Exhaust, heat load & circuit check
Size the exhaust fan, estimate the heat your equipment adds, and check the circuit against the 80% rule.
Room & ducting
Exhaust
Recommended fan rating
272m³/h
Room volume
3.2m³
Before derating
190m³/h
Fan ratings are at zero static pressure. Choose a fan whose curve still delivers this flow at your filter's pressure drop.
Equipment & circuit
Lights at wall draw, plus fans, dehumidifier, pumps
Heat & electrical load
Heat added
2,047BTU/h
Current draw
5A
How this is calculated
Exhaust
CFM = room ft³ ÷ minutes per air exchange × derating (filter +25%, ~10% per bend, ~1% per ft of duct)
- Derating factors are rules of thumb; check the fan's static-pressure curve.
- 1 CFM = 1.699 m³/h. Common practice is one full exchange every 1–3 minutes; this interval is a rule of thumb, not a cited target.
Heat load
BTU/h = W × 3.412; 1 ton = 12,000 BTU/h
- Add envelope/ambient gains and dehumidifier heat for sizing an AC.
Circuit
A = W / V; continuous loads ≤ 80% of breaker rating
- Have a licensed electrician verify any new circuit.
Cited targets
From the genetics.guru grow library, in the units each source used. Grades: strong and moderate are peer-reviewed; community practice is untested.
air temperature (day)vegetative24–28 °CCommunity practice
Consistent with trial conditions and leaf photosynthesis optimum 25-30 C.
2 sources
- Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
- Chandra S, Lata H, Khan IA, Elsohly MA (2008-10). Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions — Physiology and Molecular Biology of Plants 14(4):299-306
air temperature (day)flower24–28 °CModerate
31/27 C lowered cannabinoid concentration vs 25/21 C. Treat sustained >=30 C as a risk.
5 sources
- Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
- Llewellyn D, Golem S, Foley E, Dinka S, Jones AMP, Zheng Y (2022-09-27). Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content — Frontiers in Plant Science 13:974018
- Westmoreland FM, Kusuma P, Bugbee B (2021-03-23). Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids — PLOS ONE 16(3):e0248988
- Holweg MM, Curren T, Cravino A, Kaiser E, Kappers IF, Heuvelink E, et al. (2025-02). High air temperature reduces plant specialized metabolite yield in medical cannabis, and has genotype-specific effects on inflorescence dry matter production — Environmental and Experimental Botany 230:106085
- Chandra S, Lata H, Khan IA, Elsohly MA (2008-10). Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions — Physiology and Molecular Biology of Plants 14(4):299-306
air speed at canopy top (upper bound observed with high yields)flower≤ 1 m/sModerate
Utah State cannabis trials ran ~0.8 m/s at canopy top; leaf photosynthesis plateau to 1.0 m/s.
2 sources
- Westmoreland FM, Kusuma P, Bugbee B (2021-03-23). Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids — PLOS ONE 16(3):e0248988
- Kitaya Y, Tsuruyama J, Shibuya T, Yoshida M, Kiyota M (2003-01). Effects of air current speed on gas exchange in plant leaves and plant canopies — Advances in Space Research 31(1):177-182