Why is humidity important?

Desert Spring furnace humidifier

Table of Contents

  1. Facts
  2. Humidification for Health
  3. Humidification for Comfort
  4. Humidification for Energy Savings
  5. Humidification for your Investments
  6. What are the Choices?
    1. Cool Mist
    2. Sponge-Wick
    3. Plastic Disk
    4. Add-ons
  7. Sizing - How much humidity do you need?
  8. Allergies and Humidity in Your Home


A 10% change in relative humidity is roughly the equivalent to a 1 degree Fahrenheit change in temperature.

Pneumococcus, staphylococcus, and streptococcus bacteria die up to 20 times faster at relative humidity between 45% and 55%, than above 70% or below 20%.

Even in a new home with a mechanical ventilation system, a humidifier may be necessary in order to maintain the proper humidity levels at the proper air exchange rate required.

Honeywell, a leading manufacturer of thermostats, recently conducted a survey of 1,000 households regarding indoor home comfort during fall and winter. Nearly 70% of respondents complained of indoor air so dry that it causes itchy skin, dry throats and cracked nasal membranes. More than 75% complained of feeling too hot or too cold.

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Humidification for Health:

One of the most common health issues that plague our society is dehydration. Most of the tissue in the body contains water. If it loses the water, the tissue dries up, its elasticity is reduced, and with it, function declines. Besides dry skin, the symptoms of dehydration include chronic joint and muscle pain, raspy throat, sore eyes, and difficulty concentrating.

There are two ways to combat dehydration, and both are essential: drink a lot of water, and maintain the relative humidity in the home and office at comfortable levels. With our society's current concern for wellness, dealing with dehydration is a good first avenue of approach.

Controlling the amount of moisture in the air is necessary for your family's health. Dry air in your home can make your throat feel dry, and cause or aggravate respiratory ailments. During extremely cold weather, your home loses humidity to the outdoors and may drop to as low as 5% relative humidity. Cold air inside a home heated to 73 degrees can have a relative humidity approaching 6%. By comparison, typical humidity in the Sahara Desert is about 25%. Generally, one does not want to have a home humidity any lower than 30%. Optimal comfort is considered to be achieved at 40-55% humidity.

Inadequate humidification during cold weather is one of the major causes of respiratory infections. The heating season causes many people to experience repeated attacks of winter colds. Winter is blamed for these problems, but the actual cause is dryness, which affects the membranes of the nose, throat and bronchial tubes. Relative humidity also has a significant effect on controlling the occurrence of airborne infections.

CLICK HERE to learn about the relationship between nose bleeds and humidity in your home.

The one thing we can all do to alleviate some of the discomfort of colds, dry noses and dehydrated skin is humidify at home, where we spend most of our time. Actually, for many, dry air is an air-quality issue. Dry air promotes the growth of some bacteria, viruses and respiratory irritants. Adequate moisture enables the body's immune system to better defend itself against indoor respiratory pollutants and irritants.

Relative humidity is a measure of the moisture content in the air as a % of the total amount of moisture the air is capable of holding. For instance, a relative humidity of 40% means the air is holding 40% of the total moisture it can hold.

Warm air is able to hold more moisture than cool air, and as cool, dry air gets warmer, its ability to hold moisture expands. Thus, a 30% relative humidity at, say 60 degrees, becomes a lower relative humidity at 75 degrees. In other words, even though the total amount of moisture in the air does not change, warmer air is drier.

In consequence, warm air absorbs moisture from other things around the house, including people and furniture. This is when throats start feeling scratchy, noses dry out, static electricity sparks start flying and, in drastic cases, furniture gets loose or even falls apart. Hardwood floors can also be permanently damaged.

There are natural sources of moisture in the home. It is estimated that the average family of four produces four to six gallons of water a day through breathing, showering, cooking and laundering clothes. Although four to six gallons seems like a lot, in most cases it's not nearly enough.

Health Institutions recommend that your home's relative humidity should be kept between 30% and 55% during the winter. Lower levels aggravate skin allergies and respiratory infections, and higher levels increase the spread of mold, bacteria and viruses. Dust mites spread when the humidity is above 50%. Experts at the Association of Heating, Refrigeration, and Air Conditioning Engineers in Atlanta say medical studies indicate that maintaining your home's humidity in this optimum zone inhibits the survival of many viruses, including influenza, measles, polio, and herpes.

