pane performance and mucb less life cycle ghgs?
A: Adding a single pane of glass or plastic (these are called window inserts) adds a similar amount of insulation benefit (R value) to going from a double-glazed window to a triple-glazed window. You will not save enough money on the heating bill to payback the full cost of taking out existing windows and replacing them with triple-glazed windows in under several decades. This is why I recommend installing triple-glazed windows only when you need to replace your windows for other reasons like they are rotting or falling apart as ours were. In this case the additional cost of triple-glazed over the cost of double-glazed is a good investment. If your windows are in good shape I suggest adding windows inserts.