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"Defogging" double-pane windows .... a gimmick??

593K views 133 replies 57 participants last post by  Nathan 
#1 ·
I posted on another home forum about removing the condensation between the panes in my two 51" x 61" picture windows. I bought the house in December when there wasn't much condensation, but now it's pretty bad. The people who responded to post noted that I'd have to have the glass replaced entirely. That's looking to be around $700 - $800. But I saw a Yellow Pages add that advertised a company that could defog windows. So I started reading about it on the internet (which always requires scrutiny and skepticism) and there are a number of companies saying that, in many situations, windows can be defogged.

Here are a few:

http://www.defogit.com/
http://www.defogusa.com/HowItWorks.html
http://www.wcofa.com/
http://www.ccwwi.com/Default.html

Here's an article in the Ottawa newspaper about it:
http://www.ccwwi.com/images/Ottawa_Citizen_Article.pdf

Is this defogging process truly possible? effective? Anybody tried it?

BTW, the person who used to own this house is no longer living and I can't find out who installed the windows. AFGD is stamped inside the window and I talked to the local dealer of this glass manufacturing company. They said I'd have to find the contractor who installed the windows to initiate any warranty that may be valid on the windows .... basically a dead end for me.

Hoping for an inexpensive solution, but trying to be realistic....

Alex Z
Knoxville, TN
 
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#59 ·
Interesting thread. I am going to have to try it with some of the windows of a house I just bought that I am planning on renting out.

I am wondering if, instead of drilling through the glass itself, maybe I can try drilling at an angle through the window frame next to where the glass is, and have the drill hole go into the channel between the panes of glass.
 
#61 ·
Any word on how to buy the flat vents from the Rep?

I just about passed out when a guy came and told me it would be about $900.0o to "vent" 12 windows in my house. I totally want to dremmel it out.... I checked out the website to get the vents that are adhesive. Any chance on buying them????? Dan can't wait to hear how your project is going. I love the fact that you gave such detailed directions. I am going to try it. Thanks, keep up this thread!!!!!:thumbsup:
 
#62 ·
waiting to hear about how folks made out

I too have several very large fogged up tempered windows that are framed in easy to disassemble wood frames which when removed provide access to the aluminum channel in most cases. I'm thinking maybe right angle drill attachment would work, maybe dremel makes one? In those where I can't get to the channel, I suppose disassembly or replacement is the only solution. I am looking forward to hearing more about the availability of the screw in vents as well as how disassembly worked out for anyone who has tried it. I have a garage side door window I will tear apart as a test and use the quick & dirty venting and post the details. If anyone has additional details or has heard or learned anything new please post. My replacement costs would be well over 10k!
 
#63 ·
Just had to register with this forum to post and say thanks so much to Dan and the other posters. I am looking to buy a new house in OC California and one of the windows is badly fogged. Agent was saying she knows some company who can defog them so I started doing some surfing for more info, but based on this thread I could buy myself some diamond drill bits and save myself a few hundred dollars. Also wondering if it's possible to buy those gore vents anywhere.
 
#65 ·
I have a question though, is there any reason why you couldn't use a regular drill with diamond bits? It seemed like everyone was using Dremel's or something similar. Is that just because it is a bit smaller and easier to be more precise?
Normally, a regular drill bit will not penetrate the glass and if it does, it is so coarse, there is a chance it will crack the glass.
 
#67 ·
What a fiasco with meager attempts to save on energy, not only with windows, but with other means. Ha, purchased ten CFL lamps a few months ago, so far, three of them exploded and most of them that were rarely used. Friends electronic ignition went out in his furnace, really stupid compared to the cheap thermocouple and reliable units we had years ago. That little bit of heat was helping to heat the home and would always turn it off during the AC season, so how much energy is being saved? Friend had to pay $560.00 to get a new ignition module, what a ripoff. Did have to replace my gas hot water heater, and looked into the power vented models, is eligible for a tax credit, but still a major loss initially. Building inspector said I cannot mount it in my basement, because the snow could cover the vents, but it's okay to mount a vented furnace, you figure that out. But in comparing energy cost, would only save about a therm per month, and with the problems in the electronics, vent motor, ignition, and the very poor warranty, only a year on these parts, could cost an extra fortune. Cheapest one was over twice the price as a conventional hot water heater, but the conventional one had a 12 year warranty, where the vented version had a 6 year tank warranty, but only a year on the electronics.

