Ventilation Part 4: The summer Langstroth hive
Here are some ideas for increasing summer ventilation in a Langstroth hive. They can be used singly or in combination, depending on your climate, weather patterns, hive strength, and personal preference.
- The screened bottom board used for Varroa control is an excellent device for increasing ventilation in a hive. Many designs have a tray or drawer below the screen that closes off the air flow. Depending on conditions, the screened bottoms can be left fully open or they can be completely or partly closed.
- In summer, the lower (main) entrance should be fully open in a strong and healthy hive. This not only allows for vast amounts of traffic but increases air flow as well. Weak colonies—especially those in areas prone to yellow jacket attacks—should have their entrances reduced to a size they can easily defend.
- Upper entrances increase air circulation and often aid in reducing congestion. Many of the returning foragers will use an upper entrance if it is available. Upper entrances range in size from a tiny slot about ?-inch high by ¾-inch wide (1 x 2 cm) to the equivalent of a full main entrance. Full-size top entrances can be created by using three sides of an Imirie shim.
- Short shims (not to be confused with Imirie shims) are small rectangular blocks about ¼-inch by ¾-inch by 2 inches (0.6 x 2 x 5 cm). A pair of these can be used between the topmost super and the telescoping cover to provide additional ventilation. The problem with these is that they create a very long opening that extends across the front and partway back on both sides—a configuration that is hard to defend from robbers and yellow jackets.
- Holes are often drilled in one corner of the upper brood box. These holes are about an inch in diameter and usually screened from the inside. They provide a small amount of additional ventilation.
- Ventilated inner covers can be used in place of regular inner covers. A ventilated inner cover is screened in the center and has end pieces that are higher than the side pieces. These end pieces hold the telescoping cover aloft so air can circulate through the sides.
- Slatted racks also aid ventilation by reducing congestion below the brood nest and providing more space for air movement.
- Feeders can be used with vented supers to reduce moisture build-up. Vented supers are just very shallow supers with holes drilled in each side. The holes are then screened from within.
 An Imirie shim is a rectangular frame the size of a Langstroth box and only ¾-inch high. By taking off one of the short sides, you have a u-shaped shim which can provide a full-size upper entrance.