How much electricity does a home grow use?

Q: How much electricity does a home grow use?

A home grow uses about 300 kWh per photoperiod run in a 2 x 2 ft tent (150 W LED plus fans) and about 850 kWh in a 4 x 4 ft tent (500 W LED plus fans), with 4 weeks of veg at 18/6 and 10 weeks of flower at 12/12. At 0.15 per kWh that is roughly 45 and 130 in local currency. Dehumidifiers and heaters add more.

Short answer

A small home grow uses about 300 kWh per photoperiod run in a 2 x 2 ft tent and about 850 kWh in a 4 x 4 ft tent, with 4 weeks of veg at 18/6 and 10 weeks of flower at 12/12. The light is most of it. Established: it's arithmetic, kWh = watts × hours ÷ 1,000.

Why

Indoor growing is energy-hungry at scale. One estimate put indoor cannabis at about 1% of US electricity use ^[1]. At home the same physics applies, just smaller.

The light dominates, and efficacy sets its cost. Good LEDs exceed 2.5–3 µmol/J ^[3]. In one trial, the best LED fixture gave about 27% more flower per dollar of electricity than a double-ended HPS, at about 1.1–1.3 cents per mole of light against 1.6 cents at 0.10 per kWh ^[2].

Hours matter as much as watts. 18/6 veg uses 50% more lighting energy per day than 12/12 flower, and 24/0 uses double.

Climate gear is the hidden bill: a dehumidifier or heater can rival the light.

The numbers

Setup	Daily use	Run total	At 0.15/kWh
2 x 2 ft: 150 W LED + 40 W fans, veg 18/6	3.7 kWh	28 days ≈ 100 kWh
Same, flower 12/12	2.8 kWh	70 days ≈ 195 kWh
2 x 2 ft photo run		≈ 300 kWh	≈ 45
4 x 4 ft: 500 W LED + 80 W fans, veg 18/6	10.9 kWh	28 days ≈ 305 kWh
Same, flower 12/12	7.9 kWh	70 days ≈ 555 kWh
4 x 4 ft photo run		≈ 860 kWh	≈ 130
2 x 2 ft auto, 20/4 for 11 weeks	4.0 kWh	≈ 305 kWh	≈ 46
Add: 300 W dehumidifier, half the time	3.6 kWh	+350 kWh per 14 weeks	+53

Use your own tariff.

What to do

Use the light's real wall wattage, ideally read from a plug-in energy meter.
Add every device and its daily hours.
Buy fixture efficacy (µmol/J); it pays back every day.
Keep the tent in a room that is already near target temperature and RH.
Keep continuous load under 80% of the circuit rating ^[4].

Common mistakes

Using a fixture's "equivalent" wattage.
Forgetting fans run 24 hours.
Ignoring the dehumidifier or heater.

Full article: Your first grow
Guide: Electrical and water safety
Answers: fire risk · what wattage for my tent · LED vs HPS
Terms: photon efficacy · LED

Follow-up questions

How do I calculate my grow's electricity use?

To calculate a grow's electricity use, multiply each device's real wattage by the hours it runs per day and divide by 1,000 to get kWh per day. Add up the light, fans, dehumidifier and heater, multiply by the days in each stage, then by your price per kWh. A plug-in energy meter gives the real numbers instead of label figures.

Do autoflowers use more electricity?

Autoflowers use more lighting power per day than flowering photoperiods, because they run 18–20 hours of light rather than 12, but they finish in about 9–14 weeks with no separate veg. A 150 W auto run at 20/4 for 11 weeks uses about 300 kWh with fans, close to a photoperiod run with 4 weeks of veg in the same tent.

Are LEDs cheaper to run than HPS?

Efficient LEDs are cheaper to run than HPS for the same light at the plants. In one trial, the best LED fixture made about 2.5 µmol of light per joule against 1.7 for a double-ended HPS, and produced about 27% more flower per dollar of electricity. Whether LED or HPS grows better buds is a separate, open question GenetixBay is testing in a Bay Trial.

Sources

Mills E, 2012. The carbon footprint of indoor Cannabis production. Energy Policy 46:58-67. doi.org/10.1016/j.enpol.2012.03.023

Westmoreland FM, Kusuma P, Bugbee B, 2021. Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids. PLoS ONE 16(3): e0248988. doi.org/10.1371/journal.pone.0248988

Kusuma P, Pattison PM, Bugbee B, 2020. From physics to fixtures to food: current and potential LED efficacy. Horticulture Research 7:56. doi.org/10.1038/s41438-020-0283-7

National Fire Protection Association. NFPA 70, National Electrical Code (continuous loads at 80 % of branch-circuit rating; GFCI requirements). nfpa.org/codes-and-standards/nfpa-70-standard-development/70