A crawl space or whole-home dehumidifier is the one dehumidifier you never stand next to. It sits in a sealed crawl space or a basement mechanical room, often right below a bedroom, and it runs whenever the humidity rises, which in a humid summer can be most of the night. The noise that matters is not what you would hear beside it. It is what comes up through the floor and out of the duct grilles.
Our guide to basement dehumidifiers covers the portable 35- and 50-pint units most people buy for an open basement, and our main dehumidifier guide is written around a bedroom. This guide covers the class above them: low-profile crawl space units and ducted whole-home units from Santa Fe, AprilAire, AlorAir and Honeywell Home. We read each maker's product pages, spec or submittal sheets, and installation manuals, and ranked the units on what matters under a lived-in floor: the figure each maker prints, how it is stated, the height of the cabinet, and what the manual says about ducts, vibration and drainage.
Our picks are listed above, with full specifications for each.
Three makers, three ways of stating noise
The first thing to know is that none of these figures can be lined up against each other. Each maker states its noise differently, and none gives the measuring distance.
- Santa Fe prints an "Average Sound Level" on most product pages: 47.5 dBA for the Ultra98, 55 for the Compact70, 55.3 for the Ultra70, 56.4 for the Ultra120, 57 for the Impact155 and 60 for the Classic. The in-wall UltraMD33, which lives in the living space rather than under it, lists 45. Its data sheets and manuals give no sound figure at all, and the Ultra-V, Oasis105 and AdvanceDry110 pages list none.
- AprilAire prints one figure per model on its submittal sheets, and always says "ducted": 45 dBA for the E080, 50 for the E130, 53 for the E070, 54 for the E050 and 55 for the E100. The E050 sheet adds 57 dBA un-ducted.
- AlorAir prints a "Sound Pressure Level", usually as an upper limit: less than 50 dBA for the HS35 and less than 58 for the HDi90. Its product pages do not always agree with its spec sheets.
- Honeywell Home (Resideo) prints nothing. Its DR90 specification data says "Reduced noise during operation" and gives no number.
- BlueDri gives no noise figure in its product listings for the BD-76, BD-130 or DH76, so none of its units could be ranked.
Because no maker states a distance or a test standard, we rank each maker's units only against its own. The E080's 45 dBA and the Ultra98's 47.5 dBA may describe the same loudness, or they may not. An upper limit such as "less than 58 dBA" is a different kind of claim again: it promises a ceiling, not a typical level. Where we write "quietest" in this guide, it means quietest within that maker's own figures.
Within a maker, the gaps are worth reading on the logarithmic scale. Roughly every 10 dBA sounds twice as loud. So the 10 dBA between AprilAire's E080 and E100 is the difference between one unit and something that sounds about twice as loud, and the 7.5 dBA between Santa Fe's Ultra98 and Compact70 is not far off. A 0.3 dBA gap, like the one between the Compact70 and the Ultra70, is too small to hear. To put 45 to 60 dBA next to everyday sounds, see our decibel chart.
What ducting does to the number
Two AprilAire documents give the same unit's figure both ways. The current sheet for the E050 lists 54 dBA ducted and 57 dBA un-ducted. The older sheet for the Model 1820, a 70-pint crawl space unit with a 12.5 by 12.5 by 25 inch cabinet and 200 CFM of airflow, lists 53 dBA ducted and 58 dBA unducted. The current E070 has the same cabinet size and airflow, and its sheet lists 53 dBA ducted, with no unducted figure.
Those 3 and 5 dBA gaps tell you two things. First, a unit sounds different depending on how it is installed, and the "ducted" figures on AprilAire's sheets assume the duct is there. Second, if a unit will blow straight out into a crawl space under a bedroom, expect it to be louder than its ducted figure.
