Option to Improve Insulation on a Victorian Louvered Window
Gail Halsaver sent this image illustrating how to increase the heat retention in Victorian Greenhouses with louvred windows using plastic strips called "Jalousie Window Glass Seal". They are available at vintagetrailersupply.com or your local camping trailer retailer.
"These plastic strips are cut to length and slid over the edge of the glass pane. Once the louvers close in the evening a tighter seal is created between the panes. Simply another way to control heat loss."