Too much moisture in the air can damage things we value. As our homes become better insulated and less drafty, moisture build-up can become a problem.
Books, artwork, musical instruments, wood trim and furniture can all be damaged by high humidity. But, perhaps worse are the health problems associated with damp conditions. If you suffer from asthma or chronic respiratory condition, a dehumidifier could help ease your symptoms.
What a Dehumidifier Can… and Can’t Help With
People usually think of a dehumidifier when they notice signs of excessive moisture in their home. If you notice the following warning signs, a dehumidifier can definitely help.
- Black mold spots. These are often noticed in bathrooms and kitchens (but can appear in any area of the home). In addition to being unsightly, mold affects your breathing, and these initial patches will spread if they aren’t eliminated through a change in humidity, temperature, or removal of their food source..
- Musty smells. This is a sign of a potential mold problem, musty smells are particularly common in basements and areas with poor ventilation.
- Condensation. Water on windows indicates too much water vapor in the air, and can be reduced with a dehumidifier.
- Allergy symptoms. Coughing and sneezing can be caused by mold growth. Mold doesn’t even have to be visible to have an adverse effect on your breathing. Spores float through the air, invisible to the naked eye.
There are, however, some moisture problems that a dehumidifier may mask, but will not fix. These include –
- Rising or wicking moisture. Moisture coming up the walls from the ground – this should be addressed by a licensed professional.
- Water damage. Often caused by blocked gutters or ice dams – keep gutters and downspouts clear to allow water to drain away from the house. Also, keep an eye on your roof during winter months if ice dams form.
- Laundry Room Moisture Problems. Moisture from a tumble dryer or drying clothes indoors – vent tumble dryers correctly (to the outside) and dry clothes outdoors if possible. If you absolutely have to dry clothes indoors, place them near an open window or in a well ventilated area.
How Dehumidifiers Work
There are various types of dehumidifiers and they all have their pros and cons. Below are three of the main types, and what each one is best used for.
Compressor Based Dehumidifiers
Sometimes called ‘refrigerant based’, these dehumidifiers work in a similar way to a kitchen refrigerator. Using gases to create a temperature difference in a set of metal coils, moisture from the air condenses on these coils (like water on a cold can of soda) and drips down into a collecting tank.
To increase the amount of air which can be processed, a fan will draw new air into the unit. Without a fan, the unit would only be able to treat the air that drifts in naturally.
- Room temperature (64-75 degrees fahrenheit), household use
- Effective at a wide temperature range
- Can handle large volumes of water
- Lower end models can be noisy
- Most are fairly large and require a bit of placement planning
- Lower end units are expensive to operate
- Works best in warmer rooms
Sometimes called ‘peltier’ dehumidifiers, these units have fewer moving parts than a compressor based system.
They work on the principle that when a voltage is applied to two different metals, the result will be a temperature difference. When warm air is directed into the machine by a fan, it moves across the colder metal surface, then condenses and drips into a tank. From there the air passes over the warmer of the two metals and out the back of the unit.
- Smaller spaces
- Rooms where quiet is a priority; bedrooms for example
- Affordably priced
- Very quiet to run
- Low capacity
- Most are not very energy efficient
Desiccant dehumidifiers can either be completely passive, semi-passive, or come as a machine. Silica gel is typically the most passive means, while semi-passive models might use electricity to recharge Silica Gel. However in their more advanced form Desiccant dehumidifiers are mechanized. And, in this type of machine, a drum/wheel, containing a desiccant material (a chemical which absorbs moisture) turns constantly.
A fan is positioned to blow air through one area of the wheel, and as the air passes through, moisture is absorbed. The moisture filled desiccant then continues to turn down towards a warm air fan which removes the moisture from the desiccant to a tank, allowing the process to continue.
- Whole house
- Cooler areas like attics or garages.
- More compact
- Works in a lower temperature range than compressor types
- Can reduce humidity to very low levels
- Compressor models typically outperform desiccant dehumidifiers in every category
The capacity (usually given in pints) refers to the amount of water the dehumidifier can remove from the air in a day. The biggest capacity commonly available for household use is a 70 pint model.
How much water the unit’s drain tank can hold is a different matter. For example, if a 70 pint model has a 10 pint tank, and works all day, removing its top quota of moisture from the air, you would have to empty the tank 7 times over the 24 hours. Check the tank capacity as well as the amount of water the machine can remove from the air, before you buy, to reduce emptying.
The tank may need to be emptied manually, but some come equipped with a gravity drain pipe, or a powered pump, which can push water up, through the pipe to a sink, for example. These systems are much, much more convenient.
What Capacity Dehumidifier Do I Need?
Charts advising which capacity to buy based on room sizes and manufacturer’s capacity ratings can be misleading for a number of reasons.
