Ventilation needed? Humidity control, comfort, and efficiency
So as I get closer to finishing my insulation and contemplate my airtightness I have begun to read more into the importance of ventilation. My newly constructed second floor is r23 wool with possibly another r3 to r6 of interior foam board that will act as my air barrier and thermal break at the studs. I am paying very close attention to airtightness upstairs.
So as I read through the site and start gather more info it is a lot to digest just on ventilation alone. I live near chicago climate zone 5 and just as our winters can be brutally cold our summers can be brutally humid. So I begin to think about dehumidification and the comfort aspect of things.
So through process of elimination I think I’m getting closer to the right answer and hopefully most economically feasible.
I started with looking at hrv and erv equipment or possibly a ventilating dehumidifier such as the ultra aire 120h. Neither of these are cheap so I began digging deeper.
I then read up on a central integrated fan supply and this seems to fit the budget better than option 1 and 1a. I Will have 3 bathroom exhaust fans on the 2nd floor and gas dryer exhaust. 1st floor will have another bathroom exhaust with a range hood in the kitchen. I figured this should be enough to exhaust stale air. But the cfis will not handle the humidity I figure it will actually add more humid air to the house.
But then I begin to ponder. Do I really need ventilation? My first floor is still the original multi wythe brick walls from 1952. Even though I do plan on pointing the mortar and replacing and air sealing the 1st floor windows sooner than later, I ask myself is this really considered a “tight” house. Does my brick exterior constitute airtightness? And is this brick 1st floor wall actually bringing in enough fresh outside air that I can omit the cfis system entirely?
So I’m undecided and truthfully unsure wether I install a CFIS on both of my hvac units(one located in the Basement and the second in a vented conditioned attic) or just one of the hvac systems(but which one?
But after all this I still haven’t addressed the humidity. A whole house dehumidifier does not agree with my pocket book. The portable dehumidifiers are looking real attractive. I could easily place one in my basement near a floor drain So the condensate can drain. For the price I’m thinking of buying a second portable unit to be placed in the 2nd floor laundry room that will also be equipped with a floor drain.
And lastly will my interior foam board help with the humidity? I’m planning on using a 3/4″ low density eps. I chose this because it is cheap, readily available near me. I do like the idea that it is more vapor open to allow my walls to dry out both ways if needed. I do not have exterior foam board just plywood, tyvek, and vinyl siding. And as Dana advised me in an earlier post, the vinyl cladding is somewhat forgiving. So given this I thought I could possibly use a 1/2 ” r3 polyiso with a reflective foil face on one side and a matte white foil face on the other. This will not allow drying to the interior but do i really need it too with vinyl siding? Will the polyiso do anything for humidy control in the summer? I am planning for a service cavity of 2×3 studs in front of my interior foam board. I believe I read somewhere that the air space in front of the reflective foil face with add some extra r value but how much does that amount to with 2.5″ between the foil face and drywall. Does my drywall then have to be airtight as well to actually reap the r value benefits of the space?
Comfort is important but cost is as well. I think I’ve gone through most options but I may have missed something along the way.
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