How Does a Furnace Humidifier Work?

Oct 19, 2021

A furnace humidifier serves your entire home as it connects directly to a forced-air heating/cooling system. Heating your home is important during the colder months, but so is preventing the air from getting too dry. The dry heat produced by furnaces can affect people, wood products, plants, and more throughout the home.

How a Furnace Humidifier Works

How a Furnace Humidifier Works

Health Impacts of Dry Indoor Air

Low indoor humidity can cause:

  • Dry skin, especially on the hands and scalp
  • Persistent sore throat and other cold symptoms
  • Aggravated allergies and asthma
  • Increased risk of infection
  • Nosebleeds
  • Dehydration


How to Choose a Furnace Humidifier

There are many products to choose from. Not all are made the same. Here are a few considerations to help you find the best one for your home.


  • Steam Humidifiers: Produce a mist/steam that can be either warm or cool and injects it into the furnace airflow. Powered by electricity, they use a small amount of power, and are easy to maintain.
  • Flow Through Humidifiers: Introduces a small amount of water into the warm air produced by the furnace, which evaporates to increase moisture content.
  • Fan-Powered Humidifiers: Also known as evaporative humidifiers, these also expose heated air to water, which introduces more moisture into your ductwork; the fan provides consistent air movement.
  • Drum Humidifiers: Contain a rotating belt that passes through a pan of water and evaporates the moisture into the air leaving the furnace.
  • Bypass Humidifiers: Adds moisture to the air using the furnace’s blower motor, which recirculates and pushes the humidified air into your living space.



The furnace humidifier must be sized to accommodate the coverage area of your home, in square feet, accounting for the rooms that your HVAC system serves. Too large a humidifier will waste water and electricity and have no added benefits.



Dimensionally, a furnace humidifier should be appropriately sized for the room it is in. Measure your basement, attic, or other space before selecting a model. Size and weight also have an impact on coverage and efficiency.

Daily Output

Output and coverage area are directly related. The maximum daily output of the humidifier is measured in gallons. For example, if you have a 3,000 to 4,000 square foot home, 16 gallons of water per day should suffice.


Furnace Humidifiers and Mold

A furnace humidifier generally does not cause mold. While mold can grow in any moist area where oxygen is available, you can prevent it by keeping your humidifier at less than 45%. Installing a bathroom ventilation fan, using a UV purifier in your ductwork, and cleaning front loading washing machines often can also help prevent mold.


Parts of a Furnace Humidifier

All types of humidifiers have:

  • Water to evaporate to increase humidity
  • An evaporator pad to collect water
  • Blowing air to allow water to evaporate
  • A water control solenoid valve to manage flow
  • A humidistat for humidity level control


Parts of a flow-through humidifier include:
  • Water tap and supply line connected to existing pipe
  • Inlet orifice to reduce flow to the inlet valve
  • Water inlet valve that adjusts flow according to demand
  • Evaporator pad, or water collection medium
  • Water feed tube to distribute water to the evaporator pad
  • Drain pan that allows water to flow into a household drain
  • Hot side air duct (if the unit is connected to a central AC)


Contact Elmer’s Home Services


Our team repairs furnaces and related equipment in the San Antonio, TX, area. We’re also trusted for repairs and air quality services. For a consultation and on-time, honest, and professional service by trained technicians, call or text 210-570-1717 today!

If you are experiencing any of the signs that your water heater needs repair or replacement, don’t hesitate to call a professional.

Elmer’s Home Services in San Antonio TX can help you assess the situation and make the best decision for your needs. We have experienced plumbers and quality service, so you can get back to enjoying hot showers and baths in no time. 

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Call: (210) 570-1717

Headquarters: 9710 N Interstate 35
San Antonio, TX 78233

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About Elmer’s Home Services

Our business provides water heater repair, emergency plumber services, and plumbing repair in San Antonio, Texas. We have proudly served over 20,000 customers. Our professional plumbers are punctual and take pride in providing reliable and affordable home services to our neighbors.

Discover the difference in our services when you get it done “The Elmer Way”. Call us today to get more information!