How best to install HVAC return duct on outside of house?
Basic facts: 3 level house built on a down slope hillside lot in 1994. HVAC zone one covers main and upper floors. Zone two heats lower floor bedrooms. Equipment room located on lower floor. Climate zone 3c—SF Bay Area home. Large SW facing windows heat up main floor (family room) and upper floor master suite.
I just had a 4 ton AC unit installed for zone one knowing it might under serve the 680 sq ft. upper floor master suite as there is no air return register upstairs and original system/ducting was designed for heating only. The AC installer said the existing return was undersized and made some modifications to slightly improve the return capacity during installation.
I am now considering installing an upper floor air return duct on the outside of the northwest side of my house, exiting the premise via an exterior wall in the master closet down two floors to penetrate the stucco wall into dead space under the house and run horizontal 25 ft to the air return in equipment room. The duct would be exposed to the sun apprx. 2 hours per day in the middle of summer.
The 3-level house “cascades” down the sloped lot so the floors do not stack up and there is not the ability for interior raceways or adding ducts. The master closest is on the opposite end of the floor from the sleeping area. I believe an air return located at the top of the closest wall is a better first step than adding another supply register in the sleeping area—which could be done but at considerably more cost and hassle.
What type of ducting? Can it be stuccoed over or will I need to build a raceway to hold the ducting? Is there a better way to camouflage the duct or a better solution all together?
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