Winter doesn’t just bring a chill — it brings with it dry air that your furnace will circulate throughout your entire home. Adding a retrofit humidifier is a great way to improve your comfort in the winter, not to mention extend the life of your wood floors, musical instruments, artwork and other objects impacted by a home made too dry. On top of that, furnace manufacturers point out that when the moisture is removed from the air, you feel colder, which leads you to crank up the heat and add to your energy bill. The Environmental Protection Agency advises keeping indoor humidity between 30 and 60 percent — any higher, it notes, and you run the risk of creating a breeding ground for mold. On the other hand, with less than 30 percent relative humidity, you and your family might find yourselves not only uncomfortable, but running the risk of the overly dry mucus membranes that can lead to nosebleeds and infections. So what should you consider before retrofitting your home with a central humidifier?

Types of Humidifiers

First, it’s important to understand your options. If you only notice dryness at night, in certain rooms or only for one or two months of the year, then a room humidifier might be the answer for you. These devices disperse either a warm or cool vapor through either an evaporative or ultrasonic process. The former generally have a lower upfront cost, but require regular replacement of their filter. Numerous options of either type, in a wide range of capacities, are available from online retailers and other sources.

However, if your home is dry for several months out of the year and is making an impact on your health and your home, consider a whole-house humidifier. These humidifiers utilize the air heated by your furnace to disperse humidity to your entire home.

There are two basic types: evaporative and steam humidifiers.

With an evaporative humidifier, warm air passes through the humidifier’s evaporator pad, a ceramic-coated pad saturated with water. The hot air absorbs that moisture and moves it throughout your home. Evaporative humidifiers are powered by your furnace’s fan and so must be installed in your ductwork. These are known as bypass units, meaning they are installed on the cold-air return. Air is supplied to the humidifier from the furnace’s outgoing warm-air supply. During warmer months when your air conditioner is running, a damper in the bypass vent pipe can close off airflow through the humidifier.

A steam humidifier operates by heating water in a canister and converting the water to steam that is forced through your ductwork. Although these units also are installed in your ducts, many do not need to be connected to your furnace to run. These fan-powered models are installed directly on the warm-air plenum (although they can be installed on the cold-air plenum if connected to a hot-water heat source). The built-in fan pushes the moisture into the outgoing warm-air flow.

Selecting a System

Which is the best humidifier for you? Consider this: a humidifier that is integrated within your ductwork generally can be installed and then virtually forgotten. Once you have selected your desired relative humidity, the unit will run as needed. Only annual maintenance is advised for these units. With standalone units, you’re looking at more frequent maintenance than with integrated units. Among other things, because these units aren’t hooked into your water supply, they require you to refill the water reservoir, often daily.

When it comes to whole-house systems, product manufacturers report that evaporative humidifiers are significantly less expensive upfront than steam humidifiers. While the upfront costs of whole-house humidifiers vary, top-rated evaporative units cost as little as $250. Estimates put professional installation at between $100 and $300. Steam units are estimated at anywhere between $300 and $1,100. Installation of the in-duct steam humidifiers, with their more in-depth hook-ups, often cost an additional $300 to $500. Evaporative humidifiers also use little electricity — but large amounts of water. Operation costs of your humidifier will vary depending on how often your unit runs and the efficiency of your unit, making it difficult to predict its impact on your utility bill. Steam humidifiers reportedly require less maintenance than evaporative systems, since evaporative systems’ evaporator pads can potentially become a breeding ground for bacteria.

Capacity and Compatibility

It is important to select a humidifier that is able to provide enough moisture for your entire home, so know your home’s square footage before purchasing. Approximately 12 gallons per day can humidify an area of up to 3,000 square feet. For a more specific estimate, humidification calculators are available.

Many furnace manufacturers will offer humidifiers that are compatible with your specific unit. Although in most cases installation of a universal humidifier will not void your furnace’s warranty, it is important to read all warranty information first or consult with your installation technician.

How It Works

How does your humidifier know when to switch on? Some humidifiers offer “smart” control options that can operate the humidification features independent of your home heating. Most, however, use a humidistat, which works much like a thermostat. A humidistat is set to your desired humidity level and, when the home drops below that level, tells your humidifier that moisture is needed. Humidistats also can be used with your air conditioning system. Because air conditioners remove moisture from the air (a benefit during the damper summer months), a humdistat may cycle your conditioner on and off in response to the changing internal humidity level.

Your humidifier’s operating manual should include recommendations on the best relative humidity setting for your climate.

Installation and Maintenance

Some humidifiers are reversible, meaning they can be installed on either your warm air plenum or cold air duct. Many will need to be connected to a drain. Carefully read any supplied instructions before installing your whole-house humidifier yourself. It also is important to note that some whole-house humidifiers require installation by a licensed HVAC technician in order to keep the warranty.

Humidifiers require routine maintenance to avoid becoming breeding grounds for biological contaminants. For evaporative units, HVAC technicians advise replacing the humidifier pad each year, as prolonged use may reduce the pad’s ability to continue absorbing water. For steam humidifiers, it is advisable to flush sediment from the tank on an annual basis. To best determine how often maintenance is required, consult your unit’s owner’s manual.

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