Ambient temperatures in a greenhouse are less a focus than they are in growing indoors. When growing under lights it is very important to maintain certain ambient temperatures so as to not allow the plant to go into transpiration or shock. When considering greenhouse heating we are more concerned about root temperatures and the temperature on the surface of the leaf. In the summer time these temps are controlled with proper passive cooling and the right coverings that block out harmful UVB and diffuse the light. In the winter time we at Forever Flowering focus first on bottom heat. With a radiant heating system the plant is heated from the bottom up. The root zone is considered to be the most important part of the plant to keep warm when temperatures drop. Root zone heat will allow the roots to stay in the low 70’s even when it’s snowing outside. Root heat will passively rise up through the canopy keeping the most important part of the greenhouse, your plants, at acceptable growing temperatures even in the dead of winter. We recommend an above canopy forced air heating system to be used in conjunction with the radiant heating system. The above canopy heat will assist in keeping the condensation down, lower the humidity and make for an overall nicer work environment.In areas with snow we recommend using heating ‘tubes’ that run across the gutter when connecting a range of structures so that snow will not accumulate in the ‘valleys’ of the greenhouse. The blackout system serves three purposes and can greatly assist your wintertime grows. These purposes are to keep light out, to control photoperiod, to hold light in, when supplementing light, and as a heat retention blanket, during the cold months, that is used during the night time to keep the heat from escaping the immediate growing area.
When used in conjunction with exhaust fans and HAF circulation fans the heat can be readily controlled to suit your growing condition requirements. Overhead heat when used by itself is very inefficient in a greenhouse. When fired up the heat will rise and try to escape as quick as it can. Greenhouses typically do not have a lot of R-value insulation covering the structure so this heat is easily dissipated into the environment. As the heat is forced into the greenhouse it will rise first and then fill the space until it eventually gets down to the roots, operating in the exact opposite approach that we have suggested. The radiant system is a closed loop system making it extremely efficient and the most effective approach to heating your greenhouse. With some added ingenuity a ‘solar hot water heating system’ can be introduced into the loop so that the Sun is heating up the water and the boiler is only acting as a supplementary heating system further increasing the efficiency of your heating system. An example of a simple system can be found at http://www.motherearthnews.com/green-homes/build-a-passive-solar-water-heater-zmaz07onzgoe.aspx#axzz3JiDO73XP