Basement dehumidifiers for Long Island and Queens

Why basements are wettest in summer

Basement walls and floor slabs stay close to ground temperature all year, which in summer is much cooler than the outdoor air. When warm, humid air reaches those surfaces its relative humidity rises sharply, and wherever the surface is colder than the air's dew point, water condenses. It is the same physics that fogs windows in winter, reversed by season.

For the same reason, airing out a basement with open windows on a humid July day adds water instead of removing it. EPA guidance (opens an external site) is direct on this point: ventilate when outdoor air is cold and dry, dehumidify when it is warm and humid. A basement fan or an open bulkhead door in summer has the same effect as the open window.

EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. Building Science Corporation (opens an external site) notes that mold is controlled by keeping the air against a surface below about 70 percent RH. Because the air next to a cool wall is always more humid than the room average, a basement reading of 60 percent can mean 70 percent or more at the wall. A practical summer target for a basement is therefore 45 to 50 percent, measured with a digital hygrometer placed away from the dehumidifier.

Stop liquid water first

A dehumidifier removes moisture from the air. It cannot keep up with water entering through walls and floors, and it does not repair the cause. In low-lying south shore neighborhoods and in homes that flooded during Hurricane Sandy in 2012, the water table and drainage deserve particular attention. Check these sources first.

• Gutters and downspouts that discharge next to the foundation instead of several feet away.
• Soil and paving that slope toward the house rather than away from it.
• Window wells without covers or drains, and clogged basement stairwell drains.
• Foundation cracks, damp lines at the base of walls, and white mineral deposits (efflorescence), which show that water is moving through the masonry.
• Sump pumps that fail, discharge too close to the house, or have no backup.
• Plumbing leaks, a disconnected dryer vent, or a laundry area without exhaust.

Sweating pipes

Cold water pipes, water meters, ducts carrying air-conditioned air and the slab under carpet are the surfaces most likely to sweat. EPA describes two remedies (opens an external site): raise the surface temperature with insulation, or lower the humidity of the air. Closed-cell foam pipe insulation on cold water lines and sealed, insulated supply ducts stop the dripping that stains ceilings and wets stored items; the dehumidifier protects the surfaces that cannot be insulated.

Sizing after the 2019 rating change

Since 2019, the Department of Energy test for portable dehumidifiers (opens an external site) has been run at 65 °F instead of 80 °F, to reflect basement conditions. The same machine now carries a lower pint rating than it did under the old test, so reviews and sizing charts written before the change (opens an external site) describe capacity in different terms from current labels.

Choose an ENERGY STAR model sized for the area and dampness of the space, set it to 45 to 50 percent, and connect it to a continuous drain. A unit that relies on its bucket fills within hours in a damp basement and stops. Place it where air can circulate, not in a closed room, and check its low-temperature rating, since cool basements reduce the output of many portable units.

Whole-house dehumidifiers

A ducted whole-house dehumidifier is a permanently installed unit that treats the basement, or the basement and the rest of the house, through ductwork, with its own drain. It is usually quieter and more efficient than one or more portable units running around the clock. It makes sense for:

• Large, open or finished basements where a single portable unit cannot hold humidity at 50 percent.
• Basements used as living space that need quiet, automatic operation.
• Houses where central air conditioning short-cycles and leaves the house cool but clammy in spring and early fall.
• Basements with no cooling load, which receive almost no dehumidification from the air conditioning upstairs.
• Spaces where the drain can be routed to a floor drain, laundry standpipe or condensate pump, which is the core of a proper installation.

Finished basements, crawl spaces, radon and winter

Many finished basements in Queens, Brooklyn and Nassau trap moisture because of their materials. Fiberglass batts pressed against foundation walls, vinyl wallpaper on exterior walls, carpet laid directly on the slab and wood framing in contact with concrete all hold moisture and support mold. A better assembly uses rigid foam board (XPS or EPS) against the foundation before framing, covered with drywall as the thermal barrier the building code requires over foam plastic, keeps framing off the slab, and uses flooring that tolerates occasional dampness. Converting a basement into a separate apartment raises legal and zoning questions outside the scope of this guide.

Crawl spaces follow the same rule: a vented crawl space admits humid summer air, while a closed crawl space with a sealed vapor barrier can be dehumidified or conditioned. On the EPA Map of Radon Zones (opens an external site), Nassau, Suffolk and the five boroughs are Zone 3, the lowest predicted potential, but EPA still recommends testing every home. If mold covers a large area, we recommend a qualified mold assessment and remediation professional before rebuilding.

In winter the same basement is often dry, and the dehumidifier's humidistat keeps it off. A basement that stays humid in January has a water source, such as a leak, a wet wall or an unvented dryer, because dry winter air does not produce that reading on its own.

We start by finding the moisture source, measuring the space and checking the drainage options, then recommend the combination of pipe insulation, portable or whole-house dehumidification and drainage that fits, and install it with our licensed HVAC partner. Where the cause is water entry, the gutters, grading or foundation work comes first, so the dehumidifier does not have to compensate for it.