Ventilation or Insulation

I don’t think it is possible to be a bee keeper for more than a month without hearing a lecture from another bee keeper about the importance of insulation OR ventilation, depending on the time of year it could quite possibly be the same bee keeper.

Insulation I get. I can console myself with the concept that the better the insulation the less work bees have to do in order to maintain an optimal temperature in their hive. Remember, bees are not warm-blooded animals, if they do not actively generate heat, there is no heat. Yet they maintain a temperature very similar to that of a warm-blooded animal (within the brood nest).

The ventilation bit I have a little more trouble with. The hollow cavities of trees are not well known for being “airy”. Also from my own experience in using bait hives the bees will not choose a bait hive that has multiple or large entrances. I am willing to accept that perhaps as the intelligent humans who can use calculators and spreadsheets we may have done the work to prove that despite what the bees think ventilation is better for them. Perhaps someone has worked it out, ventilation is what bees need. Humans know best! After all we do have digital watches.

Much of what I will now talk about is to a greater or lesser extent from Ed Clark’s book Constructive Beekeeping (available for free online from Cornell Uni Press). I am afraid this may turn into another lecture *sigh* sorry folks.

“Commercial beekeeping has for its object the production of the maximum quantity of honey at a minimum cost. Swarming adds greatly to the costs of producing honey. Most methods of swarm-prevention have in them the element of destructiveness. Ventilating, removing the queen, shaking the bees, removing the brood, exchanging brood-bodies, loosening the cover, all destroying something that the bees have done, or adding to the work to be done in the hive.” “Instead of going into the hive and telling the bees (by manipulations) ‘don’t do this’; say to them ‘keep all your brood, keep your queen, keep the cold damp air out of the hive and I will make your hive so perfect a condenser of water vapour that the work of evaporating water from nectar will be done quickly’. We will bring team-work into play, and each get the benefit of every advantage gained.” – This is a word for word transcription from the introduction on “Constructive Beekeeping” by Ed Clark originally published in 1918 and available online in full for free. The work wasn’t paid an awful lot of attention to when it was published. I enjoy the book because it doesn’t just communicate passed on lessons. It takes first principles of physics and applies them in a practical way. It is also filled with wonderful jewels displaying that his knowledge is as hard won as our own such as “Familiarity with bees makes a person wonder where the mule got his reputation for stubbornness.”

We know full well that our bees do not like ventilation. They tell us so with the way that coat the inside of their hives with propolis and close up even the smallest of holes. Propolis can be troublesome for beekeepers using framed hives but isn’t really an issue for kTBHs but it forms an important part of the bees control of the hive atmosphere. Ed Clarke uses the “urge” of swarming as an indicator of the bees contentedness with the hive environment provided, and use “room” as the primary cause of this “urge”. When we think of room in a hive we think of physical space, adding another super, adding in top bars. Space in its own right though is of little use to the bee. The bee is interested in usable comb. I say usable comb because at the time when bees have a tendency to swarm their brood is abundant, there is pollen and honey stored above it as food, and then a nectar flow starts. At this point foundation is no good to the bees, and neither is an empty bar. Nectar is 80% water and before it can’t be stored as honey it needs to be ripened. This means four times as many empty cells are required in which to keep the nectar before it is made into honey. Sticking with the idea of “room” being the primary cause of the “urge” ventilation does (in some cases) fit the bill because it generates room. The room is generated though at the expense of warmth and hive atmosphere which not only serves to increase the chance of brood chilling but reduce the opportunity for evaporation. Aha yes… we haven’t spoken about evaporation yet have we! The obvious by-product of turning nectar (~80% water) in to honey (<20% water) is all that extra water. If we use the example of just one pound of water being expelled over night (in order to ripen the honey) we know at a standard hive temperature this would saturate the air or more the 600 hive bodies.

So then “If”…..
a)            The air entering the hive was absolutely dry at 0% humidity.
b)            The air leaving the hive is 100% saturated.
c)            The bees were able to replace the entire hive volume in one minute.
Then this amount of water would take around 10hrs to pass out of the hive.

But when is the air ever absolutely dry. As you can see from the chart below in London the humidity doesn’t drop below 60% on average (in Yorkshire today it is ~90%).


Equally the air leaving the hive is not at 100%, and of course the bees could not hope to exchange a full hive body worth of air through a small opening in the front in one minute. Despite this beekeeper holds on to the idea that fanning is how bees are able to evaporate nectar into honey. In Yorkshire it is 90% humidity and about 8oC (~45 F for US readers). This is almost exactly the environment Ed Clarke worked with in Minnesota and he did “The Math”… “To remove from a hive one grain of water vapour by fanning on May 13 (93%, 8oC/45.5 F ), the volume of air that would have to be moved would be five to six times the air capacity of the hive. To remove one pound of water would require the removal of a volume of air equal to the capacity of from 30,000 to 40,000 hive-bodies.” On evening where there is close to 100% humidity no water vapour could be removed by air exchange. It is certainly beginning to sound unlikely.