Why Humidify with a humidifier

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Humidification for Comfort:

Few people realize that dry air feels cool to the skin, and fewer yet understand why. Everyone, even those who are less active, loses heat energy to the surrounding air. Heat energy takes two forms.

Your warm body at 98.6°F, in contact with room air at, for example, 75°F, heats that air by convection and radiation. The air takes the heat from your body and keeps you cool. This action is called sensible heat transfer.

Latent heat transfer takes place when moisture on the surface of the skin evaporates. The heat for the evaporation is also taken from your body, cooling you further.

Static electricity is a direct result of very dry air. Static shocks "zap" you and sensitive equipment. How many times have you shuffled across the carpet, only to be rudely surprised by the crackle of static as you reach for the light switch! It's no fun when it happens to you, and even less so when you reach out and "zap" a loved one.

With the capacity to hold a static charge up to 20,000 volts, your body can also wreak havoc on home computers and other sensitive electronic devices. By maintaining indoor relative humidity at 35 percent or higher, static shocks are greatly reduced. A humidifier can keep the indoor air comfortably moist, despite conditions of low outdoor humidity.

It would take 256 showers a day to provide all the humidity a 2,000-square-foot home needs during cold winter weather (256 x 1/2 lb./shower = 16 gallons daily). Without a whole house humidifier, air becomes desert dry in sealed up homes and steals moisture from wherever it can. That includes your nose, throat and skin. It is the extra evaporation caused by super-dry air that makes you feel chilly when you step out of a steamy bathroom - not necessarily a difference in temperature.

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Humidification for Energy Savings:

Sometimes you feel colder, even with the thermostat turned up. Dry air makes you feel colder than the actual thermostat setting because the moisture evaporating from your skin has a cooling effect. A humidifier can help lower heating bills because humidified air feels warmer. For example, a 20°C or 69°F temperature at 35% relative humidity feels just as warm as a 22°C or 72°F setting at 19% relative humidity. Setting your thermostat back by three degrees can reduce annual heating bills by as much as 5 percent.

Air is like a sponge; it soaks up moisture from wherever it can. Dry air soaks up moisture very well. When that moisture comes from your skin, it cools the skin and you feel cool, often cold. To counteract this process , many people turn up their thermostats up until they feel comfortable, thereby using more heating energy (we all know how much it costs to heat a home these days). On the other hand, raising the moisture level of the air (the relative humidity) decreases the rate of evaporation, and you feel comfortable at a lower temperature setting.

That's the key to using humidification for Comfort and Economy - turn the humidistat up, the thermostats down, and save on the gas bill!

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Humidification for your Investments:

Maintaining the proper relative humidity in your home can help to protect your investment. Dry air results in warping and splitting of furniture, woodwork and hardwood floors. Wooden instruments, such as Woodwinds, Strings and even Pianos, lose pitch and can be prone to cracking and warping, sometimes permanently disabling the instrument. A properly humidified environment can help diminish the chance of permanently damaging your precious woodwork and instruments over the long term.

Another result of dry air is static electricity. If you want to avoid the zap! every time you touch a light switch, or if kissing a loved one puts a spark in the relationship you didn't intend on, it's time to turn up the humidity. Static discharges can also be genuinely harmful to various electrical components, especially the many sensitive computers and home stereo systems that occupy today's home.

To a point, the more moisture there is in your home the better - from watered plants, an aerated fish tank, and steam from a shower. Since the gauges on humidifiers are only general indicators of change, dial in the right amount of moisture (and control it) by increasing humidity up to the point of producing condensation on windows corners.

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What Are The Choices?

Atomizing or Cool-mist humidifiers have the advantage of being portable, but they can be noisy and require a great deal of attention because they have to be refilled, washed and rinsed out frequently. If you are considering this type of humidifier, you might want to look for one that shuts off automatically when it runs out of water to prevent the motor burning out and the possibility of the unit becoming a fire hazard.

Because water stands in the unit's reservoir, it can become a source of mold and bacteria that can then disperse into the air, so it is very important that cool-mist units be cleaned frequently. To clean the holding tank, empty it and scrub away any film or scum. It's very important to clean all surfaces that come into contact with water to prevent any fungal growth. The EPA (Environmental Protection Agency) suggests that you change the water in a portable unit every day, and clean out the tank every third day of operation. These precautions unfortunately add up to a great deal of maintenance.

