Installing a whole-house humidifiers can eliminate dry indoor air conditions that forced-air and heat pump HVAC systems generate. By injecting moisture into your house through ductwork, humidifiers reduce airborne dust, are beneficial for indoor plants, and just make your air more pleasant. Let’s review the ins and outs of installing a whole-house humidifier and when to hire a local humidifier installer to tackle the task for you.
Installing a whole-house humidifier begins with a little bit of prep work. Learn about the various types of whole-house humidifiers and choose the appropriate one for your home and its size.
Choose the Right Type of Whole-House Humidifier for You
There are several types of whole-house humidifiers to meet the needs of almost any home. Houses without forced-air central heating aren’t equipped with ductwork and will need a self-contained whole-house evaporative humidifier or multiple room-sized units.
Homes with forced-air or central heat pump HVAC with ductwork throughout the house can choose from fan-powered, steam, or bypass models.
Houses over 4,000 square feet will do well with a steam humidifier, while a fan-powered unit is best for homes that have limited access to the ductwork near the furnace. This guide walks you through the installation steps for an evaporative bypass humidifier which is the most common type available.
Gather Materials and Instructions
The furnace-mounted humidifier you choose typically will likely come with every part you need, as well as installation directions. However, depending on what's in the box, you may need a few additional materials, such as extra-long water supply tubing or a specific plumbing valve for your system, if necessary. These details can vary from one type and manufacturer to the next.
This guide will give you an overview of the process but consult the manufacturer's directions in the package for specifics.
Check Permit Requirements
In many cases, obtaining a permit isn’t necessary for installing a whole-house humidifier, but it’s worth checking with your municipality before starting work to be sure. Hiring a professional humidifier installer ensures that your materials and process adheres to the latest safety and permitting regulations.
Trace Your Humidifier Template Onto Your Duct
You should find a template for cutting holes in your ductwork in the box with your whole-house humidifier. Read the manufacturer’s instructions to determine the best installation location for your humidifier and the accompanying humidistat.
For the humidifier, choose a location that best fits the instructions and has easy access to a water source and a drain. Level the template in place and use a marker to trace it onto either the supply or return air duct.
Cut the Hole and Attach the Mounting Plate
Remove the template and use a drill to make a pilot hole on one of the traced edges. Then, cut out the template shape from the duct using aviation snips and protective gloves to keep your hands safe from sharp metal edges. Use the screws in the installation kit to affix the humidifier’s mounting plate and foam gasket into the hole.
Outline the Humidistat Location
Next, you’ll deal with the humidistat, which monitors the airborne water content and allows you to choose a humidity setting. Choose a location for the humidistat on the return air duct that fits the manufacturer’s directions and is easily accessible. Repeat the tracing and cutting method of the humidifier body for the humidistat using its template.
Install the Humidistat and Connect It to the Furnace
Install the humidistat body and gasket into the new hole with the screws in the installation kit. Your whole-house humidifier needs to wire to electricity. Many models only require plugging into an outlet, while others may require basic manual wiring, in which case you may feel more comfortable having a local electrician perform this step if you’re unfamiliar with electrical circuitry.
The wiring process will vary depending on your model and may include an external transformer or harness. Turn off the electricity to the furnace, if necessary, or the outlet, and closely follow the wiring directions for your specific humidistat. Ensure that the power is off to the circuit you’re working on by testing with a non-contact or probe-type electrical tester before working with electrical components.
Connect the Humidifier
Continue following the wiring directions to connect the wires from the humidistat to the humidifier. If your humidifier has an external pressure switch, install that now by drilling the appropriate holes and making the connections following the instructions.
Install the Drain
On the bottom of your humidifier is a drain, and your installation kit may have a plastic tube in it for that purpose. If not, use 3/4-inch PVC pipes and fittings for a drain. Extend the hose or pipe to the nearest floor drain or a condensate pump. If your furnace already has a drain, you can install a pipe tee and share the line.
Run a Water Line to the Humidifier
Most humidifiers can use either hot or cold water, treated or untreated. Starting at the humidifier, insert the water supply line that came with your model into the compression fitting on the unit and tighten it with an adjustable wrench. Extend the supply line to a nearby water pipe.
Connect the line to the saddle valve’s fitting. Ensure the saddle valve is off and pierce and tighten the saddle valve to the supply pipe. If the building code in your location doesn’t allow saddle fittings, turn off the water to the house and install a tee fitting in the supply line.
Locate, Trace and Install the Bypass Vent
The vent needs to stretch from the supply or return duct. Trace the vent bypass collar onto the duct opposite the humidifier body. Cut out the hole and use the kit screws to secure the collar before attaching the flexible duct to the collar and the humidifier body.
Reassemble the Humidifier
Photo: oasisamuel / Adobe Stock
Turn the water and the electricity back on, open the saddle valve, and check for leaks. Install the filter material into the unit and close the humidifier cover.
DIY Whole-House Humidifier Installation vs. Hiring a Pro
Installing a furnace-mounted humidifier yourself will only cost you the price of the unit, any extra installation materials, and an afternoon. A whole-house humidifier price is typically between $100 and $300; additional materials could cost around $50 if necessary.
Some DIY skills are necessary to install a humidifier. Although the plumbing and electrical connections aren’t particularly complex, it can be intimidating for those without some experience in these areas. Incorrect installation can result in water damage or, in extreme cases, create an unsafe situation in your home. If you’re not comfortable with this kind of work, there’s no need to worry: A nearby humidifier installer can provide more information and installation.
Frequently Asked Questions
The cost of professional installation of a whole-house humidifier averages between $395 and $734. The materials cost between $100 and $300, so DIY installation can save some cash if you have a few skills.
Indoor environments that are too dry or wet can cause problems with your home’s furnishings, floors, plants, and overall well-being. Installing a whole-house humidifier is not only a good idea for your house and family, but will add a selling point for your home in the future.
You can install furnace-mounted whole-house humidifiers on either the supply or return air duct of your furnace with a vent that stretches from one side to the other. For portable humidifiers, the best place to put them is in a central room with good airflow.
Whole-house humidifiers can damage your furnace if a problem with the water supply happens. To avoid mechanical trouble, maintain your humidifier by keeping the filter clean and the drain line clear.
Damp air from a humidifier can cause mold in ducts if it raises the air's humidity level too high for the duct system to handle or malfunctions, but it’s not a normal occurrence. To avoid mold trouble, set the humidistat to between 30% and 35% and inspect it often to ensure accuracy.
Deane has spent 30+ years in residential construction, contracting, remodeling, maintenance, and home repair, and now contributes DIY and educational articles for publications like Forbes Home and U.S. News. Throughout his career, he has strived to help homeowners find the potential hidden within the walls of every home and empower them to take control of their household repair and remodeling endeavors.
Deane has spent 30+ years in residential construction, contracting, remodeling, maintenance, and home repair, and now contributes DIY and educational articles for publications like Forbes Home and U.S. News. Throughout his career, he has strived to help homeowners find the potential hidden within the walls of every home and empower them to take control of their household repair and remodeling endeavors.
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