physics for beekeepers ventilation

Physics for beekeepers: How does ventilation increase honey production?

This question was redirected to me from another website. It is such an interesting topic that I decided to do an entire post on it.

The beekeeper who wrote was concerned that ventilation above the honey supers would cool the hive so much that the bees would not be able to dry (dehydrate) and cap the honey. This is a reasonable thought, but it is based on the mistaken belief that heat is responsible for drying the honey. In fact, it’s not heat that dries the honey, at least not directly. Honey is dried when air with a capacity to hold moisture flows over its surface.

Forget your hive for a moment and think about your clothes dryer. It has a barrel in the center that goes round and round so the clothes don’t lie in a heap. This exposes the clothes to as much air as possible. Your dryer has an air intake, a vent to the outside, a heater, and a fan. Air comes into the machine and is warmed by the heater. Warm air can hold more moisture than cool air, so the warm air absorbs some of the water from the clothes. The fan expels this moist air through the vent as new air comes in. In turn, this new air is warmed so it can hold more moisture, which allows additional evaporation from the clothes. This keeps happening until the clothes are dry.

If you were to block the air intake or the vent to the outside, the clothes would not get dry. They would get even hotter, but they would stay wet.

This may have happened to you. If your vent gets plugged with lint the first thing you probably notice is that your clothes take forever to dry. They go round and round, they get hot, but in the end they are still wet. In fact, the lint may get so hot it ignites. Vents plugged with lint are a common source of house fires.

Now, back to the hive. Instead of wet clothes you have wet honey. It doesn’t need to be rotated because the bees have hung it up to dry in neat rows much like parallel clothes lines. Each honey cell is exposed to the air. Instead of a heater you have heat from the sun (directly or indirectly) and heat from the bees, and instead of a fan you have thousands of bee wings. You have an air intake (front entrance) and, we hope, a vent to the outside, which may be an upper entrance, a vented inner cover, or just a loose-fitting, leaky hive.

Air around the honeycombs is damp just like air around the wet clothes. To dry it, the bees fan their wings and bring in outside air. This new air has a lower relative humidity than air inside the hive and, as it passes through the hive, it gets even warmer due do the many hard-working bees. As a result, this air has lots of capacity to absorb moisture from the honey, which it does. The air current from the bees’ wings expels this humid air to the outside.

With good ventilation through the hive, the bees can dry the honey quickly. Once the moisture level reaches about 18% the honey is capped and the job is done.

However, if the vent to the outside is plugged with something like a lid, the moist air cannot be expelled and the honey cannot get dry. No matter how hot it gets, no matter how hard the bees work, it just stays wet. Once the air around the honey absorbs the maximum amount of moisture, no more can evaporate, and the honey cannot be capped.

Just remember it is air with a capacity to hold moisture that dries things, not heat. The take-home message is that more summer ventilation means the bees can dry more honey faster. In the end, that’s what we all want.


P.S. Special thanks to my M.E. consultant for checking my logic.


  • Via TweetDeck: This post shows why @HoneyBeeSuite is at the top of my Bee Blog list: Physics for beekeepers

  • Without those top vent(s) you cannot get natural convection to remove that saturated air from the colony. Good Post Rusty.

  • I’m building two more top vents (ventilator rims) for my two nucs. They’re moving into a second brood box soon. Better ventilation should help them along.

  • I don’t know what works for anyone else, but I have found that a full top entrance, with a rabbited overhang, to break the wind, and a small (one or two inch wide) bottom entrance, does the trick for me. Since I started doing it this way, things started moving faster. With the small bottom entrance, the brood nest is better protected, while allowing good ventilation, especially for really big, robust hives. I winter them the same way, with no problems.

  • I built my new & improved ventilator rim today.

    Purty neat. I think it’ll work. Then someone also asked this question:

    “Do the bees ever fill this space [inside and above the rim] with wax comb during a heavy nectar flow?”

    What do you think? If there’s extra space between the inner cover and the top cover, would the bees start building comb in it? I would think no because the extra space isn’t actually inside the hive. But I assume bees do mysterious, inexplicable things sometimes.

    • Phillip,

      I used ventilation ekes similar to yours in four of my hives this summer. The bees didn’t build any comb inside them at all. But if they had, I would have just scraped it away. I can’t imagine it would be much of a problem.

      • You don’t have any photos of said hives, do you? (Do you have a central photo gallery?)

        I found some water under the inner covers of my hives during the last round of inspections. We’ve had cold and rain for the past week. I’m wondering if my design isn’t rain-proof enough.

        Maybe a bit of water under the inner cover isn’t a big issue. The hives seemed dry otherwise.

  • Hi Rusty,

    This is not where this question belongs but I had to put it somewhere and ask someone. I combined the queenless colony yesterday with one of my weaker nucs. I took one box from the queenless colony and placed a piece of newspaper between the nuc and the queenless brood box. When I went back this morning there were dead bees all over the entrance. You could see bees falling to the front curled up and dying. So it is apparent there is some fighting.

    The only thing I could do is spray the bees in the bottom nuc from the entrance with anise laced sugar syrup and smoke both boxes to suppress the pheromones.

    Is there anything else I can do?

    I watched some of the residual bees just march right into another colony yesterday with no issues.

    Help Please…..

