Frequently Asked Questions

Top Questions

This varies by your climate and your desired indoor growing temperatures. (An energy-efficient greenhouse has a much greater payoff if you need a warm, year-round growing environment and / or have very harsh climate). We can provide an energy analysis to calculate your energy savings, or provide more information on energy savings if you send us an email with your location and growing goals.

Your options for building a greenhouse depend on, the size and complexity of the project, and whether you doing the work yourself or hiring it out. Generally, your options are:

Yes, we provide tours of our residential and commercial greenhouses in the Boulder / Denver area in Colorado. If you are in that area, we would be happy to take you for a tour to see in person how an energy-efficient commercial greenhouse looks and operates. Please contact us to schedule a tour.

A year-round solar greenhouse needs access to light particularly in the winter months. Areas that allow sufficient year-round light, with minimal shading in the winter are best. More of our recommendations are given in our blogs on the topic:

Ceres energy-efficient greenhouses range in cost from $30 to over $200 per sq. ft. We provide custom quotes for our greenhouses because every project is slightly different. Several factors influence cost, including:

  • Size. Larger greenhouses have a lower cost per sq. ft.
  • Whether pursuing a custom design
  • Whether you need a building permit (requires stamped structurally engineered plans, which we can include)
  • The growing and climate control systems you are adding

Because each greenhouse is slightly different, we work with you to find the best, most cost-effective method of building for your needs. Please contact us for a free quote.

There are two options for an off-grid greenhouse:

  • Design a passive solar greenhouse. This is a structure that does not use electricity, and is inherently off-grid. Instead of electrical fans, a passive solar greenhouse uses passive vents and thermal storage methods. We work with people on designing passive solar greenhouses, but most of our clients add electricity to the greenhouse for greater climate control. Much more information on passive solar greenhouse design is in our book, The Year-Round Solar Greenhouse, and you can get in touch with us if this your preferred design.
  • Add solar panels to the greenhouse. The feasibility of powering the greenhouse with solar photovoltaic (solar PV) panels greatly depends on how you will be growing. With a large electric demand, solar panel systems can get quite expensive. Smaller, cost-effective DIY systems are also possible. We recommend contacting us about your project, and reading more about getting started with integrating solar panels in our blog, 5 Tips for Designing a Solar-powered Greenhouse.

This varies greatly by location, and what you are trying to grow. In areas with mild winters, passive solar greenhouses can grow year-round without any back-up heating. Greenhouses in cold areas can even grow very hardy crops year-round without heating, as Eliot Coleman has proved on his farm in Maine. However, to grow a wider variety of crops, in most cold climates an energy-efficient greenhouse will require some back-up heating. This is usually turned on during a few very cold nights a year — the extreme cold snaps — when a GAHT system, thermal mass, or phase change material is not sufficient to keep temperatures high enough.

Residential growers typically add an electric heater for the coldest times of the year. Commercial growers typically integrate propane or electric heat. We can help you integrate a back-up heater when designing your commercial greenhouse.

There are too many variables to give an easy answer to this question. The top two are:

  • What are you trying to grow, or what indoor temperatures do you want to maintain?
  • What are you typical outdoor temperatures in the winter?

Once we have that information, we can give you a ballpark estimate of how often heat will be required for your situation. For a more accurate estimate and cost projections, you can take advantage of our consulting services.

Finally, it is important to note that an insulated greenhouse, passive solar greenhouse design, and systems like a GAHT system, which take advantage of free solar energy, keep the heating requirement to a minimum. Most growers in North America use back-up heating sparingly in the winter, and rely on energy-efficient greenhouse design for most of the year.

Many solar greenhouse designers recommend using a roof angle that is perpendicular to the angle of the sun in the winter. While this does indeed maximize light transmission in the winter, the effect of a lower angle is not severe. We explain this relationship much further in our blog, Choosing the Best Roof Angle for your Greenhouse. Furthermore, there are a few logistical challenges to creating very steep pitch — you cannot use glass view windows on the south; it can reduce head room or create a awkwardly tall greenhouse. Due to these pros and cons, most of our residential growers are built with a shed-style roof. If you have a need for a steeply pitched roof, just ask us about our custom greenhouse design services.

GAHT™ System / Climate Battery Questions

“Geothermal” is a broad term meaning heat from the earth. The term applies to many systems, including heat pumps and power plants using hot steam from the earth. GAHT™ systems are geothermal too: they use the ‘low-grade’ heat provided by the shallow earth. But, a GAHT™ system is NOT the same as a geothermal heat pump, a system commonly used to heat homes and commercial buildings. Heat pumps are more complex systems that use a refrigeration cycle. They circulate a fluid, not air, underground, and use pipes buried very deep — often hundreds of feet — underground. A GAHT™ system, in contrast, simply uses a fan and pipe to transfer heat to the soil. GAHT™ systems store heat in an insulated volume of soil, usually just 4′ below grade. They are much simpler, less expensive than geothermal heat pumps.

