Sanford, Scott. 2006. Greenhouse Unit Heaters: Types, Placement, and Efficiency. University of Wisconsin Extension. Accessed at: <http://learningstore.uwex.edu/Greenhouse-Unit-Heaters-Types-Placement-and-Efficiency-P135.aspx>
Greenhouse Unit Heaters: Types, Placement, and Efficiency was published in 2006 by the University of Wisconsin Extension and was written by Scott Sanford, the Senior Outreach Specialist for the Rural Energy Program. Supplemental heating is often needed for overcast days and nights when growing in a greenhouse. This publication discusses differences between unvented, gravity-vented, power-vented, separated combustion, and high efficiency unit heaters along with how heated air distribution can affect energy usage.