window locations on the west side of the house. This is the first double window I installed and has been in place a full year without issue.
The area temp got up to 72 today in central NJ and the probe right outside my window sitting in the sun all day measured 90F at it's hottest. Between the double windows the temp maximum hit 128F. The temp inside the house was 70.

I can't wait to see what the temp between the windows will be when the outside area temp hits 95 or 100F (versus 72 like it was today).

Key1

I will be interested to see what happens when it gets near 100 degrees.

Heat of deformation on vinyl is 160 in most cases. You may be very near that number once you tack on the extra 30 degrees of ambient and stronger sun.

I was concerned about the heat based on the earlier comments. That is the primary reason I am doing the test. I thouroughly inspected between the windows and I see no sign of damage even though the double window was in place all of last summer. I am hoping for the best or else I will have to come up with a solution to vent the heat.

Key1

Update:
It hit 93 degrees F hear yesterday in central NJ.
For the one window on the west side that gets the most exposure to direct sunlight, the max temperature on my thermamometer hit 145F. So far no signs of any issues.
Key1

Key1,

145 is getting up there and especially considering the ambient temps are still relatively low compared to summertime temps.

The issues will not be relegated to just the frame materials but at 145 degrees, there are extremely unfavorable pressures inside the IGU.

Keep us posted.

You are approaching temps which can deform vinyl, you could already be there depending on the formulation of that window. If you can get that baby up to 170 you would have a nice slow cooker, this would even save more energy.

That's pretty funny, Todd. He could open the inner sash and use it as a crock pot for soup etc.

Vinyl will definitely warp by the end of the summer and the glass seals will also fail eventually. Then both windows will need to be repalced. Would have been cheaper to just install a triple pane glass window with krypton gas.

Of course, you can slow-cook soup with a TP glass window. :)

Thanks for the feedback. My other windows don't even come close to these temperatures so this is the one I am primarily concerned about. However, keep in mind this window has been in place for over a year. Eventhough I did not monitor the temperature last year I recall the outside temp did exeed 100F ambient degrees once or twice. I see no evidence of any damage. I guest it never reached the magic 170F "pressure cooker" number. If I exceed 160F I may lower the inner window upper sash 1/4 inch to give the heat and pressure somewhere to dissipate....But I an not there yet. ;)

You might want to lower the top sash at least 6". Of course, at that point you are heating the house in the summertime.

Perhaps you could start baking cookies or pizza in there and then sell them and take the money and purchase new windows.

Key,

Are your exterior windows Single Hung or Double hung?

Also, how is your condensation issue going?

You might want to consider getting some desecant (sp?) bags and putting them in between the windows to help absorb moisture.

This is an interesting "experiment", kind of why window manufactures void warranties if you put storm windows over their windows.

Going to look like this before too long....

http://firecenterbeta.berkeley.edu/bwmg/images/windows/w7.jpg

Here is a link that might be useful:

Thanks for more feedback.
WindowDog
Please clarify how I will be heating the house by cracking the window, any more than if I had not added the 2nd window. Wouldn't the same amount or mabye even less heat make it into the interior?

Gulf Breeze
My exterior windows are single hung. My interior is double hung. I have never had a condensation issue. The one time I saw it was becaused I trapped moisture between the windows. Once I opened the window and allowed it to dry to the same 31% humidity of the house (at the time) problem solved. No more issue.

The dessicant bag idea is a really good one. I actually ordered a 50 pack a couple weeks ago and put a few in between my interior storm windows and my regular window.

I was unaware that having an interior storm window voids a warranty. That is unfortunate for me because I have not discussed it in detail in this thread by I have several Larson interior storm windows with LoE installed. They have the dessicant bags so no condensation issues.

WindowsonWashington,
That photo looks like the window was exposed to fire.
Hopefully mine will never look like that.

I am hoping you guys are wrong. But if you are right, I may be in a world of hurt because I have already spent hard earned cash to have the 5 double windows and an additional 11 interior storm windows.

For now all I can do is hope and observe. I will continue to share the outcome good or bad, but with so many experts telling me this was a bad Idea, even if I never see an issue I would not reccomend tring it.
Key1

C.

In the winter time you could also use your windows as a mini fridge. This would be an alcoholics dream, a beer in every window within arms reach. This is the greatest thing since the exaust pipe/manifold hot dog cooker.
One Sivlerline lost in the name of science is a small price to pay.
I'm sure everything will be okay espicailly with you keeping a close eye on things.Moisture or mold would be my biggest concerns.

Moisture is the easy one......just throw in dessicant packs. Heat and pressure build up is what has me worried.
C.

Not to steal the question from window dog, but I assume that he was referring to the fact that you will be letting super heated 140* air in from between the windows if you crack the inner unit open. Either way, you have 140* air in there where it would have been 95* otherwise, so that is doing you no favors when trying to keep the home cool. As has been joked about, you've essentially created little ovens in your window openings.

Thanks HomeSealed: But tell me if this is true.
If I did not have the double window and the sun shined on my exterior window for 1 hour at 100F then a "x" btu's of heat will enter my home. If I have the double window in place and cracked 6" at the top during the same time and outside temperature, why would anymore heat enter the home? The sun put out the same amount of btu's over the same period of time. How would the temp in my home be any warmer for the 2nd condition versus the first?
Key1

The temperature of the ambient air outside and the ambient air inside is not the issue. The heat entering the outside window will not be free to dissipate and will compound between the two windows, increasing in intensity. You would have to open the top of the inside window for 2 reasons. 1)Your outside window is single hung and won't open on top. 2)Hot air will rise and intensify in the upper portion between the two windows, so opening the bottom will not alleviate the problem. Opening the top sash of the inside window will let intensified heated air into the house, in effect, heating the house in the summertime.

To not have quite this problem, you would have to have LowE glass on the outside window, which would reflect heat away from the window. If you have LowE on the inside window, the heat is passing through the old window but not the new one, building up between the two. I know what you were trying to achieve in theory, but the science of fenestration is against you. I hope your luck is better than some of us anticipate.

Sooo Window Dog: I guess if I choose to be optamistic we could say I have a built in interior storm window where during the summer I could lower the inner upper sash all the way and have no heat build up basically like never having installed the double window. And during the winter I could close it and have the excellent energy efficiency?
Key1

There you go. That's a solution :)

well here I am about a year later.....no issues on all five windows. some have been installed 2 years and others 1 year.
Key1

Thanks for the update.

Keep us posted.

Here I am another year later after a brutal winter of over a dozen snowstorms here.

Still no issues with the windows install.

Key1

Thanks for the update key. Are you leaving the upper sash of the inner window open in the summer months as recommended above? That is advisable.... Interior storms with clear glass, or exterior storms with low-e might have been a more conventional and cost effective approach, although still with some risk of issues listed above.