How to Manage Temperatures in a High Tunnel

Iowa State University Extension and Outreach Commercial Horticulture Specialist Joseph Hannan speaks on managing temperatures in a high tunnel.
Find more information about crop production: www.iowaproduce.org/
Contact Joseph Hannan: www.extension.iastate.edu/ag/p...
For more information about Iowa State University Extension and Outreach visit: www.extension.iastate.edu/

[@Mylife0792]

You can use electronic hear

[@paulandsarahuber961]

I was told by a University of Minnesota Extension agent that you risk affecting fruit production when using propane heaters that vent their exhaust right into the structure. Any thoughts on that?

[@uknowvideos]

“Greetings Paul and Sara Huber, Under frequent and long periods of use, all heaters should be vented up and away from the high tunnel to prevent the buildup of gases such as ethylene, carbon monoxide, and carbon dioxide that form from incomplete combustion. The primary problem for plants is ethylene which can impact fruit and shoot development. Ethylene problems are normally seen in poorly vented greenhouses or high tunnels when it has been cold and cloudy for several days in a row causing furnaces (even those that are externally vented) to run for long periods without adequate ventilation. When used for just a few hours a couple nights a year, portable unvented heaters cause little to no issues for plants. They are very commonly used for getting through a handful of cold mornings each year.”

[@paulandsarahuber961]

UKNOW How-to Videos wonderful! thank you!

[@tonydetori6101]

Hey Joseph, What do you think is the best way to heat a greenhouse if I don't have natural gas available? I have 10 tunnels, 2178 sqft each, growing leafy greens. I'm up in Canada where the temp dips to -5 F at times. Would appreciate your feedback!

[@uknowvideos]

Greetings Tony, My background and experience is really high tunnels and providing a night or two of freeze protection and not so much greenhouse production requiring permanent furnace installations. Natural gas, propane, used oil, and wood are all commonly used here in IA to heat greenhouses where we can get at times below 0 degrees. I am not a huge fan of electric furnaces but they would likely get the job done as well. The key with greenhouse heating is to get a system sized large enough to heat your building as well making sure the burn chamber is in good condition and fumes created during combustion are vented outside, up, and away from the building to ensure no residual ethylene gas enters the building. You also need to make sure you are bringing in some fresh air to the building. Actual sizing and design of the system is not in my realm of expertise.

[@geoffwaterman6560]

Running cost? Cant see that being cost effective?

[@ISUExtension]

Hello Geoff, The propane heaters are intended for short term, irregular use a couple of times each season when temperatures dip just below freezing during the early morning hours. They are not intended for long term use with temperatures well below freezing for many days and nights. In other words, they are not intended to serve as a primary heat source when the high tunnel is used as a greenhouse. About four tank+heater combos should be sufficient to hold temperatures above freezing for a few hours at approximately $100 to $125 per unit. A 30’ x 96’ high tunnel with single layer plastic will use about 43,000 BTU’s per hour which is about a half-gallon of propane per hour. Assuming $1.50 per gallon of propane and a 4 hour run time per night, the nightly operating cost is $6. Amortized cost of equipment over 10 years is $50. These heaters certainly have their place but they are not the solution to all heating needs. If you are using your tunnel as a greenhouse with double poly plastic and heating for many days and nights, then I absolutely agree a permanent furnace is a much better choice for many reasons.

[@makmak151515]

Very informative for boneheads like me. Luca