E-mail - Cooling a Grow Room for Less Than 50 Bucks

Hi Doc,
I am looking to purchase a 400 hps light set from htgsupply.com and I was wondering if it would require cooling if it is left in a 12-12 cycle. I am limited in terms of cooling as I do not want to destroy my closet and am not able to drill anything. How could one go about cooling this machine for under $50 effectively?

Hi, The 400 is a good all purpose light, I use them myself. The answer to your question depends on the size of your closet. I also have a 400 watt in an old closet that is 8 feet high and 4 feet by 9 feet (I only grow under ½ that space at most). I have a carbon filter to blow the air around and my temperature never gets above 90F if I leave the door shut 24/7. You could use a circulation fan for far less than 50 dollars to move the heat if you don’t want to buy a carbon filter. Temperatures in the 90’s F may seem high but the temperature is in the low 70’s or less in the dark cycle so a few hours of 90F while not ideal is ok for most plants. If your closet is smaller space you will need to get some of the heat out. The easiest way is to have the door open during the lights on cycle. The best time to do this would be near the end of the light 'on' cycle when the temperature will be highest. The problem is you may forget to shut the door when say, you are not home, and the light will go off but the door will be open. (If you have irregular light and dark cycles you will have poor or no flowering/fruit). It would be ok to leave the door open for 5-15 minutes every day after the lights turn off to let all the heat out. It is good growing to have a big difference between day and night temperatures; you don't want to trap all the heat in the closet all night.

If your temperatures are in the upper 90’s or over 100F for long periods and you can’t open the door then you may need to use an exhaust fan. I say this because I had a small closet (3x3x7 feet) I used once and even a 250 Watt HPS needed to have the door open or it would go over 100F which will slow plant growth and make the plants grow tall and fall over, and flower poorly. You will need to do some minor construction, drill a hole a few inches in diameter, depending on the fan/duct you use.  Wall studs are usually  16 inches apart, if you find one, move the hole don't cut one , it may be holding up the roof. The fan and duct work will blow the heat out of the room. Since heat rises you should put the fan and duct at the top of the grow room.  Last option, if construction of a duct/fan or having the door open is not possible, you may want to use LED or fluorescent lights. You know I have tested the Tri-Band and you can get HO T-5 with flowering bulbs that are high in RED light

So, the first thing you need to do is to get a thermometer that has a minimum and a maximum reading and put it in the closet.  Take the reading at the top of the plants under the light.  Do not take the reading at the top of the closet, this will be the hottest spot, but is not where your plants are growing. If the temperature never goes above 90F at the plant tops you’re fine and have solved the problem for less than 50 dollars. If it is over 100F, and you are not growing cacti, your plants won't grow anywhere near their full potential. With temperatures in the upper 90F range or more you will need to do something to get rid of the heat like open the door, or use an exhaust fan/vent. You can get a squirrel cage from HTGSupply.com and I would recommend getting the duct and flange from them too so you know everything matches up. This option is sadly more than 50 bucks but is guaranteed. You can vent the air outside, or I like to vent it into the next room during the chilly months to use the heat more efficiently (think cheaper gas/electric bills with a warm room). I don’t grow in the room in the summer.

I would also send an E-mail to Sales@htgsupply.com, where a sales representative knows how to use all sorts of specific equipment. I just help with how to grow plants.

Good Growing,

Dr. E.R.Myers

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