Mold inspection and indoor air help in San Juan, PR
We do not keep an office in San Juan. Every job starts with a free call. For large and complex properties in the San Juan area we travel to you; for smaller jobs we tell you exactly what to ask for and point you to a local inspector we are comfortable recommending.
What the San Juan climate does to a house
Measured at NOAA's San Juan weather station.
- At the NOAA San Juan station, mornings average 78 percent relative humidity across the year, and afternoons 66 percent.
- The dampest mornings come in January, averaging 81 percent. Afternoons are driest in March, at 61 percent.
- A normal year brings 56.35 inches of precipitation over about 200 days, with the most in November (6.35 inches).
- In 3 of 12 months the average morning humidity is 80 percent or higher.
- Even in the afternoon, average humidity stays above 60 percent in 12 of 12 months. Indoors, 60 percent is the line where mold starts to find it easy.
| Month | Morning RH | Afternoon RH | Precip. (in) | Days with precip. | Mean temp (°F) |
|---|---|---|---|---|---|
| January | 81% | 65% | 3.76 | 17 | 77.6 |
| February | 79% | 63% | 2.39 | 14 | 77.9 |
| March | 76% | 61% | 1.95 | 12 | 78.9 |
| April | 75% | 63% | 4.68 | 13 | 80.3 |
| May | 77% | 67% | 5.90 | 17 | 81.9 |
| June | 77% | 66% | 4.41 | 15 | 83.3 |
| July | 78% | 67% | 5.07 | 19 | 83.4 |
| August | 79% | 68% | 5.46 | 19 | 83.7 |
| September | 79% | 68% | 5.77 | 17 | 83.5 |
| October | 79% | 68% | 5.59 | 17 | 82.6 |
| November | 80% | 68% | 6.35 | 19 | 80.6 |
| December | 81% | 67% | 5.02 | 20 | 78.7 |
Source: NOAA National Centers for Environmental Information, Comparative Climatic Data: average relative humidity (period of record through 2018), normal precipitation, mean temperature and cooling degree days (1981 to 2010 normals), and mean days with 0.01 inch or more of precipitation, 90 degrees or more, and 32 degrees or less. Last updated September 27, 2026.
Where moisture hides in San Juan homes
Air conditioning that runs most of the year
Every hour the AC runs, it pulls water out of the air into a drain pan and a condensate line. A clogged line or a slimy pan is one of the most common sources of hidden water damage and musty vents in warm climates. Here a normal year runs to 5,855 cooling degree days.
Ducts and air handlers in hot attics
Cold ducts running through a hot, humid attic sweat. That water soaks insulation and drywall below, often with no visible leak. 65 days a year reach 90°F or more.
Humid outdoor air getting inside
Leaky ducts, unsealed crawlspaces and bathroom fans that pull air from outside all bring damp air into cooled rooms, where it condenses on the coldest surfaces. Summer mornings here average 78 percent humidity.
Storms and wind-driven rain
Heavy rain events push water through windows, flashing and roof penetrations. The damage often shows up weeks later as a stain or a smell. The wettest month here averages 6.35 inches.
Common questions from San Juan
- Musty Smell When AC Turns On
- Mold on AC Evaporator Coil
- Ductwork Smells Moldy
- AC Drain Pan Overflow or Slime
Large, custom or multi-property situations: see Keystone.
Mold or air problem in San Juan?
Start with a free 15 minute call. We will tell you what you need, whether that is a local inspector, a virtual consultation or an on-site investigation.