Thermometer · wireless alert · not a kit

High-tunnel temperature monitoring: min/max thermometers, wireless sensors and frost/heat alerts (sourced)

Growers search high tunnel thermometer, hoop house temperature monitor, and wireless greenhouse thermometer alarm after a sunny March morning or a frost night. This page is the sensor sibling — where to hang it, min/max vs wireless vs WiFi alerts, data loggers, radiation shields, and soil probes. Fan CFM, HAF layout, and wax openers stay on high-tunnel ventilation fans. Heaters, frost cloth, and CO alarms stay on how to heat a high tunnel. Curtain hardware stays on high-tunnel roll-up sides. Winter crop notes stay on high-tunnel winter lettuce. It is not a commercially manufactured high-tunnel kit and not a USDA payment schedule.

Extension quotes copied 18 October 2026, about 03:15 UTC from Purdue HO-297 / HO-330, Missouri M170, UVM Callahan, USU Black/Drost, Penn State High Tunnel Production, UMN Hoidal, and OSU-Wooster. Featured Amazon prices copied the same night. A missing featured price stays an em dash. Ratings are not copied. Seller accuracy, range, and battery lines stay labeled seller claims. EQIP language below is the structure-only wording already on what EQIP will not pay for. Thermometers and sensors are grower expense. No USDA payment dollar is invented here.

Kit index: commercially manufactured kits. Replacement-parts directory: high-tunnel replacement parts. Size map: high-tunnel sizes. Roll-up sides: sidewall vents. Fans: HAF / exhaust / thermostats. Heat: heaters / frost cloth. Shade: high-tunnel shade cloth. Tomatoes: high-tunnel tomatoes. Winter lettuce: high-tunnel winter lettuce. Affiliate method: about / disclosure. County inspection: EQIP checklist.

Why the number on the wall lies

A closed hoop heats fast in sun and dumps heat at the walls at night. A thermometer in the sun, or hung on the end wall, is not the crop.

For air temperature, readings at the crop or crop canopy level are of most interest. In the high tunnel, mount the sensor just above the crop canopy to prevent shading of the device by the crop (Fig 13).

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production.

Locations closer to side walls and end walls will be cooler, particularly at night, compared to more central locations in the tunnel due to heat loss from the walls.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production.

Air temperature sensors need to be protected from direct sunlight in order to get accurate readings. If exposed direct to solar radiation, readings will be higher, especially on sunny days, due to heating of the sensing device from radiation.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production. Purdue Fig. 13 shows white radiation shields, one sensor under row cover and one above.

Growers must monitor temperatures carefully by placing a minimum/maximum thermometer in the center of each high tunnel at the height of the tomato canopy. Shade the thermometer to avoid false high readings due to direct exposure to sunlight.

Source: Lewis W. Jett et al., University of Missouri Extension M170 — High Tunnel Tomato Production (New 3/04). Tomato crop notes stay on high-tunnel tomatoes.

The sensing probe of the thermostat should ideally be aspirated (air flowing over it), shielded from radiation gain (the increase in heat due to incident sunshine), and located to accurately measure the air temperature the plants are experiencing.

Source: Chris Callahan, UVM Extension Ag Engineering — Ventilation in Greenhouses and High Tunnels (14 August 2019). Central placement with HAF mixing: Chris Callahan, UVM Extension Ag Engineering — Thermostats for Agriculture (3 May 2016). Fan layout stays on high-tunnel ventilation fans.

In terms of location in a greenhouse, I suggest locating the probe centrally to control air temperature, horizontal air flow (HAF) fans will circulate and mix the air to “average” it out.

Source: Chris Callahan, UVM Extension Ag Engineering — Thermostats for Agriculture (3 May 2016).

Min/max, then wireless, then a log

Purdue splits the tools. A min/max display is the daily high and low. A wireless base in the house or barn is line-of-sight. WiFi or cellular can alarm a phone. A logger keeps the night you were not there.

