A Quiet Dehumidifier
Is There Such a Thing?

A quiet dehumidifier is rather like the Holy Grail; many have sought it, none has ever found it, and many have perished... well, perhaps that's overstating the case; but many have lost sleep because they didn't find it.

The simple answer to the question is that no, there is no such thing as a quiet dehumidifier but, like the Holy Grail, we would love to believe that it does exist and that, one day, we might discover it. The best we can aim for is a model that is quieter than most of the others.

There is a very simple explanation for this unpalatable truth. These appliances depend on the movement of air through the machine to remove moisture from the air. The movement of air creates noise; after all it is the transmission of vibration through air that is perceived as sound.

Movement of air requires a fan and it is the fan that is the main culprit behind the noise that comes from these machines. Some of you own models with variable fan speeds and the lower speed is always quieter. Their effectiveness is greater at the higher fan speed or speeds so there is a trade-off between effectiveness and noise output.

A myth has grown up that the main source of noise, at least from the refrigerant type, comes from the compressor. Just listen to your appliance when it's in "defrost mode". The compressor has stopped but the fan keeps running. You can poke me in the eye if you can tell the difference in noise level because I'm darned if I can.

The compressor is much the same as the one in your refrigerator. A reasonably new refrigerator makes a low, constant humming sound when the compressor is running. Turn on the extractor fan in your kitchen and listen. How much of that low hum is still audible?

If your compressor does seem to be noisy the larger part of the noise is caused by secondary vibration. This can develop as the appliance ages, in the same way an older refrigerator is often noisier than a new one. It can also happen if the unit is not well made and parts of the casing vibrate when the compressor is operating. The first step toward a quiet dehumidifier is build quality.

If we are agreed about the fan being the number one target what else can we say about it.

Sometimes it's not simply the level of noise (the number of decibels) that is intrusive it is the quality of that noise. Some models produce XdB of noise which is of low pitch and blends into the background, like white noise. You can have a conversation and not notice the unit is running. Sometimes it's only when the TV is switched on and it's a little difficult to hear that you are even aware of the noise.

Other models produce the same XdB but accompanying the "hum" is a "whine", a higher pitched sound that you cannot block out. This is usually produced by the fan motor or fan mounting. This is also a build quality issue.

So, if we have a dehumidifier of reasonable quality (not always the most expensive model by the way) what else can we do to reduce the noise nuisance?

A bigger appliance, say a 70 pint unit, will be noisier than a smaller one, of 30 or 40 pints capacity. This is because a bigger unit needs to move more air so it has a bigger and/or faster fan. But, a bigger unit will run fewer hours per day to control humidity in a given area than a smaller one, not to mention extracting more moisture per energy dollar (or pound) expended. A louder appliance operating for shorter periods or a quieter one operating all or most of the time is the question; it's your call.

Another solution is to keep the noisy beast as far away from the occupants of the home as possible, especially at night. If you already have a HVAC (Heating, Ventilation and Air Conditioning) system installed you could consider a whole house dehumidifier. These are high capacity units so are not quiet dehumidifiers but can be installed in your basement or crawl space and operate through the existing HVAC ducting. A dehumidifier that is out of earshot is, in one sense, a quiet dehumidifier.

Whole house units are much more expensive than portable models but they are far more energy efficient, reliable and durable. Over its life-time the total cost of a whole house unit can easily be less than the two or three portables you have bought, operated and replaced during the same period. It will also provide quiet humidity control throughout most of the home even though it is not a quiet dehumidifier.

If you already have an appliance that you find too noisy the only action you can take, short of replacement, is to deaden the sound a little. A wooden floor, for example, acts like a sound-board and amplifies noise and vibration. Placing the unit on a rug will reduce this effect and make the noise less intrusive.

If you do decide to replace your existing unit look carefully at the published specifications before you buy. Most manufacturers quote noise output but this can be done in one of three ways: The noise on the quietest (lowest fan speed) setting, the loudest (highest fan speed) or as a range, from lowest to highest. Be sure you are comparing like with like.

