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Old 07-07-2013, 10:31 PM   #1
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Venting questions for coldroom/root cellar

I am finishing a cold room in my basement.

Schematic can be seen at

It is built underground on the north side of my house (floor about 6’ below grade). It has 6” concrete walls. The north wall borders outside. The west and south walls border my basement. The East wall faces my garage but the garage is a slab floor so the wall is fully underground. The door is in the center of the south wall. The concrete ceiling is the covered patio outside my front door.

There is a 4” vent in the upper western corner of the north wall that is about 2’ long and turns 90 degrees west to exit the side of the outside stairs to access the outside.

There is a 4” vent in the upper eastern corner of the north wall (but about 8” lower than the western vent). This vent run after turning 90 degrees west as exits north wall is about 8’ long and it finally exit 4” below the other vent from the side of the outside stairs.

I have framed the inside of the coldroom and am going to insulate with 8” of closed cell spray foam. Before doing so I am trying to determine which vent I should keep as my warm air outlet and which to keep as my cool air inlet. For the warm air outlet I will simply leave the duct in the open portion of the wall. For the cold air inlet I will run 4” pipe down the wall (to be encased by spray foam which is why I want to figure it out now) and then exiting at floor level and running along the floor to the corner of the south wall. In this manner the cold air will enter at floor level in one corner and the warm air will leave from the upper opposite corner.

The total interior length of the cold intake would be 6’ running down the wall and then 5’ along the floor. If I use the north-west duct (option A) the total length would be 13’. If I use the north-east duct (Option B) the total length would be 19’.

Ideally I would wait until winter and then simply test both to see which draws better, however, I don’t want to spray foam in winter and want to finish it now (currently 30 degrees Celsius outside). I’m afraid runs this long in only 4” diameter ducts with passive flow is going to be disappointing.

So what do you think. Should the warm air have 8’ and cold air 13’ of duct (option A) or should the warm air have the 2’ and cold air 19’ of duct (option B).


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Old 07-12-2013, 06:10 AM   #2
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Here's post about building a root cellar. This might help a bit.


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