For the most part, yes. Ceres’ Ground to Air Heat Transfer (GAHT™) systems and climate batteries are both ground to air heat exchangers.  Over the years, different designers have given the system their own names based on their design.  Jerome Osentowski and Michael Thompson of the Central Rocky Mountain Permaculture Institute (CRMPI) coined the term Climate Battery. At Ceres, we altered the fan sizes and pipe configuration based on our research and call the system a GAHT™ system.

Another similar concept is earth tubes, often called a ground-coupled heat exchanger. These use one-way air flow: they draw air in from outside, pump it underground and then it into the structure (home or greenhouse). A GAHT™ system and Climate Battery circulate air in a closed loop: they take air from the greenhouse, pump it underground, and then exhaust it back into the greenhouse.

The cost of a GAHT™ system depends on the size of your greenhouse. Typically, residential GAHT™ systems (under 1,000 sq. ft.) cost between $2,000-5,000. Larger commercial greenhouses and school greenhouses typically cost $5,000-$15,000 depending on size.

Our GAHT™plans provide detailed installation instructions for building and installing a GAHT™ system. Here is an overview of the process:

  • Excavate a pit beneath the greenhouse (before greenhouse construction)
  • Build and install the underground pipe network in the excavated pit
  • Back-fill the pit. Then construct greenhouse. See our residential building plans for help
  • Install fans and wiring inside the greenhouse

For our residential greenhouses, we provide plans, materials lists and instructions for installing a GAHT™ system. Armed with these tools, you can install the GAHT™ system yourself or easily hire out the work to a contractor. We also provide phone support to answer any question that may come up along the way.

Yes, we can provide all materials for the GAHT™ system, including underground pipes, pipe connections, fans and thermostats. A material list is included in our GAHT™ plans and instructions. Some growers prefer to purchase the materials on their own; other prefer to have us order and ship them, and pay all at once. Please contact us for a personalized quote your GAHT™ system.

Maximum depth for the pipes underground is 4’ deep. This is below the frost line in most climates, and the level where soil temperatures become a stable and moderate temperature year-round.

In locations where the water tables is higher than 4’, we do not recommend using a standard GAHT™ system. Other heat storage methods, like phase change material can be used to make your greenhouse as energy-efficient as possible.

The pipes of a GAHT™ system have small perforations so any water that collects in the pipes underground can drain out into the soil. Water plays in an important role in how GAHT™ systems function. During the day, hot humid air is cooled underground. The temperature reaches the dew point and water condensates in the pipes underground. Through the energy transfer of phase changes, this further cools the air. It also helps water the soil underground, where plants roots are. Essentially, the GAHT™ system takes water out of the humid greenhouse air and drops it into the soil underground where it’s useful for growth.

Water does not stagnate in the pipes underground and so mold is not a problem in GAHT™ systems. In many years of testing systems in a variety of climates, we have not experienced any issues relating to mold.

Yes, GAHT™ systems can function in any type of greenhouse. We recommend using an energy-efficient greenhouse, however. It is by far the most cost effective investment when creating a year-round growing environment.

Radon is a radioactive element that seeps into buildings through the soil. Since a GAHT™ system circulates air directly through the soil, a common question is whether the GAHT™ system adds a radon risk. In areas with high radon levels, this is a possibility and should be taken seriously. However, greenhouses are less dangerous than conventional buildings when it comes to radon. First, you are not in the greenhouse for as much time. Secondly, greenhouses have very high air exchange rates. During much of the year, air (and any radon) will be ventilated outside, and the whole structure will be flushed with fresh air in a matter of minutes. Even if the ventilation system is not on, greenhouses have many more air exchanges than a standard home, mitigating radon build-up. In our tests of GAHT™ systems in the Rocky Mountains (an area with high radon levels), the concentration inside the greenhouse was found to be slightly higher than outdoors, but much lower than a dangerous level. By no means is this a comprehensive study, so if concerned, have your soils tested for radon before installing a GAHT™ system.

Small GAHT™ systems can be off-grid if you install a solar panel system. We do not provide integrated solar panel systems with GAHT™ systems. Solar panels should be installed by a local installer in your area, or on your own if you are qualified.

