A lot of folks want to know why so many of us are saying, "Don't replace your old and historic windows", well here's my take on the issue.
I've been a historic property developer for 43 years doing primarily residential properties. I'm also associated with many energy efficiency organizations and do research on this very subject. I buy and restore historic homes (not HGTV flips) large and small and then sell them. First, I can tell you that my buyers demand original windows with quality storms. In over 160 rehabs of historic properties I've never replaced a window primarily because if I did, I would be wasting money and my houses wouldn't be as energy efficient.
Homeowners buy into the myth that a disposable replacement window is the answer to their comfort and energy efficiency issues and nothing could be further from the truth. All the science and data show that even if you have old windows with broken sash cords, loose putty and a cheap aluminum lumber yard storm, these windows, in this condition, only comprise 10% of your total energy usage. This data comes from the Department of Energy and many other energy testing organizations.
For years these disposable window replacement manufacturers and installers have been claiming 30%, 40%, 50% and even 60% energy savings. The Federal Trade Commission came out in 2012 and fined multiple companies making these claims for fraud. The FTC said prove your claims or stop making them and guess what, they couldn't prove these fraudulent energy savings claims and by law, may not make them as a result.
We also know that on a national basis, window restoration & weatherization cost about 10% less than replacing with wood windows. New wooden, clad windows have an average lifespan of 15 years before they will need to be replaced again. Think of that, an industry selling you a major house product that doesn't last as long as an asphalt shingled roof. 32 million window sashes end up in our landfills every year. Up until about 20 years ago these were all original, old growth wood window sashes being tossed. Today we observe that as many as 12 million of the 32 million are windows less than 20 years old.
Some reasons disposable replacement windows don't last include exterior sash cladding failing and allowing water to be trapped behind the cladding and rotting the sashes. Insulated glass (double paned or IG) failures are epidemic. The average IG pane fails within a few years and by year 12, often sooner, you will see the failure through condensation between the two panes of glass. This condensation then begins to rot the wood. It's also important to note that while a window that has served well for 100 years can be repaired, new windows cannot. New windows rarely have storm windows. Storms add thermal capability to the old window but they also protect the window from a direct hit from the weather.
There are hundreds of small companies in every region of the country that are rehabbing and weatherizing original windows. Save your money, don't buy into the lie that disposable replacement windows are the answer to your energy efficiency issues. Once rehabbed and weatherized, old and historic windows move up and down with one finger, have no lead paint left and stop the only thing that matters, air infiltration. Remember, all the R-value and U-value claims made by these disposable window replacement hucksters mean nothing. Glass is the worst insulator you can imagine. You can achieve similar thermal performance with single paned windows and storms. Windows are for light and air flow not thermal performance.