Hive Heaters

Hive heaters are devices in the form of plates, panels or foils that heat the inside or underside of a beehive electrically. Because a healthy colony with enough stores heats its own cluster, heating the hive in winter is unnecessary in most cases; it can even do harm by leading to early brood rearing, excessive honey consumption, condensation and fire risk. The real problem of a colony that seems to need heating is usually weakness, disease or poor wintering.

What is a hive heater and what types are there?

Hive heaters sold under various names fall into a few groups:

• Under-hive heating plate: A thermostat-controlled electric plate placed under or inside the floor.
• Between-frame heater panel: A frame-sized heating panel placed next to the brood area.
• Heating foil or cable: Thin heaters placed under the roof or wrapped around the body.
• Solar-powered systems: Kits that collect energy during the day and power the heater; their energy is limited at night, when it is needed most in winter.
• Varroa hyperthermia devices: Systems that target mites in sealed cells by heating the brood area briefly to slightly above 40 °C; their purpose is not to warm the colony.

Heated uncapping knives, decrystallising cabinets and wax melters are also referred to as "heaters", but these are equipment used on honey and wax, not on the hive, and are separate topics.

How do bees produce heat in winter?

In winter bees do not stay scattered; they form a tight winter cluster. The bees inside the cluster produce heat by shivering their flight muscles; the bees on the outside pack tightly together to form an insulating shell.

• The bees in the outer shell try not to fall below about 8–10 °C; in colder conditions they become immobile.
• When there is no brood, the centre of the cluster is kept cooler, which saves honey.
• At the end of winter, when brood rearing starts, the centre is raised again to about 34–35 °C, and consumption increases.

The key point is this: bees heat the cluster, not the hive. The empty corners of the hive can be nearly as cold as the outside air, and this is normal. A snow-covered hive may look alarming from the outside, but snow actually provides insulation against the wind.

Why is heating a hive usually unnecessary or harmful?

1. Early and excessive brood: A warmed colony may start brood rearing before the season. Brood forces the cluster to maintain a high temperature and consume more honey and pollen; stores can run out before spring.
2. Risk of starvation: While there is brood, the cluster cannot leave it to move towards the stores; when the honey next to it runs out, it can die without reaching honey even one frame away.
3. Disruption of the cluster: Local heating can cause the bees to spread out, and then small groups are left in the cold when the weather turns cold.
4. Condensation: The more the inside is heated while the walls and roof stay cold, the more water vapour condenses and drips. In winter, wetness is more dangerous for colonies than cold.
5. Losing the varroa window: The broodless winter period is the most effective time for contact varroa treatments. Heating can shorten or eliminate this period.
6. Fire and electrical risk: In the apiary, damp, rodent gnawing and flammable material turn cable, connection and thermostat faults into serious hazards.
7. Masking the problem: A colony that needs heating is usually weak, diseased or split too late. A heater does not solve this problem; it only hides it.

Situations where heating a hive may make sense

There are a few situations where heating is not entirely out of place, but in each of them the evidence is limited or the practice requires expertise:

• Research and experimental set-ups: Scientific studies requiring controlled temperatures.
• Varroa hyperthermia: The effectiveness of this method, which targets mites in sealed brood with heat, is disputed; the margin between the temperatures bees and mites can tolerate is narrow, and incorrect use harms the brood. It should not be relied on as varroa control on its own.
• Small nucleus colonies in very cold regions: Some beekeepers try low-power heating in very small mating boxes in early spring; there is not enough evidence to make it a general recommendation. Insulation and uniting colonies usually give the same result.

Brood incubators and queen rearing incubators, on the other hand, are not hive heaters; they are used only for queen cells or brood frames in a controlled, enclosed environment.

What should be done instead of using a heater?

Safety rules if you still use a heater

• A thermostat is essential: Do not use a heater that runs continuously; set a low upper limit. The aim is not to keep the hive "warm" but to soften the extreme effects of severe cold.
• Low power: Low-power heaters spread over a wide surface, which will not break up the cluster, are preferred.
• Temperature monitoring: Put a temperature sensor inside the hive; do not use a heater without seeing what it is actually doing.
• Electrical safety: Outdoor-rated, waterproof connections; residual current protection; cables protected against rodents.
• Fire: The heater must not touch flammable material, dry grass or wax debris.
• Short periods and records: The reason for use, its duration and the state of the colony should be recorded; results should be compared with unheated hives.

Common mistakes

• Trying to set the inside of the hive to a fixed value such as 20–25 °C: what the bees need is the temperature of the cluster, not of the hive.
• Using a heater to "rescue" a weak colony and putting off uniting and feeding.
• Closing the ventilation and heating; the result is a wet, mouldy hive.
• Assuming that a solar-powered heater also gives enough heat at night.
• Putting heaters without thermostats, made for non-apiary use, into hives.