Ethanol gas is yet another ripoff, first off, they didn't figure the price of corn with the increase in demand would rise the price of corn from a buck and a half per bushel to over nine bucks, this drastically affected all of us at the grocery store. Still takes over a gallon of fossil fuels to make a gallon of ethanol. Got a bad mix at a Milwaukee station, that is all you can buy, detonation was so bad, had to drive home with a MT vehicle in third gear to keep the engine from blowing apart and averaged a very poor 17 mpg instead of the usual 36 mpg I get from using real gas. On an older Toyota, ethanol swelled up the fuel pump made with plastic parts, 450 bucks for a new fuel pump, I was really teed off, took a picture of it and sent that to my governor that is really pushing ethanol. No reply as usual.

Son has a 14 month old energy efficient furnance, control board went to hell, his dealer said it was under a five year warranty, wanted a 150 bucks to come out plus another 110 bucks an hour to change it, but with my vast electronic knowledge, convinced him, I could change it to save my son a couple of bucks. But what happens after warranty? I did note they changed the new board, old board was crap. Guess they didn't hear about surge protection with microcontrollers. More made in China crap. I dropped everything when his furnace went out, have a new two month old granddaughter and determined his control board was a piece of crap.

So are our windows, have you checked these out lately? With many, even the multiple pane type, one baseball at the wrong spot means replacing the entire window and the also includes the frame! Breakage is not warranteed by anyone. And if you have a mortgage paying for that window at three times the price, you are really in bad shape.

My first approach was to contact http://www.crystalclearwindowworks.com/Default.html, what a load of BS I got from these people, no service guy in my area, so asked if I could buy the check valves, no, it takes great skill to install them, if they do even work. Later learned that this great skill is gained in a two day training period, but I never did get a quote.

Second approach is to treat the window as a broken one, a guy in town claims he can get the glass panels, would have to see the window, but would run about 200 bucks per panel, I have casements that I can remove in seconds, that would save me a lot as opposed to him coming out here, all these guys are charging a small fortune now to come out. Also contacted the window manufacturer, also about 200 bucks a panel, but comes with new weather stripping and just snaps in, but have to go to a dealer, they don't sell direct anymore, and screw you if you have a problem after the warranty. Mine were warranteed for twenty years, started having problems after twenty-one. The window manufacturer was kind enough to come to my home and look at them, asked him if I could buy that vinyl molding that holds the glass panel in, he was kind enough to give me his souce of the glass, a factory only 70 miles from me. Haven't contacted them yet, as can no longer get that vinyl molding, and any attempts to remove it will break it into tiny pieces. Did point out, they don't use that anymore, has been a source of problems for them, but did tell me the source of fogging is caused by that vinyl skinkage. On this note, did use silicone seal on the joints for the good windows.

I do have a wooded lot, but the windows exposed to the south sun are the problem ones, thank God or whoever, my large picture windows are on the north side of the house.

Well, I haven't done anything yet, but yearn for the days when I had very good storm windows on my older homes. Thinking about building a new home, but would really look into windows with easy to change panels if such a thing really exists. My neighbor with the same age home simply spend over 40,000 bucks for all new windows, that is also a solution. But where is the savings with these pieces of crap if you have to go through all that. Did write my congressman about these so called energy saving devices, said something about a war in Iraq. Maybe if enough of us wrote we could make a difference.

Best window is no window, but kind of hard to convince a wife of that. Ha, we want to bring the outdoors into the indoors, the whole concept is stupid.
 
#69 ·
Calcifying in windows

This occurs when the wet surface is sun-baked over and over. The window defogging mentioned before will tell you they have a majic potion which is actually availble from window cleaning supplier.

They will also tell you about their other majic solution that leaves no streaks to sun bake, but don't get me wrong these guy's (franchisees) are brainwashed by these Companies into believing all this.

Each one of those defoggers are franchised and they are told about these majic solutions formulated just for them and each franchisee gets to pay $20 a gal. for what is 99% water. They call this Wetter Water, well wetter water is available from people like ABC Window cleaning Supply as wetter water or slik. The window cleaning induxtry use this to lessen the wear on their squeegees and disapate water faster.

Both these products are sold in concentrates and 1 gallon of concentrate makes 1,200 gals of the majic potion. Oh yes, the concentrate sells for about $12 a gallon.

