Ventilation

[Vance G]

I have exorted against the screened bottom board movement and recently read someone lovingly describing their power ventilation system for their backyard hives. It is really amazing how much abuse bees can take and still manage to survive. For most of them, like you, honey seems to be a nuisance that they should not expect to gather. They are just keeping bees for the nobility anyway. I may not make any money at it but it is not for lack of trying.

[Allen Dick]

I have exorted against the screened bottom board movement and recently read someone lovingly describing their power ventilation system for their backyard hives.

I am not entirely against screened bottoms, especially on doubles where the bees can be up and away from the drafts, seeing as the screens are below the brood and do not force air up through the colony. In winter, though bottom screens can result in the hive filling with drifting snow and that cannot be a good thing.

As for forced ventilation, bees are perfectly capable of moving a lot of air quite efficiently through fairly small holes and do not need any 'help'.

In extremely hot weather -- especially over the 95 degree brood temperature, that hot draft may actually counteract the evaporative cooling the bees accomplish by hauling water and kill the brood with hot dry air if the bees cannot block it. Brood can survive some considerable cooling, but very very little overheating.

[karen]

Which is best ventilation from the top or bottom? Some people use screen bottom boards and some people put on a vented inner covers or just lift the telescoping cover with a stick. Me? I do nothing, solid bottom boards and some boxes with auger holes which are totally inconsistent, it depends on where the box ends up. In the summer I pull the entrance reducer out at an angle leaving one corner under the hive so it can slip back in easily.

Right now it is 63 F, raining and not going above 70 today. We have had very few days in the high 80"s. It has been a comfortable summer so far. Many beekeepers with new hives over ventilate and slow the bees when drawing out frames. Last summer every night was in the 50's and a lot of beekeepers did not get all their frames drawn, especially the bottom box when sitting on a open screen bottom board.

[Allen Dick]

Which is best ventilation from the top or bottom?

I don't think it matters.

What matters is whether a colony can control the airflow or not, especially when the ambient is dropping to clustering temperature.

Beekeeping is a compromise. At some times the hive has to dump heat and at other times conserve it.

With a single entrance at the bottom, warm, moist air naturally rises and is trapped in the upper boxes. That is a good thing until either the temperature reaches 95 F (brood temperature) or humidity exceeds approximately 75% (ideal humidity), at which point ventilation is required. In temperate regions, most of the time (95% of the year?), little or no ventilation is required.

With a single top entrance, there is little natural air circulation and the cavity is a dead air space -- natural insulation -- and the cluster heat is conserved in the cavity also.

With top and bottom entrances, especially on opposite sides of the cavity there is a natural convection air current which can be greatly increased by wind outside blowing through and heat and humidity is lost constantly. Sometimes such venting may be desirable, but at many times of year, especially springtime, it is harmful.

Bees are very good at directing air through the hive and detecting if the temperature and moisture in specific critical brood areas are acceptable or not. It only take a few bees to move a lot of air and they do so as long as the temperature is sufficient for them to function without retreating to the cluster.

Honey bees naturally choose cavities with little natural draft and fairly small entrances for good reason.
When ventilation is required, they are able to move air quite well.

They can block airflow, too, except when the temperature drops well below cluster temperature at which point, they tend to retreat to a cluster and no longer control the cavity temperature to the same extent.
Even then, though we often see bees outside the cluster. Individual bees can generate body heat, as long as they have fuel and we often see bees out and about well below clustering temperature.

So, bees naturally choose cavities with limited natural airflow and limited openings, and I think we can all see why, and the problems that excess and especially forced ventilation can cause and how disruptive it can be to colony functioning and probably, at times, to bee health.