Double hung window balance

Hello, Eric. Thank you for your patience during this busy season. I am very confident that I can get you the right balances for your window, but I can't actually narrow it down from the provided images. If possible, can you show me a picture of the pivot shoe that these springs attach to? We use that as a "key," so to speak, to figure out the whole assembly.

Can you also tell me how thick the springs are? That will allow me to make sure I get you something that fits in the track.

That is a huge help, thank you! I believe what you have here is an older version of our 15-228. With that in mind, you could use either our 1/2" thick Series 160 or the 3/8" thick Series 165. These two springs just so happen to look exactly like the ones in your first photo, so I think this is the right way to go. You just need to measure how thick your spring is and pick accordingly.

Once you have the Series, you still need to pick the strength option. This is usually pretty easy since the weight that the spring can carry is just printed on it, but you said you had no markings so it will be a little more difficult in your case. What you'll need to do instead is weigh your sash on a scale and then divide that by how many springs support it in total.

For example, if your sash is 10 pounds and you only have 1 spring on each side (2 total), then you would want the 5 pound strength option. 

Hopefully that makes sense. Let me know if you had any questions and I will do my best to assist you.