Greenhouse Heating Systems: Why Anthracite Coal and Hydronic Heat Make Sense for Growers
Greenhouse growers live in a tough business reality: the plants need what they need, whether fuel prices cooperate or not. A cold snap does not care about crop timing. A young plug crop does not care that propane spiked this winter. And prices are typically fixed, so every increase in labor, fuel, supplies, freight, and replacement equipment eats away at profits. That is why greenhouse heating systems aren't merely a matter of comfort. They can greatly affect the grower's bottom line.
Heating is one of the biggest expenses in commercial greenhouse operations. Michigan State University Extension notes that energy bills are typically the second-largest operating expense behind labor, and that heating accounts for 88% of greenhouse’s energy use in one Michigan study. A University of Wisconsin Extension greenhouse energy publication also reports that energy costs can exceed 10% of greenhouse grower sales.[1][2]
Those numbers matter because greenhouse profit margins are usually not wide enough to absorb waste. A few extra cents per square foot, repeated across thousands or hundreds of thousands of square feet, can erase a season of profit. That is especially true for growers heating through winter, starting spring crops early, holding warm crops, or trying to sustain steady production amid unpredictable weather.
The real challenge: large heat demand with slim operating margins
A greenhouse is designed to collect light, but it also has a lot of exposed surface area. Glass, polycarbonate, and poly film all lose heat faster than an insulated building wall. Add air leaks, venting, moisture management, door traffic, and nighttime temperature drops, and the heating system has to work hard to maintain crop-safe conditions.
For many operations, the question is not simply, 'Can this heater make enough BTUs?' The better question is, 'Can this system deliver the BTUs we need at a predictable cost, with reasonable labor, without creating uneven crop temperatures?' That is where fuel choice and heat distribution matter.
Forced-air unit heaters can raise air temperature quickly, but air heat alone is not always the best way to protect plants. Heat rises, stratification occurs, and the crop zone can be cooler than the thermostat suggests. Fans help, but they do not change the fact that many crops respond strongly to root-zone temperature. If the root zone is cold, plants can stall even when air temperatures are acceptable.
Why anthracite coal deserves a serious look for greenhouse heat
When growers compare greenhouse heating systems, they often start with propane, natural gas, heating oil, wood, or biomass. Those can all have a place. But for operations in or near anthracite coal regions, especially in Pennsylvania and the Northeast, anthracite coal deserves a serious look because it combines high heat density, good storage characteristics, and local fuel availability.
The U.S. Energy Information Administration describes anthracite as the highest-rank coal, with 86% to 97% carbon and a heating value that is, on average, slightly higher than that of bituminous coal. EIA also notes that coal contract prices tend to be more stable than spot purchases, even though spot prices can move with short-term conditions. For a grower trying to budget a heating season, that matters. [3]
The practical advantage is planning. Anthracite is a solid fuel that can be stored on-site for long periods without the leak risk of liquid fuels or the delivery exposure of just-in-time fuel sources. It is not immune to changes in transportation, mining, or markets, and no responsible supplier should pretend otherwise. But compared with fuels that can move dramatically with oil, gas, or utility markets, a local anthracite supply can give many greenhouse operators a more predictable fuel plan.
Alternate Heating Systems' coal boilers use anthracite coal, which has high BTU output, stores compactly, and resists moisture better than pellets. AHS also notes that its coal stokers are designed around anthracite coal and use simple, rugged combustion technology. [4]
The Coal Gun advantage: more heat with less daily attention
One of the biggest objections to solid-fuel heating is the labor required. Greenhouse operators already have enough to do: watering, transplanting, spacing, pest scouting, shipping, customer service, seasonal hiring, and equipment maintenance. A heating system that requires constant tending is a poor fit for a busy grower.
That is where the automatic Coal Gun from Alternate Heating Systems fits into the conversation. AHS's coal stokers use anthracite coal, and automatic feeding and ash removal are available to make the coal boiler more hands-free. It is also equipped with a self-cleaning Swirl Chamber heat exchanger rated at 83% efficiency. [4]
That does not mean a Coal Gun is maintenance-free. No commercial heating appliance is. Ash still has to be handled. Draft, water temperature, controls, pumps, and safety devices still matter. But compared with hand-fired or manually loaded wood systems, an automatic anthracite coal boiler can reduce the daily attention needed to keep the heat moving.
For greenhouse operations, that can be the difference between a system that works in theory and one that works during the busy spring season. When heat demand is high and labor is tight, automatic feed and ash handling are operational advantages.
Why hydronic greenhouse heating is such a strong match
A boiler is only one half of the decision. The other half is how the heat gets distributed. Hydronic heating uses hot water to move heat through piping, heat exchangers, unit heaters, radiant loops, under-bench systems, in-floor systems, or root-zone heating. That flexibility is one of the main reasons hydronic systems are so useful in greenhouses.
MSU Extension explains that the use of hot-water systems for root-zone or under-bench heating is increasing, and that root-zone heating warms plants from below, keeping roots and canopy warmer than the air above. This can allow growers to reduce the general air temperature while still maintaining adequate plant temperatures for growth and development. [1]
UMass Extension notes that root-zone heating can provide 25% to 75% of a greenhouse's total heat needs, depending on climate, and that 15 to 30 Btu per hour per square foot of floor or bench can often be obtained from root-zone systems. UMass also notes that hot water from an existing or new boiler can be used, often with circulators, tempering valves, or a heat exchanger. [5]
For growers, that means a Coal Gun boiler need not be limited to a single heating method. It can become the central heat source for several greenhouse heat zones and applications.