To remove the calcium deposit buy some calcium remover, mix it accordingly, if you have drilled a 3-5mm hole at the bottom of your window, put your solution into a garden pressure sprayer and jig a small metal tube bent at a angle, introduce into the hole and spray the inside of your thermopane a few time. The excess water will escape through the hole you drilled and suck up the balance of the liquid with a syringe.

Hope this helps.
 
#70 · (Edited)
Well, this is a very old thread but I think worth keeping alive.

In manufacture the space between the glass is purged of air and typically Argon or Krypton is fed into that space and then plugged off. Those gases are void of oxygen. Oxygen holds moisture. If there is oxygen infiltration into the space between the two sheets of glass water molecules will condense and fogging occurs.
The desiccant is added to absorb some of the moisture when the seal between the pains begins to fail. The Manufacturer puts it there to help get them through the warranty period. In any event, It does not magically make moisture go away. It absorbs it until it becomes saturated. Then your windows begin to fog up. All windows will eventually fail.
Any attempt to repair a fogged window without taking it apart and resealing the pains is a waste of time. Just my opinion and the fix is is a DIY project.
My suggestion is this. Disassemble the window. Remove all the silicone on all glass surfaces. Clean the glass carefully and thoroughly and use a lint free cotton cloth. Use 4 - ¼” sq clear plastic spacers cut from plastic rods available at most hobby stores. (NOTE: Your windows may vary with the factory spacing between the pains so measure that before disassembly, you might need a 3/16” spacer, as an example.) With the glass on a flat surface place the spacers on all 4 corners of the pain. Apply a silicon bead around the entire edge using a quality clear “glass silicon”. Place the second pain on top any align the two. Once the silicon has set-up remove the 4 spacers. Silicon over 2 of the 4 holes. That leaves you an inlet/outlet hole.
I use the argon from my wire-feed welder to purge the window of O2. After 5 seconds I’ve pushed 98+% of the O2 out of the sandwiched pains and I apply silicon to first the outlet hole while I'm still purging and then the inlet.
This process is very close to how the window was made at the factory. Argon is available anywhere that sells Oxygen/Acetylene for your gas torch set. For $250-$300 in materials you can do 500 windows +.
I’ve used lengths of silicon “rod” that you cut to fit a window and just add a dab of the tube stuff at the corners. I’ll have to look who it was that sold these to me. The rods are cut to fit and they are firm enough to hold the pains apart without using any spacers.

It's worth noting that Argon is a noble gas and is not flamable.

Just my ol 2¢
 
#72 ·
Yikes, I drilled out two holes. First I used a glass 3/16" bit, was going great until I got impatient and pushed too quickly and broke the glass. Next try I used a ceramic drill bit on my rotozip and went much slower and made a hole a little bigger than 1/8". I live in So. Cal and we have had a lot of rain. Sadly the window hasn't cleared up, it had a LOT of water streaks. Half the window has cleared but not the lower. I have some adhesive vents but haven't applied them yet. I am going to use packaging tape over the lower hole and put the vent on the top. Has anyone else done this and had success????? I've tried to contact Dan but because I haven't made 25 posts I can't PM him. Help!!!!!
 
#73 · (Edited by Moderator)
To sckarsten

You need to use a variable spped dremel with a diamond bit ball end. Start drilling at 45 degree angle to set a mark and as the bit start going deeper straighten out your angle. You need a hole at the bottom and one at the opposing top. Do not block the holes with tape that defeats the purpose. What you want to create is air flow to dry out the window. Good luck
 
#74 ·
Kent, thanks, just checked out the site, couldn't read the forum???? How long should it take for the windows to clear out the water still on the inside panes of the glass. I did do opposing corners. I figured it out with the roto zip at an angle and sprayed water while I drilled. I went really slow and it worked. I guess I have to cover one hole and then put a two way valve (which I have) on the other hole. Have you done this procedure yet? I hope it works. I initially tried on a window that his hidden to practice on. I got the valves from GORE, but you need a resale number to use them. I am going to try them on remodeling jobs. Thanks.
 
