Catching Hot Spots Early: Temperature Monitoring for Canadian Grain Bins

A hot spot in a stored grain bin almost never announces itself. By the time you can smell something off from the manhole or feel warmth on the bin wall, the spoilage is already weeks underway and the bill is going to be ugly. The grain that started the season at a contract premium is now facing a range of outcomes, anything from grade discounts to outright rejection, depending on how far the spoilage has progressed.

This article is for Ontario and prairie farmers storing wheat, canola, corn, soybeans, oats, or barley through a Canadian winter and a long spring. It covers how hot spots actually form, why probing and a single temperature cable usually miss them, what continuous wireless monitoring looks like in practice, and what to do when an alert fires. The goal is simple: keep the grain you worked all year to put in the bin.

Hot spots are a well-understood problem in the sense that we know what causes them and what stops them. They keep happening anyway because the tools most operations rely on only sample a thin column of the bin, and only when someone remembers to climb up and check.

How a hot spot actually starts

A hot spot is a localized region inside the grain mass where temperature is rising faster than the surrounding grain. Once it gets going, it tends to accelerate. Most bins have more than one of the common starting points present at any given time.

Moisture migration. Grain put up at safe storage moisture is not uniformly dry. Through fall and winter, temperature differences between the warm centre of the bin and the cold wall drive air currents through the grain mass. Moisture moves with that air and tends to collect near the top, where it can support mould growth and respiration.

Insect and microbial respiration. Living things in the grain generate heat. Stored grain insects, mould colonies, and the grain itself all respire. In a small pocket of damp or damaged kernels, that respiration heat can build faster than the surrounding cold grain can absorb it, and biological activity speeds up as temperature rises.

Fines and dockage accumulation. When grain is loaded through a centre spout, fines, chaff, and broken kernels concentrate in a column down the middle of the bin. That core is denser, holds more moisture, and resists airflow during aeration. It is one of the most common places for a hot spot to develop, and one of the easiest to miss.

Uneven aeration. A bin that aerates well on paper can have dead zones in practice. A blocked floor, fines plugging an aeration channel, or just running the fan at the wrong time can leave large pockets of grain that never see proper cooling.

Wet patches from loading conditions. Grain combined under variable conditions, or grain that picked up moisture during harvest, can enter the bin with regions wetter than the rest. Once stored, those regions become the seed for spoilage.

Why manual probing and a single temperature cable are not enough

The traditional answer to hot spots is a hand probe and a stationary temperature cable down the centre of the bin. Both remain part of standard CGC-recommended practice, and both have a place. Neither, on its own, is enough.

Manual probing samples one column of grain at one moment. It catches problems already developed enough to show up where you happened to push the probe, and it leaves gaps between checks during which a problem can develop unnoticed. It also requires somebody to do it, on a schedule, year-round, including in February when the bin is cold and inconvenient. Most operations probe less often than they intend to, and by the time a problem is visible to a probe, it is no longer small.

Stationary temperature cables are better, but they share the same limit. A cable down the centre of the bin reads only the grain touching the sensor, so a hot spot that develops off axis, near a wall, or in a pocket of fines next to an aeration channel can grow unchecked while the cable reads normal. Cables are also typically read manually, which means a developing problem can run for days between readings.

The other issue is that both methods tell you the temperature now, not the trend. A bin reading 8°C is fine if it has been 8°C for a week. The same reading, if last week it was 4°C and the week before that it was 2°C, is the early stage of a hot spot. You cannot see that without continuous data.

What continuous wireless monitoring looks like

Modern wireless monitoring puts sensors inside the bin and a gateway somewhere on the yard, and lets the data flow on its own.

A typical setup uses one or more battery-powered sensors per bin, placed where hot spots are most likely to form. The sensors transmit a reading every few minutes over a long-range, low-power radio protocol like LoRaWAN. A single gateway, often mounted on a shop, picks up readings from most bins in a typical yard and pushes them to the cloud. Operators see the data on a phone or laptop, with charts, thresholds, and alerts.

A few things matter in practice:

• Coverage. A single gateway typically reaches most bins on a normal farm yard, depending on yard layout and gateway placement, even through metal walls.
• Battery life. Sensors generally run for several years on a single battery, so the system keeps working without becoming a maintenance burden.
• Thresholds and alerts. You set a temperature ceiling for each bin, and the system sends a text or email the moment a reading crosses it. Rate-of-change alerts catch hot spots in their early acceleration before they hit an absolute threshold.
• Trend visibility. The dashboard shows what each bin has been doing over the last day, week, and month. A bin creeping up by half a degree a week is easy to spot on a chart, and almost invisible to a hand probe.

