Fresh air in a Jacksonville house without letting the 72-degree dew point in

The weather a ventilator has to work against

Jacksonville’s summer air is the problem a ventilation system exists to solve. Dew points average 71 to 73 degrees from June through August. By early August the air is muggy nearly every day, and that lasts into late September. Hurricane season brings weeks of rain-saturated air with little sun to dry anything. Every cubic foot of that air you let into the house carries water the air conditioner then has to remove, and in mild weather it cannot.

So the old advice, open the windows and let the house breathe, fails here for most of the year. Yet a sealed house still needs outside air: people exhale it, cooking fouls it, new carpet and cabinets outgas into it. The question is how to bring it in without bringing in the dew point.

Five things people believe about ventilation here

“The AC brings in fresh air.” It does not. A standard system recirculates the air already inside; the only outside air it sees leaks in through gaps.

“Bathroom fans are enough.” They remove moisture at the source, which is good, but they also pull replacement air in through whatever cracks exist, including the attic and the garage.

“My house isn’t that tight.” If it was built since 2000 in Oceanway, Intracoastal West, Baymeadows or the Wildlight corridor in Yulee, it is tighter than you think. Those houses were built to codes that assumed mechanical ventilation would follow, and in most of them it never did.

“Fresh air means more humidity.” Only if it comes in raw. An energy recovery ventilator passes the incoming air across the outgoing air through a core that transfers heat and moisture, so August air arrives having left most of its water with the air going out.

“A ventilator will fix my humidity problem.” No. It will keep a tight house from getting worse. A house that is already damp needs a dehumidifier, and often both.

What an ERV actually does in a tight house

An energy recovery ventilator is a box with two fans and a core. One fan pushes stale indoor air out; the other pulls fresh outdoor air in. The two streams cross in the core without mixing, and the core transfers both temperature and moisture from one to the other. In August the incoming air is cooled and dried by the outgoing air before it enters the duct. In January, during the dozen freeze nights, the same core warms the incoming air.

The result is a steady, small supply of outside air, filtered on the way in, delivered to the living space, with the air conditioner carrying only a fraction of the load it would carry if a window were cracked. The exhaust pulls from bathrooms and the kitchen area, so the moisture sources leave first.

Ask about an ERV

The right fit for Jacksonville houses

• Post-2000 subdivisions across Duval and the Nassau commuter corridor: the core market. A ducted ERV in the attic, tied to the return, usually sized for continuous low-speed operation.
• New construction in Yulee, Wildlight and the Baker County acreage lots: easiest to install during the build, when the duct runs are planned.
• Deeply renovated historic homes in Riverside, Springfield and San Marco that have been spray-foamed and sealed: they now behave like new houses and need the same fresh-air path.
• Not a fit: untouched 1920s bungalows and 1960s block ranches with original windows and duct. They ventilate themselves through their leaks; filtration and sealing are the better spend.

Cook’s installs ventilation products from the Lennox Healthy Climate line and sizes them to the house’s volume and occupancy. Ask which specific units are available for this market. [[CONFIRM WITH JERRY]] Estimates are free, and we will measure the house’s tightness before recommending anything.