Our 1973 built house needed some upgrades! Anong the most pressing needs were Energy-efficient windows to replace the original, rusted out aluminum ones. These NT windows are already making a huge difference in the appearance (we couldn't even get the other ones clean and these make cleaning easy) and temperature in our home. We're really pleased. My only regret is that we couldn't replace all our windows at once. We're halfway there and looking forward to finishing the job with more of these excellent windows as soon as possible.