Generators come in many types to suit your needs and budget. Standby generators like Generac’s Guardian Series provide a good amount of energy by using liquid propane or natural gas as a fuel source. They need to be installed professionally and run anywhere between $1,500 to $15,000. Portable generators are a cheaper alternative to standbys and are generally used for recreational purposes, though in a pinch, they may be used at your home in well-ventilated areas or preferably outdoors. Your HVAC repair expert can offer you recommendations.