First, the charts do not mention volume of rooms, but only the square footage. This takes no account of high or low ceilings. Second, the charts often recommend unit sizes that just aren’t available to consumers. Finally, the charts often recommend units for area sizes starting from 500 square feet, which is no use if the area you need to dry out is much smaller.
Maximum capacity ratings given by manufacturers can be confusing because they are based on tests run at very specific temperatures and humidity levels. The AHAM (Association of Home Appliance Manufacturers) tests manufacturer’s claims by running dehumidifiers for 24 hours, at 80°F and with a Relative Humidity of 60%.
The average home is unlikely to be this warm, and therefore, the tests can only be used as a guide to how much water any machine will be able to remove from the air in many different home conditions.The best advice is to buy the biggest capacity unit that you can afford, and that will fit into your space.
If the highest capacity unit you can afford dwarfs the space you need to dehumidify, you can safely assume that a smaller machine will be able to handle the job. Buying too large a capacity machine will result in a dry room, but buying a machine that is too small will prove to be an expensive mistake if you have to replace it.
Another Reason Why Bigger is Better
Buying bigger should result in lower running costs. To remove 70 pints a day, a unit must be able to remove 2.9 pints per hour. A 50 pint unit must be able to remove 2 pints per hour.
Therefore, a 70 pint unit running at full capacity can remove moisture more quickly than a smaller unit, allowing you to turn the machine off after a shorter running time.
Some dehumidifiers are automated. These machines can sense changes in the RH (Relative Humidity, see below) and adjust their settings to achieve the results you have asked for.
For example, if you choose a RH of 60%, an automated machine will run constantly until it senses that the RH has been reached. It will then switch off and continue checking the RH until it needs to switch back on and reduce moisture levels again.
Automated machines can save you money by only running when needed.
Dehumidifier Jargon Explained
Here we explain some of the terms you are likely to see when shopping for a dehumidifier –
- Direct Drain – this usually refers to a gravity fed hose that can empty water from the tank, to somewhere lower down. This can save you the effort of emptying a tank, and is silent.
- Internal Pump – this is a drainage system that uses a pump to force water out of a hose. Useful for draining to somewhere higher up than the machine (into a sink, or a larger tank, for example).
- Tank/Bucket Capacity – how much water (usually in pints) the drain tank can hold.
- Operating Temperature – this is the temperature range that the unit can work in. Outside of these temperatures the machine will not be able to create enough of a temperature difference to cause condensation to be formed.
- Auto-Defrost – will stop the machine from freezing in temperatures lower than 65 °F
- Auto-Restart – turns the unit back on after a power outage.
- Filter Indicator – lets you know when the filter needs to be cleaned
- Auto Humidistat – tests the air around the unit for humidity and switches off when the programmed level is reached.
- RH or Relative Humidity – this refers to the amount of moisture in the air relative to the total amount the air can hold. A comfortable RH for inside a home is 40-50%. In winter this might need to be lower to avoid condensation on windows.
How To Operate Your Dehumidifier
For best results you should unpack your new dehumidifier and set it up according to the manufacturer’s instructions.
Vacuuming before you turn on the machine will help to avoid dust particles being blown around the house by the dehumidifier’s fan. The unit’s filter will quickly become blocked if too much dust is drawn in.
You should clean the filter regularly (by vacuuming or washing if it gets very dirty) but the check the instructions for your model for the recommendations. A clogged filter can be a fire hazard and will impair the unit’s performance.
If the model you have chosen has vents on the sides or back, make sure that there is a minimum of 6 inches space for good airflow around it. A top vented model can be a little closer to the walls, but all dehumidifiers should remain uncovered.
At first you should run the dehumidifier on its highest setting (the setting for the lowest RH) to dry out the surrounding air as much as possible. Make sure the doors and windows are closed when you have the unit running, to prevent humid air from outside making the machine’s job impossible.
After this initial period, you can then set the unit to whichever humidity level you choose. The recommended RH for inside a home is between 40 and 50%. However in a rainy climate, 55% may be more realistic, and in winter the RH may need to be lowered to avoid condensation on windows and cold surfaces.
Before emptying the tank, or cleaning the unit, disconnect it from the electricity supply, to be on the safe side.
A dehumidifier can protect your home and possessions, and prevent ill health and unsightly mold.
Compressor based units are great for large spaces, although lower capacity units can be purchased to keep costs down. These machines are effective but a bit noisy. Thermo-electric dehumidifiers are a quiet and cheap choice for a smaller area. Desiccant dehumidifiers are quiet, long lasting and effective, but can be relatively expensive to buy.
The size of machine you go for should be appropriate to your room. A smaller machine will handle a smaller space, although a bigger machine can process the air much more quickly.
Check the tank size in relation to the machine’s processing capacity to avoid frequent emptying, and buy a machine with extra features for convenience if your budget will stretch.