I’m surprised there has been only 1 or 2 comments on HRV ERV. There are many products available to help exchange indoor air with outdoor air while conserving heat and or humidity. here is a smaller solution that is somewhat expandable. LUNOS e². I was hoping i’d get some more ideas from this discussion.
Most houses (at least in the US) are so leaky that an ERV/HRV is just going to suck all the heat out, and cold air is going to come in through all the drafty places (and that doesn't necessarily mean fresh air, could be stale air from your crawl space).
Wouldn't recommend for any existing construction unless you know how air tight your house is (get a blower door test done).
The problem with small systems like the LUNOS e² is that they're incredibly overpriced. I wouldn't be surprised if its BoM is well under $50. It's basically some fans and plastic pieces.