When start to talk about the hive as a condenser then some of this begins to make sense. To understand how the hive works as a condenser an understanding of the dew point is useful. Air that is saturated with water is said to be at its dew point. As the temperature decreases the relative humidity increases when this reaches 100% the dew point is met. Essentially put the warmer the air is the more water it can hold. If you then cool that air the absolute amount of water remains the same but the relative humidity increases. Once the relative humidity reaches 100% and the dew point is met water will readily condense from the air. When bees are allowed to control their own affairs they will arrange the hives as a condenser where the temperature difference between the outside temperature and the inside temperature will cause water to condense on the inside hive walls. The reason we don’t see this is bees being animals need a readily available supply of water and this is a excellent source within the hive. This idea is supported by the records of hive weights morning and evening during a nectar flow. If honey produced through moving the water out of the hive the hive weight would change dramatically, but the reality is there is very little variation.

It is important to remember that condensation WILL happen in your hives and it MUST happen on the coldest surface. During winter this surface will often be the surface least insulated. As such if you insulate your hives walls more than your hive roof you risk dripping water into the cluster. This will have a catastrophic effect on the bees.

By propolising the inner surfaces of the hive the bees are further increasing its efficiency as a condenser. Varnished surfaces (or smooth surfaces) readily allow the condensing of liquids. By making the surface a better “receiver” of condensation the bees therefore lower the hive humidity and allow more honey to be evaporated. On condensing the water is forced to release its latent heat back into the hive thus supporting the whole process further. The convection will circulate the released heat into the centre of the hive body and help heat the brood and evaporate the honey.

I fear if I write any more I will lose even the hard-core followers who have only got this far by pinching their thighs in order to stay awake. I am really interested though of what other people think about this one so please comment and discuss.

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5 Responses to Ventilation or Insulation

  1. Julie says:

    If you’re preaching, then your choir is calling, “Amen!”

    What an interesting post!

    I think I read Clark’s work the first year I started beekeeping, but it didn’t mean much to me at the time because I hadn’t a chance to really think it through based on my own practical experience. I’ll have to reread it now, but I’ve come to very similar conclusions, I think, about ventilation and insulation. I apologize for glossing over the math you provided — math is not even close to being my forte. (I can say this with total assurance as I struggle with helping my son solve for x & y using substitution in between typing sections of this response). However, I know what I see in my own hives, and hope that logic & deduction will be a suitable shortcut for number crunching.

    My conclusion is that most hives are not insulated well enough/properly, which makes ventilation a necessity during both summer and fall. However, if a hive is well/properly insulated, ventilation — even with a very small entrance — becomes a non-issue.

    As you point out, to be properly insulated, a hive needs much more insulation over the brood than to the sides of it. To be well-insulated, I think that we need to look for insulation that approaches what a tree trunk would provide, since that is the bees’ natural habitat. Flimsy 3/4″ walls (~R1.5), just don’t cut it.

    I have noticed that my fully insulated hive (R9 along walls, R13.5+ over the brood), never heats up during the dog days of summer when my hives with 1″ (really 3/4″ thick) walls are overheating. Although some bees may fan the insulated hive, there is never a huge beard. Moisture has never been a summertime concern. Neither is condensation a problem during winter since moisture condenses on the coldest surfaces first, which happen to be the uninsulated floor & ends, and then possibly the walls. In the winter, I leave three 3/4″ round entrances open, but they propolize them until they are nearly closed. Even with such tiny openings — about 2 bees’ width each — condensation is not a problem.

    You made an interesting point about condensed water releasing latent heat back into the hive. Never thought about it, but that’s kind of cool.

    • deweysanchez says:

      Thanks Julie. I think the math helps when speaking with people who have different experiences. Ventilating hives hives does stop bearding, adding a super can stop swarming etc. An awful lot in beekeeping is dogma which becomes “truth” through the frequency of telling. I think it is important we question these practices. I love your super-insulated hives btw. I just have to design one of my own now, how to approach the roof is the tricky bit.

  2. Erik says:

    Ditto to Julie’s comments – interesting topic. I wonder if the bees might also gather and remove water from the hive physically. If they are forcing condensation, this would be another economical way to quickly remove water from the hive, rather than trying to evaporate it out.

    • deweysanchez says:

      I suppose. Though drinking it prior to going foraging may have the same effect. Animals lose a lot of water just breathing. Humans have an “insensible” loss of half a litre every day just breathing. I know bees are smaller but what they lack in size they make up for in number and work rate.

  3. Emily Scott says:

    My hives have ventilation in the form of open mesh floors – useful to help with varroa control and also to stop debris accumulating on the floors and attracting wax moths. I like to have insulation in the top of the hive.

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