Table of contents
- Why our homes are similar to bee hives
- Bees and humans have similar needs
- How air circulates throughout a hive
- How much ventilation does a hive need?
- Too much heat is a bad thing
- 14 easy ways to increase hive ventilation
- Balance one problem against another when increasing hive ventilation
- Frequently asked questions
Increasing ventilation in bee hives is controversial, but it shouldn’t be. Like any other beekeeping tool, sometimes you need it and sometimes you don’t.
Some people swear by extra ventilation and others think it harms the bees by chilling them. Shockingly, people often say, “We don’t ventilate our own homes, so why should we do it to bees?”
That is sadly naive. In modern times, a house without adequate ventilation will not receive a certificate of occupancy. For residential homes, ASHRAE recommends adding 15 cubic feet of outdoor air per person per minute. And public buildings must replace the inside air at an incredible rate, so fast that it’s difficult for them to comply with energy conservation guidelines.
Why our homes are similar to bee hives
The air in a modern home is always on the move. For example, today we have exhaust fans galore. We eject exhaust air from the attic and showers and baths. We have exhaust fans built into fireplaces and above cooking ranges and clothes dryers. All the air that’s expelled must be immediately replaced by outside air to prevent back-drafting or pulling air from a moldy basement or garage.
Older structures didn’t have such a large air exchange problem because they leaked air around the windows, through the walls and windows, and along the baseboards. Even today, we have some leakage around every door and window, every electrical outlet, every light fixture, and every duct connection. Even so, today’s building materials and insulation are so good we also need to add outdoor air on purpose. And we do.
Although our homes mostly still have openable windows and multiple doors that aid ventilation, many skyscrapers have few openable windows and not many doors per person using the space. Instead, they have huge fans that pump fresh air into buildings night and day.
Bees and humans have similar needs
You might think a beehive doesn’t have fans, but it does. In fact, the entire colony behaves like a giant fan, circulating air throughout the hive, bringing in new air, and expelling old air.
The Environmental Protection Agency (EPA) says humans need fresh air to lower levels of indoor pollutants, odors, humidity, temperature, and disease organisms. The same goes for bee colonies. An adequately ventilated hive will have less moisture accumulation, fewer pollutants, fewer disease organisms, less humidity, and less mold. Unfortunately, it all comes with some heat loss.
But with an adequate supply of honey, healthy bees living in a clean hive can stay toasty warm regardless of moderate heat loss. To help the bees rid their home of harmful substances, beekeepers must provide ways for contaminated air to leave the hive and clean air to come in.
How air circulates throughout a hive
The air in a bee hive circulates naturally. Much of the air comes in through the hive entrance or through the screened bottom board if you have one. Some air also leaks through the cracks between boxes or joints in the wood.
Inside, the bees give off heat and moisture just as we do. The air surrounding the bees becomes warm from the bees’ bodies and respiration, then it rises to the top of the hive. This is no different from the warm air in your house that rises to the ceiling or the upper floors.
If you provide an opening to the outside near the top of the hive, this warm air will leave, carrying excess moisture and pollutants with it. As the stale air leaves, fresh air (make-up air) enters the hive at the bottom.
This circulation happens constantly, although the exchange rate will vary with the outside temperature, the number of bees, and factors like wind and humidity. When the bees are actively fanning their wings to dry the honey, the air moves even faster.
How much ventilation does a hive need?
Every colony is different, so the amount of ventilation you will need depends on the type of hive, climate, local conditions, hive population, and sun exposure. It can be hit or miss at first, but with experience, you will discover what is needed at your location.
Speaking generally, we need less ventilation in dry areas where excessive moisture buildup is not a problem. Desert areas and those with dry winds seldom have a problem with mold or wet bees, but in rainy areas, moisture and mold control can be a full-time job.
Too much heat is a bad thing
We tend to obsess about bees getting cold, but too much heat is just as bad. If a hive gets too hot, it can damage the developing brood, melt beeswax combs, and make workers lethargic.
