Home Ventilation in Florida: Fresh Air, Fans and Humidity

What ventilation means, and the three ways outdoor air gets in

EPA lists three ways outdoor air enters a building: infiltration, natural ventilation and mechanical ventilation. Infiltration is outdoor air flowing in through openings, joints and cracks in walls, floors and ceilings, and around windows and doors. EPA says infiltration occurs in all homes to some extent. Natural ventilation is air moving through open windows and doors. Mechanical ventilation uses fans. They range from outdoor-vented fans that remove air from one room, such as a bathroom, to duct systems that distribute filtered and conditioned outdoor air through the house.

EPA says advanced designs for new homes are starting to add a mechanical feature that brings outdoor air in through the HVAC system. Our reading: an air conditioner conditions the air already in the house, and fresh air is a separate feature that someone has to design in.

Why homes need ventilation, and why EPA puts source control first

EPA says indoor pollution sources that release gases or particles are the primary cause of indoor air quality problems. EPA adds that inadequate ventilation can raise indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources.

Even so, EPA says that for most indoor air quality problems in the home, source control is the most effective solution. Source control means removing a pollution source or reducing what it releases. EPA adds that source control is often more cost-efficient than increasing ventilation, because more ventilation can increase energy costs.

EPA's air cleaner guide says filtration can supplement source control and ventilation, but does not replace the need to control pollutants. What a filter can and cannot do is covered in AC filter replacement.

Spot ventilation: bathroom and kitchen fans

EPA says local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located. EPA's mold guide says to run the bathroom fan or open a window when showering, and to use exhaust fans or open windows when cooking or washing dishes. A 2014 Department of Energy Building America guideline for existing homes says exhaust ducts should always end outdoors, never in an attic or crawlspace.

The same guideline says older exhaust fans often perform very poorly, moving a very small fraction of their design flow. It says range hoods, which remove moisture and odors directly above the cook top, are preferred over wall or ceiling fans. It also says some range hoods only circulate air back into the kitchen, and such hoods do not meet most ventilation requirements. Among its steps to reduce exposure to carbon monoxide, EPA lists an exhaust fan vented to outdoors over gas stoves. The 2014 guideline adds that higher-volume fans can cause pressure imbalances that interfere with other HVAC systems, especially combustion systems.

Whole-house ventilation: three common designs

The 2014 guideline says three main types of ventilation systems predominate in homes in the United States: exhaust, central fan integrated supply, and balanced ERV or HRV systems.

In an exhaust-only system, fans run continuously or on timers to remove air from the home, and fresh air comes in through induced infiltration. The guideline says this depressurizes the home, which draws in air from outside. Depressurizing means lowering the air pressure inside the house relative to outdoors. Make-up air is the outdoor air that flows in to replace the air a fan removes. The guideline also says exhaust-only ventilation should not be used in homes with atmospheric combustion appliances, or with make-up air from damp, moldy crawlspaces or basements. An atmospheric combustion appliance burns fuel and relies on the natural rise of hot exhaust gases to carry them up a flue or chimney. Whether a home has one, and what to do about it, is a question for a licensed professional. A 2009 guide from a Building America research team does not necessarily recommend exhaust-only systems in hot-humid climates, because they force make-up air through the building envelope.

The second design is central fan integrated supply, called CFIS. In it, a duct runs from outdoors to the return plenum of the air handler. The return plenum is the box on the return side of the air handler where house air is gathered. A controller turns on the air handler fan and opens a motorized damper, and the outdoor air mixes with return air and is distributed through the home. A damper is a motorized flap that opens and closes the duct. The guideline says the outdoor air is filtered through the central air handler filter. It names the largest drawback as the high electricity consumption of using the air handler fan for modest ventilation needs. It also says outdoor air should not be drawn from an attic, basement, garage or crawlspace. The 2009 guide says a supply-only strategy is commonly recommended for hot, humid climates. Return air vent too small covers the return side of the air handler, where this duct connects.

The third design is balanced: ERV and HRV systems exhaust air and supply outdoor air at the same time, and the two airstreams cross in a heat exchanger. A heat recovery ventilator, or HRV, transfers sensible heat only, while an energy recovery ventilator, or ERV, also transfers moisture. Sensible heat is the heat a thermometer reads. The guideline says these systems do not induce a large pressure, positive or negative, on the building.

Why Florida humidity changes the question

The National Weather Service office for Tampa Bay says the rainy season typically brings dew points that stay above 70°F, and a higher dew point means more moisture in the air.

