Twenty questions, answered here

Measure the room's relative humidity for a week with a cheap hygrometer. Under 60% and you may not need one. 60 to 68% in a space under about 1,500 sq ft points to a 30 to 32-pint unit at roughly 318 W. Above 68%, or any visible moisture, go to 50 pints at about 488 W. Do not size from the square-footage claim on the box - in our registry, units with identical certified capacity claim anywhere from 4,000 to 7,500 sq ft. Full method.

In June 2019 the US Department of Energy moved the test from 80F to 65F, to reflect the basement conditions where these machines actually live. Cooler air holds less water, so the same hardware reports a smaller number - roughly 25 to 30 percent smaller. ENERGY STAR publishes the official conversion table. The full explanation.

Broadly yes. ENERGY STAR's published correlation maps an old 70-pint rating to 40-45 pints new and an old 90 to 55; manufacturers most often pair 70 with 50. Honeywell's own listing prints exactly that: 50 pints, 70 pint under the 2012 DOE standard. 50 versus 70 pint.

It is a saturation rating measured at 95F and 90% relative humidity, not a DOE rating. The AlorAir Sentinel HD55 sold under that headline is certified at 36.33 pints per day at the DOE condition - a factor of 3.1 between the two figures. Both are real; only one is comparable to a portable's rating. Crawl space roundup.

A 50-pint unit draws about 488 W. Twelve hours a day at the US average residential rate of 18.34 cents per kWh is $1.07 a day, $32.24 a month, or about $161 over a five-month season. A 30-pint unit at 318 W is about $21 a month. Calculate yours.

By class median across the ENERGY STAR certified list: 105 W at 10 pints, 258 W at 20-22, 318 W at 30-32, 351 W at 35 and 488 W at 50. Most manufacturers publish nothing, so those figures are computed from each model's certified capacity and Integrated Energy Factor. The full table and the formula.

Only if the place you want the water to end up is higher than the machine. A floor drain or sump below it needs nothing but a hose. A laundry sink or a window above it needs a pump - and that single fact rules out about half the units in any listing. Pump versus gravity.

It depends on the unit and almost nobody publishes it. Of seven pump models in our registry, one states anything at all: GE publishes a 16-foot drain hose, which is a run rather than a lift height. Where nothing is published, keep the vertical rise short. Pump lift and distance.

Most often the room is cooler than about 60F, the humidity is already at or below the target you set, or the drain cap is still fitted while a hose is connected. All three are the machine behaving correctly. Eight checks in order.

In a room below about 60F it is expected, and any unit with auto defrost handles it by pausing the compressor and running the fan. In a warm room it means restricted airflow - almost always a clogged filter. Icing up.

45 to 50 percent. The EPA advises keeping indoor relative humidity below 60 percent and ideally between 30 and 50; the upper half of that band is comfortable and much cheaper to hold than 40 percent. Ideal settings.

No, it warms it slightly. All the electricity it uses ends up as heat in the room, plus the latent heat released when water vapor condenses. Drier air feels cooler, which is why people report it as cooling. How it works.

A compressor one barely does below about 41F - the coil ices and it spends its time defrosting. Ivation's published figures put a desiccant unit at 11.8 pints a day at 41F against a compressor's 2.9. Desiccant versus compressor.

They do opposite things. Above 60 percent relative humidity you want a dehumidifier; below 30 percent, a humidifier; between 30 and 50 you probably need neither. Measure with a hygrometer before buying either. The comparison.

For a closet, a stored boat, or anywhere with no power, it is the right tool. For a room it is not close - a tub of calcium chloride absorbs a few ounces over weeks against a 50-pint machine's 50 pints a day. The comparison.

For a wardrobe, yes. For a room, no. The Pro Breeze mini removes 17 ounces a day, which is 1.06 pints - about one fiftieth of a 50-pint machine. It is not a small dehumidifier, it is a different class of device, and it is the most common mis-purchase in the category. The review.

Usually it is undersized, or humid air is entering as fast as it is removed - an open window, a failed garage door seal, a dryer venting indoors. A refrigeration fault is the least likely cause. Five causes ranked.

Monthly in a garage or workshop, every couple of months in an unfinished basement, seasonally in living space. A clogged filter starves the coil, which drops extraction sharply while the machine keeps drawing full power - it is the cause of most of the faults on this site. Maintenance.

No. Units we claim to have tested: zero. There is no chamber, no meter and no shelf of units. What we do instead is read every manual, pull each model out of the ENERGY STAR certified list, compute what it costs to run, and show the arithmetic. The full method.

Affiliate commission on qualifying purchases through links here, at no extra cost to you. It never determines a ranking - where a cheaper unit is the better buy it goes first, and every roundup names a product to skip. Full disclosure.