Ducting also moves the sound. A whole-home unit ducted into your return or supply carries some of its blower noise into the ductwork, and the grille in the living space becomes a place you may hear it. The manuals are specific about how to stop the duct passing on vibration:
- AprilAire's installation instructions for the E080 and E100 say: "Use a minimum of 12" of flex duct at the dehumidifier inlet and outlet to prevent vibration noise transmission." They also say to keep the first 4 inches of duct off the outlet free of bends.
- Santa Fe's Ultra98 manual recommends "a short piece of flexible ducting on all Santa Fe Ultra98/120 duct connections" to reduce "noise and vibration transmitted to rigid ductwork in the structure", and says 8 inches or more of insulated flex duct on the outlet "will reduce air noise from the blower".
- Resideo's DR90 installation guide says: "Flex duct is recommended in connecting to the DR90 collars to reduce vibration noise."
- AprilAire prefers ducting return to return, which mixes the dehumidified air with the rest of the house air before it reaches a room, and requires the unit to turn on the HVAC fan when it runs.
How the noise comes up through the floor
A dBA figure describes sound in the air. Under a floor, the bigger problem is often vibration carried by the structure: a compressor bolted, hung or resting on something that touches the joists will send its hum into the room above. No maker publishes a figure for that, but the manuals say plenty about avoiding it.
Do not sit it on the structure. Santa Fe's Compact70 manual says: "DO NOT place the dehumidifier directly on structural members. Provide vibration isolation in order to minimize operational vibration and/or noise." The Ultra98 and Ultra70 manuals say a unit on structural members "without vibration absorbers" may cause unwanted noise, and ask for "vibration pads and/or risers" when the unit stands on the floor.
Take out the shipping restraint. Santa Fe's Ultra98 manual warns in capitals that failing to remove the compressor shipping tie "WILL CAUSE EXCESS VIBRATION TO BE TRANSMITTED TO THE FRAME". AprilAire's instructions also say to cut and remove the strap on the compressor shipping support bracket.
Level it on something firm. AlorAir's HDi90 manual says not to put the unit directly on the vapor barrier, and to use blocks or pavers to create a level surface. Its troubleshooting table lists "Machine Is Not Level" as the cause of loud noise, with the fix "Move the dehumidifier to flat, firm ground." AprilAire's units have a bubble level on top for the same reason, though AprilAire ties it to drainage.
Think twice before hanging it. Hanging kits are popular in crawl spaces, and Santa Fe sizes the Compact70 to fit between joists. Its manual says to hang it with a hang kit if there is any chance of flooding, and never from its own cabinet. AlorAir's spec sheets say its hanging kit stops noise and vibration reaching the floor above. That is a maker's claim with no figure behind it. A unit hung from the joists is attached to the floor you live on, so if you hang one under a bedroom, the isolation in the hanger matters. If flooding is not a risk, a unit on pads on a level base is the simpler route.
For how the same ideas apply to freezers, water heaters and laundry below ground, see our page on keeping a quiet basement.
Drains, traps and pumps
A crawl space or whole-home unit has no bucket. The water leaves through a hose or pipe, by gravity or by pump.
Gravity drains need a trap and a slope. Santa Fe says a drain trap is required on the Compact70 and Ultra98, and gives a drain pitch of 1 inch per 10 feet. For the Compact70, the highest point of the trap must sit at least 2 inches below the drain port, or water backs up into the unit. AprilAire's troubleshooting points at the same thing: a unit that is not draining may be blocked or not level, and the line needs "a continuous downward slope".
A pump is for lift. When the only drain is above the unit, you need a pump. Santa Fe sells an optional condensate pump kit for the Compact70 and Ultra98. AprilAire says to install any condensate pump in the condensate pan with the unit, and its E050 sheet names a pump as one way to drain it. AlorAir's HDi90 has an integral condensate pump, and its manual says that if the reservoir overfills, the unit stops the compressor, shows E4 and, after a minute, stops the fan. The same manual says pump upkeep is not covered by the parts warranty. No maker publishes a noise figure for its pump, and none says whether the pump was running when the noise figure was taken.
