2. Insulate properly. If an HVAC system doesn't fit your budget, make sure the temperature is properly controlled through insulation. This has a lot to do with your geographic location, so consult a professional to assess your situation. If you’re in the southern United States, for example, Cravotta suggests treating the shell by creating a moisture barrier on the outside of every wall plus the floor and the ceiling, as well as adding closed-cell foam insulation to prevent condensation buildup and mold.