And because warm air can hold so much moisture, the bees must work even harder to evaporate the water from the nectar. All that hard work generates even more heat, making everything more difficult. When we increase hive ventilation, we reduce the workload on the bees.
14 easy ways to increase hive ventilation
It is very easy to add ventilation to a bee hive. Following are some proven techniques that can be used singly or in combination, depending on how much airflow you want.
- Entrance reducer: During the height of bee season when massive numbers of bees are coming and going, you can either use the largest opening in your entrance reducer or remove it completely. This will increase hive ventilation and ease congestion.
- Screened bottom board: Screened bottom boards allow air to enter the hive from beneath the brood boxes.
- Varroa drawer: If you have a varroa drawer (a wooden, metal, or corrugated plastic tray below the screened bottom board) you can remove it until you are ready to do a mite count.
- Slatted racks can be placed between the bottom board and the lowest brood box. Slatted racks provide more airflow by relieving congestion near the hive opening. You can leave them on all year, either with or without a screened bottom board.
- Vivaldi board: A Vivaldi board allows for increased airflow and moisture control. It goes above the hive boxes.
- Ventilated gabled roof: These roofs have holes on the end much like our attics do.
- Upper entrances: You can drill holes in brood boxes and supers. Upper entrances relieve congestion at the entrance and increase airflow through the hive. If you don’t want your bees to use them as an entrance, you can screen them from the inside. In winter, you can close them with a simple wooden or plastic plug.
- Elevated hive stand: Keeping your hive on a stand instead of on the ground improves airflow.
- Imirie shims: An Imirie shim comes with an entrance notched into it. These shims go between any two bee boxes to provide an extra entrance and ventilation. If you don’t want the bees to use them for coming and going, you can easily screen the entrances.
- Screened inner cover: A simple screened inner cover is my favorite answer to summer ventilation. They also allow you to look down into your hive without the bees coming out for you.
- Ventilation eke: A ventilation eke is a shallow super with screened ventilation ports drilled into it. You can add as many holes as you like and place it above the hive boxes and below the lid.
- Follower boards: Follower boards give the bees a place to congregate inside the hive. They force the bees to use more vertical space for the brood nest, because they leave only eight usable frames in a ten-frame box. This tall and slender hive structure is more tree-shaped and provides a “chimney effect” that pulls the air up through the hive.
- Inner cover: If you use an inner cover, be sure to use the type with a hole in the center and a notch at one end. The hole in the top lets warm, moist air into the very top of the hive, and the notch allows it to escape to the outside.
- Shade: If you are in a warm climate, by all means, give your bees some shade, especially in the heat of the day. The temperature in the shade can be drastically cooler than in the sun, providing your bees with a better environment for fanning the stored nectar.
Balance one problem against another when increasing hive ventilation
When adding ventilation, keep in mind the downsides of anything you do. For example, openings that are large but not screened could encourage robbing by bees or wasps.
Also remember that if you live in an area with wind-driven rains, you may need to protect upper openings from rainwater.
Keep in mind that many of these ventilation solutions are most appropriate for hot weather. You may need to seal them up or remove them completely before the weather turns cold.
Frequently asked questions
How warm should a honey bee brood nest be?
The ideal temperature for brood rearing ranges from about 93 to 95 F (about 34 C). Stress, poor development, or death can occur at temperatures above or below the optimum.
Is carbon dioxide built-up important in a colony of bees?
No. Nearly all bees have a huge tolerance for high carbon dioxide levels, so it’s not something that beekeepers need to worry about. In fact, a new paper published in the Journal of Economic Entomology shows how researchers were able to lower varroa mite levels by overwintering bee colonies in high carbon dioxide environments.
Are cross-drafts a problem in beehives?
