Here is how I usually advise my clients. If the old wooden casements are in good condition that is they open and close properly and are not broken or rotten, I say they should be fine for a while longer. Most people think the new vinyl window is going to save them hundreds of dollars once installed but this is not generally the case. Let’s think about it. Most homes in this part of the Midwest have a gas bill of $50 -$100 a month on average. Of that cost a fair amount is administration costs. So let’s assume the old window is only R-1 value. The new window is likely going to be R-3. If this window is letting in 6% of the cold the new window will let in 1- 2% instead. So how much does that 4-5% cost you? Based upon $100/month gas bill (year round) you will save approximately $5/month. The new window cost $900 to install. Therefore it will take you 15 years to pay for the new window in savings provided to paid cash for the windows. To me I don’t think this is a great way to spend your money. Of course this is my opinion and I am sure there will be people out there that will disagree with me on this. I am not suggesting that this is a great idea for all people but I am saying you need to consider all things before spending or borrowing and spending this kind of money.