As stewards of our bees, it's our responsibility to do no harm, and also study bee biology so we can assist the bees in any way we can. Each year, the approach of winter's cold leaves some beekeepers scrambling to offer the right kind of help. All fall and winter we may wonder, “Are they alive? Was there anything more I could have done?”
If your bees are preparing for a freezing cold winter, learning how heat, air, moisture, and bees interact during those months is critical. In an interview between Dr. David Peck and Bill Hesbach, some of this becomes clearer. Bill, an EAS Master Beekeeper and President of the Connecticut Beekeepers Association, has been an advocate of the concept of the Condensing Hive for many years. It doesn't involve fancy (and expensive) new gear, but simply a way to use our knowledge of heat transfer and physics to keep heat, moisture, and air just where the bees want them.
Check out the video here if you'd like to watch the hour-long discussion instead:
Please note that Betterbee deeply values Bill's insights into the movement of heat and moisture in a winter hive, but does not exclusively endorse the Condensing Hive concept as the only valid winter management philosophy.
The basic knowledge Bill starts with is not connected to bees, but the physics of airflow. The basics are that heat flows to cold, heat rises, and moisture in warm air forms liquid water on cooler surfaces (that's condensation).
Moisture is natural
The first step to grasping this whole Condensing Hive idea is to realize that bees normally create a lot of moisture in the hive, just by living. Their bodies give off moisture as part of the process of digesting their food and by breathing, much like we do. If you camp out in a truck bed with a cap on it on a cold night before a hike, the inside of the truck cap will be fogged and possibly running with moisture in the morning. That's condensation forming on the cold surface as warm moist air contacts it.
This also happens inside a hive with live bees. Rather than heating all the air and contents of the hive, they mainly just heat their own bodies and the region of frames within their ball-shaped cluster. By vibrating their flight muscles and eating honey, our bees can make it through a long cold winter. The center of the cluster may be 80-85°F in mid-winter and 95°F when brood is being raised, but the bees on the outer shell of the cluster might be more like 50°F. Some heat does inevitably rise up and out of the cluster though, to become a heat dome. The air in the heat dome is warmer and contains more moisture than other air in the hive. When the heat dome's air touches a cold surface, condensation forms on that surface.
If the surface that the warm moist air touches is the ceiling (usually the inner cover) over the bees, there's a chance the droplets condensing there will later drip back onto the bees. Or the moisture may freeze for a while and collect into an ice layer, and later melt and drip a lot! How can we help our bees avoid this cold rain inside their home?
Insulation, especially rooftop insulation
This well worn (and chewed) board of insulation sits between the inner and outer covers of a hive. In this hive, the upper entrance was left open through the winter. Was that the right or wrong move?
The next key to The Condensing Hive model is insulation, with top insulation being especially important. Most hives are milled lumber, with an R-value (insulation value) of 1 or less. Even polystyrene hives have just an R7 value above and at the sides. Bees in the wild live inside hollow trees, which may have 3-7 inch thick walls (insulating value of R3 to R7) and a whole tree's worth of wood above the colony's cavity (with an R-value we can't even guess ). The natural hive is insulated, particularly on its roof.
By using rigid foam insulation between your inner and outer covers, you can take the most basic step toward changing the cold surface above the cluster into a warmer surface. You can use more than one layer if you like. Or you could create your own box filled with fiberglass insulation, wool, or another insulating material. The most insulation we know of for a hive cover is the BeeSmart Duo with a value over R10, due to the thick inner cover insulation plus the airspace within the outer cover.
Condensation is fine - in the right places
Roof insulation keeps the top of the hive from becoming cold, which means that warm moist air rising above the cluster doesn't condense on their ceiling but instead forms a vapor plume that rolls outward and condenses on the cooler walls. Moisture on the inside walls or on frames away from the cluster is fine since bees cluster in the middle of the hive. It's also good because when they have slightly warmer days and can move around inside the hive, they lick up that dripping water and consume it. Bees need water! It helps them eat their honey and is needed when they start raising brood before spring. It may still be too cold for flights, but they can collect moisture indoors.
Bees during warm months always have water being brought into the hive from water forager bees. Some beekeepers see moisture on the inner cover, and the walls, or trickling out the front entrance of hives in winter and feel that something must be wrong. However, it's perfectly natural. The unnatural part of the picture is artificial hives, which lack the shape and insulation level of a hollow tree.
Wall insulation counts too
Rooftop insulation prevents dripping condensation above the cluster, but insulating wraps also help to contain heat.
We've discussed top insulation, but adding insulation to the hive walls is also common as winter prep. Folks with polystyrene hives never "remove" their insulation. Insulation can't hurt anything, and just brings hives a little closer to their natural home in thick-walled tree trunks. But whether you wrap a wooden hive with a Bee Cozy Winter Hive Wrap or a Vinyl Coated Wrap or something homemade, be sure to keep it on until spring nights warm up. Late winter/early spring with its huge fluctuations in temperature can be quite stressful on a colony at its lowest population size, raising early rounds of temperature-sensitive brood.
