[jyl]

Thanks everyone.

I have wood siding over lath and plaster exterior walls, zero added insulation. I guess this is pretty typical of 100 y/o construction. I have no plans to cut holes in the walls and foam in insulation, because its so expensive that (so far) I can't see a financial payoff over 10 or even 15 years. The attic is finished so there is limited scope to add insulation there.

Since starting this thread, I've calculated that the windows we plan to replace represent appx 1% of the exterior surface of the house. I've also looked up the R-values of lath/plaster walls (around 5, supposedly), of good double pane windows (seeing a wide range of claims, from 3 to 6), and of the best triple pane, krypton filled, low E windows (also seeing a wide range of claims from 6 to 8). I'm thinking that even if the double pane is R=3 and the triple pane is R=8, the difference to my house's heat loss from replacing 1% of the exterior surface with triple pane rather than double pane is - well, pretty much nothing.

So my inclination is to look for a decent double pane low E argon filled vinyl window, ideally good enough to get the 30% tax credit, from a solid local installer - that is not Penguin.