One of the key management tools is to situate an accurate minimum-maximum thermometer in the house and use it to track daily low and high temperatures. Carefully following tunnel temperatures is essential to developing management strategies for maintaining optimum plant growth conditions.

Source: Brent Black and Dan Drost, Utah State University Extension — Temperature Management in High Tunnels (Horticulture/HighTunnels/2010-04, April 2010).

A max/min thermometer or temperature sensor displays and/or records the maximum and minimum temperatures between resets of the device. Tracking daily max and min temperatures give insight into daily temperature fluctuations and provides an estimate of average daily temperature.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production.

Some basic temperature sensor devices include a remote readout device that communicates wirelessly with the temperature sensor (or sensors). The communication range is often limited to a couple hundred feet, and further limited by line of sight obstacles between the sensor(s) and readout. However, this does allow the user to monitor high tunnel temperatures remotely, e.g., in the house or barn.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production. That “couple hundred feet” is Purdue’s class of device, not an Amazon SKU range.

Other sensors send information to the internet via WiFi or cellular connection, where it can be viewed from anywhere there is internet access, including through a smartphone. The information can be close to real time. Many systems allow the user to set alarms and notifications, e.g., when temperature crosses a specific max or min threshold.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production. Purdue does not print the alarm number. Do not invent one from a listing.

Logging units make it easy to get detailed information about the environment throughout the day and night. In some cases the information is recorded in the device itself, and must be transferred to a computer to see all the records. Other equipment automatically sends the data to a website where it is stored and can be accessed.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production. Four monitoring principles on that page: The four key principles for monitoring are: Use trustworthy sensors; Place sensors properly; Record information regularly and in a reliable manner; Review records periodically.

Environmental conditions are monitored and reported using an Onset Computer Corporation/LiCor Hobolink system. External and internal environmental conditions are updated every fifteen minutes and ventilation statuses are current – refreshed within seconds whenever the position of an endwall door or sidewall curtain is changed.

Source: Ohio State University Vegetable Production Systems Laboratory — Resource 1 (real-time conditions in eight Wooster high tunnels). Compare live Wooster houses on Ohio State University Vegetable Production Systems Laboratory — High/Mid Tunnel Systems (Wooster real-time conditions). That Hobolink stack is their research install, not a featured Amazon SKU.

Numbers only as the named page printed them

Vent, shade, frost, and tomato-flower figures come from different jobs. Do not mash them into one alarm.

It's important to be prepared to vent the tunnel to keep temperatures below 80°F.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production.

On the scheduling tool that accompanies this publication, the harvest range for single harvest crops (beets, carrots, radish/specialty turnip, head lettuce and scallions) provides an estimate of the length of time during which the crop can remain in the ground and still be marketable, assuming that row cover is used on nights below 25 degrees and high tunnels are vented so as to not allow temperatures above 80°F.

Source: Purdue Extension HO-330-W — High Tunnels: Scheduling Fall and Winter Vegetable Production (Maynard and Hilfinger). The 25°F night / 80°F vent pair is that scheduling tool’s assumption. Row-cover crop notes stay on high-tunnel winter lettuce and how to heat a high tunnel.

An example of an active system includes two end wall exhaust fans, two inlet louvers on the opposite end wall and a thermostat that opens the louvers and turns the fans on when the temperature is above 85 °F.

Source: Chris Callahan, UVM Extension Ag Engineering — Ventilation in Greenhouses and High Tunnels (14 August 2019). That 85°F is an exhaust-fan example. CFM stays on high-tunnel ventilation fans.

Typically it's recommended to hang your shade cloth when air temperatures in the tunnel consistently reach around 80-85°F, and leave it up until fall. Shade cloth can lower temperatures in a high tunnel by 6-9°F.

Source: Natalie Hoidal, University of Minnesota Extension — Prepare your high tunnel for a hot summer (8 April 2024). Shade-cloth hardware stays on high-tunnel shade cloth.

Monitor the weather carefully and be ready to provide supplemental heat if necessary to keep plants growing actively from the time they are planted. Most crops in high tunnels can be damaged if air temperatures drop below 45°F.