A solar PV system can be a few thousand dollar investment, which greatly depends on the electric demand of your greenhouse. As an example, a 12 x 20 greenhouse normally includes 2 GAHT™ fans, each 120 Watts. Along with exhaust fans, we estimate this greenhouse would have an energy usage of 1,000 kWh per year. In a sunny climate like Colorado, this could be powered by a 600 Watt solar panel system. At current prices (roughly $3.00 per installed Watt) this would cost $1,800 to the greenhouse project. Please note this is a rough estimation based on a typical greenhouse and solar PV system. For a more accurate estimate and to discuss the practicality of powering your greenhouse with solar PV, please contact us

Phase Change Materials

Ceres Phase Change Material is $3.50 per sq. ft. before shipping. Please contact us for a personalized quote and / or energy analysis of your greenhouse.

There are a variety of substrates for PCM. Our standard PCM product is a salt-hydrate, which has an energy capacity of 100 Btu / sq. ft. (We help you calculate the energy capacity for your greenhouse, and determine how much PCM you need).

Phase change material works by taking advantage of the latent heat that is absorbed or released when a material changes phases. In this case, the material is changing from a solid to a liquid. The physics of this process is responsible for the functioning of many common appliances, like refrigerators and evaporative coolers (both take advantage of the energy transfer as liquid converts to a gas). It is a basic chemical reaction can be harnessed to stabilize the temperature of a year-round greenhouse.

Like all passive thermal mass strategies, PCM can’t guarantee a set temperature for your greenhouse. It does help keep your greenhouse in a stable range for year-round growing. The material is selected to change phases as a given set temperature. We work with you to select the right product and quantity you need to grow what you want, when you want to.

A thin, flexible mat, PCM has many locations and applications. We recommend locating it on top or inside the North wall of the greenhouse — a large area that is exposed to sunlight.

BioPCM is sized material is embedded into a mat which is installed between stud bays. It provides temperature regulation like thermal mass (water), without taking up space in the greenhouse. The greenhouse wall becomes the thermal mass.

Phase change material comes in a mat, 16” or 24” wide, and is stapled or nailed onto the framing of the greenhouse wall, a simple process any greenhouse owner can do. For commercial greenhouses, we provide installation instructions tailored for your structure.

It can also be installed on top of an existing wall, making it an excellent material for retro-fitting a greenhouse to be more energy-efficient. We recommend placing a thin siding or covering over it to protect the packaging material from sunlight and UV degradation (This makes it last longer and easier to clean.)

Compared to the same volume of water, Phase Change Material has 5-10 times the energy storage capacity. (This depends on how effectively water can be used as thermal mass in a greenhouse.) Thus, instead of stacking several large drums of water in the greenhouse and sacrificing growing space, PCM can be sleekly installed in the wall. It creates a naturally controlled environment that grows the most fresh food possible. 

Commercial Greenhouses

We provide tailored quotes for commercial greenhouses, as each structure is optimized for the climate and growing considerations. Pricing varies according to structure type — commercial greenhouse structures, our DIY HighYield Greenhouse Kits – as well as your indoor growing requirements and climate. Pricing starts at about $30 / sq. ft. for a turn-key greenhouse (materials). Please contact us with some information about your project to get a quote.

Our commercial energy-efficient greenhouses are made with galvanized steel frames. Steel is the strongest framing material, and can be insulated in a variety of ways. We combine the frame with insulated metal panels, commonly used in warehouses or large industrial buildings, because of their high insulation values and ease of install.

We use triple wall, 16mm polycarbonate on all of our commercial greenhouses as a standard. In colder climates, the triple wall polycarbonate allows us to retain more heat while still allowing in more than enough sunlight. Our polycarbonate is incredibly durable and can stand up to the harshest weather.

Our typical commercial greenhouse is a shed-style roof with a single slope. If this does not fit your site, or in cases of very large (over 5,000 sq. ft.) commercial greenhouses, we employ alternate building styles such as gutter-connected bays of the greenhouse. In any case, we work with you to create a custom structure that meets your needs, site and budget.

Our [HighYield Greenhouse Kits] use two building depths – 23’ and 30’ – and can be as long as needed. Our [commercial steel greenhouses] are more flexible in sizing and layout, and are typically used for greenhouses with a minimum square footage of 4,000 square feet. We have in-house drafters who can draw any custom building based on your design criteria.

We custom engineer each structure according to your site’s snow and wind loads. This streamlines the building permit process, which we can also help with. We have designed greenhouses with snow loads of up to 85 lbs/square foot, and with wind loads of up to 135 mpg.

