Wrong channel guide size in existing window

Question

Hey there,
The windows in my house take 385 series. Several of them are broken and need to be replaced. The curious thing is this. One of my medium sized windows, which has a sash of 32x30 and weights 18 lbs, has some aftermarket channel guides marked 2610. I'm thinking they're aftermarket by the style of the stamps compared with all the other windows in the house.

What surprises me is that they're 2610. An identical window to it's right has original channel guides stamped 2640. According to your guide, 2630 might also be appropriate. I could see either 2640 or 2630 working because they're sort of between the two weight-wise.

What I don't understand is why the 2610's are working. Not only are they working, but working nicely! They open and close with appropriate effort, and stay up without falling.

I'm hesitant to get more 2610's for other windows of the same size since they're so far off the recommendations. Any advice here?

Thanks, --scott

Tom · Accepted Answer

That is peculiar, Scott, but not totally unheard of. There are a couple different possibilities that come to mind.

The first is that for whatever reason this sash is lighter than on the other windows. It could be that the glass pane itself is lighter, which happens sometimes if the other glass panes were upgraded and this one was ignored, for whatever reason.

Another explanation is that the 2610 stamp is too weak, but not weak enough that you'll notice for another several years. The wrong strength spring can still work for a while without you realizing anything is amiss, but in my experience they always fail sooner or later, and earlier than the correct spring.

The third explanation, and least likely, is that these balances are misprinted. This isn't something that happens much, if ever, so I wouldn't put my chips on this, personally.

All that said, my thinking is: if it ain't broke, don't fix it. That law has served me well in this industry.