The Ultimate Guide to Buying a Dehumidifier

Here at Seaira Global we want to make buying a dehumidifier as easy as possible. It can be a complicated process with so many different models on the market. Because of that, we have created this guide to ensure that not only do you understand dehumidifiers, but that you can make an informed decision on which model will work best for you


Dehumidifiers protect your home and family from unwanted problems

If the humidity gets too high in your home, it not only affects the people living in it but also the condition of home itself. In both cases, too much moist, humid air can cause serious issues.

Excess humidity can make your home quite uncomfortable for you and your family. You may start to notice that it always feels clammy inside or that there’s a musty odor in the area. In addition to discomfort, high humidity can exacerbate medical conditions, such as asthma or allergies. Over time, excess humidity can lead to mold or mildew problems, which can pose serious health problems, as well.

Besides affecting the people in it, high humidity also has a harmful effect on the condition of your home, especially the structural integrity. For example, you may start to notice that doors don’t align properly or that that there’s always condensation in the windows. If ignored, excess humidity can cause larger problems, such as wood rot or sagging floors.

The structural issues can be worsened by external factors like mold and pests, that are attracted to the damp, moist areas of your home. For instance, mold spores are most often found in wet, humid spaces. As the mold feeds and grows, it can weaken the structure of the home. This is also true for pests such as termites, centipedes, silverfish, and mites. Insects need water to survive and are always looking for moist areas. Once inside, pests can severely damage the wood throughout your house.

High humidity compromises the longevity of your home and the health of the people living there. The good news is that installing a Seaira Global dehumidifier can help maintain a consistent humidity and help prevent these issues.

Back to Top


Understand the difference between absolute and relative humidity

Before buying a dehumidifier, it’s helpful to understand a little bit about humidity. If you’ve ever been to an area with high humidity then you’re familiar with going outside and experiencing the heavy, muggy feeling that lingers in the air. Unfortunately, humidity doesn’t just stay outside since high humidity and all of it’s problems can spread throughout your home, too.

Most of the time humidity is referred to as either a relative or an absolute humidity. Absolute humidity is the mass of water vapor in the air divided by the mass of dry air that is in a volume of air at a specified temperature. The result of this is that the hotter the air, the more water it can contain. On the other hand, relative humidity refers to the ratio of the highest possible humidity in the air compared to the current absolute humidity. For example, if an area has a relative humidity of 100 percent then the air currently contains as much water as possible. Since the air can no longer hold water at 100% humidity, rain is created.

There is a reason that humans are particularly susceptible to high humidity. The way our skin works, it relies on the air to get rid of excess moisture. When we sweat, that is our bodies way of trying to keep cool and maintain the appropriate temperature. Because of this, when there is a high humidity level, you will feel warmer than when there is a low humidity level. This is because at lower humidity, sweat can evaporate more easily off of our skin. For instance, according to NOAA if there is a temperature of 86°F and a relative humidity of 50% ,then the real feel will be 88°F. On the other hand, if there is a relative humidity of 95 percent, then that same 85°F will feel like 100°F.

In regards to a dehumidifier, the more relevant term is relative humidity. This is what is monitored by the built-in humidistat in your machine. When the humidistat senses the relative humidity getting too high, it will activate to maintain your desired set point.

Back to Top


Common terms when talking about dehumidifier

Pints Per Day (PPD):

Pints Per Day is the volume (in pints) of moisture extracted from the air daily by your dehumidifier.

Vapor Barrier:

A vapor barrier is a thin layer of impermeable material, typically polyethylene sheeting, included in building construction to prevent moisture from damaging the foundation of the building. Vapor barriers are used in crawlspaces to prevent moisture in the ground from seeping back into the space once the dehumidifier has removed it.

Gravity Drain:

A dehumidifier with a gravity drain uses gravity to move water through the drain line to an acceptable area for drainage out of the crawl space. In order for a gravity drain to work effectively, the drain tube must be set up properly on a downward slope with no kinks or twists.

Condensate Pump:

A dehumidifier with a built-in condensate pump pumps the condensate (water) from the dehumidifier to an acceptable area for drainage outside of the crawl space. Condensate pumps turn on intermittently depending on the water level in the pump reservoir. As the water rises in the reservoir, it raises a float switch which energizes the pump. The pump will then run until the level of water in the reservoir is substantially lowered. It is important to note that a condensate pump is a mechanical device and will require yearly maintenance to ensure it is functioning properly.

Condensate Pump Lift:

Condensate Pump Lift describes how high the condensate pump is capable of moving water. For instance, the Watchdog 900c has a 15-foot condensate pump lift.

