We are in the planning stages of a small addition to our home that will add 50 sq. ft to each of our three floors and I am trying to figure out the HVAC needs. The house has an oversized forced air heat/ac system, so picking up the additional square footage.
On one floor the space will serve as a foyer/mudroom and will connect without a door to a conditioned living room. On the next floor, the addition will be subdivided into a mudroom and a very small powder room, just 16 sq. ft. The mudroom and the powder room will of course be divided by a door, but the mudroom will connect to the conditioned kitchen without a door. On the third level, the addition will function as an annex to a conditioned bedroom without a door.
On all three levels, the adjoining conditioned space has sufficient supply air to service the addition. By adding supply vents to the addition spaces, is there any risk of over conditioning the space, making is hotter or cooler than is desirable? I am especially concerned with the 16 sq. ft. powder room, where it seems even a 3" duct would overwhelm it.