How to lower humidity in your home by choosing the right dehumidifier

If you have incorporated a humidity sensor or two into your home and monitoring routine, bravo for you!  We at HypoAir believe that these are among the most important tools you can have in your air quality toolbelt.  Now, what you do with that information–home or room humidity–-is equally important!  If the monitor tells you that a space is consistently above 60% relative humidity, after you’ve checked and mitigated the sources of moisture (see our post “Humidity and an Indoor Moisture Inventory”), then a dehumidifier can bring it down into the 40-60% range.

The great thing about dehumidification is that by reducing the humidity, you are also increasing comfort.  In hot climates, excess humidity in the air prevents our bodies from cooling effectively by evaporation, because the air is already loaded with moisture.  In cold climates, excess humidity in the air (such as in coastal regions) causes us to feel colder than in dry air at the same temperature.

You are also saving on energy usage for 3 reasons:

• Air conditioners use less energy to cool dry air than more humid air at the same temperature, and heaters use less energy to heat dry air than more humid air at the same temperature.
• In the summer you will feel cooler at any given temperature, when the air is drier versus more humid.  Therefore, you may be able to set your thermostat higher during the summer!
• In the winter you will feel warmer at  any given temperature, when the air is drier versus more humid.  Therefore, you may be able to set your thermostat lower during the winter!

Dehumidifiers come in all sizes for all applications.  When choosing a portable one for a room, it’s important to know the following things:

• Square footage determines capacity:  Just like air purifiers, dehumidifiers are limited by air flow, so standalone units can’t effectively dehumidify through walls and doors.  If you are choosing a standalone unit, measure the floor space.  The square footage measurement incorporates standard 8-foot ceilings, because it really translates to air space, which is ft3.  For 500 ft2, start with a small dehumidifier (10 pints for a moderately humid space and 12 pints for a more humid space) and add 4 pints capacity for every additional 500 ft2 (bobvila.com).  The capacity is usually measured in pints or liters per day, which is the amount of moisture the unit can draw from the space in 24 hours.  The Department of Energy changed capacity testing and ratings for models released in 2020, so newer models are not comparable to older ones.  This page shows a table comparing older and newer capacity ratings.
• Additional/ongoing moisture sources:   Human occupancy = moisture!  We sweat, breathe, and generally exude H20, and rooms with higher activity or temperature levels (like a home gym or sauna) will need more dehumidification capacity.  Also, leaks in the building envelope like doors and windows can allow moisture from outdoor air to come in.  Then, there are those inherently humid spaces that incorporate running water like bathrooms and laundry rooms.  
• Energy Efficiency:  Dehumidifiers are very much like air conditioners, with similar parts and operation.  A coolant is pumped in a closed loop system from the hot side (condenser) to the cool side (evaporator) to draw moisture from the air, collecting it in a reservoir or allowing it to drain to a permanent drain.  The compressors in these dehumidifiers used to draw significant energy (amps) to do their work of changing the fluid from gas to liquid, but newer models are much more energy-efficient.  Inverter technology decreases the energy draw most of all, because the compressor will have a variable speed motor, allowing it to run continuously at a lower speed to keep a constant humidity, or ramp up when the humidity increases.  
• Method of dehumidification:  There are two main types of dehumidifier: refrigerant and desiccant.  Refrigerant is by far the most applicable to residential needs because it can remove large amounts of water from rooms above 50 degrees F.  These work when humid air is drawn across the cold evaporator coil containing refrigerant; the refrigerant removes moisture from the air and produces condensate, and the dry air is blown into the room.  Desiccant dehumidifiers work in lower, less humid spaces by absorbing water directly into a material (desiccant), which is dried out to be used again.  There are some desiccant humidifiers on the market for small spaces like closets or cars; these require that the desiccant be regenerated in an oven or replaced with new desiccant. 

Installing a portable refrigerant dehumidifier is pretty simple; you will need to: 

• Place the unit in the room you want to dehumidify (not inside of a closet), at least 1 foot away from walls or other obstacles so that air is free to circulate around it
• Make sure it’s placed on a flat and stable surface. Sometimes carpet can be too plush for this purpose, so try to find a board or other flat surface
• Choose your drainage method (ideally you should have this in mind before selecting the unit).  If using the bucket, make sure it’s properly installed (most new units will not start working if it’s not).  If using continuous drainage, make sure that the hose is attached securely, the drain end is placed into a sink or drain, and check for leaks once it starts to operate.  Unless the dehumidifier has a condensate pump included, the drain hose end will need to be lower than the unit so that water doesn’t back up in the unit.
• Plug in and set the desired humidity level.

If you have a humidity problem in several rooms or the whole house (this is common situation in hot, humid regions), it’s wise to choose a whole-home dehumidifier. This is a permanent installation that uses your home’s HVAC ducts to distribute dry air throughout the home.  Whole house dehumidifiers are a bit complicated (not generally a DIY installation) essentially involving hanging the unit, running the ductwork, running the condensate line, connecting the unit to an electrical supply and installing the controller.   In addition, you need to make sure that the ductwork is connected to the right places: having a dedicated “return” vent for the dehumidifier, and sending the dry air to the distribution plenum for your AC, are critical for getting the most out of this unit. (pvhvac.com, bobvila.com)

One slight drawback of dehumidifiers is the heat that they produce.  Unlike air conditioners, the hot and cold sides of the heat transfer system are not separated by a wall, so the heat generated by the unit goes into the air surrounding it.  Unless the unit is placed in a small room, this usually doesn’t make a noticable difference in the temperature of the space, but it’s something to take into consideration.

Dehumidifiers need maintenance, just like HVAC units.  With standing water inside, mold can grow fast.  Some manufacturers require that the maintenance on whole house units is performed by a qualified HVAC technician, for warranty purposes.  Here is in essence what they do:

• Turn off the power
• Clean or change the air intake filter
• Clean the condensate drain line and/or add anti-microbial agents to the line
• If there is a condensate pump (typical in crawl space units), make sure it is clean and operating properly
• Make sure that the house humidity is staying in range of its setpoint

For portable dehumidifiers, you can do the following (cnet.com):

• Unplug the unit
• Wipe down the outside
• Empty and clean the bucket thoroughly with dish detergent.  If your unit is plumbed to empty the condensate into a garden hose or other hose line instead of the bucket, then unscrew the connection at the unit and use a towel to wipe any slime from inside the fitting.  Also at this time, you can dump a cup of vinegar or hydrogen peroxide (not both!) into the hose so that any algae forming in the line will die and be flushed out.
• Remove and check the bucket filter (if your unit has one) and clean it out.
• Rinse off the air filter
• Replace the bucket and air filter, and you’re good to go!

Dehumidifiers work best with air circulation!  With portable units, that means that using a ceiling or portable fan to move the air around the room, so pockets of drier or more humid air don’t form.  With a whole house dehumidifier, the fan inside the unit (if operating independently) or the HVAC fan will provide the circulation.

If you decide to invest in a dehumidifier, be sure to check the Department of Energy’s Buying Guide for additional tips, and to find Energy Star Products and rebates ($!)