Drum and flow-through (sponge or wick) whole house humidifiers are common evaporative units for forced-air systems. They put as much moisture into the air as it will absorb.

The advantage of whole house humidifiers is that they connect to your central water supply so you don't have to refill them yourself. These units are not maintenance free, however; they should be checked periodically, cleaned in the spring, and generally shut off for the summer.

The disadvantages of whole house systems are that people have a habit of not checking them and their sponges or wicks tend to become clogged with messy hard water deposits. These systems also tend to use more water than they should because the high airflow will sometimes blow it from the sponge into the duct. Sponges have to be replaced periodically as hard water sediments clog them up or create white dust, often rendering the humidifier completely ineffective. If you purchase a traditional sponge humidifier, budget for the cost of replacing sponges at least once per year. Units that attach to your furnace aren't any more expensive than portable ones and have the benefit of sometimes including air purification systems.

A central humidifier system may have sponge-like pads that dip into a pool of water and move moisture in front of a fan. If you haven't cleaned last winter's mineral deposits from one of these systems, warm air coming out of the ducts may be surprisingly dry.

On wick-type humidifiers, mineral deposits can eventually block the grill. When this happens, the fan will blow moisture against a solidly caked panel, and the air coming from the furnace will take up only a little, if any, moisture. In order to resolve this problem, you should clean mineral deposits from the grill annually, preferably before each heating season. Although softeners will reduce the amount of mineral in your water supply, you should check and clean the grill regularly. Wick and sponge humidifiers can also cause a build-up of bacteria and other allergy-causing organisms. While replacing sponge pads and metal evaporator grills can limit this problem, they will not necessarily remove the risk altogether.

The Plastic Disk whole house (The Desert Spring Furnace Humidifier) is an innovative, evaporative unit for forced-air systems. The amount of moisture added to the air is controlled by the humidistat. This unit is easy to run because it connects to your central water supply and is virtually 100% water efficient (as the disks carry only a thin layer of water). A simple annual cleaning is all the maintenance required, and the disk-type system does not have a sponge or wick to become clogged with mineral deposits exacerbated by hard water. The Desert Spring is also easily installed by the homeowner, and is clearly the best option with very low maintenance and no room for bacteria and other pathogens to grow.

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Accurately Control the Amount of Humidity in your Home

One important feature to consider in a humidifier is the humidistat. Humidistats are used to control the amount of moisture that is added to the air by the humidifier. Without one, the level of moisture in your home can end up being too high, which can promote the growth of allergens such as mold and dust mites, as well as the spread of disease-causing bacteria and viruses. With a humidistat, you can set your relative humidity to between 30% and 50%, which is found by medical experts and industry observers to be the most comfortable and beneficial level.

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Choosing the Right Sized Unit

In choosing the best size for your home humidifier, you should consider the size of the area you wish to humidify and how well insulated that area is. Output is measured in gallons of water per 24 hour period. A tabletop model designed to humidify one standard sized room in 24 hours generally holds one or two gallons of water. One that is intended to humidify a whole house will have a 10 to 12 gallon water reservoir.

Keep in mind that you won't need to use your humidifier during the summer months when fresh air circulates through your home and keeps the air naturally moist. During the summer you should turn the humidifier off and clean it as per the manufacturer's instructions.

How Much Humidity Do You Need
Proper water output capacities for humidifiers.
Figures are in gallons per 24 hours
Size of Residence in Sq.Ft.500 sqft1000 sqft1500 sqft2000 sqft2500 sqft3000 sqft
Tight (Well Insulated, Vapor Barrier, Tight Storm Doors and Windows With weather-stripping, Dampened Fireplace)*
Average (Insulated, Vapor Barrier, Loose Storm Doors and Windows, Dampened Fireplace)
Loose (Little Insulation, No Storm Doors or Windows, No Vapor Barrier, Undampened Fireplace
*Humidification not necessary to maintain conditions of 70 degrees F and 30% relative humidity. An amount of approximately 2 gallons per 24 hours provided by internal sources of humidity (based on a family of four) has already been deducted from the above values.
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