Useful greenhouse applications for hydronic heat
In-bed heating: PEX or other approved tubing can be installed in growing beds or below bench media to keep the root zone warmer. This is valuable for crops that respond to warm roots, early propagation, winter greens, and operations that want to avoid overheating the entire air volume just to protect root temperature.
Under-bench heating: Hydronic piping, fin tube, or tubing under benches can put heat close to the crop zone. This helps reduce cold spots at bench level and can improve uniformity compared with relying only on overhead air heat.
In-floor heating: Greenhouse floors or walkways can be heated with hydronic tubing when the design allows. This can help provide gentle radiant heat, reduce cold-floor effects, and improve worker comfort in propagation or retail areas.
Perimeter heat: Hydronic perimeter loops can help mitigate cold-wall and sidewall losses. This is especially useful where heat loss is highest along kneewalls, endwalls, doors, and exposed sidewalls.
Unit heaters and fan coils: Hot water can feed unit heaters or fan coils to provide quick air-temperature recovery when doors open, vents close, or weather changes quickly.
Snowmelt and utility uses: Depending on system design and boiler capacity, hydronic heat can also support snowmelt for key walkways, loading areas, equipment pads, or other utility areas where ice poses safety or operational problems.
A practical way to compare greenhouse heating systems
When evaluating heating options, do not compare equipment price alone. A low-cost heater with high fuel volatility, poor heat distribution, or heavy labor requirements may be expensive over the life of the system. A better comparison includes:
- Delivered fuel cost per million BTU
- Fuel storage requirements and delivery risk
- Labor required for loading, cleaning, ash handling, and maintenance
- Ability to heat the root zone, bench zone, floor, air, and perimeter
- Backup heat strategy and controls
- Boiler life, serviceability, and parts availability
- Crop uniformity and whether the system helps reduce cold spots
Anthracite coal has high BTU output, stores compactly, and resists moisture better than pellets. Alternate Heating's coal stokers are designed around anthracite coal and use simple, rugged combustion technology. [4]
Bottom line: the right greenhouse heating system protects both plants and profit
Greenhouse growers cannot control the weather, retail price pressure, or every shift in the fuel market. But they can control the design of their heating system. A properly sized automatic anthracite coal boiler paired with hydronic heat can give growers a strong combination: high heat output, on-site fuel storage, reduced hands-on tending compared with manual solid-fuel systems, and flexible heat delivery where the crop needs it most.
For operations with large heat requirements and tight margins, that combination is worth considering. The Coal Gun is not just another boiler. In the right greenhouse application, it can be the central heat plant behind in-bed heat, under-bench heat, perimeter loops, fan coils, and other hydronic zones that help growers safeguard crops without wasting heat.
If your greenhouse operation is fighting high propane, oil, electric, or natural gas costs, Alternate Heating Systems can help you compare your load, square footage, crop goals, and hydronic layout options. The best greenhouse heating system is not a one-size-fits-all. It is the system that keeps your crops healthy, your labor manageable, and your heating costs under control.
Contact Alternate Heating Systems to discuss a Coal Gun boiler and hydronic greenhouse heating layout for your operation.
Sources Cited
[1] Michigan State University Extension, “How do I use less energy to heat my greenhouse?” Heating accounts for 88% of greenhouse energy usage. In the referenced Michigan study, energy bills are typically the second-largest operating expense behind labor. Root-zone heating can allow for lower air temperatures while keeping the plants happy. https://www.canr.msu.edu/news/how-do-i-use-less-energy-to-heat-my-greenhouse
[2] University of Wisconsin Extension / Farm Energy, Scott Sanford, “Reducing Greenhouse Energy Consumption: An Overview.” Energy costs are reported as the third-highest cost for most greenhouse growers, over 10% of sales, with heating at 70% to 80% of typical total greenhouse energy consumption. https://farm-energy.extension.org/wp-content/uploads/2019/04/2.-A3907-01.pdf
[3] U.S. Energy Information Administration, “Coal prices and outlook.” EIA describes anthracite carbon content and heating value, and notes that coal contract prices tend to be more stable than spot purchases. https://www.eia.gov/energyexplained/coal/prices-and-outlook.php
[4] Alternate Heating Systems WordPress export/coal boiler content, July 2025. AHS content describes anthracite coal stokers, automatic feeding and ash-removal options, the self-cleaning Swirl Chamber heat exchanger, and the advantages of anthracite storage and cost stability. https://alternateheatingsystems.com/product/coal-boiler/
[5] UMass Amherst Center for Agriculture, Food, and the Environment, “Root Zone Heat - Installation Techniques.” UMass states root-zone heating can provide 25% to 75% of greenhouse heat needs, depending on climate, gives typical Btu/hr per square foot ranges, and discusses using hot water from an existing or new boiler. https://www.umass.edu/agriculture-food-environment/greenhouse-floriculture/fact-sheets/root-zone-heat-installation-techniques