Two-system AC replacement and humidity fix in Fuquay-Varina

The scope

A two storey house in Fuquay-Varina with two systems, both fourteen years old, and a complaint that had nothing to do with temperature. The thermostats held their setpoints. The house was still clammy, the hardwood had cupped in two rooms, and there was mould on the inside of a closet wall on the north side.

The challenge

Both systems were a full tonne oversized. That is the single most common defect we find in Triangle houses and it is counter-intuitive to explain, because bigger equipment cools faster.

Cooling faster is the problem. An air conditioner removes moisture only while it runs, and a dehumidifying coil needs a long steady run to do it. Oversized equipment hits the setpoint in eight minutes, shuts off, and leaves the moisture in the house. The thermostat reads seventy two and the house feels like a swimming pool changing room, which is exactly what the owners described.

Sealed duct leakage in a vented crawlspace made it worse, because every cubic foot of air lost down there was replaced by humid air pulled in from outside.

What we did

Load calculations on both systems first, room by room, rather than replacing what was there. Both came out smaller than the equipment they replaced.

The duct systems were sealed at every joint and boot with mastic, the crawlspace plenums rebuilt, and the returns opened up. Then both systems were replaced with correctly sized variable-speed equipment that runs long and slow, which is what actually pulls water out of the air.

Correct sizing gets a Triangle house most of the way but not all of it, particularly on a mild damp day in May when there is no cooling load at all and the outdoor dew point is still high. So a whole-home dehumidifier went in on the downstairs system, ducted, draining to the same condensate line, with its own humidistat.

The outcome

Indoor relative humidity now sits in the low fifties through a Triangle July instead of the high sixties. The cupped hardwood has largely flattened back out over the following months, which we told the owners might happen and were careful not to promise.

Five days on site across a week, with one system done at a time so the house was never entirely without cooling. The mould on the closet wall was cleaned by a remediation contractor we referred them to, because that is not work we take on and we said so at the first visit.

Finished 15 May 2026.