TwoSeven:

You may find timber frames have a good R value (depending on the type).


 

 

 

Timber has a good R value but those old wooden frames usually leak huge amounts of air and may be rotten. In a moderate climate the window frame type isn't going to make too much difference to the overall window R value unless it's something terrible like aluminium without a thermal break, which is the common alternative to wooden frames found in New Zealand houses. Glass can make a big difference as the best low-e glass double glazing retains nearly three times as much heat as plain double glazing.