Set Point:

Set point is the desired value in a closed-loop feedback system. When using a dehumidifier, you choose humidity set point, which is the desired humidity level you wish to maintain in the area.

Stack Effect:

Stack Effect describes the the process of humid air entering your crawlspace and rising up throughout your home. As the warm air rises and escapes through your roof, it creates a vacuum. The warm air is then replaced with cool air. This is considered the natural airflow pattern of your home. As the air from the crawlspace is drawn up into your home it brings moisture and all of it’s harmful side effects with it.

Coils (Evaporator and Condenser):

The condenser coil condenses the refrigerant from a hot gas to a cold liquid by the use of the metering device. This then moves into the evaporator coil where the refrigerant evaporates as it absorbs heat from the indoor air passing over it. The evaporator coil is the one you can see on your dehumidifier that is cool and wet to the touch.

Inlet Filter:

The inlet protects the evaporator coil from dirt and debris as the air is being pulled into the dehumidifier to be conditioned. All Seaira Global dehumidifiers have a filter that protects the coils. The Watchdog 900 and 900c come standard with a washable prefilter. The Watchdog 550 comes standard with a Merv8 filter, which is also available for the Watchdog 900 series. All Watchdog dehumidifiers can also be upgraded to HEPA filters or carbon filters.

Relative Humidity (RH) Sensor:

The RH sensor reads the relative humidity of the space within +/- 5% to determine when your dehumidifier needs to run.

Supply Duct Collar:

The black collar on the side of your unit is the supply duct collar. You can attach flexible 6” tubing to this collar and blow the warm conditioned air to any place you would like. For example, if you have an area of your crawlspace that tends to be damp and is cut off from the rest of your crawlspace by your HVAC system, you can attach the flexible duct and run it over to that closed off area to help dry it out.

Drain Line:

The drain line is how the water is moved out of the unit and into the drain system. The Watchdog 550 and Watchdog 900 both have 12” of drain line for the water to flow from the drain tray to the system you or your installer has put in place to move the water out of your crawlspace. The Watchdog 900c has 20 feet of drain line to move the water away from the dehumidifier using the condensate pump.


MERV stands for Minimum Efficiency Reporting Value. A MERV rating varies from 1-20. The higher the value, the more efficient the filter will be in trapping airborne particles.

MERV8 Filter:

A MERV8 filter is capable of trapping airborne particles in the 3.0-10.0 pm size. The disposable filters have an extended surface area and are made with a thick cotton-polyester blend media.

HEPA Filter:

HEPA filters are also also known as high-efficiency particulate air filter. To qualify as a HEPA filter, it must remove 99.97% of particles that have a size of 0.3 micrometers. The filters are composed of a mat of randomly arranged fibers that are typically composed of fiberglass. HEPA filters are commonly marketed in HVAC systems for people with allergies.

Carbon Filter:

Carbon filters, also known as activated carbon filters, aid in odor removal. The activated carbon attracts and removes odor molecules by trapping the molecules in the pores of the activated carbon.

Hot Gas Bypass (HGB):

The main purpose of having HGB is to prevent condensate from freezing on the surface of the evaporator coil when the dehumidifier is operating at extremely low load conditions. The HGB diverts hot, high-pressure refrigerant vapor to the evaporator side of the system, which raises the suction temperature to prevent frost from forming.

Back to Top


How do dehumidifiers work

Dehumidifiers are essentially small air conditioners. The difference is that instead of cooling the air, dehumidifiers warm the air up. A built in fan pulls the air through a filter and into the unit. This air then passes over a set of coils that are filled with a refrigerant to keep them cold. Whenever humid air passes over these cold coils, the air is cooled down. This in turn causes the moisture in the air to condense and settle onto the cold coils. The water then drips down the coils into a drain tray. Depending on your exact model, the water is either drained through a gravity drain or into a reservoir to be pumped out.

Once the air has passed over the cooling coils and has had moisture pulled from it, it then goes over a second set of warmer coils where the air is reheated (usually to a few degrees higher than when it started). This dry, warmer air is then pushed back into the room, thus reducing the overall humidity in the air of the room.

Back to Top


When purchasing a dehumidifier, there are a few key factors you will want to consider:

1. Coverage Area

The first thing to figure out is how much cubic footage you need to cover. The cubic footage is important to know, otherwise, you may end up with an underpowered machine that can’t maintain your desired humidity. If that happens, not only will you not see any improvement in air quality but, you will also waste time and money. To prevent this, simply calculate the cubic footage of your crawl space using this formula: Square Footage x Average Height= Cubic Footage. Keep in mind that this is NOT the square footage of every level in your home, but rather the outline of the structure or “footprint”. If you have a three story home, you do not calculate the square footage of each story, just the footprint.

