The degradation of the insulating qualities of the windows is overstated. The energy savings reaped by fixing the failed seals (usually replacing the glass units), pales in comparison to the cost of replacing the glass. The economic payback is long and energy savings cannot justify the repair. That is why failed seals are basically a cosmetic issue. No one wants to look through a foggy, streaked window. Manufacturer's warranties should be closely consulted (via the current owner), since these can sometimes pay for the glass replacement (at least materials) if the windows are less than 10 years old, and sometimes when they are even older.
If you know the failed seals are a widespread problem in the home, I would recommend contacting a glass repair company that can replace the glass units without replacing the entire window. They will have the best idea regarding which windows have failed seals. They will also be able to give a repair cost estimate. Having the glass company at the home inspection, as a specialist, would be the ideal situation. Otherwise, they can be called in after the inspection, based on the inspector's recommendations, to provide a quotation.
Gary at SiteTech Home Inspections, LLC http://www.sitetech-llc.com
I have used HomePro for a great majority of my inspections over my last 17 years in real estate. They are licensed by New York State and follow ASHI guidelines for their inspections. The best three there that I am very familiar with are George, Chris , and Steve.
There are a few option for repairing. Replacing the entire window. Replacing he glass and using the existing window frame. Or adding a "valve' to the window that vents the condensation out.
RE/MAX Realty Group
The home inspector should be able to provide you with a clear understanding of the efficiency of the windows in question. Our recommendation is when you schedule the home inspection, make the inspector aware your concerns with the property. Ask him up front, if he is qualified to provide you with accurate window information.
The Eckler team