Q: We need a new clothes dryer and are wondering whether to invest in a heat-pump model. I know they are more energy-efficient, but are there big maintenance issues, such as cleaning the condenser coils? Are they noisy? And how much longer do they take to dry clothes?

A: Heat-pump clothes dryers are more energy-efficient, and they offer other benefits, too. Long popular in Europe but relatively unknown in the United States, they work without heating the clothes or venting warm, humid exhaust air to the outdoors, as traditional dryers do. Instead, they use air-conditioner technology to extract water from clothes as they tumble at room-temperature air. There is no exhaust air, just extracted water, which can be plumbed to drain automatically into the same pipe where the washer drains.

Using a refrigerant in condenser coils makes heat-pump dryers at least 28% more energy-efficient than standard dryers, according to the federal Energy Star program.

As with other dryers, heat-pump models have lint screens, which need to be cleaned after each load. Heat-pump models often have a pair of lint screens, one finer than the other, so there’s a bit of extra maintenance. And they have condenser coils, which need to be kept clean for efficient operation. Bosch’s WTW87NH1UC model has a self-cleaning condenser, but with most models, cleaning is a manual task that might need to be done weekly or once every few months, depending on how much laundry you do, said Germaine Bennerson, a sales consultant at M & M Appliance, which has showrooms in Washington, D.C., and Alexandria, Virginia. Vacuuming off the coils isn’t complicated, he said; there’s a hatch on the front that opens to give access.

The trade-off for having to ensure condenser coils stay clean is that you don’t need to pull out the dryer periodically to clean out the exhaust piping, because there is none. The ventless nature of heat-pump dryers is one of their main selling points: There is no need to cut into the exterior of the building for a vent pipe. And the ventless feature helps save energy, beyond just what the dryer uses. Exhausting indoor air, as conventional dryers do, wastes the energy a heater or air conditioner used to bring that air to a comfortable temperature. And because a heat-pump dryer doesn’t add heat, it doesn’t increase the load on an air conditioner.

Heat-pump dryers have a bad reputation for taking a long time to dry clothes. It’s true that they generally take longer than traditional dryers, which use heat to speed evaporation. But if you pair a heat-pump dryer with an energy-efficient washer, which takes longer to complete a cycle than older, less-efficient washers, then loads should move along roughly in lock-step. “You won’t have wash loads waiting for the dryer,” Bennerson said.

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The Energy Star program lists the “test cycle time” for models it rates, which is useful for comparing models, but it doesn’t say how long it will take to dry a specific load. That depends on what’s in the load. A machine full of wet towels will take much longer to dry than one full of tablecloths. Dryer capacity is also an issue, because you can stuff more wet towels into a big dryer than a small one.

Heat-pump dryers often cost more than vented electric dryers, which usually range from $600 to $700. Energy Star’s top-rated heat-pump dryer for 2021, ranked according to estimated annual energy use, is Bosch’s WTW87NH1UC ($1,399 at Lowe’s and Home Depot, as well as local appliance retailers). Energy Star estimates its annual energy use at 125 kilowatt hours (kWhs) and its test cycle time at 44 minutes. Another highly ranked heat-pump dryer in terms of annual energy use, at 133 kWhs, is Miele’s TWF160 WP ($1,499 at M & M Appliance and appliancesconnection.com). Its estimated test cycle time is 35 minutes. Both models have a drum capacity of about 4 cubic feet, which is common for heat-pump dryers but considerably smaller than the capacity of traditional dryers, which is about 7 cubic feet.

For comparison, one vented electric dryer that’s Energy Star-certified is the LG DLE7100W, which sells for $799 at Home Depot. It has a drum capacity of 7.3 cubic feet, uses an estimated 607 kWhrs/year and has an estimated 55-minute test cycle time.

For those who need a larger capacity and want heat-pump technology, Whirlpool’s WED99HED is an option. It has a 7.3-cubic-foot drum, but the trade-off is a longer estimated test cycle time (71 minutes) and higher estimated annual energy use (531 kWhrs). It runs on heat-pump technology alone but has a heater that can be switched on to dry clothes faster.

In online reviews, some purchasers have complained about the noise of the Whirlpool machine, but Bennerson said he’s never heard any customers complain that heat-pump models are especially noisy, nor has he sensed that from his own observations.

Many heat-pump dryers offer a setting that helps prevent wrinkles by keeping the clothes tumbling even after they’re dry. You can’t reheat clothes to relax wrinkles, as you can with a standard dryer, because heat-pump dryers don’t add heat. But there’s a trade-off here, too: By not adding heat, a heat-pump dryer is much gentler on clothes.

If you compare heat-pump models, you’ll probably encounter the fact that Miele advertises some models as suitable for running on a standard 120-volt, 15-amp electrical circuit. Most electric dryers, whether heat-pump or standard, need 220-volt, 30-amp circuits, so being able to run on a standard circuit can be a big selling point, especially for people who live in houses with old wiring. But this can be “deceiving,” Bennerson said, because the dryer won’t run if anything else is plugged into that circuit, he said.

He also offered some shopping advice: Check warranties. Many dryers come with only a one-year warranty, which he said is code for the manufacturer believing the machine will not break during the typical life span of a dryer, which he said is seven to 10 years. “Miele, Speed Queen and Maytags have a life of 15-20 years,” he said. “You can tell by the warranty. If it says three to five years, they are expecting it to last longer than average.”