A draft that goes from one side of the hive to another is generally not a problem, especially in summer, and especially when the air crosses above the honey supers. This helps the bees dehydrate the honey. However, you don’t want a cross-draft traveling through the brood nest, so consider where the drafts will go before you add ventilation.
Honey Bee Suite
A very simple method that not only improves ventilation but allow the bees multiple entrances with height so they don’t have to come in at the bottom and work all the way up. Place each super 1/2” to 3/4” inch back above the super below. You will be amazed at how many bees come in at these different openings.
I’ve seen this done, but I always wonder if robbers or yellowjackets would take advantage of the openings in the back of the hive on the underside of the overhang. Have you had any trouble with that?
Have you read this free book by Ed Clark? https://archive.org/details/cu31924003100306 It isn’t very new, it was published in 1918. In my words, it shows that condensation is the answer not ventilation. But in any case, I would be interested in your opinion if you think he was wrong. Needless to say, I don’t support the ventilation argument whatsoever.
I have not read it, but I just now downloaded it. Thanks! I’ll let you know.
I am interested too Rusty. Thanks.
Great suggestion. This book is insightful. It gave me the confidence to run hives with no top vents. The bees handle it just fine. Almost all the hives in my bee yard have plexiglass inner covers. I’ve seen the bees collecting moisture off the cover at times, but most of the time the covers are clear.
With an insulated hive, during the winter the coldest spot near the top of the hive is along the rim of the inner cover. I suspect moisture condenses around the rim of the inner cover, and bees harvest water there, but I’ve never witnessed it. In any case, I think there is a lot of merit to the condensing hive idea.
During the flow this spring, I plan to test a hive or two with a vented box on top to compare to the sealed hives. Derek Mitchell contends that the bees utilize the higher temperatures in a non-ventilated hive to lower the relative humidity so that the bees can evaporate the moisture faster. In any case, I’m going to observe the bees and let them demonstrate which they “prefer”.
Surely, just adding more vents would do the job. As vents are screened, they don’t create extra entrances for pests.
Sounds good. Where do you recommend placing the vents?
I like to put pennies on the four corners between the inner cover and the hive top.
Good idea. The small space lets air in and out without attracting pests.
How would you suggest increasing ventilation in a top bar hive? You note that cross drafts could be problematic if the draft goes over the brood nest, but not sure how to avoid that in a top bar as the most likely location for vents would be on each end of the hive.
In a top-bar hive, you don’t have the same choices. I put my vents hole at the ends, just like in an attic. I realize that all top-bar hives are different, but in mine, the bars butt up next to each other. In Langstroths, there is space in between. The spaces will increase the airflow substantially. So, at least in my case, the end vents didn’t adversely affect my bees. My top-bar hive is always the most healthy and strong of any of my colonies.
Most of my inner covers are labeled “This side up” putting the notch on top. I’ve been thinking that if the notch were down, the fresh air would flow up from the entrance along the front of the hive and out, and the bees could fan into it or not as they chose. Notch up, air will flow up and out the center, which is going to go through the middle of the box whether the bees want that or not.
Also, I’ve seen YouTubers with the notch to the back of the hive and I can’t figure out why that choice, since it would make it hard to avoid a flight path. Opinions anyone?
I always worry about any openings in the back of a hive because they aren’t guarded as well as front openings. I worry that predators like wasps or robbers may take advantage of that.
In cold weather, I try to remember to “telescope” the outer cover to close off the notch, but for the rest of the time I slide it to leave the notches open. My colonies vary in how much they use the inner cover notch opening, but they generally like having an Imrie shim opening somewhere in the stack as well.
I had one colony that chewed their own slit opening along the side of their main brood box. I shielded it with a sloped board in the winter as it was on the windward side. Early in the spring they promptly chewed another opening further down the side. I take this as an indication that more ventilation is better. So I usually put the topmost opening facing the back to maximize the air current cross-flow (like ventilating my house – open windows in the front AND the back). No one has complained. Well, not any more than they complain anyway about having their house periodically dismantled and reassembled.
