Common glass is absorbing in the mid-infrared but transparent to sunlight, keeping our greenhouses and rooms warm. But a visibly-transparent and infrared-reflective material will perform much better than glass. Engineered multilayer optical coatings have been able to achieve both visible transparency and infrared reflectivity, but manufacturing cost has prevented their use on a large scale. Here, we predicted and successfully synthesized a transparent wavelength-selective metal-polymer hybrid films with low emissivity of less than 0.1 in the infrared range. The films, based on silver nanowires and PMMA, exhibit high transmission (>85%) through the visible wavelength range and high reflectance (>90%) in the mid-wavelength and long-wavelength infrared range. Our films are more transparent than a commercially available multilayer engineered coating in the visible and are much easier to fabricate. On an average sunny day, our films in this work warm up a prototype greenhouse 8 degrees Celsius more than that of glasses. We believe that our films hold promise for large-scale applications, leading to significant energy savings for indoor heating.