Installing mini-split, need advice on vented/sealed and co2

Ok so after much thought I’m installing an18000btu mini-split in my flower room next week.. I’m currently running 1890w of Cmh over a 4x8 table but I’m plotting on adding a further 4x4 and another 630de Cmh for my next run as it will just fit. I’ve been growing for a few years now but I’ve got no firsthand experience growing with an a/c but it’s now time to learn.. My room is obviously currently vented so my first question is when running a mini split is it best to seal the room and if so do I then have to supplement co2? Could I vent during the lights out period and would this venting supply enough co2 or would I have to periodically vent during the lights on period to have sufficient? My room vents 24/7 as it is now but surely that will have a hugely negative effect on the efficiency of the a/c? Constantly sucking all the cooled air out..

I’m definitely not against completely sealing the room and running co2, although the initial outlay is pretty heavy but if it significantly increases my yields I’m fine with that, if it’s marginal however then I’d rather do without if possible. I’ve read various findings on how much difference supplementing co2 makes.. from significant to marginal

Please give me some guidance on this guys.. I know I need the a/c but I want to set things up right the first time.. I hate doing shit twice

They make DIY mini splits with the refrigeration already loaded in the linesets if you have someone to wire it. I believe a dedicated 20A would be needed for that size unit, but check with the manufacturer.

A mini split is just like a window AC in that you can vent it but you waste the energy. I did it this summer with a window AC and vented for 5 minutes every 30 min so I wasn't wasting much cooling.

You could certainly seal the room though. I would seal it for sure. Pump co2 and raise your ambient temps = cooling less.

18k btu is good. Your cooling load is probably around 10k btu. Oversizing will allow it to run less and room for expansion of lights if needed

firsttimeARE said:

They make DIY mini splits with the refrigeration already loaded in the linesets if you have someone to wire it. I believe a dedicated 20A would be needed for that size unit, but check with the manufacturer.

A mini split is just like a window AC in that you can vent it but you waste the energy. I did it this summer with a window AC and vented for 5 minutes every 30 min so I wasn't wasting much cooling.

You could certainly seal the room though. I would seal it for sure. Pump co2 and raise your ambient temps = cooling less.

18k btu is good. Your cooling load is probably around 10k btu. Oversizing will allow it to run less and room for expansion of lights if needed

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Ok thanks for the advice man.. yeah I opted for a larger unit hoping for more efficiency and also to have scope for a further light.. The cycle timers I use only have increments of 15mins so should I vent 15mins every hour or every two hours? I’m not sure how fast the plants go through the available co2 after venting? I’m heading for supplementing co2 though but maybe not straight away, I just want to digest the cost of the new a/c initially..

Tkboy said:

Ok thanks for the advice man.. yeah I opted for a larger unit hoping for more efficiency and also to have scope for a further light.. The cycle timers I use only have increments of 15mins so should I vent 15mins every hour or every two hours? I’m not sure how fast the plants go through the available co2 after venting? I’m heading for supplementing co2 though but maybe not straight away, I just want to digest the cost of the new a/c initially..

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My thought is that with venting, you would be wasting a lot of supplemental C02 and cooling with intake/exhaust. After you get the minisplit, you are half way there to having a fully sealed climate controled room/environment , why stop there? A good dehumidifier is pretty much all you will have left after mini split and co2 injection. I just bought two twenty lb co2 tanks to swap with each other for the sealed room I’m building and i plan on filling the room up with CO2 an hour before my lights come on, and on a timer releasing CO2 the first 15 min of every hour while lights are on. This is without any intake exhaust setup in a 8x12 room and even so my tanks will likely last 6-12 days each releasing 1000-1500ppm I’m told, maybe a tad longer . I might even opt to get a third twenty lb tank just to have on hand. The 50lbs where just too heavy for me to lug around. Sorry to keep editing I’m waiting on my first cup of coffee lol. Still waking up.

Iriemedicine said:

My thought is that with venting, you would be wasting a lot of supplemental C02 and cooling with intake/exhaust. After you get the minisplit, you are half way there to having a fully sealed climate controled room/environment , why stop there? I just bought two twenty lb co2 tanks to swap with each other for the sealed room I’m building and i plan on filling the room up with CO2 an hour before my lights come on, and on a timer releasing CO2 every 15 min while lights are on. This is without any intake exhaust setup in a 8x12 room and even so my tanks will likely last 6-12 days each releasing 1000-1500ppm I’m told, maybe a tad longer . I might even opt to get a third twenty lb tank just to have on hand. The 50lbs where just too heavy for me to lug around.

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Yeah I am definitely heading that way.. I just want to get my temps in check at this stage and then work on the co2 setup.. So do you plan on having zero vents/ venting in your room? Does one not have to dump the co2 at lights out somehow..? Also are you not planning on utilising a co2 controller?

It would be nice to have a completely sealed room eventually without any vents if possible..

Tkboy said:

Yeah I am definitely heading that way.. I just want to get my temps in check at this stage and then work on the co2 setup.. So do you plan on having zero vents/ venting in your room? Does one not have to dump the co2 at lights out somehow..? Also are you not planning on utilising a co2 controller?

