Beehive insulation, condensation and ventilation

In winter and spring you will often hear beekeepers talk about beehive insulation, condensation and ventilation, and the different ways in which a hive can be set up to deal with the issue of dampness in the hive. While many novice beekeepers worry about the cold, more experienced beekeepers know that it is the dampness that can cause real damage to a colony of bees in the winter. But why is this and how can we deal with it?

Winter cluster

At the onset of winter, honeybees start to form their winter cluster. The cluster is ball shaped and formed with the frames and comb running through it. The uppermost part of the cluster is usually in contact with comb containing food. The bottom part of the cluster is packed into empty cells. The purpose of the cluster is to reduce heat loss and maintain a temperature at which the colony will survive.

The inner temperature of the cluster ranges from about 20 degrees Celsius if brood-less, to the mid-thirties if there is brood present. As the outside temperature drops down to the low teens, the cluster is fully formed. It will tighten further as temperatures drop and loosen as they rise. The bees in the cluster produce heat by eating and metabolizing honey. They also create heat as by shivering or vibrating their flight muscles.

The cluster is not static throughout the winter. It allows for bees to pass from the outer layer to the inner layers of the cluster and vice versa. As the winter progresses, some of the older bees will die, causing the bee-mass to diminish. Because of our very mild climate, there is often only a very short brood-less period around the winter solstice. Brood-rearing often starts again soon after that, sometimes as early as January.

Condensation inside the hive

Warm humid air will rise from the cluster. This is the source of condensation created in the hive. I’m not sure if you remember the lessons in convection currents form your schooldays. In case you don’t, here it is in beekeeping language:

In a closed box with a heat-source in the middle (cluster), the warm air will rise and spread along the top of the box. As the air cools, and more warm air pushes up, the cooler air will fall along the walls of the box creating circulation. If you add to the equation that the air is also humid, and if the ceiling or top of the box is able to conduct heat through the material (as in a thin plywood or Perspex crown-board), the now cooled moisture will stay on the underside and drip down onto the cluster or near it.

While the readings on the hygrometer in my weather-station is skyrocketing during the winter months, it is not the moisture in the ambient air that is most likely to do harm in the hive, but the dampness which is caused by condensation inside it. It is this form of condensation within the beehive that we want to avoid or at least find ways to deal with it.

Ways of dealing with condensation in the hive 

What approach you take to the issue of condensation will also determine how you go about setting up your hive for the winter and spring. I mentioned earlier about the convection current, and what can happen when heat is escaping through the crown board leaving excess moisture in the hive. There are a few different schools of thought on how to deal with the issue. They are largely three, and I will explain them below.

Top ventilation

Moisture is removed by top ventilation. This is done by inserting a matchstick in each corner under the crown board. This will create a small gap whereby the warmer air containing the excess moisture can escape. This method can be great for making bees go into cluster early and to maintain the cluster. This is because it creates a cooler hive environment. However, if using this method in the spring, it is important to ensure that you do not create too much of a draught by having bottom ventilation. Too much cool air will put increased pressure on the cluster to maintain heat once brood rearing has begun. Hence, the bees will consume more food and expand more energy in the brood rearing process. This is especially true for a small or weak colonies.

The bees are not always keen on top ventilation, especially if it is provided too early (in autumn). They will seal any gaps with propolis as you can see from the images below. The vents have been sealed or nearly sealed with propolis in the autumn.

Circular airflow and top beehive insulation

Moisture is removed by facilitating a circular airflow. This is done by insulating the top of the beehive. The top insulation ensures that the heat is not lost through the crown board. Instead the air with the moisture will fall or be pushed down the sides as new air rises from the cluster below. Once the now cool, damp air reaches the floor, it will be replaced by fresh air either from the entrance or increased bottom ventilation. As there will be moist air falling down the sides, some beekeepers insist on removing one or two of the outer frames. This creates more space for the air to circulate. It is therefore less likely that those frames would be susceptible to forming mould on the pollen in them.

Absorption

Moisture is removed by absorption. This method is not widely used in Ireland, but it is the way that most mimic how condensation is dealt with in wild honeybee colonies. In wild colonies living in hollow trees, rough wood absorb and wick away by capillary action any excess moisture. How it is translated into our beekeeping practices is by adding material that will absorb moisture above the crown board. These materials include wood shavings, natural fibres and fabric. This is usually done by having a crownboard with holes. On top of that place an empty super with the absorbing material. The easiest is to stuff it into pillowcases, hessian bags or similar, so that they can be removed or replaced easily.

Cheap and effective beehive insulation

If opting for the setup with circular airflow and top beehive insulation as described above, you might want to try foil bubble wrap insulation. This type of insulation is usually used to insulate behind radiators etc. It is also a very effective, slim and cheap alternative to bulky and costly Styrofoam or polystyrene. They are available from the builder’s providers and hardware stores in a range of different sizes and can easily be cut to size with a normal kitchen scissors.

Read more about spring preparations and first inspection here: https://hannasbees.ie/spring-preparations-and-first-inspection/