The ceiling outlets of ducted evaporative cooling systems can be a significant source of heat loss. Heated air can escape from around the outside of the outlets, as well as through the louvres into the ductwork. Although the louvres can be closed off manually after each summer, they do not form a tight enough seal to stop heat loss in winter.
Special care needs to be taken in houses with certain types of internal gas appliances, as they require fixed ventilation to expel the products of combustion from the home and operate safely.
Covers that can be fitted over the ceiling evaporative cooling outlet are commercially available. A cover should be fitted in winter to eliminate air leakage through the louvres. Roof mounted evaporative coolers should also be covered when not in use.
It is important to ensure that the covers you purchase are suitable for the type and size of your ceiling outlets. You may need to use a caulking compound around the outside of the ceiling outlet to create a nice tight seal.
If you are unable to find covers that are suitable for your evaporative cooling outlets, there are inexpensive do-it-yourself solutions such as covering them with an adhesive plastic product like Contact.
Install insulation in your ceiling, walls and floors to create a sealed envelope which acts like a thermos in winter and an esky in summer.