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Hey guys,

This is my first time posting, but I have listened to the show for a while now and always appreciate how much there is to learn from the feedback you guys  give to growers.

So, somewhat of a multifaceted question for you today… I have recently started growing indoor hemp for fem seed production about 6 weeks ago and joined a team that was growing about 450 hemp plants per cycle.

Here’s the set up:

We are in a 3000 sqft warehouse (well insulated) with 20-25ft high ceilings.

We have 91 Growers Choice Double Ended CMH’s placed on 4 foot centers. The lights are about 8 ft off the ground. We are 4 weeks into flower on our earliest transplants and about 2 weeks into flower on our latest transplants. The lights are about 2-3 ft above the largest plants. The ballasts run 600-1000 watts, however we are running them at 420 watts with a separate controller.

In order to cool the building we have a 10-ton HVAC. I originally thought this unit wouldn’t have any problems cooling our space, but as I started to calculate BTU’s, I had a reality check.

Technically a 10-ton unit could move 180,000 BTU’s per hour (equivalent to a 5-6000 sqft home with 8 ft ceilings). However, when you add the lights at 4BTU’s per watt:

1680 BTU’s per light

91 lights

152,000 BTU’s!!!

Prior to this generation, they had only run half the lights in the building because of tighter plant spacing. Now we have everything happy and spread out, but all the lights are heating the place up.

It is critical that we bring the heat down in the room because we have been trying to pollinate our plants and we start the day at around 66F, but then by the end of the day it is nearly 80F in the flower room. The RH stays around 50%, but the increasing temperature is not recommended for a successful pollination.

Here’s the thing, we’ve had a few sunny days now that it’s warming back up and it has been exceedingly difficult to keep the heat down in this room. After running the BTU’s yesterday, I realized that something has to happen with our lights in order for the HVAC to be able to cool effectively.

So, the question is:

Do I turn off some lights and increase the wattage?

Or do I leave all the lights on and decrease the wattage?

What do you think will cause the least stress to the plants and keep them stoked and on their way to making us some nice seeds?

Thanks guys!!

Let me know if you have any other questions!!