A pan if it sits above a finished space. AprilAire says to always install the unit in a condensate pan when it is in or above a finished space. Santa Fe asks for a drain pan with a float switch under a unit above a living area. That applies to an attic or a closet install more than a crawl space, but it matters for anyone putting a whole-home unit above a ceiling.
This is not safety advice. Electrical, refrigerant and drain work should follow the manual and your local codes, and AprilAire recommends a professional install for its units.
Sizing for a crawl space
A unit that is too small runs longer, which means more hours of noise. Capacity in this class is usually given at 80°F and 60% humidity, which is warmer than most crawl spaces. Look for the cooler figure too, and compare only figures at the same condition.
- At 80°F, 60% humidity: AprilAire E130 130 pints a day, Santa Fe Ultra98 100, AlorAir HDi90 90, AprilAire E080 80, AprilAire E070 and Santa Fe Compact70 70, AprilAire E050 50, AlorAir HS35 35.
- At 73°F, 60% humidity: Ultra98 71.4 pints, E080 65, E070 53, E050 42.
- At 65°F, 60% humidity: Compact70 43.7 pints, E050 35.
- At 60°F, 60% humidity: the HDi90 is rated 47.71 pints under what AlorAir labels a DOE condition.
Santa Fe sizes by how well the crawl space is sealed: the Compact70 covers up to 2,600 square feet if tightly sealed, 2,200 moderately and 1,800 loosely. AlorAir sizes the HS35 for up to 1,000 square feet. AlorAir also advertises capacity "at saturation", 70 pints for the HS35 and 198 for the HDi90. Those are measured in far wetter air than any sealed crawl space should hold, so use the 80°F or cooler figure.
The noise floor under your feet
A crawl space unit competes with very little. At night, the room above a crawl space may be one of the quietest in the house, and a unit that is inaudible in the afternoon can be noticeable at 2 a.m. That is why a steady, isolated install matters more here than in an unfinished basement next to a furnace. The humidity control also cycles the unit: AprilAire says the dehumidifier runs until the setting is reached, then shuts off until periodic sampling finds a need. Each start is a change in sound, and changes are easier to notice at night than a constant hum.
The trade-offs
Price and installation. AprilAire and Santa Fe show no price on their own sites, and AprilAire recommends a professional install. AlorAir sells direct: the HS35 was $359.73 on sale and the HDi90 $1,032.39.
Height against figure. The lowest AprilAire figure belongs to the 15-inch E080, and the lowest Santa Fe figure to the 19.5-inch Ultra98. The 10 to 12.5 inch units that fit a low crawl space all print higher figures than those two within their own brands.
Controls. The Ultra98 has only a low voltage terminal block and needs an external control. That suits a whole-home install wired to a wall control, and not a plug-in crawl space job.
Warranty terms vary. AprilAire gives 5 years. Santa Fe advertises 6 years. AlorAir advertises a 6-year limited warranty with the first 2 years full coverage, while its HDi90 manual refers to a 1-year parts warranty for pump maintenance.
How we chose
We read the product page, spec or submittal sheet, and installation manual for every unit, and recorded each noise figure in the maker's own words with the condition it gives. AprilAire's sheets are its own documents, but we found current copies on distributor and retailer sites, which we cite. We did not rank figures from different makers against each other, and we treated AlorAir's "less than" figures as upper limits. Within each maker, we then ranked for a unit under a lived-in floor: the lowest published figure, a cabinet low enough for a crawl space, and a manual that says how to keep vibration out of the structure. To read the figures themselves, see dBA explained and why dB ratings do not line up across brands.
We did not measure these dehumidifiers, and we did not install any of them. Every noise figure here is the maker's own, quoted as the maker states it, and none of the makers gives a measuring distance or test standard. Capacities are the makers' own at the conditions they state. AlorAir's prices are as shown on its site when we checked, and AprilAire, Santa Fe and Resideo publish no price.
