Plan heat lamp placement around seedlings and pots. Compare heater types, reflectors, and mounting heights. Avoid cold spots with practical range and spacing guides.
| Power (W) | Eff. (%) | Beam (deg) | Height (m) | Wind | Threshold (W/m²) | Typical radius (m) | Spacing @15% overlap (m) |
|---|---|---|---|---|---|---|---|
| 1000 | 80 | 90 | 1.6 | Calm | 180 | 0.85 | 1.45 |
| 1500 | 85 | 60 | 2.0 | Calm | 200 | 1.06 | 1.80 |
| 2000 | 90 | 45 | 2.4 | Breezy | 250 | 0.98 | 1.67 |
| 3000 | 90 | 90 | 3.0 | Windy | 300 | 1.16 | 1.98 |
The model treats the heater as a uniform radiant source inside a cone (beam angle). It converts heater power to effective radiant power using the efficiency setting.
The effective range is the smallest radius limited by beam geometry and by the minimum irradiance target. Wind exposure increases the required threshold to reduce cold-edge risk.
Radiant heaters warm plants by delivering energy directly to leaves, soil, and benches, reducing reliance on heating air. In protected growing, target edge irradiance often falls between 150 and 400 W/m² for frost buffering, depending on crop sensitivity and humidity. Use higher targets for wet foliage or exposed soil that loses heat quickly. For reflective mulches, raise input power or reduce mounting height to compensate for lower absorption.
Beam angle and mounting height control footprint. The geometric radius is r = h·tan(θ/2), so doubling height doubles radius, but intensity drops rapidly with distance. Narrow beams can create hot centers and cool edges; wider beams improve uniformity but require more wattage to maintain a given threshold. When moving heaters, re-check clearance to prevent scorching and to keep wiring away from irrigation.
Wind and ventilation increase convective losses and effectively raise the flux needed to hold temperature. A simple adjustment multiplies the irradiance threshold by a wind factor, such as 1.0 for calm greenhouse bays, 1.2 for breezy setups, and 1.5 for open rows. If you can add windbreak cloth, curtains, or low tunnels, you may lower the required threshold and extend practical range.
Temperature-rise mode links desired warming to a loss coefficient, using required absorbed flux ≈ U·ΔT. Typical U values can range from 15 to 40 W/m²·°C, depending on airflow and surface moisture. A 6°C edge rise with U=25 requires about 150 W/m² absorbed. Dividing by absorptivity converts this to incident irradiance, so dark soil (0.9) needs less than reflective groundcovers.
Spacing and overlap determine how evenly heat is distributed across beds. Start with spacing equal to diameter times (1 − overlap). For propagation benches, 15–25% overlap often reduces cold strips without excessive power density. Validate by measuring leaf temperature at several points, then tune height, angle, and overlap until edge conditions match your crop risk level. Record nighttime setpoints, outside temperature, and heater duty cycles to compare scenarios and budget electricity use.
Start at 150–250 W/m² for mild frost risk in sheltered beds. Use 250–400 W/m² for tender crops, wet soil, or colder nights. Confirm by checking leaf temperature near the edge during worst-case conditions.
Air movement strips heat from leaves and soil, so the same radiant flux produces less warming. The wind factor raises the required threshold, which reduces the computed radius. Windbreaks and low tunnels can restore coverage.
Wider beams usually give smoother coverage across flats, while narrow beams can overheat centers. Many growers prefer 60–90° with moderate height to avoid hot spots. Always verify with thermometer readings at several tray positions.
Use 0.85–0.95 for dark, moist soil or black fabric. Use 0.60–0.80 for lighter soils, straw, or reflective films. If you are unsure, pick 0.80 and compare results with measured surface temperatures.
For general bed protection, 10–20% overlap is a practical starting point. For uniform propagation or sensitive crops, try 20–30% to reduce cold strips. Higher overlap increases heater count and energy use.
Yes. Set wind exposure to calm, use your mounting height above canopy, and choose a threshold that matches your crop stage. For enclosed spaces, the temperature-rise mode can be helpful, but calibrate the loss coefficient with observations.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.