The Essential Dehumidifier Buying Guide

Who Needs a Dehumidifier?

In tropical areas and coastal regions, humidity is a common issue. Cold areas, particularly those places that experience rain and snow in winter, can have high levels of humidity. Though central heating systems usually dry out the air sufficiently in our homes and businesses. Despite this, humidity is often a problem in cold climates too. This may be limited to confined spaces, basements and bathrooms.

A dehumidifier is as much about human comfort as it is for our health. Humidity also damages woodwork and buildings. So there is a need for dehumidifiers in almost every region, for any number of reasons.

It starts with understanding Relative Humidity (RH). Understanding the science behind relative humidity can get quite complicated, as can measuring and calculating RH. So I’ll try keep it simple. After all, we only need to understand what RH has to do with a dehumidifier.

Basically, relative humidity is the ratio of moisture in the air, relative to the saturation point. This has to do with the amount of water vapor present and the ambient temperature. Hot air will hold more moisture than cold air. Hence, southern states generally experience greater humidity than northern states.

Saturation, or 100% humidity, is the maximum amount of water vapor that can be contained in the air at a given temperature. If we look at our homes, at a temperature of 68°F, the maximum amount of moisture in the air (100% RH) will be 18g/M³, or 0.63 Ounces for every 35 cubic feet.

Air humidity is measured using a hygrometer. The simplest of these devices uses a human or animal hair and was first used as far back as the 17^th century. Today, there are many types of hygrometers, but hair is still used for some. It’s a simple principle because hair curls as the humidity increases. Relative humidity is calculated by using a formula to determine the humidity level in relation to the temperature.

A comfortable RH (at 68°F) is between 30% and 50%. It will depend on the individual what the ideal RH in the home should be. Generally, anything higher than 50% RH is considered to be undesirable and this would call for the use of a dehumidifier. Most dehumidifiers are equipped with a built-in humidistat that measures and calculates the relative humidity for you. All you need to do is set the RH that you prefer and the dehumidifier will automatically adjust to obtain that level.

How Does a Dehumidifier Work?

There are several types of dehumidifiers and these work on different principles, I’ll be discussing the three main principles used for dehumidifiers.

The most common type of dehumidifier uses a compressor, it works in pretty much the same way as an air conditioner. The main difference being that a dehumidifier concentrates on removing moisture and not cooling the air. Unlike an air conditioner, that blows cold air into the room, a dehumidifier uses the heat exchange to reheat the air. So there should be no noticeable difference in the room temperature when using a dehumidifier.

To understand how these dehumidifiers work, you just need to look at a cold drink on a hot day. Water droplets form on a glass of ice water. So by using a refrigerant (usually Freon) that is compressed into a gas and then decompressed, the heat in the air is transferred to the gas. This cools the liquefied gas, which is passed through a radiator. A fan blows the air in the room through this radiator, thereby cooling the air. As the air cools, the water vapor condenses into drops of water. This water is directed to a tank, or is discarded into a drain by means of a pipe. This is the most effective way of removing large volumes of moisture from the air and is used for larger dehumidifiers. One of the concerns that some people experience when using this type of dehumidifier, is the noise generated by the fan and compressor. Though many manufacturers have done a lot to reduce this noise. Even then, they are the nosiest type of dehumidifier.

Peltier cooling is used for some smaller dehumidifiers. The main advantage to using a Peltier coolant instead of a refrigerant gas and compressor is the noise level. A Peltier generates basically no noise, just a barely audible electronic hum. They are also very compact units and are popular for small, tabletop dehumidifiers. The disadvantage is that Peltier coolers are not as efficient as compressors. So these smaller, quieter dehumidifiers will remove less moisture from the air.

The most basic type of dehumidifier uses a desiccant, like Silica Gel. You will recognize these by those small sachets that you find in some packaging. Electronic goods, medication, and leather products usually have a small amount of sealed silica gel to absorb any moisture that could harm the product. The media has reported health related issues relating to the use of silica. Though you need not concern yourself with this, when considering this type of dehumidifier. Manufacturers have ensured that the silica gel dehumidifiers are safe for both people and our pets. In fact all dehumidifiers are family and pet friendly. They make our homes healthier, ad don’t pose any type of risk. This provided that that install and use any dehumidifier according to the manufacturer’s instructions.

