A: I found that Sierra-Pacific was very competitive for pine-framed windows (good if you intend to paint them on the inside) and Loewen was very competitive for vertical grained Douglas fir frames, which look a lot nicer than pine if you want the wood to show. A double pane low-E window can get to about R3 whereas triple pane low-E can get you to about R5. If you can get only double-glazed where you live, or that is all the space you have room for in the window frame, then adding thick, lined, pleated curtains that go all the way to the floor can add R3 to R6 to any window.