p><strong>Windows need to be pretty bad in order to justify a full replacement.</strong> If they were single pane we would probably agree, but double pane windows mean they are at least fairly modern, so <strong>repairing them could be a lot more affordable</strong>. The seals around the thermal units of the window (that’s the glass part) will degrade over time so it is possible that they are leaking a bit of air. You may be able to take care of that with a tube of caulking.</p> <p>The problem could also be that they are not well-insulated between the window and the rough opening, or it could also be a case of air leakage. We would recommend taking off the trim boards and inspecting between the window and the rough opening (the wall framing). If it looks like there is water damage, remove and replace the insulation, and make sure it is well-sealed against air leakage at that point.</p> <p>Some people use spray foam for air sealing, we’re not big fans of that as we have seen some failures. Cured spray foam is not at all flexible, so if there is any shifting of the house and frame structure (not uncommon, certainly with older houses) it is very easy for the foam to become un-adhered and allow air to leak through.</p> <p>For sealing between window frames and rough openings, we would recommend using a high-quality tape (Delta MultiBand, Air Stop and Siga are a few examples). If none of those solutions solve the problem it is also possible to just replace the thermal units, that will save you a lot on installation as you avoid having to remove and replace the trim inside and out, as well as the entire frame.</p> <p>People often get talked into replacing old windows unnecessarily, even by well-intentioned contractors, but just do that math – how much will it cost to purchase new windows, remove and dispose of old ones, install new windows and repair finishing and trim inside the house and out. Now figure how much energy will you save with new windows compared to your existing ones.</p> <p>Except with very old and badly damaged windows on a house that is otherwise in very good shape, the odds are you will not recoup an investment in new windows. Using the window kits with a thin sheet of plastic and two-sided tape will also make a big difference with both comfort and efficiency. For more info we have pages on <a href="/guides/2263/high-performance-windows-what-to-look-for-when-shopping/" target="_blank">choosing new windows</a>, <a href="/guides/2225/when-should-you-replace-old-windows/" target="_blank">replacing or repairing windows</a>, and one on <a href="/guides/2261/how-to-install-windows-for-the-best-performance-and-durability/" target="_blank">proper window installation</a> if you do end up having to replace them.</p