Desiccant dehumidifiers use larger quantities of reusable silica gel crystals than the small sachets that you see in packaging. They absorb the moisture in the air and can be dried out many times simply by heating the crystals. Although silica gel dehumidifiers don’t remove large amounts of moisture from the air, they are very popular for closets, gun safes, and other confined spaces. These dehumidifiers don’t use electricity, though most will come supplied with an electric heating pad to assist in drying them. However, when in use, they don’t need an electrical outlet or batteries. They are very compact and make absolutely no noise. Desiccant dehumidifiers are also very cheap to buy and quality crystals can last for as long as 10-years.

Guide to Choosing a Good Dehumidifier

Knowing what a dehumidifier is and how it works is good starting point. Now we should look at all the factors that you should consider when choosing the best dehumidifier for your needs. There are several attributes that may be important and this will vary from person to person. Here are some of the main pointers:

What Size Dehumidifier Do you Need?

The size of a dehumidifier is determined by how many ounces of water it is capable of removing from the air over a 24-hour period. This specification will be represented by ounces per day or pints per day. European models will usually specify liters per day. The physical size of the machine will vary. You can generally expect a larger capacity dehumidifier to be larger in size. Though this is not always the case.

Note that this is a rough guide and there are very compact, inexpensive dehumidifiers that will handle less than a pint day. Some silica gel dehumidifiers are rated for as low as 6 Oz per day.

Along with the moisture removal capacity, the fan that circulates the air is also important. Air circulation is measured in Cubic Feet per Minute (CFM). A room with poor ventilation will need a higher CFM rate. Since most dehumidifiers have adjustable fans with several speed settings, you can be assured that a dehumidifier should be able to work in any environment, as long as the moisture removal rate is met.

To accurately determine what size dehumidifier you need, can be quite a process. You need to measure the humidity, using a hygrometer. Calculate the cubic feet of the area and determine the air change rate to estimate the CFM needed.

Since a dehumidifier has a variable range, and we don’t require 100% accuracy in our calculations, most people would probably prefer an easier way to estimate the size requirements for their dehumidifier.

You should easily be able to decide whether the area has extremely high humidity (90% - 100% RH), you’ll see damp patches on your walls and even pools of water collecting. If there’s visible mold in the room and damp stains, you can see this as high humidity (80% - 90% RH). If you constantly smell mold or mildew, you can assume moderate humidity (70% - 80% RH). If the room feels uncomfortable with an occasional musty smell, the humidity is relatively low (60% - 70% RH). By these estimates, you should consider the following guide as an indicator as to how many pints per day your dehumidifier should remove from the air.

In addition to this, you may want to consider how the moisture that is removed from the air is contained. Dehumidifiers can use a tank to collect the water or it can be a continuous drain dehumidifier with a pipe. A smaller water tank is easier to carry, but will need to be emptied more often. A continuous drain hose is very convenient because the water is removed through a pipe and you never need to empty the tank. However, the pipe needs to be directed to a drainage point where the water can be disposed of safely. Most dehumidifier drain hoses use a gravity feed, so the drain point has be lower than the dehumidifier. Some have a pump, so that the drain pipe can be directed to a higher point, like a window.

Dehumidifier Noise Levels

The type of dehumidifier will determine the amount of noise it makes. A loud dehumidifier can be annoying, particularly in a bedroom at night. Most of the larger dehumidifiers use a compressor and a fan, these can be quite noisy, ranging from 50dBA to 65dBA. To put this into context, a normal conversational voice is roughly 60dBA. Most dehumidifiers have a quiet or “sleep” mode. This basically sets the fan to the lowest speed, to reduce the noise. At the lowest fan speed, noise levels will be around 50dBA, perhaps a little lower. This is not too noisy, but is louder than a whisper.

