Plan the whole tent in one go
Enter your tent and lights once. The planner chains every calculator: fan, intake, filter, cooling, dehumidifier, CO₂ and circuits, sized for the worst case (lights at 100%) with a typical dimmed figure alongside. Copy the link to share it or print it for the shop.
Your plan
How it works, in plain words
The order
Light first, then the heat it makes, then the water the plants breathe out, then the air or AC to remove both, CO₂ only if the room is sealed, and finally the circuits for all of it.
Oversized lights
Left blank, the planner uses the GenetixBay recommendation of 50 W/ft² of dimmable light (the founder's rule of thumb: 800–900 W for a 4 × 4, about 50–56 W/ft²). Often called overkill, but cannabis can use far more light than most guides assume: yield kept rising up to ~1,800 µmol/m²/s in trials (Rodriguez-Morrison 2021). Ramp up gradually, with the climate and CO₂ to match.
Worst case and typical
The cooling and the wiring must cope with everything at 100%, so they use your lights' full wall watts (or 50 W/ft² if you leave it blank). The dimmed figure is a typical day at the stage's target.
Vented or sealed
Vented: the exhaust fan, passive intake and carbon filter carry the heat and water out, and the AC figure only matters if the intake air is too warm. Sealed: the exhaust stays off at lights-on, and the AC and dehumidifier do the work.
Estimates in the plan
The fan's power (about 0.12 W per rated CFM) and the AC's power (BTU/h ÷ 10) are rough figures for the circuit count. Use your equipment's real wall watts in the electrical calculator.
Every number this calculator uses
The same constants feed the Calculate it properly guides, so the tools and the articles agree. Rules of thumb are labelled as such.
| Constant | Value | What it is | Evidence |
|---|---|---|---|
BTU_PER_W | 3.412 BTU/h per W | Every watt drawn from the wall becomes 3.412 BTU/h of heat in the room, whatever the device | Established |
SENSIBLE_AIR | 1.08 BTU/h per CFM per °F | Heat one CFM of standard air carries per °F of temperature rise (60 min × 0.075 lb/ft³ × 0.24 BTU/lb·°F) | Established |
INTAKE_RATIO | 2.5 × exhaust duct area | Passive intake opening area (KB rule of thumb 2–3×; we default to the middle) | Grower practice |
CANOPY_CAPTURE | 0.85 fraction | Share of the fixture's photons that land on the canopy in a reflective tent (assumption) | Estimate |
GB_W_PER_FT2 | 50 W/ft² of dimmable capacity | GenetixBay recommendation: oversize and dim down. Too much is better than not enough | House position (founder) |
AC_MARGIN | 0.2 + | Cooling margin over the calculated load (homes keep within ~15%; grow rooms run near flat out, so 20% is common) | Grower practice |
AC_EER | 10 BTU/h per W | Rough efficiency of a room or portable AC, for the electrical estimate (mini-splits do better) | Estimate |
FAN_W_PER_CFM | 0.12 W per rated CFM | Rough power draw of an EC mixed-flow inline fan at full speed (for the planner's electrical total) | Estimate |
DEHU_MARGIN | 1.25 × | Dehumidifier margin over the average daily water (the AC also pulls water while it runs) | Grower practice |
CONTINUOUS | 0.8 × breaker rating | Continuous loads (3 h or more, which every grow light is) may use only 80% of the breaker | Established (code) |
Sources
- NIST. Guide for the Use of the International System of Units (SP 811), Appendix B: conversion factors (1 W = 3.412 142 BTU/h; 1 ft³ = 0.028 316 8 m³; 1 US gal = 3.785 412 L). https://www.nist.gov/pml/special-publication-811
- ASHRAE. 2021. ASHRAE Handbook: Fundamentals. Ch. 1 (psychrometrics: sensible heat of air, q = 1.08 × cfm × ΔT at standard air), Ch. 18 (heat gain from people, lighting and equipment), Ch. 21 (duct design: fitting and friction losses), Ch. 26–27 (thermal resistance of building assemblies). ASHRAE, Atlanta. https://www.ashrae.org/technical-resources/ashrae-handbook
- GenetixBay Knowledge Base. LED vs HPS: the heat and power-bill hype, and an LED buyer-beware guide (fixture µmol/J tiers, 85% canopy capture, watt-for-watt house advice, 1 W = 3.412 BTU/h). https://genetixbay.com/knowledge/equipment/led-vs-hps-hype-and-buyer-beware.html
- GenetixBay Knowledge Base. Airflow: air exchange, canopy air speed and fan placement (one tent volume every 1–3 min; +25–50% for a carbon filter and ducting; passive intake ≈ 2–3× exhaust duct area). https://genetixbay.com/knowledge/environment/airflow.html
- GenetixBay house position (founder's field experience, decades of indoor rooms): passive intake for most growers; oversize lights and dim down; replace HPS watt for watt unless the LED is top tier. https://genetixbay.com/editorial-policy
- Rodriguez-Morrison V, Llewellyn D, Zheng Y. 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020
- ACCA. Manual S: Residential Equipment Selection (cooling equipment kept close to the calculated load; oversizing short-cycles and dehumidifies poorly). https://www.acca.org/standards/technical-manuals/manual-s
- US DOE. 10 CFR 430 Subpart B, Appendix CC: Uniform test method for portable air conditioners (seasonally adjusted cooling capacity, which counts the infiltration a single-hose unit causes). https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-B/appendix-Appendix%20CC%20to%20Subpart%20B%20of%20Part%20430
- GenetixBay survey of published free-air ratings for mixed-flow inline fans sold for grow rooms, 2026 (ranges only; no brands).
- NFPA 70, National Electrical Code (2023): Art. 100 (continuous load = 3 hours or more), 210.19(A)(1) and 210.20(A) (conductors and breakers at 125% of continuous load, i.e. load ≤ 80%), 210.8 (GFCI locations), 400.12 (flexible cords not a substitute for fixed wiring). https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70
- CSA C22.1, Canadian Electrical Code, Part I: Rule 8-104 (continuous loads limited to 80% of the breaker rating) and Rule 26-700 series (receptacles and GFCI). https://www.csagroup.org/store/product/CSA%20C22.1:24/
- GenetixBay Knowledge Base. PPFD and DLI by stage, with the evidence (stage targets; DLI = PPFD × hours × 0.0036). https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.html
- GenetixBay Knowledge Base. CO₂ enrichment (targets 800–1,200 ppm at lights-on only; worth it only sealed and at high light). https://genetixbay.com/knowledge/environment/co2-enrichment.html
