Greenhouse Unit Heaters Redefined
The revolutionary tubular heat exchanger inside the Lennox LF-24 series of greenhouse heaters ensures you years of performance and high efficiency. Combustion is precise because of special "in-shot" burners and fan assisted exhaust. Equipped with a TrueLeaf Combustion Air Separator, it's bullet-proof.

Warm Floor Projects

Greenhouse Construction Considerations


Do I Have a High Water Table Problem?

If you are contemplating construction of a new greenhouse, site selection is very important. Not only should your new greenhouse be constructed in an area without shading from other structures or trees, but you should also be careful not to site your facility in an area with a high seasonal or year ‘round water table level. Normal construction practices would typically have you create a compacted site with adequate drainage, even in a low-lying area. But, if you must build a greenhouse on a “wet” site you should make special provisions.

This is especially true if you plan to install a warm-floor heating system. If you install a warm-floor system and the water table “impinges” or touches the warm concrete, you could lose a tremendous amount of efficiency as the ground water will “wick” away precious heating BTU’s.

How do you determine if you have a high water table on your site? If you haven’t already been put on notice that you’ve got “wetlands” on your hands, (in which case you may not be doing much building anyway), there are some very simple procedures to check. The first and most obvious is to dig a test hole the depth of your excavation for the site and observe if it fills with water. Keep in mind that the local water table probably fluctuates with the season. If the test hole indicates that your water table may be close to the level of the bottom of your greenhouse floor, you have a “high” water table. If you have even a slight doubt, follow the procedures for setting up a warm-floor with a complete layer of insulation below.

Most warm-floor heating systems are created by encasing thermal tubing in the concrete pour. Boilers make hot water that pumps circulate through the tubing. The heated water gives up it’s heat through the tubing and warms the mass of the floor. A thermostat at or near the floor level monitors and controls the whole thing.

The goal of a warm-floor is to provide very even and efficient heat transfer to the entire greenhouse.

To help maximize the efficiency of this type of system, attention should be paid to reducing “parasitic” losses that can reduce the amount of heat making it from the boiler, through the floor, and into the greenhouse. All warm-floor installations should have perimeter insulation installed previous to pouring the concrete. This is typically done with 2” thick extruded styrene panels placed vertically on the inside of the forms, at a minimum 2’ depth into the ground. The best practice would be to insulate with 2” panels down below the depth of the frost line.

In high water table areas, it is necessary to insulate the entire site with extruded styrene insulation, otherwise your system installation could be a big disappointment. We know first hand of growers that skipped this step and found that their fuel use was double or triple what it should have been. We recommend a minimum of 1” thick material, which gives an “R” rating of 5. Place this insulation horizontally under the entire floor. If you plan to use heavy equipment on the slab, consult with a structural engineer to determine the compressive strength necessary for this material to handle the loading. For most greenhouse applications, standard compressive strength panels (25 PSI) will be fine.

In either area, perimeter or below slab, it is very important to use true extruded insulation, and not “bead-board” as the latter tends to absorb water and lose it’s insulative ability over time.

In these times of high fuel costs, properly insulating your warm-floor application is more than just a good idea, it’s paramount to helping make a profit from your new greenhouse.