    • Jeff,

      Hmm. I’ve never had the newspaper technique fail. Are you certain the queenless hive was really queenless? How long was it queenless? Since your swarm? My first guess is there is another queen in there.

      Is it possible you were seeing robbing? Sometimes when you stir up a hive, honey cells break open and robbing begins. Is that possible? If the bees later marched into another colony, I would put my bet on robbing.

      Spraying with anise oil will help with the introduction but could make things worse if robbing is the problem. Make sure the entrance is small so more robbers can’t get in. Check the dead bees for a queen, just to be sure there wasn’t an extra queen in there.

      Is it still going on?

  • I like the ventilator eke Phillip provided a link to. With my bees, I have had comb built above the inner cover which needed to be scraped away.

    I also believed I read somewhere (I’ll look to try and find the source) that the bees will set up a system where the air is forced in at once side of the entrance, and pulled out at the other end, creating an air current within the hive. Personally I like the ventilated top cover to help move the air through (I purchased my first one from Brushy Mountain) though I have had some issues with the girls putting propolis on the wire.

  • Nope not robbing. It’s only 11°C today. I was talking to a master beekeeper and he figured there was a virgin queen or not laying yet queen in the colony that I thought was queenless. That is what is causing all the strife.

    Beginners mistake and hard learning practice. Now I’ve gone from 6 colonies to maybe down to 4 if the queens like each other. This was a crappy lesson on my part.

  • Hi Rusty,

    I have 70 hives and have placed them at my farm in Mombasa. I was told heat is good for bees to make honey. Mombasa is a pretty humid place. At the moment i have 30 colonies and already 7 hives have supers on them.

    As I am still learning, could you please advise weather heat is good for bees or does it tire them cooling the hives?

    Best Regards.

    • Yunus,

      Many people believe that morning sun and afternoon shade is the best situation. The bees do spend a lot of energy trying to cool the hive, so I believe a little afternoon protection is a good thing.

  • Rusty I know this is an older thread but I had a question… I read the title of the article but I didn’t see in the body how the ventilation increased production. I see how it would have increased the speed at which the honey is cured, but does this lead to an actual increase in production? Are you extrapolating that since the bees cure the honey faster, more honey can be made in the same amount of time? Have you seen an actual increase in yield since providing more ventilation?

    I’m a firm believer in ventilation and see a definite benefit for overwintering… but I haven’t yet used it for summer honey production so I was curious. I’m going to try leaving my venting boards on over the summer this year and see if there is a difference in yield.

    • Matt,

      With good ventilation the honey can be dried very quickly and capped. If it doesn’t dry quickly, the bees keep working it, and fanning, but since the honey won’t dry a lot of bee labor is lost, and a lot of food needs to be eaten by the fanning bees, so not as much get stored. The bees are fanning the same section of comb for hours or days and can’t go on to new sections. Sometimes when you are extracting honey from a non-ventilated hive, you find frame after frame of uncapped honey, only about ten percent of which can be used without further drying. So yes, the production per hive is definitely less when the bees can’t get rid of the water.

  • Hi Rusty,

    I’ve been following your website for a while now and as a new beekeeper I am finding it extremely useful. (I imagine I’d still be finding it extremely useful if I was an experienced beekeeper!).

    An upper entrance has been an interest of mine for a while and I was wondering if you could make available the pictures of Doug’s hive, Or if Doug could?

    Many thanks,

    • David,

      Doug never replied with those photos, and that’s been about 6 years ago. I think you could do a long entrance with an Imirie shim by lengthening the entrance it comes with. Also, have you read about Tonybee’s hives? If not, catch them here: Access holes. In the meantime, I will ask around about the type of entrance Doug uses.

      • Rusty,

        Imirie shims and the entrances for Tonybee’s hives are following the same concept correct? They are very interesting, I certainly like the addition of a platform, and as another reader said, putting a slight upward angle on the holes would solve any rain issues, although it looks like Tony doesn’t have those issues.

        My initial interest towards an upper entrance was given when reading an article about internal hive temperatures in winter and how it would be logical to assume that once the cluster has started its journey higher into the hive its harder for the bees to brave the cold trip to a bottom entrance in order to relieve themselves.

        It looks like Tony shuts his additional brood entrances though…perhaps he has an upper entrance elsewhere?

        • David,

          Same idea. The imirie shim just sits between two boxes, while Tony drills through the boxes. I’ve done both. You are more apt to get brace comb in the imirie shim, but not much in winter.

          I too have written about the issue of bees traveling through the length of a cold hive vs using an upper entrance. There is always a lot of disagreement about upper entrances in winter. I’m of the opinion they are generally a good thing, as long as the size is commensurate with the size of the colony. I like moist air to be able to escape through the top, but I don’t want a huge hole that allows too much heat loss. It’s a balance, like lots of good things. In winter my bees use the upper entrance almost exclusively, and they use the lower one in summer. I never gave them instructions; they just do it that way.

          I don’t know if Tony uses an upper entrance in winter; I will ask him.

  • Thanks Rusty,

    Can’t tell you enough how much I appreciate your time and effort put into this website. The style of writing allowing me to hang onto every word while still making my own decisions on how I’ll proceed. Priceless!

    Just for clarity it was your article I was referring to
    Love the thermal imaging. Unsurprising that it was your article as about 90% of articles I read are on here…love the no-cook-candy-board by the way, I’m spreading the word!

    Please keep up the good work,
    All the best from the UK,

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