Heating & Lighting Your Greenhouse

Ample light and ventilation are essential in any greenhouse, while heating, humidification, and cooling must be considered in most operations. What you need will depend on where you are located and the crops you grow.

HEATING
There are many types of heating units. Choose one which will keep the temperature of your greenhouse at desired levels for the full 24 hours. With any of the nationally advertised heating systems, spare parts are easily purchased. This is a good feature as it may save you time (and thus money) in case of a breakdown.

Hot Water and Steam Heat

In cold areas, hot water systems using coal, oil, or natural gas are the most popular for greenhouses.
If you have a large enough household heating system, you may be able to pipe hot water into the greenhouse pipes. This furnishes economical heat. But if the greenhouse is very large or is located over 100 feet from the household boiler, it may be better to install a separate system.

Hot water furnishes an even, warm temperature minus the harmful fumes that are produced by some portable-type heaters. With a separate hot water system, it is necessary to install a boiler. The boiler can be automatically fired with oil, stoker, or gas, thermostatically controlled, or hand-fired with coal. If it is fired by hand, it should have sufficient capacity to run for 10 or more hours without attention.

Automatic firing and thermostatically controlled temperatures are a saving in time and money. They also assure more accurate heating.

I use oil for heating my greenhouse. The system is inside the greenhouse annex. Units burning natural gas can be safely installed directly in the greenhouse or in an open attached unit. If you are using coal, artificial gas, or a mixture of natural and artificial gas, the boiler must be placed in a separate room or building, since fumes from these fuels are detrimental (sometimes fatal) to plant life.

The heated water circulates through pipes or fin radiation. I have fin-type radiation. Each foot of fin radiation has several times the radiating surface of a foot of standard pipe, and much less footage is required to maintain desired temperatures. For easy calculation, 1 foot of 2-inch fin-type radiation will equal about 6 feet of standard 2-inch pipe. These figures vary with the size of the fin and the number of fins per foot. The hotter you need to keep your greenhouse, the more pipe or fin sections you should have.

Steam heat, which also utilizes piping or fin radiation, is cheaper to install but it dries out the air and the plants.

Oil Heat

A forced-air oil heater is inexpensive. If you need heat in your greenhouse but a few times during the year, one of these fan-type heaters may be just the thing for you. The fan forces a brisk circulation of hot air through ducts running underneath plant benches.
You can pipe the smoke out through a chimney or through pipes running under the bench and vented out one end of the greenhouse. This pipe surface gives off added heat and removes the necessity of a chimney stack.

Gas Heat
Many owners of profit-making greenhouses live in areas where natural gas is available. A natural gas unit is quite reasonable in cost. One low-priced heater is all-aluminum and about 121/2inches in diameter and 22 inches high. A somewhat larger heater, 15 inches in diameter and 25 inches high, naturally is about double the price. This type of heater is set under the side benches so that heat goes out into the walk. It is vented and piped into the outer gutter or directly outdoors.
These heaters are not recommended for use with fuels such as Butane or Propane.

Electric Heat
Where the cost of electric current is low, it might be feasible for you to heat with electricity. The heating coils are the same as those used for soil-heating cables. These coils are wound around 3/4-inch pipe which is run around the inside of the greenhouse. A thermostat controls the heat. Automatic Temperature Alarm

An automatic temperature alarm-a thermometer hooked up to a bell-is good crop insurance. An unexpected cold night, failure of electricity, or trouble with your heating system might cause you to lose an entire crop. So that a power failure will not affect it, the alarm operates on batteries or dry cells. When greenhouse temperature drops below a pre-set mark, the thermometer actuates the bell.

The bell for our greenhouse alarm is placed just outside our bedroom door. Thus we are able to hear it even in the noisiest stormy night.

Emergency Heating

Even the best heating facilities sometimes go wrong, and an alarm system has little value unless you have on hand some emergency heating equipment, ready for use.
My emergency setup consists of two portable electric heaters. I set them on boxes, one at each end of the greenhouse, and place an electric fan behind each of them. Although not recommended for daily use, this setup serves the purpose and keeps plants from freezing or chilling and so suffering a setback in growth.

A still simpler from of emergency heating can be provided with a candle inside a flower pot. Light the candle, then invert a similar sized pot over the first one-pot rims together. The candle will receive oxygen through the hole in the top pot. Place several of these heaters around the greenhouse and you will maintain an above-freezing temperature. The number of these units you’ll need will depend on the snugness as well as the size of your greenhouse.