None of my inner covers have labels. When I first started, I bought a working hive from a club member. At one club meeting, I heard a detailed discussion of why you place the [shallow or deep] side up in the summer and switch it around in the winter. I’ve put the depth in brackets because I don’t remember what it was, and the logic didn’t make sense to me anyway. I checked during my next visit to the hive and discovered that the hand-made inner cover was the same depth on both sides. So I decided not to worry about it!
I have some inner covers with different depths and some that are equal so, like you, I just don’t worry about it.
And I also have bees that chew wood and add ventilation wherever they want it…amazing for insects without teeth.
On a tilted winter hive, excess warm humid air will run uphill and exit at the high point, the rear hole at the top. I find it loaded with ice crystals some mornings from the exit flow. I use a notch front and rear but it’s the rear that is the workhorse.
Currently, I have 9 hives set up like this and they all are thriving my Maine winter.
Thanks Ames. That at least sounds plausible, so now I won’t think it’s just Why would anyone do that!
Years ago, I tried increased ventilation. I used an inner cover with extra openings covered by 1/8″ mesh. The bees propolized it shut completely within two years.
There is another line of thought on this. Derek Mitchell has studied hives that are insulated and have no top vents for increased honey yields. See the following article and podcast.
Two years? You got off easy. I’ve seen them propolized in two weeks. I think that’s a good thing because we’ve given them an option. If you provide ventilation and they don’t want it, then they will close it down. Other colonies will leave them open. I like that because they make the final decision, not us.
As far as differing opinions, that’s good, too. If everyone agrees, no one is paying attention. I came to my opinion on ventilation by A/B testing my hives for many years. Ultimately, my well-ventilated hives produced about double what the unventilated ones did. Also, read this: Surplus secrets: access holes with platforms and this: The upstairs-downstairs intrance.
By way of background, I have mostly insulated 10-frame medium hives. They are in about 75% shade by May 1st.
If I have at least 4 strong hives this spring, I’ll do my own A/B test. There is no arguing with results! 🙂
Thanks for the reply.
That sounds awesome. Can’t wait to hear how it goes. Thanks!
Sorry to cause confusion with another “Chris,” but I will anyway. I’ve built a total of 91 full-size top bar hives over some years now and 27 nuc hives (but I’m still not even half of a Mangum). Typically I’ve put four 22mm holes in the end board, two for a nuc. They use cheap plastic nuc entrance discs on each hole to manage from open to vent only, or partly open/closed for smaller colonies to defend more easily. I have put the four holes in four corners of the trapezium end boards but have developed unease about that over the years. I live by the sea in a sub-tropical marine climate. I’ve found colonies will easily propolise vents they no longer want to vent in winter and they will re-open vents and remove propolis during the warmer season. I don’t live in a really hot climate, so it is easy to give advice!
My feeling is that in really hot climates it would be easier for the bees to manage with less ventilation because they are better able to control a closed space. If say the ambient temperature was 50C and the entire base was mesh it would be impossible for them to lower the temperature in the hive because the inflow of hot air would defeat them. However, inside a tree with a thick trunk, they can use evaporative cooling of water vapour to cool the hive down. Another example is driving along in your car in really hot summer temperatures. If you run your aircon you can keep the car cool. However, if you open all the windows, you can’t keep the car cool and the aircon can’t defeat the hot air coming into the car. Bees can’t use their aircon if you’ve opened all the windows! Have a think about opening all the windows next time you need to run the aircon.
