Why is the mini-split ductless air conditioner installed in a sunroom enclosed with acrylic plastic windows called a “dehumidifier” on the building permit?

Monday, July 1, 2019

It is likely that the sunroom was originally a screen porch that has been enclosed. Unfortunately, simply enclosing the room with clear acrylic plastic windows does not make it acceptable by the building code for air conditioning and to be considered as “habitable space.”  

    The code requires that conditioned (heated and cooled) spaces be insulated, and clear plastic panels have minimal insulation value. There is also usually no insulation above the ceiling. The builder did not install it there because insulation is not necessary over a screen porch, and it is often difficult to retrofit. To complicate things further, the floor of the former screen porch should be at the same level as the main living area, which it is often not. 

    Then some ingenious person noticed that many mini-split heat pumps also have a “dry” mode, besides cooling and heating, so they can be used as dehumidifiers that only activate when necessary to lower the humidity in the room. And they were able to convince the building department that it was alright to issue a permit for the installation of a mini-split in a sun room as long as it was intended only for dehumidifcation. Yeah, sure…that’s a very expensive dehumidifier. Also very popular here in The Villages and surrounding retirement communities.

   While this not exactly a defect, we try to point out these two things to homebuyers:

  • Because the HVAC unit is supposedly only a dehumifier, the sunroom (sometimes referred to as an enclosed lanai) is not considered a heated and cooled, habitable conditioned living space. And if the square footage of the sun room is showing up on the real estate listing for the house as part of the living area square footage that you pay premium dollars for, it probably shouldn’t be.

  • The room will be also expensive to heat and cool because of lack of adequate insulation.

    The Residential Edition of the Florida Building Code (R301. has five categories for sunrooms:

  • Category I is an open or screened porch. 
  • Category II is “a thermally isolated sunroom with enclosed walls. The openings are enclosed withtranslucent or transparent plastic or glass. The space is nonhabitable and unconditioned.” 
  • Category III is “a thermally isolated sunroom with enclosed walls. The openings are enclosed with translucent or transparent plastic or glass. The sunroom fenestration complies with additional requirements for air infiltration resistance and water penetration resistance. The space is nonhabitable and unconditioned."

     Sunrooms with a mini-split “dehumidifier" are in Category II or III. In order to qualify to be a conditioned—but still not habitable—space, the room must comply with Category IV, which means weather-resistant and insulated. Only Category V can be habitable and conditioned, and it has to be weather-resistant, insulated, and open to the main living area. As a habitable space, Category V must also be compliant with electric receptacle outlet spacing and lighting requirements.

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  To learn more about heating and air conditioning systems, see these other blog posts:

 How can I find out the SEER of my air conditioner? 

 My air conditioner won't turn on. What's wrong? 

 How can I find out the size of my air conditioner? 

 How can I find out the age of my air conditioner or furnace?

 How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

 Where is the air filter for my central air conditioner and furnace? I can’t find it? 

 Does an old air conditioner use more electricity as it ages? 

 How did homes stay cool in Florida before air conditioning?

 What is wrong with an air conditioner when the air flow out of the vents is low?

 Why has the thermostat screen gone blank? 

 Why does it take so long to cool a house when an air conditioner has been off for a while? 

 Why is my air conditioner not cooling enough? 

 What are the most common problems with wall/window air conditioners?  

 Will closing doors reduce my heating and cooling costs? 

    Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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