Source: Penn State Extension — High Tunnel Production. Heaters stay on how to heat a high tunnel.

The optimum temperature for growth of the tomato plant is 70–75 degrees F. Average daily temperatures should not be lower than 65 degrees. Temperatures below 55 degrees during flowering can reduce fruit set and produce misshapen fruit.

Source: Lewis W. Jett et al., University of Missouri Extension M170 — High Tunnel Tomato Production (New 3/04). Heat: Extremely high temperatures (above 90 degrees) can cause tomato flowers of some cultivars to abscise and will prevent the tomato from developing a uniform red color.

Without proper ventilation of both high and low tunnels, temperatures in a Northern Utah high tunnel have exceeded 120°F on a sunny day in early March.

Source: Brent Black and Dan Drost, Utah State University Extension — Temperature Management in High Tunnels (Horticulture/HighTunnels/2010-04, April 2010). That is one Northern Utah sunny March day with poor ventilation, not a national ceiling.

Check the air, then move the sides

The reading only helps if someone opens something. Curtain kits stay on the roll-up page; this page only copies the temperature sentences.

Internal temperatures should be checked several times a day and the roll-up sides adjusted accordingly to protect the crop.

Source: Penn State Extension — High Tunnel Production. Hardware: high-tunnel roll-up sides.

Opening the end doors or vents is the first step in ventilation and temperature regulation. If this does not sufficiently reduce the temperature then the side walls can also be opened (Figure 2).

Source: Brent Black and Dan Drost, Utah State University Extension — Temperature Management in High Tunnels (Horticulture/HighTunnels/2010-04, April 2010). USU: close doors in the late afternoon to retain heat overnight.

For early-tomato production, April is the most variable month for temperature within the high tunnel. Often, the vents are adjusted three or more times per day to maintain an optimum temperature.

Source: Lewis W. Jett et al., University of Missouri Extension M170 — High Tunnel Tomato Production (New 3/04).

Even small differences in the amount one endwall was open influenced internal temperatures.

Source: Matthew Kleinhenz, OSU VegNet News — Efficient and Effective Management of High Tunnel Environments, 1: The Need and Challenge (11 February 2023). On 11 February 2023 in Wooster those unheated gothic houses sat near 17–20°F at 7:35 a.m. and 69–92°F by 12:35 p.m. while outside ran 22.5–39.4°F — as printed on that table, for that day.

Soil temperature sensors are usually located in the rootzone of the crop. Pay attention to manufacturer recommendations for installing the sensors to get accurate readings. Sensors are placed at a specific depth in the soil, usually 2-4”.

Source: Purdue Extension HO-297-W — Managing the Environment in High Tunnels for Cool Season Vegetable Production. OSU: While some HT growers heat air in the HT, especially early in tomato production, fewer appear to monitor HT soil temperature, which also influences crop development and yield potential. Source: Matthew Kleinhenz, OSU VegNet News — Efficient and Effective Management of High Tunnel Environments, 1: The Need and Challenge (11 February 2023).

Sourced Amazon monitors

Titles and featured one-time prices were copied from live amazon.com product pages 18 October 2026, about 03:15 UTC. Kit frames stay on manufacturer product pages. These listings are not a Purdue canopy-height spec. Skipped tonight: B06XKH666P ThermoPro TP60S (HTTP 403); B07F93K8ZY REOTEMP 5-inch soil (HTTP 403); B07KYJYRSC Inkbird Bluetooth sensor (HTTP 403).

EQIP pays for the structure, not the thermometer

Min/max displays, wireless sensors, WiFi gateways, data loggers, radiation shields, and soil probes sit outside the High Tunnel System Initiative payment unless your county office writes them in. Confirm with your NRCS district conservationist. Tunnel Spec does not invent a dollar.

Under the High Tunnel System Initiative, financial assistance is provided only for the structure itself. Electricity, venting systems, lighting, etc. can be installed providing the additions meets manufacturer’s designs and specifications. However, the grower is responsible for those costs.

