Upstream vs. Downstream Grain Bin Heaters | Benny's School House
Benny's School House: Upstream vs. Downstream Grain Bin Heaters
Class is in session. Today's lesson: where the heater goes, and why it matters.
A heater can be the difference between getting grain dry and waiting on the weather. But "upstream" and "downstream" confuse a lot of people. Here's what they mean and how to pick one.
First, do you need a heater at all?
Natural-air drying works when the air has room to take moisture from your grain. Cool, damp fall weather doesn't give you that. A heater fixes it.
- Heat lowers humidity. Every 10°C (about 18°F) you add to the air going into the bin cuts its relative humidity roughly in half. [albertagrains.com]
- It turns a poor drying day into a good one. Heat can cut natural-air drying time from weeks to days, but it takes management. [albertagrains.com]
- Your fan still matters. AGI says supplemental heat is beneficial when your fan and equipment provide about 0.75 to 1 CFM per bushel. Research on canola found heat helped as long as airflow was at least 1 CFM per bushel. [aggrowth.com] [canolacouncil.org]
- It isn't for very wet grain. Researchers recommend a heated-air dryer when grain is more than 3 points above "dry." [topcropmanager.com]
Not sure whether your fan can support a heater? Our lesson on choosing a grain bin fan covers CFM per bushel and static pressure.
What "upstream" and "downstream" mean
The names tell you where the heater sits in relation to the fan.
- Upstream: The heater is mounted on the intake side, ahead of the fan. Air gets warmed before it enters the fan.
- Downstream: The heater sits between the fan and the bin. The fan pushes air through the heater and into the grain. [grainhandl...direct.com]
Side-by-side
| Upstream heater | Downstream heater | |
|---|---|---|
| Location | Ahead of the fan | Between the fan and the bin |
| Heat output | Low temperature rise. AGI's upstream heaters give about 5°C to 15°C (10°F to 30°F). [aggrowth.com] | AGI's low-temperature downstream heaters give about 18°F to 22°F on 60K and 100K BTU models, and about 45°F to 55°F on 200K BTU models. [grainhandl...direct.com] |
| Best for | A slight rise in temperature to help dry your crop. [aggrowth.com] | Kick-starting drying when conditions are tough. |
| Fan match | Centrifugal fans. AGI sizes its upstream heaters for 10 to 40 HP low-speed fans. [aggrowth.com] | Axial fans (Caldwell and Sukup options), and centrifugal fans (Sukup and AGI options). |
Why the difference? Upstream heaters are built for gentle, consistent heat. AGI says its low-temperature models deliver a steady amount of heat, which means less cycling and longer component life. Downstream models offer more range if you need a bigger boost, especially in the larger BTU sizes. [aggrowth.com]
How to choose
1. Start with your fan
The heater has to match the fan. Caldwell and Sukup axial heaters are made for axial fans. Centrifugal fans can take upstream or downstream heaters. Mix up the two and you get an airflow problem.
2. Decide how much heat you need
- A little heat (10°F to 30°F rise): A low-temperature upstream heater is a good fit for slightly damp conditions.
- More heat (up to 45°F to 55°F rise): A larger downstream heater makes sense when the weather is cold and damp.
More isn't automatically better. Too much heat can over-dry grain near the bottom. Researchers found over-drying at the bottom may not be avoidable, so they recommend targeting an average moisture and mixing the grain afterward. [canolacouncil.org]
3. Pick your fuel
Heaters run on vapor propane or natural gas. Gas supply matters:
- AGI's low-temperature downstream heaters need at least a 100 lb propane tank, or at least 4 psi for natural gas. [grainhandl...direct.com]
- Regulators come with the heater, but hoses and fittings may not. [grainhandl...direct.com]
4. Confirm compatibility before you order
This is the step people skip. Some manufacturers say specific fan designs can't take a heater at all. For example, GSI says its in-line and 3500 RPM centrifugal fans can't be used with heaters. Others, like AGI and Caldwell, make heaters or upgrades for their in-line fans. Compatibility depends on the brand and model, so always confirm your exact fan before you buy a heater. [grainsystems.com]
Running a heater well
- Match the fan, heater and bin size. AGI says it's important to closely match all three to get the right airflow and temperature for your grain. [aggrowth.com]
- Use heat when it helps. It's most useful when it's cool, damp and late in the fall. [topcropmanager.com]
- Monitor and mix the grain. Heat takes management, and turning the grain is part of it. [albertagrains.com]
- Follow the manufacturer's manual. Gas heaters need correct installation, clearances and safety checks.
Quick checklist
Gather these before you shop or call:
- Fan brand and model
- Fan type (axial, in-line, low-speed or high-speed centrifugal)
- Fan horsepower and diameter
- Bin size and grain depth
- Crop and starting moisture
- Fuel available (vapor propane or natural gas)
- How much heat you're aiming for
Still not sure? Ask Benny's friends at A&S.
Send us your fan model and bin details and we'll help match a heater to your setup. We carry heaters from AGI, Sukup and Caldwell for axial, in-line and centrifugal fans.