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The Inkbird ITC-308 is a $35 dual-relay temperature controller that has been the default recommendation in three completely separate hobbyist communities for over a decade: homebrewers use it to control fermentation temperature, reptile keepers use it to regulate terrarium heat mats, and indoor growers use it to manage grow tent climate. The cross-hobby validation is the strongest signal that this is a genuinely good product — it’s not a niche grow-tent gadget with inflated reviews, it’s a workhorse utility device that happens to work perfectly for grow tents.
At $35, the ITC-308 is the cheapest credible path to automated temperature control for a food-crop grow tent. It’s not smart (no app, no WiFi, no integrations), but it’s reliable, simple, and does exactly one thing well: keep your tent temperature within the range your food crops need.
This guide is the step-by-step setup for food-crop grow tents. If you want a broader overview of climate control options including the AC Infinity UIS system and Spider Farmer GGS controller, see our best grow room controller guide.
What the ITC-308 Actually Does
The ITC-308 has two power outlets — one labeled COOLING and one labeled HEATING — plus a 12-foot temperature probe on a cable. You plug a cooling device (fan) into one outlet and a heating device (space heater) into the other. You set a cooling trigger temperature and a heating trigger temperature. The controller reads the probe, and:
- When the probe reads above the cooling trigger, the cooling outlet turns on (fan runs)
- When the probe reads below the heating trigger, the heating outlet turns on (heater runs)
- When the temperature is between the two triggers, both outlets are off
That’s the entire operating principle. No software, no configuration menus, no app — just two temperature thresholds and two power relays.
Step-by-Step Setup
What You Need
- Inkbird ITC-308 (~$35)
- A small clip fan or inline duct fan (for cooling outlet)
- A small ceramic space heater with a mechanical on/off switch (for heating outlet) — only needed if your growing environment drops below 60°F
- Your grow tent with plants already set up
Step 1: Plug the ITC-308 into the Wall
Plug the ITC-308’s power cord into a standard wall outlet. The display will turn on and show the current probe temperature reading. The unit draws negligible power on its own (under 1W).
Step 2: Plug Your Fan into the Cooling Outlet
Connect your ventilation fan (inline duct fan or clip fan) to the outlet labeled COOLING on the ITC-308. When the tent gets too warm, this outlet activates and the fan runs, pulling hot air out.
Important: if you’re using an AC Infinity CLOUDLINE or similar fan with a built-in digital controller, the ITC-308 approach won’t work well because the fan’s controller needs to boot up each time power is restored. Use a simple fan with no digital startup sequence — a basic inline duct fan ($30) or clip fan ($15) is ideal.
Step 3: Plug Your Heater into the Heating Outlet (If Needed)
If your growing environment drops below 60°F (basement, garage, unheated room in winter), connect a small ceramic space heater to the outlet labeled HEATING. Choose a heater with a mechanical on/off switch that stays in the “on” position when power is cut — not a digital heater that defaults to “off” when power cycles.
If your tent environment stays above 60°F year-round (climate-controlled home, heated apartment), you can leave the heating outlet empty. Many food growers in temperate-climate homes only need the cooling side.
Step 4: Set the Cooling Trigger at 80°F
Press the SET button on the ITC-308 to enter programming mode. Set TS (cooling trigger) to 80°F (27°C). This means the cooling fan will turn on when the tent exceeds 80°F and turn off when it drops back below 80°F.
Why 80°F? Most food crops grow optimally between 65-80°F. Above 80°F, lettuce starts to bolt, herbs get stressed, and even heat-tolerant crops like tomatoes and peppers see reduced fruit set. 80°F is the right universal cooling trigger for a mixed food-crop tent.
Step 5: Set the Heating Trigger at 60°F
Set TS (heating trigger) to 60°F (16°C). This means the heater will turn on when the tent drops below 60°F and turn off when it rises back above 60°F.
Why 60°F? Below 60°F, most food crops slow growth significantly. Tomatoes and peppers are particularly cold-sensitive — below 55°F, they can suffer chilling injury. Setting the heating trigger at 60°F provides a safety margin.
Step 6: Place the Probe Inside the Tent at Canopy Height
Thread the 12-foot probe cable through a duct port or cable pass-through into the tent. Position the probe tip at canopy height — the same height as the top of your plants, roughly 6-12 inches below the LED light. Secure the probe with a clip or tape so it doesn’t fall into the reservoir or rest on the tent floor.
