Which Spiral Balance to get?

A quick learner from Richardson, TX says:
I am replacing the spiral balances on wooden windows in a house built in the 50's. The window sashes come in 2 different widths:

36" width sash - weighs 12.4 lbs.
48" width sash - weighs 15.6 lbs.

I want to purchase the 27" Series 500 spiral balances, and I'm not sure if I need the red tip or the blue tip. The guide on tip colors doesn't say anything about actual weights, just standard vs heavy. Can you tell me which one is most appropriate?

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Donna from SWISCO responded:
It is best to match up to the original color tip.

For 27" Series 500 the Red Tip will carry a window sash weight range of 7 through 29 pounds.

For 27" Series 500 the Blue Tip will carry a window sash weight range of 12 through 31 pounds.

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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