ENERGY STAR says a portable unit's hose can go into a floor drain or sump, and that whole-home dehumidifiers usually drain only to a floor drain or a condensate pump (ENERGY STAR dehumidifiers).
Floor drain: simplest, with one Philadelphia catch
A floor drain is the easiest target. Set the unit close enough that the hose stays short and doesn't cross a walkway. ENERGY STAR warns against long, unwieldy hoses and tripping hazards. Keep the hose sloping down the whole way, with no loops or high spots where water can sit. Rest the end just inside the drain opening instead of jamming or taping it in.
In Philadelphia, check where that drain leads. The Water Department says sewer backups come up through basement fixtures in areas served by the older combined sewer system, which carries both storm runoff and household wastewater. Low-lying parts of Germantown, Kensington, Northern Liberties, Center City, South Philadelphia and Port Richmond are hit hardest (PWD on basement backups).
If your floor drain has ever backed up in a storm, keep the dehumidifier and its cord up off the floor. The City's Basement Backup Protection Program offers free backwater valve installation, which lets wastewater leave the house but closes to keep it from coming back in. It also does downspout changes when needed. For an active backup, the program lists a hotline at (215) 685-4901. A drain that smells like sewage is a separate problem; see why a basement floor drain smells like sewer gas.
Sump pit: fine if the lid stays sealed
A sump works well too, as long as you don't leave the pit open to get the hose in. The Building America Solution Center, a U.S. Department of Energy resource, says a sump needs a tight, gasketed, airtight cover. An open pit lets radon, water vapor and other soil gases into the basement (Building America: drain or sump pump). Its basement checklist also flags an uncovered crock as a moisture source (pre-retrofit assessment).
- Feed the hose through a sealed grommet or an existing port in the lid. Don't prop the lid open.
- Look at where the sump pump sends water. Building America says sump outflow should go to a storm sewer, if your municipality allows it, or to a dry well away from the foundation. Outflow dumped next to the house just cycles back in (Building America). Our guide to where a sump discharge line should send water in winter covers freezing lines.
- Remember the sump pump now has to move the dehumidifier's water too.
When you need a pump
If the only drain is a laundry standpipe or a sink higher than the unit, or it's across the room, gravity won't work. You have two choices: buy a dehumidifier with a built-in pump, or set a separate condensate pump next to it. Either one can push water up through a small line run overhead to a drain, which Building America describes for other basement equipment (Building America: condensate routing).
- Check the lift height and tubing length in the manual before buying. They vary by model.
- Check whether the pump has an overflow safety switch and whether it can shut off the dehumidifier if the pump fails.
- Don't run the line outdoors where it can freeze. Building America warns against that for condensate lines. A frozen line backs water up the same way our furnace condensate line guide describes.
- Look at the pump and line now and then. Building America notes clogged condensate lines in basements can go unnoticed until there's water damage (Building America: drain pans).
Safety and settings
ENERGY STAR says to keep drainage away from electrical circuits and devices, keep hoses away from cords, and plug the unit into a properly grounded outlet.
For the setting, ENERGY STAR puts the best range at 30 to 50 percent relative humidity. The EPA advises keeping indoor humidity below 60 percent, ideally 30 to 50 (EPA on biological contaminants). Building America notes that basements above 50 percent can support mold. If you're still deciding between equipment, see sump pump vs. dehumidifier.
Who to call
- A plumber, for a drain that backs up or drains slowly, a backwater valve, or hard-piping a pump line into a standpipe.
- An HVAC contractor, for a whole-home or ducted dehumidifier. ENERGY STAR notes these are typically installed by HVAC professionals.
- A waterproofing or sump contractor, for a pit with no lid, a pump that cycles constantly, or discharge that dumps at the foundation.
Ask whoever comes where the drain or sump actually discharges, whether the connection needs a permit where you live, and what happens to the dehumidifier's water if the drain backs up.