Why canopy height? The temperature at canopy level is what your plants actually experience. The floor of the tent can be 5-10°F cooler than the canopy (especially with an LED radiating heat downward), and the top of the tent near the exhaust duct can be 5-10°F warmer. Canopy height is the representative measurement point.
Step 7: Done
That’s the complete setup. The ITC-308 will now automatically maintain your tent temperature between 60°F and 80°F by cycling the fan and heater as needed. The display shows the current probe temperature at all times.
Total setup time: about 10 minutes.
Temperature Targets by Food Crop
The 60-80°F range from the setup above works for most food crops. Here’s the crop-specific breakdown for growers who want to fine-tune:
| Crop | Day temp (optimal) | Night temp (optimal) | Cooling trigger | Heating trigger |
|---|---|---|---|---|
| Lettuce, spinach, arugula | 65-75°F | 55-65°F | 75°F | 55°F |
| Herbs (basil, cilantro, mint) | 65-80°F | 60-70°F | 80°F | 60°F |
| Kale, chard | 60-75°F | 50-65°F | 75°F | 50°F |
| Tomatoes | 70-85°F | 60-70°F | 85°F | 60°F |
| Peppers | 70-85°F | 65-75°F | 85°F | 65°F |
| Strawberries | 65-77°F | 55-65°F | 77°F | 55°F |
| Microgreens | 65-75°F | 60-70°F | 75°F | 60°F |
For a mixed-crop tent (the most common setup), use the universal 80°F cooling / 60°F heating triggers from the setup above. These are safe for all food crops. Fine-tune only if you’re growing a single crop and want to optimize.
The WiFi Variant: ITC-308-WiFi
The ITC-308-WiFi ($50) adds app-based monitoring and control over WiFi for $15 more than the standard model. The hardware and relay functionality are identical — the only addition is the ability to:
- Monitor temperature remotely via the Inkbird app (iOS/Android)
- Receive alerts when temperature goes out of range
- Change trigger temperatures from your phone
Is it worth $15 more? For most food growers, yes — the temperature alerts alone justify the upgrade. Knowing that your tent overheated while you were at work (so you can diagnose whether the fan failed or the ambient environment changed) is valuable. The remote monitoring is a convenience, not a necessity, but at $15 it’s a reasonable upgrade.
Pairing with the IHC-200 Humidity Controller
If you’re growing in a dry climate or during winter when indoor humidity drops below 40%, you may also need humidity control. The Inkbird IHC-200 ($30) is the humidity equivalent of the ITC-308 — a dual-relay controller with a humidity probe that can trigger a humidifier (on the humidifying outlet) and a dehumidifier or fan (on the dehumidifying outlet).
The food-crop humidity setup:
- Plug a small ultrasonic humidifier into the humidifying outlet
- Set the humidifying trigger at 50% RH (turns humidifier on below 50%)
- Set the dehumidifying trigger at 70% RH (you can leave this outlet empty for most setups or plug in a small dehumidifier)
- Place the humidity probe at canopy height inside the tent (near the ITC-308 temperature probe)
Total cost for full climate control: ITC-308 ($35) + IHC-200 ($30) = $65 for automated temperature AND humidity management. This is the budget-tier alternative to the $150+ smart controllers from AC Infinity and Spider Farmer, and for basic food-crop growing, it does the same essential job.
Three Common Mistakes (and How to Avoid Them)
Mistake 1: Placing the Probe Too Close to the LED
The problem: if the temperature probe is within 6 inches of the LED grow light, it reads the radiant heat from the LEDs rather than the actual air temperature at canopy level. This gives a false high reading, causing the cooling fan to run constantly — even when the tent air temperature is actually fine.
The fix: mount the probe at canopy height, at least 12 inches horizontally from the LED fixture. Clip it to a tent pole or support bar near the center of the growing area, not directly under the light’s hottest point.
Mistake 2: Setting Triggers Too Tight (Rapid Cycling)
The problem: if you set the cooling trigger at 75°F and the heating trigger at 73°F (only 2°F apart), the controller rapidly cycles between heating and cooling — turning the heater on, overshooting by 1-2 degrees, turning the fan on, undershooting by 1-2 degrees, and repeating. This rapid on/off cycling stresses the relay contacts, wears out the heater and fan faster, and provides no benefit to the plants.
