Heating with wood: What's the hype about?
Heating a greenhouse here in Wyoming is not an easy task.
In a place that consistently gets winter temperatures below -20 and howling winds roaring at 40-60 mph sustained, there's a reason why we're really the only farm in business all year in this environment.
That said, we needed to figure out a way to keep our plants and fish tanks warm throughout the long Wyoming winter.
Standard greenhouse heating
Most greenhouses today are heated by natural gas, a common and relatively inexpensive source of heat- if you have the infrastructure in place that is.
When constructing our first greenhouse, installing gas lines wasn't in our budget as they can be rather pricey.
Choosing wood as a heat source
Once we understood that natural gas was outside of our reach financially, we began to look around for other options and ultimately came across wood as a heat source.
We made this decision based on a few factors:
On a per-Btu (British thermal unit) basis, wood is one of the cheapest forms of heat available.
The abundance of beetle kill wood in the forest surrounding Laramie that is dried and ready to burn.
Choosing a wood burning boiler
Once we decided that we would be heating a greenhouse with wood, we needed to select the appropriate boiler for the job.
Now, there are a lot of great options out there in this space. Heck, a lot of people even weld their own boilers, but we decided to make the investment in something reliable, long-lasting and with enough volume to keep our greenhouse nice and toasty in these cold Laramie winters.
Our Central Boiler being unloaded!
That said, we ended up choosing a boiler from Central Boiler.
How do wood boilers work?
While our boiler system acts as a heater for our greenhouse and fish house, the boiler heats differently from a standard wood furnace or stove.
A boiler, as you can infer, uses water to heat a space.
Inside the boiler, there is a firebox (where the wood is burnt), with baffles to act as a heat exchanger (where the heat is actually transferred from fire, to metal, to water) and surrounding both of these is a water jacket (essentially, the firebox is inside of a tank of water).
The water surrounding the firebox is heated to the optimal temperature and is then circulated through insulated tubing or pipes.
This type of system is called hydronic heating - that means it's a heating/cooling system that uses non-boiling water as a heat transfer medium.
And, while the word "boiler" sounds like we heat the water to 212 degrees, it's a bit of misnomer. We heat our water to 185-195 degrees and therefore don't have to deal with high pressure steam, which is much less dangerous.
Instead, the water is heated to around 185 to be pumped through coils in our fish tanks and finally to the heat exchangers/blowers inside our greenhouse.
We control the temperature of the boiler with a thermostat located on the front of the boiler (see photo on left).
There is a damper on the front of the boiler door that will close and smother the fire once the temperature hit 185 degrees. Even though the damper may close, the water inside the boiler continues to circulate throughout the coils in our tanks and to the heat exchangers inside the hoop house.
Over time the water will slowly cool down and once it hits 175 degrees, the damper opens up and fuels the firebox with more oxygen and once again begins to heat the water back to 185 degrees.
That means the fire in our boiler has only been lit one time back in November - it runs constantly and self regulates in accordance with our preset temperature on the thermostat.
Inside the boiler a pump moves the hot water from the water jacket to insulated tubing strung throughout our greenhouse and fish house.
Our model in particular provides more than one pump hookup so that as we grow we can use the hot water from this boiler to heat additional greenhouses.
Rounds vs. split wood
Unlike many smaller scale wood furnaces or stoves, our boiler can actually accommodate rounds (whole logs cut up to 3.5 foot sections). This saves us A TON of time and energy having to split wood throughout the harsh winters.
*Bonus: We've found that our boiler will even burn fairly green Lodgepole Pine - it doesn't ALL have to be completely dried, cured wood.*
We order our logs in by the truckload - a decision we made after realizing how time intensive hauling it in by the pickup truck can be.
Using beetle-kill wood
As you may or may not know, the Rocky Mountains are in the midst of a bark beetle outbreak that is 10 times larger than any previous outbreak. Over 3,600,000 acres of Colorado, southeastern Wyoming (that's us) and surrounding states are undergoing a massive pine beetle epidemic posing a hazard to human recreation, infrastructure like power lines and increased fire intensities with the increase in woody biomass on forest floors. All of this puts a lot of stress on the forests.
That said, we're able to truck in and burn this wood very inexpensively and feel good about doing so since we're helping reduce fire loads and hazard trees in our surrounding forests.
Using wood to heat our greenhouse not only saves us money, it also affords us the privilege of using a renewable resource.
PS - If you're living in the West and need some help protecting your trees from the devastation pine beetles inflict, check out our neighbors and friends at TigerTree Land Management.
Why is this boiler a good match for our application?
For starters, let me just reemphasize how brutal Wyoming winters can really be...
Our heat calculations for a 2000 ft2 hoop house + fish house told us we would need to supply about 250,000 Btu/hour(!) to keep our plants at a comfortable temperature during the lowest temperatures of the year. Of course, there's no way we could be profitable with this type of utility cost to heat such a small space UNLESS we doubled or tripled our production per square foot. (See more advantages of vertical farming below!)
This boiler could supply the necessary Btu levels we needed!
In addition, the access to inexpensive beetle kill wood also helps our bottom line and ensures our plants and fish can make it through the Wyoming winters.
Are wood burning boilers a good choice for your application?
Do you have access to reliable, inexpensive wood to burn?
Are you already set up with natural gas lines?
Answering these questions will help you start figuring out whether or not wood is a good choice for your greenhouse heating application.
From there be sure to do your heating calculations for your greenhouse and do a rough cost estimate over time.