For background on how the underlying wireless layer works, see LoRaWAN vs WiFi for Farm Monitoring.

Setting thresholds for a Canadian winter and spring

Targets depend on the crop, the moisture content at binning, and the time of year. Canadian Grain Commission guidance generally recommends keeping stored grain cool, uniform, and dry, typically below about 15°C, with cooling to that range as soon as practical after harvest. Many prairie storage recommendations aim closer to 5°C or lower for winter where conditions allow. Lower temperatures slow insect activity, slow microbial respiration, and slow moisture migration. The colder and drier the grain, the longer it stores safely.

A reasonable starting framework for thresholds looks like this:

Fall, post-harvest. Aerate to bring the bin below 15°C as quickly as conditions allow. Set an alert at a few degrees above your current bin average so you catch warming early, not late.

Winter storage. Aim for grain at or below 5°C where practical in most prairie and Ontario conditions, recognizing that the right target depends on crop (wheat, canola, corn, soybeans all differ), moisture content at binning, and how long the grain has to keep. Tighter targets matter most for wetter grain and longer storage. Set alerts so that any sensor reading more than 3 to 5°C above the bin average triggers a warning, even if the absolute temperature is still cool.

Spring transition. This is when hot spots most often appear, because outside air warms faster than the grain mass and the temperature differential drives moisture movement. Tighten alerts and check trend lines more often.

Set thresholds for the bin, not just the bin average. A single sensor that diverges from its neighbours is often the first sign of trouble, regardless of where the absolute reading sits.

What to do when an alert fires

An alert is information, not necessarily a crisis. The right sequence is usually the same.

Verify. Check the reading against other sensors in the same bin. A single sensor jumping while others stay flat can be a real hot spot or a sensor issue. Two or more sensors trending up together is a hot spot until proven otherwise.

Aerate. Run the aeration fan when outside conditions are cooler and drier than the grain. Avoid running the fan when ambient air would add moisture to the bin or warm the grain unnecessarily, since the wrong air can make the problem worse. Cool, dry air through a warm bin is the most common fix in the early stage. Trend lines on the dashboard tell you whether the aeration is actually pulling the temperature back down, or whether the hot spot is winning.

Inspect. Climb the bin, smell the headspace, probe near the alerting sensors. If you find caked grain, mould, or off odours, you are past the early stage and into the action stage.

Turn or move. If aeration is not enough, turn the bin or transfer the grain to break up the hot spot, expose it to air, and identify any spoiled material. This is unpleasant work, and it is much less unpleasant than discovering the same problem two months later.

The cost of missing one

The downside of a missed hot spot scales with how long it ran. Early stage: a small volume of off-grade grain and grade loss, discounts, rejection risk, or cleaning/drying charges depending on the buyer and condition. Middle stage: a downgraded load, a price cut, and a hard conversation with the buyer. Late stage: partial or total loss of the bin contents. Worst case, and it does happen, an undetected hot spot can ignite a bin fire.

Continuous monitoring does not eliminate the underlying causes. Moisture still migrates, insects still respire, fines still pile up under the spout. What it does is shorten the gap between when a problem starts and when somebody knows about it, from weeks to minutes. That gap is where almost all the cost lives.

If you are storing grain through this winter, walk your bins and ask one question for each: if a hot spot started in there tonight, when would I find out? If the honest answer is "next time I climb up," there is a better way.

Storage Sentry is a wireless monitoring platform purpose-built for Canadian agricultural operations. We help grain farmers track temperature across many bins in the yard with continuous wireless sensors, threshold alerts, and trend charts you can check from your phone. Learn how Storage Sentry can help.

References

1. Canadian Grain Commission. "Storing Grain on the Farm." grainscanada.gc.ca

2. Canadian Grain Commission. "Protect Stored Grain from Insects." grainscanada.gc.ca

3. Canadian Grain Commission. "Monitor Stored Grain." grainscanada.gc.ca

4. Government of Saskatchewan. "Grain Storage Management." saskatchewan.ca

5. Prairie Agricultural Machinery Institute. "Grain Storage and Drying." pami.ca