Ventilated hives in Rusty’s climate might well be best there, but it is unlikely to apply to all places. I’ve been doing a drawing exercise on SolidWorks to create a model and drawings of my top bar hives. I’ve drawn up an entrance under the floor of the hive that so far I’ve never built. It’s centred on the brood nest with a tunnel along to end of hive that is easy to defend. With 36 top bars and no inner cover and open roof space, I think there will be natural ventilation out the top without any need to ever add a specific vent. I’ve seen the bees will propolise all the top bar gaps and/or as moisture affects the wood. If they want more ventilation I trust them to get what they need. In a Lang hive with both an inner cover and tight fitting lid, they are often/effectively denied permission to make those fine adjustments in ventilation, but they are allowed to run their aircon. In some cases they may be forced to run their aircon when ventilation would have used less resources and this is where Rusty’s result is most important I think.
Wow, they sound like interesting hives. I’d love to see some photos.
All your info Rusty, is completely opposite to what I read on this website. https://www.keepingbackyardbees.com/ventilation-its-complicated/
They say to leave it all alone-bees sort themselves out.
Now that’s not surprising. Susan and I are nearly always on opposite sides of the fence, not only in regards to ventilation but also on treatment-free beekeeping and skep beekeeping. But that’s okay because she has her reasons and she’s a passionate beekeeper. Like I said earlier, if everyone agrees, no one is paying attention.
So it’s back to trial and error?
A novel approach to ventilation is the “Bee Cool.” I’ve used them for 8 or 9 years now. Essentially it is a three-inch box that goes on top of the stack. It has a small computer fan mounted in it and can be powered by a plug-in transformer (for backyard use where electricity is available) or a solar panel for hives where electricity isn’t available.
It has a thermostat to turn on the fan above a certain temperature inside the hive. The fan draws air in through the entrance, up through the hive then through the fan and out vents in the device.
I believe it helps my bees as they don’t have to work so hard to ventilate thus more bees can do other work.
Check-out http://www.beecoolventilators.com for more info. BTW, I do not represent the product and I am not getting any compensation for mentioning this product.
The Average Joe Beekeeper
Parker, CO, USA
Thanks, Joe. Sounds like a “cool” idea!
I was surprised you did not mention a Warre’ type quilt box as one means of ventilation and moisture control.
I did consider it, but I think of a quilt box as more of a winter tool. Here I was trying to emphasize ventilation for honey drying, which is a summer thing. But you’re right. I should probably go back and add it to the list.
Good to PROVE that the ‘TEK’ vents I designed back in the 1980s are a winner for high honey production & still being used today.
I live in southeast Queensland, Australia, in small hive beetle territory.
Another reason for using ‘TEK’ vents is that there is a lot of light being accessed into the hive through the lids.
Small hive beetles do not like light, which chases the small hive beetles into my traps – reduces the number of beetles in my hives.
NOTE:- ‘TEK’ vents are near the full width of the lids. They also serve another purpose when viewing through the lid, you can tell if burr comb is being constructed on the tops of frames.
Nothing to do with this post. I imagine you have beekeepers reading and commenting on your posts from around the world. I am in South Australia. Can you please start a debate on how to keep wax moths out of beehives? DON’T SAY WAX MOTH ONLY ATTACKS/DESTROYS WEAK HIVES! Over the years we have tried reducing the entrance of the hives, keeping the baseboards clean, and checking the hives often.
I will work on your request. Sounds interesting.
As we have just been harvesting honey, I have been taking notice of our hive lids. Most have only a single vent in the lid. A few newer ones have 4 vents in the lid. Vents are 2.5 cm in diameter. With your post on increasing ventilation, I am wondering if all lids should have the 4 vents. Also, that book the guy mentioned. Yes, it is easy to find online, but it is over 100 pages! If it was possible to find a printed copy in a library, I would read it.
Not everyone wants or needs extra ventilation, so I think the manufacturers take the conservative approach. After all, extra holes are easy to make but harder to close.
You guys are one of my “Go to” sources for bee information. I have been the keeper of bees for about 10 years, and they are truly amazing creatures. In these past few years I have come to realize there is so much to learn, and your website sure makes it easier.
I just want to thank you for sharing your information.
I’m glad to hear it’s working for you. Thanks so much.