Also be aware that the difference between 45dB and 47dB will be imperceptible but between 45dB and 55dB will be very, very noticeable. This is because the decibel measure is a logarithmic scale, not a linear one, rather like the Richter scale for measuring the power of earthquakes.

For smaller areas, particularly bedrooms and RV's for example, one of the quietest and most compact refrigerant models I can recommend is the DeLonghi DD45

If you are still convinced that the compressor is your main enemy there are models without refrigeration systems and, therefore, without compressors. These are desiccant dehumidifiers which remove excess water by absorbing water molecules in a material which attracts water, a desiccant, such as silica gel. The desiccant is mounted on a slowly turning wheel.

Unfortunately this type, although a few decibels quieter, also has a fan. In fact it has two fans; one which draws in and expels the air and a second to blow warm air across the desiccant wheel to drive the water out and "reactivate" the desiccant. For this reason a desiccant unit is scarcely quieter than a well made and well designed refrigerant model.

Desiccant models have disadvantages. They are more costly to run and the air they return to the room is 18°F to 22°F (10°C to 12°C) warmer than the ambient temperature in the room. Although a possible advantage in cold conditions this makes them unsuitable for use in warmer seasons or areas.

The principal advantage of the desiccant type is not that it is a quiet dehumidifier but that it can operate effectively at temperatures close to freezing point. This is useful in cold weather in an unheated space, such as a garage or a boat, but for these applications a quiet dehumidifier is not usually needed.

Portable desiccant models are widely available in Europe but are very difficult to find in North America and where they are available they are very expensive, at least twice the price of those sold in Europe, at current exchange rates.

Desiccant models designed for industrial use are readily available in North America but this type is even more expensive, approaching $1000 for the smallest capacity units. These machines do not deposit condensate but expel the warmed air, with the moisture still in it, outside the building, for which a ducted installation is required.

For the sake of completeness we will acknowledge that there are indeed quiet dehumidifiers on the market, rechargeable models, which have no moving parts. Their water extraction rate is far too low for them to be effective in a room and they are only useful in small, enclosed spaces, such as closets.

There is also the heated rod type which lowers relative humidity by raising the temperature. These also have no moving parts but are, once again, only suitable for small areas, such as a gun safe.

Finally there are mini-dehumidifiers. These use the "Peltier Process" to extract water from air. The Peltier Process does not involve moving parts but these appliances also have fans and make some noise. Like the two types we have just mentioned they are low capacity units suitable, at most, for a smaller walk- in closet.

In summary, the quiet dehumidifier is a myth but we can reduce the nuisance of noise by selecting a model of good build quality, by putting up with more noise but over shorter periods with a larger unit, install a whole house unit in a basement or deaden the sound a little.

If a quiet dehumidifier is a myth so is the "whisper quiet" model. On this site you will only find the phrase "whisper quiet" in inverted commas. It is sales talk and requires no further comment.

What Other Visitors Have Said About This Page

Submitted Thu Oct 13 2011
By: Anon

Just what I was looking for: Wonderful sensible advice!

Submitted: Wed Sep 28 2011
By: Dell, Charlottesville, VA

Frigidaire-FAD704DUD - QUIET!! I have owned 6 models in 6 years: Maytag, Fedders, Danby, EdgeStar, SPT and Frigidaire. None has lasted more than 18 months and some less than a year. Service is a joke. I've never been able to get any repaired. I have a new SPT and Frigidaire, so don't know yet how they perform long-term or how ineffective the warranty will be. All are noisy--nature of the beast. BUT!! The Frigidaire is definitely the quietest I've ever had. I just hope it lasts.

Submitted: Fri Sep 09 2011
By: Anon

Nice Comprehensive Explanation.

Submitted: Wed Aug 24 2011
By: Anon

This article was very useful to me. Now I know far better what to look for in a dehumidifier. Thanks for all the help and the sense of humor of the writer.

Submitted: Sat Jun 25 2011
By: Anon.

Dehumidifier Noise Explained. Thorough and very helpful.

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