A whole house dehumidifier connects to your HVAC system and removes moisture from the air as it circulates through your home

Unlike a portable unit that sits in one room, a whole house dehumidifier integrates with your existing furnace or air handler. It pulls humid air from your home, removes the moisture, and returns the dry air through your ductwork. The installation happens in your basement, crawlspace, or mechanical room—wherever your furnace and ducts are located.

The job requires cutting into your ductwork, running drain lines, and making electrical connections. Most homeowners hire a licensed HVAC contractor for this work. If you have basic plumbing and electrical knowledge, some steps are manageable yourself, but the ductwork modifications and system integration are best left to a professional. The entire process typically takes one to two days.

Key Takeaways

  • A whole house dehumidifier connects to your furnace or air handler and requires cutting into your supply and return ducts.
  • You will need a dedicated drain line running to a floor drain, sump pump, or exterior location, plus a separate electrical circuit.
  • Most installations require an HVAC contractor because they involve ductwork modifications and system integration that affect your heating and cooling.
  • The unit itself costs between $1,500 and $3,500, and professional installation adds $500 to $1,500 depending on your home's layout.
  • After installation, the dehumidifier runs automatically when your furnace fan runs, and you set your target humidity level on the control panel.

What you need before you start

Gather these items and information before calling a contractor or beginning work. First, locate your furnace or air handler and measure the space around it. You need at least 24 inches of clearance on the side where the dehumidifier will mount. Check whether you have a floor drain, sump pump, or exterior wall nearby—the unit needs a gravity drain or a condensate pump to move water out of the system.

Verify that you have an available electrical circuit near the furnace. A whole house dehumidifier draws 15 to 20 amps and needs its own dedicated 240-volt or 120-volt circuit (depending on the model). If your electrical panel is full or far from the furnace, installation costs rise because the electrician must run new wire.

Photograph your furnace and ductwork, including the size of the main ducts and how they connect. If you are hiring a contractor, send these photos ahead so they can estimate materials and labor. Know the square footage of your home and the current humidity level in your basement or main living areas—this helps the contractor size the unit correctly.

Choosing the right dehumidifier size

Whole house dehumidifiers are rated by the number of pints of water they remove per day. A unit that removes 95 pints per day works for homes up to about 5,000 square feet in humid climates. Smaller homes or drier climates may need only 70 pints per day. If you oversize the unit, it cycles on and off too frequently and wastes energy. If you undersize it, humidity stays high.

Your HVAC contractor will calculate the right size based on your home's square footage, your local climate, and how often your furnace fan runs. In very humid basements or homes in the South or Midwest, a larger unit is worth the extra cost. In drier climates or smaller homes, a mid-range unit is sufficient.

Preparing your ductwork and drain line

The dehumidifier connects between your furnace and your ductwork. The contractor will cut into your return duct (the one that pulls air back to the furnace) and insert a connection fitting. They will also tap into your supply duct (the one that pushes conditioned air out) to return the dried air. These cuts must be sealed carefully to prevent air leaks that reduce efficiency.

Next, a drain line must be installed. Most units produce 5 to 15 gallons of water per day, depending on humidity and how often the furnace runs. The contractor will run a PVC or vinyl drain line from the dehumidifier to a floor drain, sump pump, or the exterior of your home. If no floor drain exists, they may install a small condensate pump that automatically moves water to a drain or outside. The drain line must slope slightly downward to prevent water from pooling inside the unit.

Running the electrical circuit

A dedicated electrical circuit is required because the dehumidifier cannot share power with other appliances. The electrician will run wire from your electrical panel to a new breaker, then to an outlet or hardwired connection near the furnace. The wire gauge and breaker size depend on the unit's voltage and amperage—your contractor will specify these before work begins.

If your electrical panel is in a different room or far from the furnace, the electrician may need to run wire through walls or the attic. This adds time and cost but is necessary for safety and code compliance. Once the circuit is installed, the dehumidifier plugs in or is hardwired to the outlet.

Connecting the dehumidifier to your furnace

The dehumidifier must communicate with your furnace so it runs only when the furnace fan is running. The contractor will connect a wire from the dehumidifier's control board to your furnace's fan circuit. This ensures the dehumidifier does not run when the furnace is off, which would waste energy and allow humidity to rise again.

Some newer furnaces have a built-in connection point for a dehumidifier. Older furnaces may require the contractor to splice into the fan wire. Either way, this connection is straightforward but must be done correctly to avoid damaging your furnace's control board. The contractor will test the connection before leaving to make sure both systems start and stop together.

Setting humidity levels and testing the system

Once everything is connected, the contractor will set your target humidity level on the dehumidifier's control panel. Most homes are comfortable between 30 and 50 percent relative humidity. In basements, you may want to set it lower—between 40 and 50 percent—to prevent mold and musty odors. The dehumidifier will automatically maintain this level by running whenever humidity rises above your setting.

The contractor will run the system through a full cycle to check for leaks, proper drainage, and correct operation. They will also show you how to access the filter (if your unit has one) and explain the maintenance schedule. Most whole house dehumidifiers need the filter cleaned or replaced every one to three months, depending on dust levels in your home.

When to hire a professional versus DIY

You can handle some preparatory tasks yourself: clearing space around the furnace, locating your floor drain, and identifying where the drain line will run. You can also install the drain line if you are comfortable working with PVC fittings and have access to the route from the furnace to the drain.

Do not attempt the ductwork cuts, furnace connections, or electrical work yourself. Cutting into ducts incorrectly can create air leaks that reduce your heating and cooling efficiency by 10 to 20 percent. Connecting the dehumidifier to your furnace's control board risks damaging the furnace if the wiring is wrong. Electrical work must meet local code and be inspected by your municipality. Hiring a licensed HVAC contractor and electrician costs more upfront but ensures the system works safely and efficiently for years.

Frequently Asked Questions

Can I install a whole house dehumidifier if my furnace is in an attic?

Yes, but it is more complicated and expensive. The dehumidifier can still mount near the furnace, but the drain line must run a longer distance to reach a drain or the exterior. Some contractors install a condensate pump to move water upward and out, which adds cost. Discuss your attic layout with the contractor before they arrive.

What if I don't have a floor drain or sump pump?

The contractor can run the drain line to an exterior wall and terminate it outside, or install a small condensate pump that collects water in a tank you empty manually. The pump option costs $200 to $400 extra but avoids cutting through your foundation. Ask the contractor which option works best for your home's layout.

How often do I need to maintain a whole house dehumidifier?

Check and clean the filter every one to three months, depending on dust in your home. Inspect the drain line once a month to make sure water is flowing freely. If the unit stops removing moisture, the filter is likely clogged. Most units run for 10 to 15 years with basic maintenance.

Will a whole house dehumidifier increase my energy bills?

Yes, but usually by $10 to $30 per month during humid seasons. The dehumidifier uses electricity and makes your furnace fan run more often. However, lower humidity reduces mold, dust mites, and musty odors, which many homeowners consider worth the cost. Running it only during humid months can lower the energy impact.

Can I add a whole house dehumidifier to a heat pump system?

Yes. Heat pumps have an air handler similar to a furnace, and the dehumidifier connects the same way. In fact, heat pumps often run their fans more frequently than furnaces, which means the dehumidifier runs more often and removes more moisture. This makes whole house dehumidifiers especially effective with heat pump systems.