p>There is an ‘aftermarket’ solution for installing HRV and ERVs during renovations, though I can’t guarantee how much it will cost.</p> <p>First though, you need to realize that rely on opening a window for fresh air will in the long run be an expensive solution to bring fresh air into a home, and when you aim to sell it you would likely benefit by having a ventilation solution beyond just 'open window'. I can't guarantee this will fit your budget but have a look here at ductless wall insert ERVs and HRVs can be a more simple ventilation solution for older homes than gutting it to run ducts.</p> <p><strong><a href="/products/1134/productair-ductless-energy-recovery-ventilator/" target="_blank">Ductless wall insert ERVs for renovations and new home builds</a></strong></p> <p>This system works in pairs, where each unit has a ceramic core and its own fan. One blows in while the other blows out, and the change direction every 70 seconds, this way the incoming air passes through the ceramic core until it is cooled, then as the fan changes direction it is warmed again by exhausting stale air. By having two synchronized units the air pressure in the house stays balanced. You can see a <a href="/guides/2244/diy-lunos-hrv-air-exchanger-installation-video/" target="_blank">DIY Lunos Ductless ERV installation video here.</a></p> <p> </p