Wood Burning Boilers
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. And, as upstart farmers, we needed to do it in a way that wouldn’t
break the bank.
Standard Greenhouse Heating
Most greenhouses today are heated by natural gas – a common and relatively inexpensive
source of heat, that is, if you have the infrastructure in place.
When constructing our first greenhouse, installing gas lines weren’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
Choosing a Wood Burning Boiler
Our Central Boiler wood boiler
Once we decided that wood would be our fuel source, 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.
That said, we ended up choosing a boiler from Central Boiler.
So, what is a wood burning boiler?
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. See a video on this here:
Heating A 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
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
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 fishhouse.
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.
Pine Beetle Outbreak
Beetle kill trees in Wyoming
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, in
combination with decades of _______ (insert desired explicative here) fire management
practices 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?
ZipGrow Towers maximize yields.
For starters, let me just reemphasize how brutal Wyoming winters can really be…
Our heat calculations for a 2000ft2 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 with ZipGrowTM Towers. (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. For more information, visit