The 2014 guideline says that when humid air is brought into a home, air conditioners often cannot remove all of that additional moisture. It says the problem is worse in efficient homes, where air conditioners are smaller or run less often and so remove less moisture. It adds that when a ventilation system brings in more outdoor air, extra dehumidification may be needed to hold indoor humidity at comfortable levels.

Florida Solar Energy Center researchers compared two kinds of ventilation in ten high-performance homes in Gainesville. One was a supply system that ran only while heating or cooling ran. The other was continuous exhaust at a higher airflow. The continuous exhaust used more energy to condition the homes. Indoor humidity also ran higher, because the homes had no equipment for enhanced humidity control. The authors said additional data was needed to verify the significance of their findings. Our reading: that was one cooling season in north Florida, so it is not a Tampa Bay measurement.

EPA says natural ventilation, used properly, can at times help moderate indoor air temperature. Our reading: when the Tampa Bay dew point is persistently above 70°F, an open window lets in moist air, so opening one is a moisture decision as well.

Why your house feels humid with the AC running covers how an air conditioner removes moisture. Whole-home dehumidifiers in Florida covers when one is needed, so this page does not repeat it. Mold in HVAC systems covers growth on the system itself.

ERV or HRV in Florida, and what an ERV does not do

The 2014 guideline says the ERV or HRV question is easiest to answer in hot, humid climates. For Florida, it says air inside comfortable homes is relatively cool and dry, while outdoor air is quite humid. It says that when outdoor air passes through an ERV, the exhaust air somewhat cools and dehumidifies it. The guideline then adds that this does not mean an ERV dehumidifies the home. Running an ERV still increases the humidity in the home, it says, but by less than an HRV would. The 2009 guide likewise recommends an ERV in hot humid climates, to reduce the humidity in outdoor air brought into the home.

The 2009 guide also says that in efficient homes in humid climates, a ventilating dehumidifier may be a good option. It says these units can introduce a controlled amount of outdoor air and can dehumidify indoor air.

The 2014 guideline says some of the higher-performing ERVs require checking or cleaning filters, heat exchange media and exterior duct terminations quarterly. It says that if systems are not maintained, ventilation flow rates will decrease over time, eventually to a small fraction of the design rates.

What Florida law says about whole-house ventilation

Section 553.908 of the 2025 Florida Statutes addresses two sections of the 5th Edition (2014) Florida Building Code, one in the Mechanical volume and one in the Residential volume. It says those sections shall not require mandatory mechanical ventilation unless the air infiltration rate in a dwelling is less than 3 air changes per hour. A blower door is a fan fitted into an exterior doorway that measures how leaky a house is, and the statute sets the test pressure at 50 pascals. Our reading: under those two sections, only a house that tests tighter than 3 air changes per hour could be required to have mechanical ventilation.

A 2014 Florida Solar Energy Center paper said whole-house mechanical ventilation was not required by Florida code, and that market penetration of systems meeting ASHRAE 62.2 was poor. The Department of Energy guideline says ASHRAE Standard 62.2 is, or is becoming, the most common standard referenced for home ventilation requirements. The standard is revised from time to time, and these Department of Energy documents refer to its 2007, 2010, 2013 and 2016 editions. Our reading: a code rule says what a permit must meet, not what a particular home needs. This page does not say which code edition applies to any one job. The building department that issues the permit can say which edition applies.

What to ask before changing ventilation

These questions come from the documents above. They are not a diagnosis of any home.

1. What ventilation does my home have now, and where does each fan duct end? The 2014 guideline says an inspection should trace the exhaust duct run and look for disconnects, crimps and leaks.
2. Does the home have a fuel-burning appliance, a fireplace or an attached garage? The guideline warns that air forced in through an attached garage can bring traces of car exhaust, fuel or solvents.
3. What problem is the change meant to solve, and can the source be reduced first?
4. What will the change do to indoor humidity, and which equipment will handle the added moisture? A fact sheet for the 2004 Florida Building Code said that in Florida's humid climate it is critical to calculate the latent load. The latent load is the amount of dehumidification a building needs.
5. Who maintains the system, and how often? The guideline says a malfunctioning ventilation system in a tight, efficient home can lead to moisture, mold and other problems.
6. How will the airflow be measured after the work, and which edition of the standard or code is the design based on? The guideline says it is important to measure the delivered airflows and make sure they meet specifications or requirements.
7. Is the contractor licensed? To check a contractor's license, the Florida Department of Business and Professional Regulation says you need the license number, the contractor's name or the business name.

Get the answers in writing, so they can be compared later. Leave fans, wiring, outdoor-air ducts and anything near fuel-burning appliances to licensed professionals.