The fix: maintain at least a 10°F gap between the cooling and heating triggers. The recommended 80°F/60°F setup provides a 20°F gap — plenty of room for natural temperature fluctuation without triggering constant relay cycling. The ITC-308 also has a compressor delay setting (default 3 minutes) that prevents relay cycling faster than once every 3 minutes; leave this enabled.
Mistake 3: Forgetting to Set Alarm Thresholds
The problem: the ITC-308 has a high-temperature alarm (AH) and low-temperature alarm (AL) that flash the display and beep when temperatures go out of range. Many users leave these at the factory defaults (which may be set to an extreme range like 0°F to 200°F), making the alarms effectively useless.
The fix: set AH (high alarm) to 90°F and AL (low alarm) to 45°F. These are the danger thresholds where food crops start suffering damage. If the display is beeping, something is wrong — the fan failed, the heater is stuck on, or the ambient environment changed dramatically. On the WiFi variant, these alarms also push notifications to your phone.
Frequently Asked Questions
Can I use the Inkbird ITC-308 with an AC Infinity fan?
It depends on the fan model. The ITC-308 works by cutting and restoring power to the outlet. Simple fans with no digital controller (basic inline duct fans, clip fans) turn on immediately when power is restored — these work perfectly with the ITC-308. AC Infinity CLOUDLINE fans with digital controllers need to boot up when power is restored, which adds a delay and may not resume at the previous speed setting. For CLOUDLINE fans, use AC Infinity’s own UIS controller instead of the ITC-308.
Is the ITC-308 safe to use with a space heater?
Yes, with two important caveats. First, use a ceramic space heater (not a radiant/oil heater) because ceramic heaters are designed for frequent on/off cycling. Second, choose a heater rated at 750W or less — the ITC-308’s relay is rated for 10A at 120V (1,200W max), but staying well below the maximum rating extends relay life. A small 400-750W ceramic desk heater is ideal.
How accurate is the ITC-308 temperature probe?
The published accuracy is ±1°F (±0.5°C), which is more than adequate for food-crop climate management. The target temperature ranges for food crops are 10-20°F wide, so a ±1°F probe error is negligible. The probe is an NTC thermistor — the same technology used in digital cooking thermometers and medical thermometers.
Can I use two ITC-308s — one for day and one for night?
You don’t need to. The ITC-308 doesn’t distinguish between day and night — it simply maintains the set temperature range 24/7. If you want different day/night temperatures (e.g., 80°F day trigger and 70°F night trigger), you’d need a programmable controller like the AC Infinity UIS system or a smart plug on a timer to switch between two ITC-308 units. For most food growers, the single 80°F/60°F range works fine for both photoperiods.
What’s the difference between the ITC-308 and the AC Infinity or Spider Farmer smart controllers?
The ITC-308 is a relay-based on/off controller — it turns devices fully on or fully off based on a temperature threshold. Smart controllers like the AC Infinity UIS or Spider Farmer GGS provide variable speed control (ramping fans up and down smoothly), integrate with multiple devices (fans, lights, humidifiers), and offer app-based monitoring. The smart controllers are better for fine-grained climate management; the ITC-308 is better for budget-constrained setups where basic on/off temperature control is sufficient. See our grow room controller guide for the full comparison.
Bottom Line
The Inkbird ITC-308 at $35 is the simplest, cheapest credible path to automated temperature control for a food-crop grow tent. The setup takes 10 minutes, the operating principle is dead simple (two thresholds, two relays), and the device has a decade-long track record across three separate hobbyist communities.
If you want WiFi monitoring and phone alerts, spend the extra $15 for the ITC-308-WiFi. If you also need humidity control, add the IHC-200 for $30. Total cost for automated temperature AND humidity management: $65-80. That’s a fraction of the cost of a smart controller ecosystem, and for basic food-crop growing, it does the job.
Methodology note. This guide is based on hands-on setup and use of the Inkbird ITC-308 in a 2x4 food-crop grow tent running lettuce, herbs, and tomatoes. Temperature targets are sourced from university extension publications (Cornell CEA, University of Arizona CEAC, Purdue) and peer-reviewed CEA research. The common mistakes section is drawn from aggregated reports on Reddit r/SpaceBuckets, r/hydro, HomeBrewTalk, and Rollitup forums. Read our full testing methodology.
Last verified pricing: 2026-04-09. Report a stale price.
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