Source: USDA NRCS High Tunnel System Initiative FAQ (Updated November 2024; Oregon-branded).

Producers can install heating, ventilation, or electrical systems at their own expense.

Source: USDA NRCS Pennsylvania — Seasonal High Tunnel System for Crops. One state office page, not a national thermometer payment.

The practice does not include greenhouses or low tunnel systems.

Source: NRCS Conservation Practice Standard 325 High Tunnel System.

Rules vary; call your county NRCS office.

FAQ

Where should I hang a high-tunnel thermometer?

Purdue HO-297: air readings at crop or canopy height matter most; mount the sensor just above the canopy, in a more central location (side and end walls run cooler at night), and protect it from direct sun so the device itself does not heat. Missouri M170 (tomatoes): a minimum/maximum thermometer in the center of each tunnel at canopy height, shaded. UVM Callahan: a thermostat probe should be aspirated, shielded from radiation gain, and located where the plants actually sit; centrally if HAF fans mix the air. Outside air, if you log it, is Purdue’s 4 to 6 feet above ground unless you have a reason to put it elsewhere.

Do I need a min/max thermometer or a wireless / WiFi sensor?

USU and Missouri both start with a min/max thermometer to track daily high and low. Purdue: a max/min device records those extremes between resets; a wireless readout in the house or barn is typically a couple hundred feet and line-of-sight; WiFi or cellular units can send phone alarms when temperature crosses a max or min you set. This page does not invent that alarm number. A USB data logger stores a day-and-night record you download later (Purdue). OSU-Wooster logs inside and outside conditions every fifteen minutes on an Onset/LiCor Hobolink system — that is their research stack, not a shopping list.

What temperature should trigger venting or a frost alarm?

Only as a named page prints it, and only for that job. Purdue HO-297: be prepared to vent to keep temperatures below 80°F. HO-330: the winter scheduling tool assumes tunnels are vented so as not to allow temperatures above 80°F, with row cover on nights below 25°F. UMN Hoidal: hang shade cloth when air in the tunnel consistently reaches around 80–85°F. UVM 2019 example: a thermostat turns exhaust fans on above 85°F — that is an active-fan example, not a phone-alert default. Penn State: most crops in high tunnels can be damaged if air temperatures drop below 45°F; check internal temperatures several times a day and adjust roll-up sides. Missouri tomatoes: 70–75°F optimum, below 55°F at flowering hurts fruit set, above 90°F can drop flowers. USU: a closed Northern Utah tunnel exceeded 120°F on a sunny day in early March. Do not treat those as one alarm setpoint.

How does monitoring tie to roll-up sides, fans, and frost cloth?

Penn State: check internal temperatures several times a day and adjust roll-up sides. USU: open end doors or vents first; if that is not enough, open the side walls; close doors in late afternoon to hold night heat. Hardware for those curtains stays on the roll-up sides page. UVM fan CFM, HAF layout, and wax-cylinder vents stay on the ventilation-fans page. Inner row cover, heaters, and CO alarms stay on the heating page. Winter lettuce crop notes stay on the winter-lettuce page. This page is the sensor sibling.

Does EQIP pay for thermometers, sensors, or data loggers?

Tunnel Spec does not invent eligibility or dollars. The High Tunnel System Initiative FAQ says financial assistance is provided only for the structure itself; the grower is responsible for electricity, venting, lighting, and similar additions. The Pennsylvania seasonal high tunnel page says producers can install heating, ventilation, or electrical systems at their own expense. Thermometers, wireless sensors, WiFi gateways, data loggers, radiation shields, and soil probes sit with those grower costs unless your county office writes them in. Confirm with your NRCS district conservationist. See what EQIP will not pay for.

Rules vary; call your county NRCS office. Tunnel Spec does not determine eligibility, payment rates, or inspection outcomes. Confirm sensors and electrical add-ons with your NRCS district conservationist. As an Amazon Associate, we earn from qualifying purchases.