#77 ·
Drilled opposite, inside

My first attempt was with a 3/16" glass cutting bit for a drill. Big mistake. Just happened to buy some glass for our church and the glass man even said it would crack the glass. It did. I went slow and sprayed water, but I got impatient and cracked the glass.
Then I used a roto zip ceramic straight shaft bit, went at it at a 45 degree, with water spritzing, really slow. It took forever about 15 minutes. It worked. I drilled inside opposing corners as close as I could get to the edge considering the roto zip. Another person suggested that I buy a ball end dremmel diamond bit. I've checked them out on line for less than 10 dollars.
I am still a little confused about covering the holes. I think only one hole gets the vent and the other hole gets covered after the moisture is gone, otherwise little ants would cruise in. I have windows out in site and am hesitant to use my rotozip straight shaft ceramic bit, but the cracked window is out of sight. Hope this helps.
 
#78 ·
Successful drilling on a good window!

:no:Well a lot of patinece and it worked. I haven't ordered the ball bit diamond dremmel bit and used my straight shaft ceramic drill bit with my rotozip. It took a long time, it took about 45 minutes for two holes. I had to go slow because this was a big window in my living room. I left the vents off the window to let it air out and let the moisture escape and then I'll put the vent on it. My question is.... Do the pros seal one hole and leave a vent on the other, or two vents on the both holes. Any ideas would be great.
 
#79 ·
Dan's method seems to work

Thank you, Dan. Our "problem" window is a large semi-circular one, with several metal ribs between the inner and outer panes. Moisture's been accumulating for years. The problem with replacing it (besides $$$) is that the window is embedded in the outside stucco and inside plaster, so walls would have to be torn open, and I don't know how weather-proof the repaired surfaces would be. Before finding this thread, I'd been thinking about making holes in the glass, but didn't know what to use, whether it would work, or whether it would just shatter the window (not a good idea in mid-winter).

Now that it's (almost) Spring, I used a variation of Dan's method: drilled two 1/8" holes through the interior pane, but had to put both at the bottom, because a hole at the top would have been very visible as well as hard to reach. Each hole took about 30 minutes, using a variety of diamond bits from that $6 kit at Amazon. More than half that time was spent pausing to let things cool off, and I occasionally wiped the glass and the bit with a damp sponge. Nothing cracked; I never used much pressure, so the Dremel mostly ran at full speed.

In an effort to keep bugs out while letting the window dry out, I cut 2-inch lengths of drinking straws that fit snugly into the holes, and wrapped Scotch tape around the loose ends of the straws, so that only a little of the tape was on the straws and the rest presented a sticky inside surface. (The sticky tape became an extension of the straw, providing a tunnel that has a sticky inside surface.) This is easy to remove and re-insert, lets air circulate a bit, and hopefully will trap any bugs or dust particles that enter the sticky passageway. The straws are stiff enough to insert and remove without collapsing from finger pressure; tape alone is not.

Since the holes are at the same level, there won't be any convection currents to circulate air through the window, so I've been blowing air into one hole with a low-pressure air-mattress inflator: remove one straw, partly cover the hole with the inflator nozzle, run it for a few seconds, remove and cover the hole with a finger until the air stops whistling out of the other hole; then repeat. I'm afraid to do this for more than 10-15 seconds at a time, because air pressure's clearly building up between the panes and I don't want to break the window. Even though I can feel air coming out of the uncovered hole while the pump is running, it takes almost as long for the pressure to return to normal as it took to pump air into the window. I do a few reps of this at a time, and a few sets a day. Works best when the window's warmed by the sun.

The holes were made two days ago and the pump's been used maybe 10-15 times since then. Originally, every section of the window showed moderate to severe condensation, but now, about half of the window looks clear and mostly or completely dry. The two triangular wedges at bottom-center still look very, very wet, so it'll take a while longer before I know how close to being completely successful this method is. I'll post an update sometime in the future.

When finished, I'll follow the rest of Dan's suggestion to cover the two holes with small pieces of clear packaging tape and make a few pinholes through the tape.

Again, thank you Dan.
 
#80 ·
It worked and it didn't work

Update on my earlier post: using a small air pump to blow air through the double-pane window eventually dried it out, but as soon as the blower was removed, the window started to fog again. The seals probably are too badly compromised for a lasting benefit. Also, this is a semi-circular window with internal struts and, consequently, a dozen semi-isolated compartments. That made it harder to dry out all of them.

Bottom line: Dan's method is excellent, but when the window is in really bad shape, only a replacement will solve the problem.
 