Formula to calculate cubic footage

For instance, if a crawl space is 2,000 square feet and 4 feet high, the cubic footage would then be 8,000. Once you determine the cubic footage, you can pick which size will work for you.

An example of a formula to calculate cubic footage

2. Efficiency (L/kWh)

Another factor to consider is the efficiency of your dehumidifier. To determine how efficient your dehumidifier will be simply look at what is called L/KwH or Liters per Kilowatt Hour. This refers to the number of liters of water that can be removed from the air, per kilowatt of power, per hour. The higher this number, the more energy efficient the unit is. All of Seaira Global dehumidifiers are Energy Star Rated and provide a well above average L/kWh.

3. Fan Power (CFM)

A powerful fan is a crucial component of any dehumidifier. The fan draws the air from the space into the machine to begin the moisture removal process so you want a fan that’s effective. The amount of air the dehumidifier can process is measured by CFM or cubic feet per minute. Both the WatchDog 900 and 900c models have an impressive CFM of 370. The WatchDog 550 has a CFM of 250, making it quite powerful for it’s size.

Help choosing the right dehumidifier

4. Drainage System

All dehumidifiers need some method for draining water. There are two options for draining- a gravity drain system or a built in pump system. As the name implies, in a gravity drain system, the dehumidifier uses gravity to drain the water. For the system to work, you need a setup that will allow the drain line to run at a decline the entire time, since water cannot flow uphill. As long as you have a suitable area, gravity drains are quite simple to set up. They do require annual maintenance, but it only takes a few minutes. Both the Watchdog 550 and the Watchdog 900 have gravity drain systems.

If you need your dehumidifier to drain uphill, then a built in pump will be a better option. With the a built in condensate pump, the drain line can be set up to run up to 15 feet uphill. Just like the gravity drain, condensate pumps also require annual cleaning to prevent problems. The Watchdog 900c comes standard with an internal condensate pump.

5. Digital Controls

One important feature to consider is what type of controls are on the dehumidifier. Some dehumidifiers use a simple dial while others have a digital display. A digital display screen makes a dehumidifier much easier to program. It will give you the capability to set the dehumidifier to your exact desired humidity level. All Seaira models have a digital readout that not only allows you to set your preferred humidity level but also shows you the current relative humidity. Another electronic control to look for is an on/off switch. While all Seaira models include a power button, some lower end models do not come with a simple power switch. This means that you may have to unplug the unit or adjust the humidistat just to get the unit to power off.

6. Digital Humidistat

In addition to digital controls, it’s quite useful to have a digital humidistat. Having a built in humidistat makes it easy to set and maintain your desired humidity level. For instance, you can use the digital screen to set your humidity level to 50% and the dehumidifier will run until the humidity is within 5% of the set point. At that point, the dehumidifier will automatically shut down. The humidistat will continue to monitor the humidity levels and turn the machine on and off, as needed. All Seaira Global dehumidifiers come standard with this feature.

7. Auto Defrost

The Auto defrost feature is highly useful to keep your dehumidifier running in colder temperatures. When temperatures drop below 65°F, the coils can accumulate frost as the condensation on the coils freezes. The built in defrost mechanism monitors the temperatures on the coils and when a predetermined temperature is reached the defrost function will activate. Once the defrost cycle has completed the dehumidifier will continue its normal operation.

8. ENERGY STAR® Certification

If you’re worried about higher electric bills, be sure sure to look for a dehumidifier that is ENERGY STAR Certified. Dehumidifiers that are ENERGY STAR Certified have more efficient compressors, refrigeration coils, and fans. In general, these dehumidifiers will use at least 15% less energy than non-certified models. To qualify for an ENERGY STAR Rating, there are strict standards that must be met. If the dehumidifier has a capacity of less than 75 pints per day, then it must have an efficiency greater than 1.85 L/KwH. For larger dehumidifiers that produce more than 75 pints per day, the efficiency level must be greater than 2.80 L/KwH. All WatchDog dehumidifiers are ENERGY STAR certified.

9. Noise Level

Noise level might not be your first thought when searching for a dehumidifier, however, it is an important consideration. For example, if your dehumidifier is directly under a living area, you’re going to notice if it’s unusually loud. The last thing you want is a noisy dehumidifier to keep you awake at night. An average dehumidifier will have a decibel level that ranges from 65 to 75 decibels at a distance of 4 feet. A sound level of 65 could be compared to a loud conversation while 75 decibels is similar to the sound of street traffic. The WatchDog 900 and 900c models are rated at 58 decibels, while the WatchDog 550 is rated at an ultra-quiet 52 decibels.