Peltier dehumidifiers don’t make much noise at all. One only hears the fan which can range from a little under 30dBA to around 35dBA. This will be quieter than a whisper.

Desiccant dehumidifiers have no mechanical components and are, therefore, completely silent.

Installing and Using Your Dehumidifier

Although all dehumidifiers are quite easy to install and use, you should consider how, and where, you intend using the dehumidifier. A dehumidifier with a tank is completely portable and can be used anywhere. Most people who use a dehumidifier for camping, in a trailer or RV, prefer one with a tank.

While a continuous drain humidifier is very convenient, there are some installation factors to consider. It is not complicated to install the drain pipe. If you can hook up a washing machine, you’ll have no problem installing a continuous drain dehumidifier. All that you need to keep in mind is how you direct the pipe. If your dehumidifier does not have a pump, you’ll always need to ensure that the drainage point is lower than the pipe outlet on the machine. These dehumidifiers are not as portable. They tend to be fairly large and heavy. They can only be used where there is a suitable way to drain the water. There are quite a number of dehumidifiers that offer the option to use a tank or drain pipe. These will obviously be the most versatile.

If you’re considering a whole house dehumidifier, you will need to use a qualified technician. These are large machines and are connected to your HVAC ducting.

If you need to use a dehumidifier where there is no electrical outlet, a desiccant dehumidifier is going to be your best option. These dehumidifiers also don’t have a tank that needs to be emptied, nor do they use a drain pipe.

Dehumidifier Controls

Operating a dehumidifier is never too complicated. Some, very basic dehumidifiers, only have an on/off switch. There are no fan speed settings, or any type of automation. These dehumidifiers will generally have a light to tell you when the machine is on, and one to inform you as to when the tank is full. Just about all modern dehumidifiers will switch off automatically when the tank is full.

More sophisticated dehumidifiers give you the option to control it manually, or let the machine do everything automatically. They will often have intuitive touch controls that allow you to toggle, or use a numeric pad to set your desired RH. Generally there will be screen to display your settings and some will also give additional information, like the actual RH in the room and temperature.

Many will have a timer that allows you set the dehumidifier to switch on or off automatically at a scheduled time. Some even have remote controls and phone apps for maximum user ease. A silent mode can be a great function for bedroom dehumidifier.

How Much Does a Dehumidifier Cost?

I usually list the cost of a product last on my list of priorities. One should first consider your needs and there is always the issue of quality. You get what you pay for. Be that as it may, everyone has a budget and it’s a good idea to have a basic price range in mind. As one would expect, a smaller dehumidifier is going to cost less than machines with a larger capacity. More sophisticated machines with better controls and automation, will usually cost more. Of course, prices vary a lot between the brands. In this regard, I always prefer the better brands, with an established reputation. It’s worth paying a little extra in the knowledge that you’re spending your cash on a product that is going to deliver on its promise.

The cheapest dehumidifier is always going to be a desiccant model. The very smallest of these cost less than $10, though this will be for a very small area that doesn’t have a high RH level.

Next up the list will be Peltier dehumidifiers, starting out at a little under $40 for a small machine of a reasonable quality standard. You shouldn’t expect to pay much more than $100 bucks for a quality Peltier dehumidifier. Though none of these products have very high moisture removal rates.

The most effective dehumidifiers use a compressor, and these will always be the most expensive. You should expect to pay anything from around $120 to over $500. This will depend on the size, functions, and brand of the machine.

A useful buying tip for dehumidifiers is to time your purchase. The highest demand for these appliances is in the spring and summer months. From fall through winter, it is more likely that you’ll find discounted prices and special offers. If you want to spend less, it’s always better to buy a quality product at a discount, rather than buy a cheap (possibly inferior) product during peak season.

Apart from the purchase price of your dehumidifier, you should look at the power consumption. One that uses a lot of electricity might be cheaper. But, in the end, you’ll be paying more for it over time through your electricity bills. Especially when looking at larger capacity dehumidifiers, look for an Energy Star rating, these will be the most economical to use.