You may ask, "Would adding supplemental heat help?" Occasionally an inventive, well-meaning beek installs a small lightbulb below a hive. In the long run, this is not recommended. Consider, for example, observation hives. In these, the bees sometimes struggle during the winter, not because they can't keep warm, but because they stay constantly slightly active and eat all their honey before spring. Also, in southern states with not much blooming all winter, it's common to feed syrup for months because the bees are active. It's better to spend winter in a steady, quiet, dormant state eating less stores.
Ventilation: Going against the trend
The most controversial aspect of the Condensing Hive concept is its recommendation that the hive has no upper hole(s) where hive gasses can exit. Many beekeepers (including some Betterbee beekeepers!) use the notch in the inner cover as an upper air/bee exit or drill a half-inch hole in the front wall of an upper box. Other people use small wedges on the upper surface of the inner cover to raise the outer cover a tiny bit. Ventilation is often considered critical for overwintering bees, but it may not be all it's cracked up to be (say advocates of Condensing Hives).
When beekeepers check their hives in spring and discover that one of their colonies has died, they are often quick to blame moisture, since the bees and frames are wet and may be moldy. However, unless condensation is raining down on the cluster, bees and combs should remain dry and mold-free in a winter colony. It's only after the colony dies that moisture from decay soaks their bodies and mold is free to grow. It's easy to see why beekeepers started ventilating hives aggressively to keep their bees dry in winter. Strangely though, in recent years Professor Tom Seeley has written and spoken widely about his decades of research on bees in trees, and the fact that bees in nature don't have upper holes, just one low entrance.
The ideal Condensing Hive has none of this upper ventilation, and Bill Hesbach compares a hive's upper hole to a person leaving a 2nd story window open a bit all winter. When the outside temperature is colder, there would be a constant outward flow of warm air. Logically this means that as some heat (produced by the furnace with expensive fuel) is being lost, more fuel is needed to maintain the home at the desired temperature.
For the bees, their expensive fuel is the honey they created and stored away during summer. If a stream of warm air from the heat dome above the cluster is lost all winter, more honey must be eaten during those months to keep the colony at the same temperature. Will there be enough to make it to spring? If varroa mites and mite-related viruses are under control, the next biggest threat to overwintering bees is starvation, and anything to help bees conserve "heater fuel" will help them.
Winter bees like a stuffy house
With high ventilation, carbon dioxide is also flowing out of the hive. Normally, a high concentration of CO2 helps keep the colony in a dormant state. The Condensing Hive model suggests that the loss of CO2 keeps bees too active throughout the winter, with a higher metabolic rate compared to a hive without upper ventilation. This is a second way that ventilation can make the hive consume more energy (honey) than necessary.
Condensation recaptures energy
A third thing that flows out of that upper hole is energy, trapped inside the very moisture that some beekeepers are trying to get rid of. When water vapor floats away through the upper hole, both the water and the energy contained within it are lost. If that water vapor is kept inside the hive, and allowed to condense on the walls, latent heat would be released within the hive. This means that forcing condensation to take place inside the hive releases a great deal of heat energy back to support the colony, instead of venting it off to the environment.
Physics Alert: Latent Heat! If you don't remember latent heat from your high school physics class, we'll quickly summarize: When liquid water becomes a gas, the energy that broke the water molecules apart and let them become vapor is still contained in the water vapor. Consider a pot of water on a stove. The flame is adding heat to the pot, and it increases the temperature of the water until it hits the boiling point. After that, the water stays at the same boiling temperature, even though the flame is still pumping heat into the pot. That heat is no longer increasing the temperature of the pot of water. Instead, the flame's heat energy is being used to break some of the water molecules free as steam. The water vapor molecules float off, carrying that extra heat with them. What happens if that steam touches a cold surface and condenses? It's going to release all that latent heat as it shifts from gas to liquid again. This is the heat that is being conserved in a hive that doesn't vent that moist air out into the environment.
The take-home message from Betterbee
We have watched colonies survive the winter in uninsulated hives, and we have watched other colonies die in the same setup. We've watched bees live through the winter in an insulated hive, with or without an upper hole, and we've watched colonies die in such colonies too! Bees are amazing and resilient creatures, and none of these winter configurations are guaranteed to make or break your colonies. Exploring the topic of Condensing Hives is our way of getting you thinking about hive physics and bee biology. Your job is to use this information as you're getting your bees ready for winter. If you have a tried and true wintering strategy, we won't tell you to stop it. If you're disappointed in your track record at getting colonies through winter, see if some of these topics give you ideas of what to try this year. We strongly recommend some kind of rooftop insulation for hives in cold climates, but whether you decide to follow the rest of the Condensing Hive concept is up to you.
Hopefully, as we all become better beekeepers, our bees won't just survive but will thrive when the spring flowers return next year.
