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We’re finishing our basement. The basement currently is totally unfinished has 2 vents and it’s pretty cool down there (in July) so I think the vents are functioning properly. One vent is in a room which we are making into a gym room and another vent is in a space which we are going to leave unfinished. My question is - do we need more vents? Especially if we keep the doors open for the gym room and the unfinished space?

Basement is about 2400 sqft - about 400-500 of which is going to be left unfinished. The bedroom + closet is going to be close to 200 sqft. The gym room which is adjacent to the bedroom and has a vent already is about 150 sqft. Bathroom is going to be about 80-90 sqft. Walking space/ Rec area/ sitting area is the remaining space. Same vents for heating. We are in Virginia so it won’t get cold enough to snow - it may go below freezing a couple weeks a year.

Alternative - a window AC unit in the bedroom? Would this work too!?

Thanks!

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    Vents to/from where, for what purpose?
    – keshlam
    Jul 4, 2023 at 2:59
  • How big is the basement? How big is each room? Will the same vents be used for heating in the winter, and if so, how cold does it get outside? Jul 4, 2023 at 4:14
  • Basement is about 2400 sqft - about 400-500 of which is going to be left unfinished. The bedroom + closet is going to be close to 200 sqft. The gym room which is adjacent to the bedroom and has a vent already is about 150 sqft. Bathroom is going to be about 80-90 sqft. Walking space/ Rec area/ sitting area is the remaining space. Yes - same vents for heating. It’s in Virginia so it won’t get cold enough to snow - it may go below freezing a couple weeks a year
    – AISHWARRYA
    Jul 4, 2023 at 9:28
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    Cool air sinks, so basements are usually the coolest/cold space in any house without any help from vents.
    – crip659
    Jul 4, 2023 at 11:13
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    You will likely want at least one vent in each room, because once you put up walls air will not flow that much between rooms. Always plan for the "worst" season - in your case that is heating for the basement. If you put in more vents than you really need for cooling (because basement naturally cooler than the rest of the house), you can close some of them during the summer and open them during the winter. Jul 4, 2023 at 14:13

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This is the usual balance problem we get with vents, with summer A/C vs winter heating.

Sunlight is 1000 watts per square meter or 300 BTU/hr per square foot, so by summer, some rooms get punished while other rooms are made in the shade. Whereas in winter, sunlight helps heat those same rooms, while leaving others in the cold. So the vent balance you need summer vs. winter is wildly different.

The right answer to this is to abandon this designed-in-1930s scheme of having ducts from an air handler that handles both the furnace and the A/C, and go with a split heat pump system with head units in each space with their own thermostat on each head unit.

But otherwise I would say if a basement is well balanced in summer you'll be able to store meat down there in the winter. It will help to set the fan to "always on", if your return ducting is set up correctly. Then it will steal heat from other rooms in the house, including the room with the main thermostat.

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