WAYS TO HEAT YOUR GREENHOUSE
Just like with cooling your greenhouse, heating it can get expensive unless you create a DIY solution.
Below is a list of various ideas I’ve found across the internet for heating your greenhouse. Please note that I haven’t tried many of these options and have identified those I have and what we experienced:
Before you read any further, remember...
Which every solution you decide to try, remember to ventilate the greenhouse or you will end up with mold growing all over the greenhouse and plants. Place fans throughout the greenhouse to keep the air moving around.
Remove your greenhouse shade cloth...
If you put on a shade cloth for the summer, make sure you remove it for the winter. In the winter, the sun is further from the Earth and not as strong, so it is important that you get as much light into the greenhouse as possible.
Propane is a popular but at the cot of propane these days, it’s an expensive way to heat a greenhouse.
There are several types of propane heaters for greenhouses.
Wood / Coal Stove:
If your greenhouse is large enough, it may be worth installing a wood or coal stove. A wood stove is probably the most cost effective way to heat a greenhouse (after the initial cost of purchasing the stove and piping.) It is typically easy to find/buy wood either cheap or free, depending on where you live.
Based on what I’ve seen on the internet, the wood pellet stove is favored as you can buy a hopper to automatically feed the pellets as needed to help keep the stove going throughout the night. Be sure the stove is installed correctly and the smoke doesn’t find it’s way back into the greenhouse and the embers don’t burn the poly on your greenhouse.
These stoves became popular as DIY projects, making them out of cement blocks, etc.
Today they can be purchased. Because of the way they are made, these stoves use little fuel (twins, branches, etc.) but can heat a large space.
Double the Poly and "Pillow" it...
For those who have a greenhouse that is covered with poly, double the poly and install a blower fan to push air inbetween the two sheets of polly, forming a pillow effect. The sun will warm the air that is between the two sheets of poly which will provide an insulation.
Use thermal mass to heat your greenhouse...
You can use thermal mass to store solar heat energy in your greenhouse. This method involves placing items in your greenhouse that will absorb heat during the day and then slowly releasing the heat in the evening when it gets cold.
Below are some materials that can be used and how to use them:
Heat Absorbing Materials:
How They Can Be Used:
- dark gravel
- cinder blocks
- clay pots
- dark colored mulch
- Cement blocks and rocks naturally absorb heat.
Note: I place a row of cinder blocks along the southern side of the greenhouse, in two rows. Not only do they help to absorb and release warmth into the greenhouse, I use it as shelves for my plants.
- cover the entire greenhouse floor with dark stone, or black landscaping cloth (make sure you use the good quality type or you will need to replace it every year.
Many people build a compost bin in their greenhouse and use it to not only create compost for their garden, but to generate heat for the greenhouse.
As the material in your pile composts, bacteria that break down organic material generate a considerable amount of heat to the environment. A compost pile can get hotter than 100 degrees (F).
By no means will these methods entirely replace a powered greenhouse kept at tropical temperatures, but they can keep a space warm enough for plants suited to temperate climates, likely several USDA zones warmer. Plus, a greenhouse like this will keep cold-hardy greens and vegetables growing all winter long, and once it’s up, it doesn’t cost a thing to keep warm.
Set up an open worm bed.
This works similar to the compost pile- except you have to be careful what you add to the worm bin; no meats, dairy, etc. The worms generate castings which is similar to dirt as it will absorb heat. The worms will stay in the bin as long as you continue to offer them scraps of veggies, dirt, ripped newspaper, etc. They will only try to climb out of the bin if it isn’t cleaned out periodically and goes anerobic.
- Dark plastic barrels, filled with water
- Dark gallon water bottles filled with water
Water is a great heat conductor and can absorb and hold heat better than most other materials. Painting the barrels black will help attract the sun to the barrels to heat up the water. It will slowly release the heat back into the greenhouse as it gets colder. As with the cinder blocks above, keep your plants close to the barrels to benefit from the release of the heat in the evenings.
Note: For our Aquaponic System, we had a 300 gallon stock tank used for the fish and four 50 gallon growbeds with another 50 gallon sump tank. Because the beneficial bacteria begins to die back once the water temperature begins to drop below 71 degrees (F), I kept a water heater in the stock (fish) tank and another in the sump tank as the water cools down from traveling through pvc pipes from the fish tank to the grow-beds then down to the sump tank. We also had two 275 gallon IBCs and a 150 gal stock tank where we housed our tilapia, which also needed to be heated during the winter. We found that heating approximately 1,100 gallons of water provided enough heat in the 25′ x 40′ greenhouse to keep it at a minimum of 40 degrees (F) at night.
Insulate, insulate, insulate!
If you live in the Northern Hemisphere, don’t bother placing glass on the northern side as the sun never shines from the that side. Instead, place thermal mass heating against that way to absorb more sun and insulate it to prevent heat loss from and stop the cold north winds from finding it’s way inside.
- We built 3′ wooden walls around the greenhouse to keep the groundhogs from scratching and ruining the poly. Along the inside of the wood we placed 3″ foam board which makes a big difference.
- Look for drafts in the greenhouse and use liquid insulation to fill them.
- Protect your plants by sectioning off part of your greenhouse, insulate it well and use other methods of heating the area. This is where you would keep plants you wish to either grow over the winter months or just winter-over.
- Cover the windows and doors with plastic. Be sure you don’t cover the exhaust fan(s) to keep the air moving outside of the house.
- Don’t put your plants up against the wall.
Considerations before building your greenhouse:
- If you are just considering building a greenhouse, you might want to consider building a ‘basement’ by sinking the floor down below the front line (deeper than 4 feet) into the ground. The deeper you go the better; the temperature becomes more consistent and never falls below the freezing point in the winter.
In addition, this will also keep your greenhouse cooler in the summer months.
- Dig the floor down about 1′ and run pipping in which you can later move air heated by a stove throughout the floor which will radiate in the evenings as it gets colder.
If you are planning to make a compost pile in the greenhouse for heat, you might want to consider installing some solar water heating pipes on a closed loop to pump through the garden beds. Coil these pipes in the center of the compost heap so that the warmth will heat the water, which can be move through the pipes and heat the soil within the garden beds.