The majority of pooches shed year-round. Just like people, this is their way of getting rid of old or damaged hair. Some breeds undoubtedly shed more than others, and they aren't all long-haired breeds either, as corgi and pug owners will testify. Coat blowing is a seasonal occurrence in breeds with a double coat.
Some dog breeds have a double coat comprising a soft undercoat and a coarser top coat. Siberian huskies are a good example of this. In colder months the coat is thicker, but when the temperature rises, the dog blows his coat. This typically happens in spring and fall and can last for several weeks. This is more than simple shedding, and owners are likely to find large quantities of hair coming out during grooming. Outdoor dogs have bigger blow coats than dogs who spend most of their time indoors. Some owners collect enough hair during a "blow coat" period to spin yarn and knit a scarf and mittens.
Daily grooming and vacuuming helps control the amount of hair around the home. You need a slicker brush, undercoat rake and shedding comb. If you are concerned that your dog's extreme hair loss is not due to blowing his coat, consult your veterinarian to rule out health problems.