A whole home dehumidifier connects directly to your furnace or air handler
A whole home dehumidifier is installed as part of your existing HVAC system, usually mounted on the return air duct or the furnace itself. Unlike a portable unit that sits in one room, it removes moisture from all the air your system circulates, then drains the water outside or into a floor drain. The installation involves connecting refrigerant lines, a condensate drain, and electrical power—work that requires basic plumbing and electrical knowledge, or a licensed HVAC technician.
Most homeowners hire a professional for this job because it involves working with refrigerant (which requires EPA certification in many states) and ensuring proper drainage and airflow. However, if you have HVAC experience and your local code allows it, you can do parts of the work yourself, such as running the drain line or mounting the unit. This guide covers what the process looks like so you understand what a technician will do, or what you'll need to handle if you're doing it yourself.
Key Takeaways
- A whole home dehumidifier mounts on your furnace or air handler and requires refrigerant lines, a drain line, and an electrical connection.
- Most installations require an EPA-certified technician to handle refrigerant, though you may be able to install the drain line and mounting yourself.
- The unit must be sized to match your home's square footage and humidity level, or it will run constantly without controlling moisture.
- Installation takes four to eight hours and costs between $1,500 and $3,500 for the unit plus labor, depending on your system and how accessible your furnace is.
- You will need a dedicated 240-volt circuit for most units, which may require an electrician if your panel does not have a spare breaker.
Sizing the unit to your home and humidity level
A whole home dehumidifier is rated in pints per day—the amount of water it removes from the air in 24 hours. A unit that is too small will run constantly and never bring humidity down; one that is too large will cycle on and off, wasting energy and failing to maintain steady humidity. The right size depends on your home's square footage, how many people live there, and how wet your climate or basement is.
Most manufacturers provide a sizing chart based on square footage and current humidity level. For example, a 2,000-square-foot home in a humid climate (above 60% relative humidity) typically needs a 70-pint unit, while a drier climate might need 50 pints. If you have a wet basement or live in a very humid region, you may need to go up one size. Ask the equipment supplier or your HVAC technician to size the unit for your specific situation—this is not a guess-and-see process.
Choosing between ducted and non-ducted installation
A ducted dehumidifier pulls air from your return duct, removes moisture, and sends it back into the supply duct. This works with your existing furnace fan and requires no separate ductwork. A non-ducted unit (sometimes called a standalone whole home model) sits near your furnace and pulls air from the room around it, then returns it to the same space. Non-ducted units are simpler to install but only work well if your furnace room is the source of the humidity problem.
Ducted installation is more common because it conditions all the air your system moves, not just the furnace room. However, it requires access to your return and supply ducts, and your furnace must have enough airflow capacity to handle the extra resistance the dehumidifier creates. Your technician will check your system's static pressure to make sure the furnace fan can handle it; if not, you may need a larger fan motor or a bypass damper to prevent the system from working too hard.
Running refrigerant lines and the condensate drain
The dehumidifier contains a compressor and evaporator coil, similar to an air conditioner. Refrigerant lines carry cold refrigerant from the outdoor condenser (or from a separate indoor unit) to the dehumidifier's coil. These lines must be insulated, routed carefully to avoid kinks, and charged with the correct amount of refrigerant. This step requires EPA certification and specialized tools, so it is not a DIY task in most states.
The condensate drain is simpler: a PVC or vinyl line that carries water from the dehumidifier to a floor drain, sump pump, or outside. The line must slope downward at least 1/8 inch per foot so water flows by gravity. If you do not have a floor drain nearby, you can run the line outside through a wall or basement rim joist, or connect it to a condensate pump that pushes water upward if needed. Make sure the drain outlet is at least 10 feet from your foundation or in a location where standing water will not damage the house.
Electrical connection and circuit requirements
Most whole home dehumidifiers run on 240 volts and draw 15 to 20 amps, which means they need a dedicated circuit breaker in your electrical panel. If your panel has a spare breaker and the distance from the panel to the furnace is less than 50 feet, an electrician can usually run the wire and install the breaker in a few hours. If you do not have a spare breaker, you may need to upgrade your panel, which is more expensive.
