If a ac system is set up right no out side air is pulled into the house. Where in fan,, heat or cool all temperature exchange id done in the refrigerant gas inside the A coil, evaporator coil and compressor. not actual air exchange with the out side air.

the windows units actually work the same way only way fresh air is taken in is if the ac unit has a door in it to open for air to be drawn in.

Quote: ZiggyRoss wrote in post #6

---

This is related to something I don't understand. If my tent is in a shed do I need to bring fresh air in from the outside or just from within the shed.

---

unless the shed is airtight no. most houses and sheds have enough air leaks and movements(door opening and closing) to sustain co2 level at normal levels for plant growth. drawing from the sheds you basical made the sheds the lung room as they are calling it now, it conditions the air beit either warming it up some or cooling it down before it enters the grow space.

In that case outside air would be better and easier on you heating/cooling system. I just like indoor air better because of there is less change of bugs getting to the plants.