#81 ·
De fogging insulating units

A great thread, and some very inventive contributions.
I think I can clear up a couple of the unknowns.
Firstly, the inside or outside drilling question;
If you live in an area where you are in heating mode most of the year and hardly ever use A/C (like here in the UK), then it is only worthwhile drilling the outside. That is because the outside atmosphere has lower absolute humidity (less mass of water for a given volume of air) than the indoor air. What happens when the unit warms up is that the trapped air goes out of the small hole and the absolute humidity equalises with the outside eventually when the desiccant has dried out somewhat. It is known as vapour pressure equalisation. The air between the panes will always be a bit warmer than the outside air, lower relative humidity, so condensation will not form between the panes.
If you live in a hot humid region in cooling mode most of the year, it might work to drill the inside. In those conditions it will be lower absolute humidity inside the room than out of doors, and again the cavity will be a bit warmer so will not condense.
If you drill the hole the wrong side then comparatively warm humid air gets into the cavity and reaches a colder pane of glass and condensation forms. That may be the reason some people have reported the technique not working.

Secondly tempered glass:
The glass type question limits where you can use vapour pressure equalisation because, as many people have rightly said, you can't drill tempered glass, and it is often used as exterior lites. Polaroid sunglasses work fine to detect it; if you can't find a brand mark in a corner of the glass and you can't see a pattern of marks through the polaroids (or other polarising filters like 3d glasses, experiment with rotating the lens) then it is probably not tempered.

Hope this helps.:)
 
#82 ·
That E coating could well be the problem.

Sure most of you used a garden hose to spray off your car or home windows and while wet, the windows were super clear. Just happened to play with a piece of glass from an old double pane argon filled E glass window. That E coating is on the inside of the glass, has a grit like feeling, no smooth like glass.

When spraying the E side with a garden hose with the glass laying on my deck, could barely see my deck as that window really became cloudy. I wiped that side with a clean rag, and when the sun hit it and it dried, it was crystal clear again, but just wiping the E coating with a damp rag, it clouded up like crazy again.

I flipped the glass over with the outside of it facing me, the smooth side, getting water on the outside of the glass does not cloud it up.

Has to be a reaction between that E coating and the slightest bit of moisture.

This particular window was from an old patio door, has a 3/4" thick aluminum frame with approximately 7/32" glass. Gathering in manufacturing that laid the glass on each side, E coating on the inside and some managed to either dip the edges in some kind of soft rubber. It was easy to cut around the sheet of glass from that assembly to remove the glass.

This particular window, foggy, had one tiny corner that was dipped or some kind of automatic applied rubber coating that wasn't properly applied leaving a very tiny crack in that rubber coating. That must be all it takes to have a foggy window.

Piece of glass was 30" wide and 75" high, I was handling it very carefully, but in haste, lifted it off my deck from the center letting the ends bend just a bit. The glass exploded like a bomb just like the side windows of your vehicle with thousands of bubble like pieces all over my deck. Would really think twice about drilling any kind of hole in it.

I found this old door panel at our garbage dump and took it home to play with it to see what I am in for with my own foggy patio doors. I can remove the glass panel, but without a factory, really doubt if I could repair mine. I called my door company, they want 415 bucks for just the glass panel, but only 350 bucks for a new door panel with the glass installed, this whole country is crazy with replacement parts, cheaper to buy new than to buy parts anymore.

Thinking now just about replacing the entire door, we live in a throwaway society today. Looking at a lot of new windows, even with one broken pane of glass, you have to replace the entire window. Now I am interested in learning how more effective these argon filled windows are instead of the old fashion single pane windows with storms, least those could be repaired.

If you have kids, do not buy them a baseball.
 
#83 ·
With luck, found a clear glass for my patio door at the garbage dump

Guy said take it, also had a bottle of Windex and roll of paper towels to make sure it was clear.

Practiced removing the glass from the old frame, that was chopped up for firewood using a razor blade on the inside without hurting the wood.

In inspecting the glass, that rubber seal was perfect at the sides and the top of the glass, but just starting to separate at the bottom. The seal between the molding and the glass wasn't exactly perfect at the point and suspect water is dripping down into the frame.

This gives me a hint to check all my other good windows and doors for leaks at the bottom of the frame. My guess is that water that does get in freezes and is disturbing that rubber seal. Thinking about a thin bead of silicon at the base of each window after a good cleaning.

