I have ahouse with a bunch of aluminum double-hung thermopane windows that were installed in 1987. All of the seals are fine, but the latches are crappy. Is it possible to remove the old latches, drill some new holes, and install new latches in the alumunium frame? Are there any worries with the drill possibly breaking the seal?
Re: Window Latches
I wouldn't drill into the frame unless you absolutely have to. Most of the time if you want to replace a latch on a window you can just unscrew the latches and replace them. There are cases were special screws are used which make removing a latch almost impossible but for every special screw there is usually a special screw driver. If you want to add latches for extra security then I can see why you would want to drill into the frame of the window.
So if you really must drill into the window frame here is a tip. Match your drill bit to the screws you are going to use but make the drill bit a little bit smaller than the screw. If you make the drill bit smaller then the screw will bite in better and stay in. Use masking tape on your drill bit so that the drill doesn't go too deep into the frame. You definitely don't want to drill any deeper than the screws are long that comes with the hardware. Match the screw up with the old hardware being used as a guide for your new hardware and very carefully drill the frame at slow speed making sure that you keep your bit straight at all times. It will be a challenge for you but can be done if you absolutely have to.
I myself though would consider either vinyl or wood windows as replacements. Aluminum windows tend to sweat and let in the cold by transference meaning even if the seals are good the window still gets very cold. The same is true for summer time as they can get very hot to the touch. Good luck and Merry Christmas.
Re: Window Latches
I wouldn't recommend doing this work with a power tool when the sashes are in place. I'd recommend you remove the sashes bracing them, and supporting the glass if you are going to use a power tool.
Are your window sash frames all aluminum or just aluminum skinned?
P.S. Not sure what the issue is with the original latching system. More often than not it is a concern about the ability of the latches to draw together the meeting sashes and provide a tight weatherproof and windproof seal - and often it is an issue of needing to clean and adjust, or replace the weather stripping at that point. That having been said, when the latch hardware is replaced even with that of the same type, they're never exactly the same and the amount of pressure between the sashes changes somewhat - therefore, and especially with older weather strippping (20 years in this example IIRC), you'd want to replace or renew(clean up, check it out) it (the weatherstripping) or consider that likely necessary step when you addressed this project.