# Using a Mini-Split outdoor unit Indoors; Hot Box construction



## ugmjfarmer (Apr 12, 2016)

I plan to locate a 12000BTU outdoor unit for a mini split in its own vented/carbon scrubbed box for steal reasons. This will be mounted indoors and vented up and out an open window. I will pull air from the same window for the cold side of this loop.. The nice thing is I can easily adapt this into my cold air return vent and hot air vents in the colder months, without worry that it is too cold outside that my A/C stops working thereby failing my closed growing environment cooling.

What is the airflow that I should shoot for to cool the out-door unit? 745 CFM 8" vents or 400 CFM 6" Vents? My hunch is that the 6" is enough.. But could a house HVAC tech answer. Help? CFM - BTU conversion formula? Anything? Crickets? 

Thanks in advance.


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## thursdaythunder (May 20, 2016)

You should be fine if you keep the air temperature around the outdoor condenser down below 90-100 degrees. Obviously with this particular design you're going to have to bring fresh air in to cool the room the outdoor unit condenser's in. The make up air cfm & exhaust air cfm should be based on the size of that room. I would definitely maximize my air exchanges per minute in order to keep outdoor unit room temps down (That's the ONLY goal here), it's going to be trial and error. You might not need as much air exchange as you think to keep temps down into operating range.
The cooler air around the outdoor unit condenser coil is what's "subcooling" the refrigerant. If the subcooling suffers so does the actual cooling performance and efficiency of the unit. This will in time cause the compressor to fail. The coil has to get rid of the "Hot Gas" heat from the compressor to adequately work. These things are designed to work in temps up to 130 degrees with no problem. I've seen them work perfect during a 120 degree Afghan summer. 

Good Luck!


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## Joken (Jun 29, 2016)

You need at least 400CFM as stated and you won't get it through a 6", 8" will move that much air if you gave the appropriate fan pushing it. See if there is a 8" inline that will do it. Remember the fan rating may be with no ductwork attached. The more ducting, the less air. See this https://www.grainger.com/product/FANTECH-Plastic-Inline-Fan-15W686?functionCode=P2IDP2PCP


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## gPod (Jul 27, 2016)

What type of Mini-Split did you end up going with and how has it performed for you?


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