At Ceres we focus on building the most energy-efficient commercial greenhouses as possible. Our primary heating and cooling method stores the greenhouses’ heat (free thermal energy) in the walls and in the earth below the greenhouse. We are well-known for our GAHT™ system, a Ceres designed ground to air heat exchanger, which we have designed for many years all over the world. We also use phase change material. Finally, by using passive solar greenhouse design principles we minimize the heating / cooling load as much as possible, making our commercial greenhouses much easier to regulate and much more cost-effective versus traditional greenhouses. We also integrate back-up heating, cooling and ventilation systems as needed.

Like many commercial greenhouses, we often install gas powered heaters, dehumidifiers, and exhaust fans. Oftentimes, because of the built in efficiencies of our greenhouses and smaller heating and cooling loads that we deal with, we can design smaller systems to save our clients money during initial installation, and because the systems are needed less often, they save money over the long term.

We are also leaders in designing light deprivation systems as well as shading systems, and work with industry leaders to incorporate their systems into our highly efficient greenhouses.

Yes. We source growing systems and equipment from high-quality suppliers, according to your needs. These include:

  • Hydroponic and aquaponic growing systems
  • Black out / light deprivation systems
  • Shade systems
  • Irrigation systems

You can see some of the companies we work with on our partners page. We work directly with suppliers to ensure that growing systems integrate seamlessly with the greenhouse structure, handling all the planning and details for you.

As one of our clients put it, “On a scale of 1-10, with 1 being not knowing the head of a hammer from hog’s ass and 10 being a general contractor…how difficult are your kits to build if I am handy?” We estimate about a 6. Building a commercial steel greenhouse like our HighYield Greenhouse Kits requires some construction experience. We recommend having a crew of at least 2 people, preferably 3. Installation time depends on size. Most greenhouses are built within a couple of weeks (not including foundation and site work).

Foundation & Floors

This depends on the size of your commercial greenhouse. For more on basic greenhouse foundation types see our blog, Greenhouse Foundations. We work with engineers who can design your greenhouse foundation. However, because structural engineers are licensed by state, we oftentimes work with a structural engineer that you find in your area so that they will have be able to stamp the drawings in the state you are building in.

Whether or not the greenhouse needs a foundation depends on size, it’s location and the snow and wind loads. Small solar greenhouses do not need a foundation. They can be built on a level base (dirt or gravel) and anchored to the ground using rebar or products called earth anchors. For moderate to large residential greenhouses (over 120 sq. ft.) we recommend adding a foundation. Foundations can often be simple concrete piers. More about them and other foundation types in our blog “Greenhouse Foundations.”

We offer consulting on choosing a foundation type and recommend hiring a contractor to install the foundation.

This predominantly depends on how you want to grow. If growing with aquaponics, hydroponics, or in a commercial greenhouse with potted plants, concrete floors provide a clean surface to -efficient greenhouses do not need a floor. This is because the perimeter of the greenhouse is insulated. The soil below ground stays a warm constant temperature year-round. Normally, raised beds connect directly to the soil below ground. This is best for drainage and robust root growth. Flooring materials can be used in walkways. We recommend gravel, flagstone, or pavers. If planning to grow on tables, or with an aquaponics system, you may elect to install a concrete slab to create a level floor (this can also serve as your foundation). More information in our blog “Three types of floors for a greenhouse”.

Solar Panels, Electricity and Water

This depends on what type of systems you want to use for growing, and controlling the greenhouse environment. Typically, our residential greenhouse growers install electricity in the greenhouse to run fans and lights if necessary. These have a very small power draw but do require electrical hook-up. The simplest option is to wire the greenhouse to the home. Another option (though usually more expensive) is to install a solar panel system to run the electrical components.

You can also build a completely passive solar greenhouse – one that does not use any electrical components. For this we recommend using passive solar vent openers to provide automated ventilation. There are several pros and cons to building a passive solar greenhouse vs. an active one. Much more information on solar panel systems and passive solar greenhouse is in our book, The Year-Round Solar Greenhouse as well as “Integrating Solar Panels into the Greenhouse.”

There are a few different ways to handle watering in a residential greenhouse. These depend on the size and water requirement of the structure (climate dependent). They vary from a water hook-up (spigot) to using self-watering growing beds. For more see “Solar Greenhouse Basics: Watering Systems.”

Our greenhouses utilize passive solar design, called ‘solar greenhouses’ for short. Passive solar greenhouses are designed to maximize heating from the sun, to create an efficient self-sustaining year-round growing environment. While they can be powered by a solar PV (solar panels), Standard models do not include solar panels (photovoltaic systems). We can help you integrate solar panels into your design to make the greenhouse completely self-powered, net-zero energy or off-grid. Please see our blog, “Integrating Solar Panels with the greenhouse” for our tips on doing this.

Ceres Greenhouse Solutions

4760 Walnut St., Suite 106
Boulder, CO 80301
United States