The below information is from www.clopaydoor.com
A drafty, un-insulated garage door may not be an obvious culprit in rising monthly utility bills, but it’s worth giving it a second look if you have an attached garage.
Garages are more susceptible to temperature fluctuations given how often the garage door is opened and closed every day. Since attached garages typically share one or two common walls with the house, any hot or cold that travels through the door will ultimately affect the adjacent living areas.
An insulated garage door can help stabilize temperatures in the garage to reduce heat loss or gain.
The same principle applies to your front door.
If you’re thinking about upgrading to a more energy efficient model, stop making excuses.
Myth: Upgrading my garage door or entry door won’t save that much energy.
Reality: A new, energy efficient garage door can reduce energy loss through the garage by up to 71%.
Depending on the specifics of the home, a well insulated door can keep an unheated garage 10 to 20 degrees warmer on a cold winter day. That can have a significant impact on the comfort of family rooms or bedrooms located above or next to the garage.
It’s also important if items like refrigerators, washers and dryers or water heaters are located in the garage.
There are two different types of insulation used in garage doors: expanded polystyrene and polyurethane. The higher the R-value, or the lower the U-factor, the more energy efficient the insulation is. Doors constructed from both kinds are strong and durable.