Mold inspection and indoor air help in Honolulu, HI
We do not keep an office in Honolulu. Every job starts with a free call. For large and complex properties in the Honolulu 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 Honolulu climate does to a house
Measured at NOAA's Honolulu weather station.
- At the NOAA Honolulu station, mornings average 74 percent relative humidity across the year, and afternoons 56 percent.
- The dampest mornings come in January, averaging 79 percent. Afternoons are driest in August, at 52 percent.
- A normal year brings 17.10 inches of precipitation over about 93 days, with the most in December (3.24 inches).
- No month averages 80 percent morning humidity, which is why mold here almost always traces back to a water event rather than damp air.
- Even in the afternoon, average humidity stays above 60 percent in 2 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 | 79% | 61% | 2.31 | 9 | 73.2 |
| February | 77% | 59% | 1.99 | 8 | 73.1 |
| March | 76% | 58% | 2.02 | 9 | 74.5 |
| April | 73% | 56% | 0.63 | 8 | 76.1 |
| May | 70% | 54% | 0.62 | 7 | 77.8 |
| June | 69% | 53% | 0.26 | 6 | 80.2 |
| July | 70% | 53% | 0.51 | 7 | 81.2 |
| August | 71% | 52% | 0.56 | 6 | 81.9 |
| September | 73% | 54% | 0.70 | 7 | 81.5 |
| October | 74% | 57% | 1.84 | 8 | 80.0 |
| November | 76% | 59% | 2.42 | 9 | 77.6 |
| December | 78% | 61% | 3.24 | 10 | 74.8 |
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 Honolulu 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 4,628 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. 24 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 70 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 3.24 inches.
Common questions from Honolulu
- 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 Honolulu?
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.