I saw these on QVC. They are called BurglaBar 6-piece Silent Entry Security Set Item # V22466 They are for sliding glass doors as well as doublehung windows. You get a set of 6. Basically, a BurglaBar is a small rectangle of incredibly strong clear lucite plastic. It adheres to your window (or sliding glass door). It has a part that flips up or down. In the down position you can open your window. In the up position it blocks the window from moving. You can even place them on the window so that you can open your window only a few inches but no more than that (for people who want to have a little fresh air but don't want anyone to enter thru the window). It is hard to explain what they are and the photos on QVC. com don't really help, but you can go to QVC.com and read about the product. Read the reviews of it too. If you buy something from QVC and don't like it, you can send it back for a full refund within 30 days, no questions asked. I have done the drilling a hole for a nail thing too, as other posters have suggested. It works but is not very attractive. I even painted the nails white to match the window frame to try to improve the appearance of it. What I found was that you have to align both sashes perfectly while you are drilling the hole. SO if your sashes are kind of old and crooked like mine, have someone tightly hold the window closed while you are drilling.

I opened up the sash balance mechanism by grinding the staked keepers that hold the cover in place. Then inserting a putty knife into the housing (had to bend the end cover up for access) and over the spools (to protect them), then a flat screwdriver on top of that knife and turning it to pry the cover free. Not much pressure is required, if you have ground enough of the staking away. I was then able to replace the broken cord with some nylon masons line. I wound the new line around the drum and used it to rewind the spring, repeating until it looked like the other one that was not broken. I then used a small c-clamp to keep it wound and proceeded to place the correct number of wraps of lines on the drum to duplicate the unbroken one (total of 3 ½ turns). Then threaded the line out through the hole in the housing and through the plastic pellet and tied a big knot in it. Then released the c-clamp, while holding the spool with my thumb, and slowly allowing the tension to pull the plastic pellet into place against the housing hole. (I wore work gloves during the rewinding operation so I could safely hold the spool with my thumb when needing to do subsequent rewinding on it. From past experience replacing tape measure tapes, I was careful to watch for and avoid the spring going ballistic on me. It never really threatened to though.) Then I replaced the cover so that the ground away posts were in the opening where they belonged and taped the cover on with USPS packaging tape. :) The cover isn't in danger of coming off since it's held in compression when in the installed position. I wish I had been able to find some heavier line but I think the masons line will likely last well enough. It's rated at 155-pound test. If it doesn't, there is a heavier masons line available that is 216-pound test that I'll replace it with. A tip getting that left side track back into place without breaking it or hurting yourself is to slather some liquid dish soap onto the window stud. It slid right into place easily after I resorted to that method. It also helps to file the sharp end of the spline on the back of the track so it doesn't gouge into the stud. It has taken me nearly as long to post this than to replace the broken sash cord line. I hope it helps someone like me who couldn't find any info on doing this and had to stumble through it. I like fixing things rather than tossing them, especially when it only needs a piece of string replaced. YMMV

The reasoning behind this is the manufacturer doesn't make a good DH unit. The vinyl DH's need to be better built and stronger than the others. Anytime you have two fully functional sashes you require a more precise installation with more patience. The Single Hungs are just cheaper to make and easier to hang. Almost idiot proof in most cases. They are also more energy efficient from air infiltration becuase a lot of installers don't take the time to shim the DH unit properly. They end up leaking around the sashes, creating that ever so hated call back. With a stationary top sash they don't have to worry about anything leaking around the upper sash. The downfall of the SH is you can't tilt the sash in for cleaning. This can be quite trouble some for the windows off the ground a ways. There are ways around that for cleaning if shown the proper way. The history of the DH window goes back to the old farm houses that never had AC or Central Air. They would pull the top sash down about six inches and the lower sash up about six inches. This would let the air circulate better in each room by creating the drafting affect (Firefighters call it breathing during a house fire). With todays AC in almost every house the DH windows aren't really required for the drafting situation. You can still get them from almost every dealer. If they are balking at DH's with reasoning like they gave you. I would steer clear of them and start shopping for another supplier. Hope this makes sense to you. God Luck!!!

YES, the windows are still leaking just as much cold air as BEFORE the replacement of the weather stripping. The locks are NOT aligned as I would thing they should be. The lock that is on the lower sash does not align 'flush' with its counterpart attached to the upper sash. Infact, all of the window locks seem to be this way to some degree and ALL seem to have the upper sash locking part 'skewed' to the right. There is varying degrees of movement (from miniscule to what I'd call rather noticeable) and some upper sashes will move down when the two are locked. This did not seem to be a concern to the installer(imagine that) when I pointed these out as well. Also, measuring the space where the upper sash fite into the frame, I have 1 3/8 ths space; whenI close and lock the window, draw a line where the upper sash meets the frame then open the upper sash and measure just how far down the line is that I drew, I do not get the entire 1 3/8ths, I get 3/4's of an inch. (missing 5/8ths??) I've rechecked this with Bite Registration paper (carbon paper dentists have you bite on) and do not see 'any' transference of color. I placed a 3/8ths piece of foam insulation there and retested with the paper and still did not see any transference. Looking around for a 1/4" piece to make the full 5/8ths to retest again.