, This post is for Jen. With winter  officially here in our neck of the woods it’s time to start heating.
People heat for different reasons. Some heat just enough to hold over their semi hardy plants like fuchsias and geraniums. Some want that tropical feel year round. If you want the latter then install a good quality hanging propane or gas heating unit with a power vent to carry out the unburned gas. You can find these units in any greenhouse supplies catalog.
If you don’t happen to have that extra thousand dollars to throw at the problem this post gives examples of what I use in my 10×40 and 20×40 greenhouses

Having 6 greenhouses of differing sizes I use a variety of heating methods. At this time of year I am using only two houses. One for holding over and one for my greenhouse manufacturing shop. The house I use for holding over also has my citrus and lots of succulents and cactus plants that I will be selling next year. The cactus, succulents and the new cuttings that I am starting are in the front half of that greenhouse. The citrus and some of the plants I am holding over are in the back of the greenhouse. To accomplish two heat zones I simply drop a piece of cheap thin plastic down from the ceiling to the floor at about the middle of the greenhouse. Now I have the warm 20′ zone on the front side of the plastic and the cooler side (around 10 degrees cooler) on the back side.

My primary heat is a 4000 watt 220 volt electric heater called the Hot Shot. This heater will keep the whole 40′ house up to around 50 degrees even when it’s 20 degrees outside. This year I have also been experimenting with a portable propane heater called the Blue Flame that I got from someone like Amazon. They put out 30,000btus which seems to be more than enough to heat the entire house. I am using mine though as kind of a backup to my electric. I set the thermostat on the blue flame to come on when the temp gets below 50 degrees or so. It runs a few minutes heats the area up to about 58 degrees then shuts down. A couple of the things I like about this unit is that it has a manual thermostat, you turn it until you hear it click and kick in then you leave it alone. It also has a thermometer in the top that shows the ambient temperature around the heater. This thermometer doesn’t work if the power goes out but the heater does keep working since it has a standing pilot. This is huge, if the power goes out at night and you are all toasty in bed this heater will keep your babies from turning to popsicle. Another nice thing is that you can run this unit on a propane bottle as small as 10 gallons. That way you aren’t trapped paying the high delivered propane price you can pick up your propane at the local farm store or propane place.

For my shop greenhouse which is a 20′x40′ greenhouse I use a salamander, rocket type propane heater with a huge blower on it. They come in 60,000btu to 250,000 sizes. I went with the 125,000btu size as it is the smallest one that comes with a thermostat. I am able to set this one at 65 degrees or so and it will keep cycling on and off and keep the house at a pretty constant temp. I do vent the house once in a while and I also am going in and out constantly while I work so I’m not too worried about carbon monoxide. I have however gotten a slight headache after working in that house for most of the day.  I plan to get a carbon monoxide detector today and installing it in that house then cranking the heat for a couple of hours keeping the house at 80 degrees or so to see if it is set off by carbon monoxide.

I also have one of these type of heaters in a 60,000btu which I got at Home Depot for $99. It hooks up to the small barbeque size bottles and can be used to take the chill off of a house in just a few minutes if I want to work in there. This one doesn’t have a thermostat but is useful for a quick heat and is very portable.

Ventilation. For me that’s more of a summer thing. My philosophy is don’t build your greenhouse super tight and you will have enough air coming in to support the heating unit. As far as fumes damaging your plants. The orchid that I posted a picture of is about 6 feet away from the heater and has suffered no ill effects from the propane.

Air Movement. We’re talking fans here. I use the cheap 16″ box fans that you can find at the thrift stores at this time of year for $5. I locate one of them sitting on the floor a few feet in front of my heat source and have it pointing toward the back of the greenhouse. I then have one hanging from the ceiling at the back of the house blowing toward the front. This helps mix the heated air as well as keeping the moist humid air mowing. Most greenhouse plant diseases begin with moist air settling on the plants leaves.