We have 4 wooden exterior doors and one aluminum single pane sliding glass door in our home. I’ve just begun to realize how leaky all these doors are. In your opinion, what are my options for stopping all the heat loss through these doors?

You are absolutely right about heat loss through doors. The estimated square footage of these doors (including the sliding glass door is about 120 square feet (11.14 sq. metres) of wall area that probably has an average thermal retention value of about R3. If you compare this to a modern wall assembly that is required to have a minimum R20 thermal retention value, you begin to realize that your doors are like big holes in your exterior walls.

There are four common varieties of exterior doors. The least energy efficient doors are wood raised panel and hollow core flat panel doors. You can distinguish a hollow core door from its more efficient solid core cousin by knocking on it. The hollow core will be obvious from the sound it makes. The forth door is a modern Styrofoam filled, metal clad door which probably achieves the best insulation R-values. If your home has raised panel or flat panel hollow core consider replacing them with these modern insulated, metal clad doors.

Any door, whether energy efficient or not, can be vastly improved by installing a metal combination storm / screen door on the outside of the existing doorframe. These secondary doors are a great way to save on your heat bills because they create an air lock between the two doors that helps slow down heat loss and control the escaping interior air whenever you pass through the door to the outside. I prefer the aluminum storm doors to the vinyl doors because one glass panel can be raised in the summer to convert the door to a screen door. These storm doors are available at your local building supply store for about $2400.00 per door. Remember to install new, good quality weather stripping and new threshold door sweeps as well.

Your poorest heat-retaining door (about R1) is the single pane aluminum slider. Unfortunately, the only way to improve the significant heat loss through this door is to replace it. If your budget can stand the bite, consider installing a vinyl clad thermoseal unit with a low "E” argon filled reflective coat glazing (about R4), because this is your biggest and least efficient door (approximately 36 square feet / 3.35 metres of wall area). So your highest heat savings will be achieved with this door replacement.