Some smaller units run on 120 volts and can plug into a standard outlet, but they are less common in whole home systems. Check your unit's specifications before assuming you can use an existing circuit. The wire must be sized correctly (usually 12-gauge for 20 amps, 10-gauge for higher loads) and run in conduit or through walls according to your local electrical code. This is a job for a licensed electrician unless you are experienced with residential wiring.
Mounting the unit and sealing connections
The dehumidifier mounts on the return air duct or directly on the furnace, depending on the model. The technician will cut an opening in the duct, install a collar or flange, and bolt the unit in place. All seams and connections must be sealed with mastic sealant (a thick, putty-like caulk) to prevent air leaks. Even small gaps will reduce efficiency and allow undehumidified air to bypass the unit.
If you are installing the unit yourself, use a duct saw or reciprocating saw to cut the opening, and wear a dust mask because duct insulation can irritate your lungs. After the unit is mounted, run your hand around every seam while the furnace is off to feel for air leaks, then seal any gaps with mastic. Do not use regular caulk or tape—mastic is flexible and stays in place as the ductwork expands and contracts with temperature changes.
Testing and adjusting the system after installation
Once the unit is installed and powered on, the technician will check refrigerant pressure, airflow, and drain function. The dehumidifier should begin removing moisture within a few hours. You should see the humidity level in your home drop to your target setting (usually 45 to 55% relative humidity) within a few days. If humidity stays high, the unit may be undersized, the drain may be blocked, or the refrigerant charge may be low.
Monitor the condensate drain for the first week to make sure water is flowing freely. If the drain backs up or water pools around the unit, the line may be kinked, clogged, or sloped the wrong way. Check the drain outlet outside to make sure it is not blocked by debris or ice in winter. Most units have a float switch that shuts off the compressor if the drain backs up, protecting the system from water damage, but you should not rely on this—keep the drain clear.
When to call a professional versus DIY tasks
Call a licensed HVAC technician for: sizing the unit, handling refrigerant lines, charging the system, checking static pressure, and testing airflow. These tasks require certification, specialized tools, and knowledge of your specific furnace and ductwork. A mistake with refrigerant can damage the compressor or void the warranty.
You can do yourself (if experienced): running the condensate drain line, mounting the unit on the duct, sealing seams with mastic, and running the electrical wire if you have wiring experience. Even then, have a technician inspect your work before the system runs. If you are not comfortable with any of these tasks, hire a professional—the cost of a mistake (a flooded basement, a damaged furnace, or a refrigerant leak) is much higher than the labor cost.
Frequently Asked Questions
Can I install a whole home dehumidifier myself?
You can handle the drain line, mounting, and sealing if you have HVAC experience, but refrigerant work requires EPA certification in most states. Electrical work should be done by a licensed electrician unless you are may have access to. Most homeowners hire a technician for the full job to avoid costly mistakes.
How long does installation take?
A typical installation takes four to eight hours, depending on how accessible your furnace is and whether new electrical circuits or ductwork are needed. If your panel needs upgrading or you need to run long drain lines, add another day or two.
Do I need a new furnace to install a whole home dehumidifier?
No, the dehumidifier works with most existing furnaces and air handlers. However, your furnace fan must have enough capacity to handle the extra resistance. Your technician will check this before installation and may recommend a larger fan motor if needed.
What if my furnace room does not have a floor drain?
You can run the condensate line outside through a wall or basement rim joist, or install a condensate pump that pushes water upward to a drain. Make sure the outlet is at least 10 feet from your foundation so water does not pool near your home.
How much does a whole home dehumidifier installation cost?
The unit itself costs $800 to $2,000, and labor typically runs $700 to $1,500 depending on your location and system complexity. If you need electrical upgrades or a new drain line run a long distance, add $500 to $1,000. Total cost is usually between $1,500 and $3,500.