MINI SPLIT: how many BTUs needed for 8x8 with 4000w HPS?

Many have told me 18-24 k btu would be fine..

who recommends I buy a 30-36k btu mini split ? Or would that be a bit excess and waste of money?

I have 8” inline ac infinity fan hooked to carbon filter inside the room hanging from the ceiling blowing outside, through a window that’s in the room. And I also have a 8” ac infinity inline hooked to carbon filter outside of room blowing fresh air in. I also have a 12” 1500 cfm fan outside of the grow room that is hooked up to the lights by ductwork and sucks air from outside of room on one side.Ducted though the room/lights and blows the hood/light heat outside room.

I don’t want it working it’s guts out and constantly running 24-7.. well 12-18 hrs while the lights are on



the question I asked is all I need to know..
Not worried about breakers panels/boxes or any of that, I have that covered.

Pauly1118 said:

Many have told me 18-24 k btu would be fine..

who recommends I buy a 30-36k btu mini split ? Or would that be a bit excess and waste of money?

I have 8” inline ac infinity fan hooked to carbon filter inside the room hanging from the ceiling blowing outside, through a window that’s in the room. And I also have a 8” ac infinity inline hooked to carbon filter outside of room blowing fresh air in. I also have a 12” 1500 cfm fan outside of the grow room that is hooked up to the lights by ductwork and sucks air from outside of room on one side.Ducted though the room/lights and blows the hood/light heat outside room.

I don’t want it working it’s guts out and constantly running 24-7.. well 12-18 hrs while the lights are on



the question I asked is all I need to know..
Not worried about breakers panels/boxes or any of that, I have that covered.

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18K BTU would JUST cover it IMO. 30K BTU would be what I would do so you have room in your wattage for dehumidifiers, fans etc.

I have a Friedrich18K mini split, it had no problem cooling a 12 x 24 garage turned into a den with an 5 x 5 open rack grow using (2) 600w HPS. Actually where the split was mounted was directly above the lights. Unit ran non-stop while lights were on. I set the thermostat on 76 and there the temperature stayed day and night.

MidnightSun72 said:

18K BTU would JUST cover it IMO. 30K BTU would be what I would do so you have room in your wattage for dehumidifiers, fans etc.

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what do you mean room in my wattage ?
Like I said electrical is no problems. I literally replaced every electrical component in my home few weeks ago.. literally, from the plug/receptacles all the way to the service pole (had DTE come install new service line/wire) and I’m running each 1k HPS light on their own 20 amp breaker so they’re only running about half power since they use about 10 amps each

medicaloutlaw said:

I have a Friedrich18K mini split, it had no problem cooling a 12 x 24 garage turned into a den with an 5 x 5 open rack grow using (2) 600w HPS. Actually where the split was mounted was directly above the lights. Unit ran non-stop while lights were on. I set the thermostat on 76 and there the temperature stayed day and night.

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Yeah idk if I would call that good or good enough for me.. I don’t think I want it running the entire time the lights are on… ya know ? Maybe I’ll get a 24-30k just to give me that lil extra relief. So the unit can have few small breaks here n there even if it only gets to rest for 10 minutes every 30 minutes or whatever lol. I’m running onee light at the moment and I’m not really using anything except 16” oscillation wall mount fan and the temps stay within range 75-85… but that is if I leave the grow room door open.. which it’s built into the basement and my basement is just always cold. But if I close the door. It’ll get about 93 in there.. and that’s without running my 3 inline fans or my second oscillation fan

Pauly1118 said:

Yeah idk if I would call that good or good enough for me.. I don’t think I want it running the entire time the lights are on… ya know ? Maybe I’ll get a 24-30k just to give me that lil extra relief. So the unit can have few small breaks here n there even if it only gets to rest for 10 minutes every 30 minutes or whatever lol. I’m running onee light at the moment and I’m not really using anything except 16” oscillation wall mount fan and the temps stay within range 75-85… but that is if I leave the grow room door open.. which it’s built into the basement and my basement is just always cold. But if I close the door. It’ll get about 93 in there.. and that’s without running my 3 inline fans or my second oscillation fan

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Sizing an AC for a ventilated growroom is sort of a guess game.
in a SEALED room, 5-6k btu of cooling per 1000w of light is a safe bet. Air-cooled lights you can get away with less.
This is usually the most efficient way to use an AC. The AC is continuously working the same air, combating only the given heat load produced by the electrical equipment and the room itself (hopefully insulated well)

In a ventilated room you are also continuously introducing new air which is usually going to be hot due to the fact you are needing an AC. The AC can only do so much in this scenario. But what you can do is dial shit in by slowing down the exchange of air by slowing down your intake and exhaust fans. Give the AC more time to drop down the temps.
If you have the available power from the electrical panel the AC will be on, i would go with the larger minisplit. 30-36K.

Pauly1118 said:

what do you mean room in my wattage ?
Like I said electrical is no problems. I literally replaced every electrical component in my home few weeks ago.. literally, from the plug/receptacles all the way to the service pole (had DTE come install new service line/wire) and I’m running each 1k HPS light on their own 20 amp breaker so they’re only running about half power since they use about 10 amps each

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As in you will have headroom to spend more watts in your room. The more watts you use (fans, pumps, dehumidifiers, chillers, all contribute 3.41btu/w.

so your lights will be close 1100W at the wall so 4400W x 3.41btu = 15000 BTU. Just to cover the lights. Oscillating fans are 55W ( 187BTU) or so each inline 8" fan is around 200W (682 BTU). Dehumidifier typically around 700-1000W (2380-3410 BTU).

MidnightSun72 said:

18K BTU would JUST cover it IMO. 30K BTU would be what I would do so you have room in your wattage for dehumidifiers, fans etc.

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I like when people use common sense!!!

Since you are doing what I consider a technical installation (you have computed your needs and have a very clearly designed setup), maybe what would be most important is to get the highest possible SEER rating for the unit you buy.

Minisplits are designed to run a lot more than the larger home units. If you get a really high rating and buy a good brand, you should have it ramping up and down as much or more than turning on and off.

So why not buy a larger size than needed and get the highest SEER rating affordable?

You also can get a 2 zone setup to cool another part of the home or another room. Plenty to spare with an efficient oversized unit!

Yes bigger, and the highest efficiency u can afford

piratebug said:

I like when people use common sense!!!

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Just have to size it though just right so it won't short cycle or run too long. Both scenarios will lessen the life of the unit at the very least the compressor.

Pauly1118 said:

Yeah idk if I would call that good or good enough for me.. I don’t think I want it running the entire time the lights are on… ya know ? Maybe I’ll get a 24-30k just to give me that lil extra relief. So the unit can have few small breaks here n there even if it only gets to rest for 10 minutes every 30 minutes or whatever lol. I’m running onee light at the moment and I’m not really using anything except 16” oscillation wall mount fan and the temps stay within range 75-85… but that is if I leave the grow room door open.. which it’s built into the basement and my basement is just always cold. But if I close the door. It’ll get about 93 in there.. and that’s without running my 3 inline fans or my second oscillation fan

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Yeah bro you definitely need a little bigger unit. I just shared my setup as a comparative scenario. I didnt mention that the outside temps here are in the high 90s and this unit would run pretty much most of the day until the sun goes down whether there were any lights in it or not. Last summer there was not a grow in there so I left it off all day and just turn it on if I went out there to watch TV. That former garage is not as well insulated as the rest of the house. But I will say that since I made the switch to LED a few weeks ago I noticed the cycled unit off a couple times this week while going out there and tending plants.