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Whole-House Humidifiers

January 15, 2016

You may be familiar with a space or room humidifier, but did you know you can get a whole-house humidifier? This is a device that gets mounted to your furnace’s hot air supply. Warm air is sucked into the humidifier, where it absorbs moisture. Then, the now moisture-rich air is passed back through the vents of your home.


Whole house humidifiers offer several advantages compared to room humidifiers:

Convenience: They condition the whole house evenly with a single unit, so you do not have to have space in every room to plug in and setup a separate room humidifier. Plus, furnace humidifiers are typically plumbed directly to a water line, so there is no need to constantly clean and refill a water reservoir, as is required with a room humidifier.

Maintenance: Maintenance is easy with a furnace humidifier: just have it checked and filter changed once at the start of each heating season.

Safety:  Because there is fresh water plumbed into a furnace humidifier, water doesn’t sit around to accumulate mold.  Also, with room humidifiers, there is always the danger of someone tipping the unit over and splashing water everywhere.

Control:  A furnace humidifier can be controlled by a humidistat, which is a device similar to a thermostat that allows you to adjust or set the desired humidity output. This is a great way to avoid air that is too dry or too moist with a simple dial, panel or switch. Some units actually replace your existing house thermostat with a single, integrated humidistat/thermostat.

Types of Whole House Humidifiers

There are many types of whole-house humidifiers:

  • Fan-powered humidifier units have their own fans separate from your heating unit’s fan – that add moisture directly into your ducts.
  • By-pass humidifiers, on the other hand, work with your furnace’s existing system to deliver enhanced moisture throughout your home.
  • Flow-through humidifiers are the most common, and operate by sending water directly through the unit to add moisture to the warmed air.
  • A reservoir humidifier uses an actual reservoir of water that then gets gradually funneled into the air to reach the ideal level of humidity. There is a filter that water flows through and your furnace’s warm air blows through the filter.
  • A steam humidifier, as the name suggests, incorporates steam into the air that is evaporated from water. It is the most expensive type of humidifier, but also the most effective and allows more precise control of the humidity. They come in cold and hot water forms, injecting hot or cold steam into your supply line.

Important Tip: If you have two HVAC units in your house one upstairs and one downstairs you only need a single furnace humidifier on your downstairs unit, since humidity rises.


Costs for a furnace humidifier range from $350-$500 including installation.  Although some are marketed as do-it-yourself, we recommend calling a professional, since a water line and electrical line may need to be run for the humidistat and fan. Call Interstate AC Service for help at 615-802-2665.