Solved! Why Is My House so Humid? (2024)

Q: My family recently relocated to a new home, and it feels incredibly muggy indoors. Our air conditioner seems to be working just fine, so why is my house so humid?

A: Figuring out why a house is so humid can take some troubleshooting, but it may prevent many issues in the future. But what is high humidity? According to Energy Star, the ideal indoor relative humidity should be between 30 and 50 percent—anything higher than 50 percent is considered high.

High humidity levels can cause discomfort and health issues, and excessive humidity can even cause damage in a home. Some telltale signs of excess moisture include an AC system that smells musty, a humid feeling in the house, or visible mold and mildew growth. Excess humidity in a house can also cause condensation on windows, toilet tanks, and pipes. Wondering what causes condensation? It happens when warm, moist air comes in contact with cool surfaces, and the vapor in the air turns into liquid water. Traces of moisture can spread to ceilings and walls, causing discoloration and mold growth. Peeling paint and creaking or buckling floorboards can also be a sign of excessive moisture.

Ultimately, high humidity levels have many different causes: climate, daily activities, HVAC issues, and poor ventilation are just a few of the culprits. Depending on the cause, solutions can range in cost from the price of one of the best dehumidifiers to the cost of HVAC service or AC repair cost. Read on to see if any of these issues may be present, and find out how to restore the home to a comfortable humidity level indoors.

The climate affects the humidity level in your home.

Climate can contribute to high humidity in a house. If it’s exceptionally humid outside, chances are it’s going to be muggy inside a home. The changing seasons and temperature can be significant factors for rising indoor humidity levels and the main culprit for an uncomfortable environment.

Some parts of the country are more prone to high humidity than others, and inside humidity levels tend to be higher in regions with muggy climates. For those wondering “How humid should my house be?” the EPA offers recommendations on indoor humidity levels relative to outdoor temperatures for reference.

Everyday activities like cooking, washing, and showering can contribute to humidity levels.

Humidity levels can be affected by simple activities that take place in a household every day. These tasks can naturally add more moisture to the air. Cooking and running the dishwasher can add more water vapor to the air in the kitchen. Long, hot showers add a lot of moisture to the bathroom.

Keeping areas ventilated by opening a window or installing an exhaust fan can lower humidity inside the house. A professional can direct certain appliances, such as clothes dryers and stoves, to vent outside of the home. A whole-house dehumidifier costs $1,500 on average and can also help eliminate some of the moisture created by these activities.

Leaks coming through cracks in the plumbing system may be the culprit.

An interior plumbing leak from a bathroom or kitchen sink can cause increased moisture in the air. It’s important for homeowners to check pipes often for cracks and corrosion; according to the EPA, leaks can lead to the growth of harmful biological pollutants. Early plumbing leak detection could help prevent water damage, musty smells, and potential mold growth.

While some leaks are easy to spot, others are not. Homeowners can look for wall discoloration, bubbling paint or wallpaper, a dripping sound, or a musty smell. If any of these are present, they’ll want to contact a professional for plumbing leak repair.

Poor insulation could be increasing the home’s humidity levels.

Ever wondered “Why is my house so humid with the AC on?” It’s generally understood that poor insulation can allow uncomfortably cold air into a home during the winter, canceling out the efforts of a furnace. The same principle applies to humidity. When outdoor humidity is high, that damp air can make its way inside via gaps not sealed by insulation. This also means that cool, air-conditioned air can escape instead of circulating indoors. So while it may seem like the central AC is not blowing cold air, it actually may be working overtime (and driving up energy costs, too).

Having old insulation replaced, especially in the attic and basem*nt, could be the key to eliminating excess moisture in the air. If it isn’t possible to completely replace the home’s insulation, caulking or sealing windows throughout the home can be another effective way to restore the home to a more ideal inside humidity level.

Moisture from soil under your home may be penetrating the house.

The soil outdoors may not be the first thing that comes to mind when homeowners wonder “Why is it so humid in my house?” However, humidity can come up through the soil underneath the foundation of the home. This is called rising damp, and ineffective grading can be a significant factor since groundwater and rain can accumulate in a home’s foundation. Basem*nts can be humid since they’re often poorly insulated and don’t have windows, and this can compound any issues.

Homeowners who live in a climate with excessive rain will want to ensure that gutters and downspouts work correctly and rainwater is directed away from the house to keep moisture out. Professionally installed awnings placed above windows and doors are an excellent way to keep water out as well.

A poor ventilation system may be to blame.

Adequate ventilation can help control a home’s humidity level, impacting health and a home’s structural integrity. If there are high humidity levels in a home, poor ventilation can be to blame. Homeowners who suspect this is the likely reason behind their home’s humidity levels, they’ll want to open windows and keep them open for extended periods for humidity control, particularly in high-moisture areas such as bathrooms and kitchens. Also, homeowners will want to consider having a ventilation system professionally installed.

Your AC unit may be too big for the home.

Bigger isn’t always better: An oversize window or central AC unit may be the reason for excessive moisture in a home. The evaporator coil found inside the AC unit acts as a dehumidifier and pulls humidity from the air as it runs. However, the best AC installation companies will confirm that if the unit is too large, it may cool a room or home too quickly, running for only 10 to 15 minutes on a hot day before it abruptly shuts down.

This is commonly referred to as short cycling, and a professional can diagnose the problem as part of HVAC inspection cost. A longer runtime is needed to dehumidify a home correctly. While the cost of HVAC replacement may seem high to homeowners at first, investing in a smaller unit may make a home more comfortable and energy efficient in the long run.

Additionally, even if an HVAC or AC unit is the proper size, it can contribute to high humidity if it is not functioning properly. HVAC systems last from 15 to 25 years on average. In some cases, HVAC costs may be partially covered by a home warranty (and if not, it may be worth a homeowner investing in one of the best home warranties for HVAC such as American Home Shield or Liberty Home Guard in the future). If it’s been a while since the system has been serviced or it is reaching a fairly old age, it may be wise for a homeowner to call one of the best HVAC companies, such as One Hour Heating & Air Conditioning or Aire Serv.