10. Low Operating Temperature

To prevent problems in cold weather, be sure to check what the operating temperature range is when looking at dehumidifiers. Most crawl space dehumidifier will work in temperatures higher than 41°F. This is fine for many situations, however, if use your dehumidifier year round in a unheated basement or crawl space, that might not be enough. To ensure that your dehumidifier continues to work through winter, choose one with a low operating temperature in the thirties. All three models of WatchDog dehumidifiers are able to run in temperatures as low as 33°F.

11. Filter

Filters are an important component in the operation of a dehumidifier as they help preserve your unit. Using a filter helps to prevent dust and dirt build up inside the unit. Keep in mind that filters typically need to be cleaned or replaced at least once a year (depending on the environment). If you’re looking for the more cost effective option, choose a filter that can be washed and replaced. The WatchDog 900 and 900c are equipped with a prefilter that can be easily cleaned and reused. Simply slide the prefilter out of the machine and rinse with water. This will ensure that the prefilter does not get clogged so your dehumidifier can continue to run effectively. There is also the option to upgrade your dehumidifier with a MERV-8, HEPA, or carbon filter. The WatchDog 550 comes standard with a highly efficient MERV-8 filter.

12. Auto Reset

Another convenient feature to have on a dehumidifier is automatic reset. Having a dehumidifier with automatic reset means that in the event of a power loss, the machine will turn back on by itself and continue maintaining the last humidity level that was set. This useful feature means you won’t have to crawl under your house every time you lose power. Instead, simply let the machine turn back on by itself once the power is restored. You don’t even have to worry about settings, the machine will automatically maintain the same settings it had when the power was lost.

13. Duct Adapters

Depending on your desired set up, you may want the option to duct your dehumidifier. Ducting allows you to control where the airflow will be directed. It can also be great for special circumstances such as tying your dehumidifier into an existing HVAC system or placing the dehumidifier in a separate space than what’s being dehumidified. If you think ducting will be a good option for your home, be sure to look for a dehumidifier that comes with a built in duct adapter.

Back to Top

Seaira Global NXT Dehumidifiers

NXT Dehumidifiers by Seaira Global

•WatchDog NXT85c (up to 15,000 cubic feet)
The WatchDog NXT85c is the same space-saving size as the NXT85 with same 85 pint per day capacity. The only difference is that the NXT85c features an integrated pump which makes it ideal for spaces where a gravity drain system is not an option.

With a powerful capacity, the NXT85c can maintain areas up to 15,000 cubic feet. The dehumidifier produces 185 CFM at 2.71 L/kWh and 4.8 amps.

The WatchDog NXT85c also includes multiple features to make it easy and efficient to use. First of all, the digital display makes it easy to choose your desired set point. Then, the automatic humidistat, temperature controlled defrost, and auto restart features make the machine quite low maintenance while it is running. Just like any mechanical device, the 85c require some annual maintenance. The good news is that the unique side panels make it simple to access internal components.

•WatchDog NXT85 (up to 15,000 cubic feet)
The WatchDog NXT85 is the largest crawl space dehumidifier in the Seaira Global lineup. With an 85 pint per day capacity, the NXT8 is perfect for bigger areas that need moisture control.

The WatchDog NXT85 can maintain areas up to 15,000 cubic feet. The machine produces 185CFM airflow at 2.71 L/kWh and only 56 dBa. Not to mention that it is the same compact size as the NXT60.

The WatchDog NXT85 includes several features that make using the dehumidifier simple. For instance, when setting the humidity set point, simply use the digital display. After the initial setup, the dehumidifier requires minimal attention with features such as, temperature controlled defrost, auto restart, and an automatic humidistat. While the NT85 needs a small amount of annual maintenance, it’s quick and easy, thanks to side access panels.

•WatchDog NXT60 (up to 11,000 cubic feet)
At 60 pints per day, the NXT60 is the smallest crawl space dehumidifier offered by Seaira Global. When you need a dehumidifier for a compact area, the NXT60 is the ideal solution. At only 12 inches tall, it’s easily maneuverable in practically any space.

While it may be the smallest dehumidifier in our lineup, the ENERGY STAR® rated WatchDog NXT60 can easily maintain areas up to 11,000 cubic feet. The unit produces 135CFM airflow at an efficient 2.6 L/kWh.

The WatchDog NXT60 also includes several convenient upgrades that make using the machine quite simple. For instance, when you need to set your desired humidity level, simply use the digital display. Once the set point is in place, the NXT60 requires very little input from you, thanks to features like an automatic humidistat, hot gas bypass, and auto restart. Since it’s a mechanical device, the NXT60 does require minimal annual maintenance. The good news is that it features unique side panels to give you quick access to internal components.

Back to Top