If your dream is to run a commercial greenhouse business in a climate prone to winter storms, you will soon know what long, sleepless winter nights are all about. When the the power goes out and the heat shuts off, emergency heating is vital to save your crops. Having an emergency heating plan in place will give you the peace of mind you need.
Forced Air Heaters
The most commonly used emergency heaters for greenhouses are portable forced air heaters. Smaller heaters usually run on propane, but some of these heaters can run on diesel, kerosene or #1 and #2 heating oil.
Most portable forced air heaters for greenhouses look and work like hot air cannons. They are capable of pushing out up more than 329,000 BTUs of heat into your greenhouse. Larger models with cabinet-type housings are capable of producing up to 765,000 BTUs of heat.
Calculating Which Size Heater is Required
During winter emergencies, you are not trying to get plants to grow -- you are just trying to keep them from being damaged. The heat required depends on your crop. More cold-hardy crops only need to be kept above freezing, but tender crops, such as young seedlings or tropicals, need to be kept a little warmer. The temperature range desired is generally from 40F to 50F.
The calculation for BTUs per square foot of heated space is complicated, and your heating professional should provide that information to you when he sets up your heating system. There are handy online calculators that can help determine your needs in an emergency. As an example, for a 50 x 100 foot greenhouse with a 10 foot ceiling, it would take approximately 160,000 BTU/hour -- or 46,891 watts -- of heating capacity to keep it at 50F. It is always better to have more capacity than you need, and the rule of thumb is to buy a heater that generates at least 10 percent more heat than you calculate is needed. In the above example, you should buy a heater capable of generating at least 175,000 BTU/hour.
Venting for Forced Air Heaters
Forced air heaters produce carbon dioxide, so the greenhouse needs to be properly vented. Since your venting system operates on electricity, you will also need a generator capable of opening and closing the vents and running the exhaust fans.
It is best to have a heating professional set up your emergency greenhouse heating system initially and train you in how to use it. While emergency heat is viable for short periods of time, it isn't a long-term solution. If the power outage is going to last more than a couple of days, you need to contact a reliable and experienced heating company like Kennard - Pace Co. Inc to suggest and install an alternative heating system.