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Ahh yes man I got you 100%. It is an expensive endeavor for sure. I plan on having zero vents for my room. I have a 24k BTU mini split, a quest 105 dehumidifier I just got in yesterday and I’m having installed today (Thing is a beast! It runs on 4.9 amps and is capable of removing 105 pints per day), and CO2 injection with a tank and a basic regulator. I don’t have any fancy environmental controllers yet, I estimate co2 output just by doing math and have a thermostat with temp and humidity I monitor and adjust my equipment accordingly. In my 8x12 room I’m running two 1000 watt lights bare bulb and they get hot AF with out any cooling, the mini split however, allows them to run without being air cooled and I still can have full control of the grow room climate regardless of the outside temps.

firsttimeARE said:

They make DIY mini splits with the refrigeration already loaded in the linesets if you have someone to wire it. I believe a dedicated 20A would be needed for that size unit, but check with the manufacturer.

A mini split is just like a window AC in that you can vent it but you waste the energy. I did it this summer with a window AC and vented for 5 minutes every 30 min so I wasn't wasting much cooling.

You could certainly seal the room though. I would seal it for sure. Pump co2 and raise your ambient temps = cooling less.

18k btu is good. Your cooling load is probably around 10k btu. Oversizing will allow it to run less and room for expansion of lights if needed

Click to expand...

Question
With the pre-charged unit how do you get the blower part through wall is there a 2 part sealed connector line that comes apart to snake it through the hole in wall?
Our is it always attached and you feed it in a window sill and seal the opening around it?

Many of the units on sale these days can be DIY installed by the homeowner...
Just make sure to double check it doesn't need an HVAC guy to hook up that hose if you take the wrong kind.

Tkboy said:

Does one not have to dump the co2 at lights out somehow..?

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So it is my understanding, I may be wrong (someone please correct me if so), that plants in darkness, can not utilize CO2 near as efficiently as they can during light period (I’m guessing this is to do with photosynthesis). Some people I’ve talked to even go as far to say that releasing CO2 during the dark is a waste of CO2. I have not done any expirementing with CO2 during lights out, so there is a possibility the plants would receive some benefit but I will leave that to people who are smarter than me to play around with and determine. Also another thing to think about, with lights out your humidity will rise so your exhaust fan may be running more while the lights are out to deal with removing some of the RH from the air.

ANC said:

Many of the units on sale these days can be DIY installed by the homeowner...
Just make sure to double check it doesn't need an HVAC guy to hook up that hose if you take the wrong kind.

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All I needed HVAC guy for was to fill mine with refrigerant for $70 and it was ready to run. It was a pretty easy DIY project. Will say check your electrical capacity first because these things pull a lot of juice.

@firsttimeARE good info bro. Appreciate ya.

Yeah, but they make them now so it is filled already and there is a special hose connector to hook the inside and outside parts up.
I saw it on youtube a while ago.

Iriemedicine said:

So it is my understanding, I may be wrong (someone please correct me if so), that plants in darkness, can not utilize CO2 near as efficiently as they can during light period (I’m guessing this is to do with photosynthesis). Some people I’ve talked to even go as far to say that releasing CO2 during the dark is a waste of CO2. I have not done any expirementing with CO2 during lights out, so there is a possibility the plants would receive some benefit but I will leave that to people who are smarter than me to play around with and determine. Also another thing to think about, with lights out your humidity will rise so your exhaust fan may be running more while the lights are out to deal with removing some of the RH from the air.

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That is about correct. CO2 in the dark is a waste of money.

Some other food for thought, I bought my minisplit direct from the manufacturer and they gave me a free life time warranty on the unit.

ANC said:

That is about correct. CO2 in the dark is a waste of money.

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Yeah I’m having my a/c pre-charged with refrigerant, it has quick connect hoses and just requires bleeding - no vacuum pump necessary. Is it not true that excessive co2 during the lights out period is actually harmful to the plants..? If one is dosing just via calculations and timer it might be best to stop sometime before lights out if the room has no exhaust vent at all? As I said sealed environments are new to me so I’m trying to fully understand the intricacies of them..

I don't think it is a problem as long as the plants can access all the O2 they need.
CO2 and O2 are not mutually exclusive. i.e. you can have lots of both (just not in your blood).

A proper designed CO2 room would have a backdraft valve somewhere for venting. at lights out

Tkboy said:

Is it not true that excessive co2 during the lights out period is actually harmful to the plants..? If one is dosing just via calculations and timer it might be best to stop sometime before lights out if the room has no exhaust vent at all? As I said sealed environments are new to me so I’m trying to fully understand the intricacies of them..

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I don’t know that it would be harmful to the plants unless it was insane amounts being released, and at that level it may or may not even be safe for you to be working in the room lol I’m not sure. The reason I stop at dark cycle is because CO2 will still remain in the air because it is 100% sealed with no exhaust. The plants will use less CO2 at night because light is required for photosynthesis and the remaining co2 in the room will gradually dissipate through out the course of the night cycle before the room is filled up again with co2 one hour before lights come back on. During the night cycle , the dehumidifier is doing its thing removing the rising humidity from the air and mini split turns on and off when needed to adjust temp.

Iriemedicine said:

The reason I stop at dark cycle is because CO2

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is expensive enough not to waste plus we don;t want to add to the whole CO2 debacle.

ANC said:

is expensive enough not to waste plus we don;t want to add to the whole CO2 debacle.

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Fuck yeah, a 20lb tank costs $7 to refill here. Again I’m no scientist lol just a pot head going off of what I have read over the course of time haha.