My door, the door I wrecked, and this one all seem to have the same problem with that rubber seal between the glass and internal aluminum frame at the bottom of the window, that's three out of three.

Perhaps an ounce of prevention will save all of my other windows and doors.

Met a man with young kids that recently purchased a home, ironically new in 1985 just like my home with cloudy windows. Hired a contractor, with these flanged windows, all of the siding had to be removed, but since his was plastic, would crack so all that had to be replaced. Also they couldn't find the exact size, so had to modify the rough opening. I didn't ask him what he paid, but you can assume he not only has his primary mortgage but a second mortgage as well.

I look at the way they are building homes today, pure crap, and wonder if that couple of extra bucks you may save in energy costs is really worth this extra expense.

It's seems perfectly stupid to me they are making doors and windows where you can't even replace the glass. That is stupid, stupid, stupid.
 
#84 ·
South facing windows are my major problem, but do have a large white pine tree blocking the sun on eight panels, they are okay. Kitchen is my next challenge, and is hit directly by the sun. They want 154 bucks for just the glass, and only another 30 for the complete panel with the glass installed, so I ordered those.

If I did order just the glass, would be a challenge just to change it, the four frame pieces are mitered over that glass and all glued together, heck of a lot easier to glue something than to take it apart.

Got to thinking about the good old single pane windows and storms, all can be cleaned. But what is the cheapest way to get an equivalent of a single pane window and a storm window?

Simple, just slap two pieces of glass in the same frame. Call it energy efficient and charge a bundle for it. Believe that is where we are today.
 
#85 ·
Trying it with one hole inside

I "drilled" one hole in a foggy window by grinding. I'm in no rush, so we'll see how that one hole works by itself, and I'll repost..

I used a 30,000RPM Dremel and a "Dremel Silicone Carbide Rotary Tool Grinding Stone". Item #94739 at Lowes, and it costs about $3 bucks. It took less than ten minutes, the tool never bucked, and I never felt like I wasn't in control. I didn't use any kind of sprayer for cooling while grinding, and the hole is clean on the inside and outside edges. Don't push too hard, just let the tool do the work and take away the unwanted material.

Just had a few thoughts to share here...

If you do this, making the hole(s) inside the house is the only way it should be done in my opinion, for several reasons.

First off, you want the windows to keep your house warm or cool. Hopefully, the air in your house is cooler than the outside air in Summer, and warmer than the outside air in Winter. By opening a small hole on the interior of your double pane glass, you are exposing it to the flow (or convection) of air. This minimal flow of your indoor air into the window is still going to push the hot or cold temperature out and a little bit further away from you, thus keeping you warm in Winter and cool in Summer. This is my theory anyway... I think that's why you could feel such a temperature difference in your testing Dan.

Think of it like those expensive heated windows they have for Winter. Instead of electrical energy being used to warm the glass and keep the cold away from you, you're using the power of convective air flow from the heat in your house to warm the interior of the window and keep the cold further from you.

Secondly, if you make these holes outside they are subject to filling with water in a heavy rain.

Thirdly, think of a strong rain followed by a cold snap. A window even slightly full of water is likely to break as that water expands from freezing.

Fourth, if you put the holes outside, you are bringing the outdoor temperature that much closer to you inside. Thus, pretty much negating having a second pane of glass at all.

Thanks to everyone for contributing to a very helpful and interesting thread! :thumbup:
 
#86 ·
hi i am not advertising but giving some advice which i defiantly know about as i have been doing this for 4 years now

there are many presumptions with drilling glass and venting

first of all IT DOES WORK

tools/parts needed

1 dremmel mains or battery
2 diamond burr(drill) cylinder type
3 water sprayer
4 valves

i am obviously not go into the full process of repairing DGU's but here is a brief out line if you want more info you can of course contact me if admin and moderators of this forum don't mind

you drill 2 holes in the glass from the outside in opposite corners through 1 lite of course then you apply valves the valves are not too ready available but i know where sorry this part doesn't help much but as i said i am not advertising just helping out

these so called valves shelter the hole from driving rain and of course stops water getting between glass

the effectiveness of the r value of your DGU is hardly altered and no figures are out as yet

i short the small amount of cold air that enters the DGU is quickly warmed up by either sunlight or indoor heating

i have done 1000,s units and no complaints

hope this help some who doubt and encourages some further
 
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