Goose, what type of heat do you have in the house? If you have warm water you could add a second heat zone either with a zone valve or a second circulator pump.
I would consider adding an exhaust fan, just put a vent somewhere in the wall that you can put a filter over. You could probably get away cheapest with adding insulation and drywall/or paneling to your existing exterior walls rather than building a whole new room.
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