Help with mini split btus

I am building a 8x8 or 10x10 grow room in my garage it will be insulated very well I will have 2 tents in there one for veg one for flower I am going to run 1 mh/hps in each tent 400watt I am wanting to put mini split in the room but dont know what size btu to go with I want the mini split to have an inverter also I am deciding on running c02 havnt made my mind up on this part yet I need help with what size btu to install I know with a house centeral unit if u over size it will cause issues not sure I'f it is the same with a mini split please help

It's not the same as a house unit, they have inverter compressors that can ramp up and down. In my opinion you need to oversize as with a room that big you will prob be like everyone else and expand, lol.

I'm confused on what lights your using cause you said 1000 watts and then 400 watts. How many total of each? And are the reflectors open or air cooled?

For right now 2 400watt mh/hps an they are air cooled

You can oversize a mini, as @Apalchen stated, they aren't just on or off, they can run just as hard as they have to.

If you will be running it when it's cool/cold outside then make sure the unit you select has an adequate low ambient rating. Some mitsubishi units I have seen will run down to -29F.

Auto restart after a power outage is a feature you require.

To estimate the required BTU/hr you can take 3.5 x watts in the room (include deuhumidifier fans, pumps, all power except the AC).

Make sure to consider the manual J calculations for the structure as it will have cooling requirements aside from the electrical.

If running a CO2 generator you should account for that as well.

Well 2 air cooled 400s doesn't require much cooling at all, but I would be willing to bet you will upgrade. For that size room even lit wall to wall a 24k btu will cool it. As long as you don't go over like 4k watts. If you plan to stay under 3000 watts then maybe an 18k btu mini split. That's as small as I would go in that size room, but I always have the urge to expand and I'd end up with atleast 2000-4000 watts of light in that size room. Plus not sure how hot your garage is but I'm guessing it's not conditioned air so I'd def do atleast an 18k btu personally would just go with the 24k btu, they will only work as hard as they have to, to keep it cool so might as well make sure to have enough cooling.

I'd love to put in a mini split unit....a friend just did and his electric bill went way down, plus now he has AC that he didn't before. My conditions are constantly changing with the seasons and I know it would save me too, after installation! Smart move OP!

10 x 10 space = 100 sqft. So even if we lit all that space at 50 watts per sqft thats 5kW or about 17,500 BTU/hr. Of course we wouldn't actually ever do that but a good 18,000 BTU/hr (1.5 ton) unit would handle anything you ever would imagine doing in there provided the room is well insulated against the garage heat. If you have to fight the garage heat at all and light the whole space, run a dehumidifier perhaps then go with 2 tons.

Of course for the 800 watts you need much less like 2800 BTU/hr, so if you will never ever add lighting then even a one ton unit is overkill. Of course the garage heat is a real thing and the one ton unit would have ample headroom for that if only running 800 watts.

It's funny to see the look on a HVAC techs face when you wanna put a 2 ton unit in a 10 x 10 room. lol

The unit my buddy put in his home also has a "dehumidify only" option...He was showing me how it drastically reduced the humidity in 1 hour, in his home though, not a grow room. Plus they heat cheap in the winter!

manfredo said:

The unit my buddy put in his home also has a "dehumidify only" option...He was showing me how it drastically reduced the humidity in 1 hour, in his home though, not a grow room. Plus they heat cheap in the winter!

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Many of the minis will do the dehu function, it can be handy, of course they also pull a lot of water when cooling. They aren't as energy efficient at the dehu only mode as a dedicated quality dehumidifier but they are not terrible either.

Some of the units are capable of the heating mode, they typically cost just a little more and they start calling them heat pumps. This mode can be really handy if you have lights off temperatures trying to drop too low for some reason.

You can also use a wifi controller with most of the minis, these will communicate to the AC unit using the signals the remote control uses. Then you can put it on your wifi router. Now you can setup schedules to change the settings say when the lights come on and go off, check temps from where ever using your smart phone, change settings from where ever, get alerts when things get out of range. Pebble, Sensibo are a few...

Yes even ac techs that claim to know grow rooms looked at me weird when I was getting my old mini hooked up, it was a 8x11 room with a 2 ton unit. It cooled 4 gavitas well when it wasn't out of freon that thing always leaked. My original installer wasn't as experienced with mini splits as he claimed.

Apalchen said:

Yes even ac techs that claim to know grow rooms looked at me weird when I was getting my old mini hooked up, it was a 8x11 room with a 2 ton unit. It cooled 4 gavitas well when it wasn't out of freon that thing always leaked. My original installer wasn't as experienced with mini splits as he claimed.

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Yeah you have to have a really good flare that is installed straight and torqued properly and use nylog properly. It's too much for many techs that are used to brazed linesets. One fella I know was installing a shit ton of minis for a chain of motels, he said that his rarely leaked, very rarely.

The most common mistake is actually over torquing the flare out of uncertainty. Using a flare nut torque wrench will eliminate the guess work. A nitrogen pressure test is also a step that many tech skip because it takes time and uses nitrogen gas.

the pseries from mitsubishi is the best if i had the money id get one of these

we used to use the basic 3000 btu for every se 1000 watts
a DE brought it up to 4-4,500 for 1000 watts

Thanks for all the info I will start a need thread when I start the build an keep everybody updated on the build

Dude you don't need a mini split for 2-400 watters,lol. I have a 2 ton(24,000 btus) mini split unit and I run 4630watts of hid...4/1000s hps + 1/630 cmh in my sealed flower room, plus dehu. Its honestly a lil oversized for my room but it lets me not have to run it kike crazy, its on auto and kicks on low alot. Usually people go by this- 5000 btus per 1000 watts of HID. So your not even in the threshold.

xox said:

the pseries from mitsubishi is the best if i had the money id get one of these

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I love my daikin. I have Mitsubishi mr slims upstairs in my living space and I have to take them apart almost twice a year to clean blower wheels and other areas because of mildew buildup. Its such a pain in the ass. Haven't had to do that once with my daikin in grow room.

Also if your going to do invest a mini split, I'd say screw the 400watters and get either a couple 630 cmh or a few 1000w hps and go ball to the wall mayne!

Dividedsky said:

Dude you don't need a mini split for 2-400 watters,lol.

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Yeah but since his room is in a garage he likely needs one just to cool the empty room on a hot summer day.