LX-140 WITH 14,000 BTU AC AND 14,200 BTU HEATER. Yes I know its pricey at $419.89 but when you think what even a portable air-con is going to cost you, this all in one heater / air conditioner / fan and dehumidifier will cover all year round climate control for your grow room. One thing that really makes it stand out is its big capacity dehumidifier (60 pints).
The person should pass out in 6 - 20 seconds. Depending on the person, irreversable brain damage will begin somewhere around 4 to 6 minutes. At 7 minutes, the brain will be dead but the drowning person missed it all as they passed out at 6 - 20 seconds.
Assuming a normally fit person, otherwise conscious and uninjured, who is drowning in warm (21C/70F) water, I would estimate 2-3 minutes before full loss of consciousness, and 5-10 minutes before brain damage, and 15 minutes before irrecoverable death.