Wiring A Trane S9V2 Furnace To An Aprilaire 720A Humidifier

Nov 6, 2025 by Admin 60 views

Hey everyone! Today, let's dive into the nitty-gritty of wiring an Aprilaire 720A humidifier to a Trane S9V2 furnace. I know, I know, wiring can seem a bit intimidating, but trust me, with the right information, it's totally doable. I've seen variations of this question pop up before, but let's get into the specifics to make sure we get it right. This guide aims to provide a clear, step-by-step approach to help you get your humidifier up and running smoothly. We'll cover everything from identifying the correct terminals to troubleshooting common issues. So, grab your tools, and let's get started!

Understanding the Basics: Furnace and Humidifier Compatibility

Before we jump into the wiring, it's crucial to understand a few basics. The Trane S9V2 furnace is a common and reliable unit, and the Aprilaire 720A humidifier is a popular choice for adding moisture to your home's air. The good news is, these two are generally very compatible. The Aprilaire 720A is designed to work with most furnaces, including the S9V2. Compatibility issues are rare, but it's always good to double-check the specifications of both units to ensure they're a match. The main thing we need to ensure is that the furnace has the necessary terminals to control the humidifier, which the S9V2 typically does. Also, you need to think about the voltage requirements. Both the furnace and the humidifier need to operate at the same voltage for everything to work properly and safely. Make sure you turn off the power at the breaker before you begin any electrical work! Safety first, always.

The Aprilaire 720A is an evaporative humidifier, meaning it uses a water panel and the airflow from your furnace to add moisture to the air. It needs to be connected to your furnace's control board to know when to turn on and off. This is where the wiring comes in. The furnace provides the power and control signals to the humidifier, allowing it to work in sync with your heating system. The S9V2 furnace usually has terminals specifically for a humidifier, which simplifies the wiring process. These terminals are typically labeled as HUM or HUMID, and they provide a 24VAC signal to the humidifier when the furnace is running and calling for humidity. Remember, this is a low voltage system, so don't be alarmed; but it is still necessary to disconnect the power before working with any of the wiring. Understanding these basic concepts will make the wiring process much easier. Now, let’s get to the fun part!

Gathering Your Tools and Materials

Alright, before we get our hands dirty, let's gather all the necessary tools and materials. Having everything ready will make the job much smoother and prevent those frustrating trips back and forth to the hardware store. Here's a checklist of what you'll need:

Aprilaire 720A Humidifier: Obviously, you need the humidifier itself. Make sure you have all the parts that came with it, including the water panel, solenoid valve, and mounting hardware.
Trane S9V2 Furnace: Ensure you have access to the furnace's control board. This is where you'll be making the electrical connections. Refer to your furnace's manual to locate the control board and the humidifier terminals.
Low-Voltage Wiring: You'll need some 18-gauge or 20-gauge stranded wire. This is the standard for low-voltage applications like this. It's usually available in various colors, which can help you keep track of your connections.
Wire Strippers/Cutters: Essential for safely stripping the insulation from the wires without damaging the conductors.
Screwdriver: A small, insulated screwdriver will be handy for tightening the terminal screws on the furnace and humidifier.
Wire Connectors (Optional): Wire nuts or crimp connectors can be used to join wires if needed. It's generally best to avoid them and connect the wires directly to the terminals.
Multimeter (Optional): A multimeter can be used to verify the voltage and check for continuity. This is helpful for troubleshooting.
Drill and Drill Bits: You might need these to mount the humidifier and run the water line. Make sure you have the correct drill bits for the materials you're working with.
Water Supply Line: You'll need a small diameter flexible tubing (like ¼ inch) to connect the humidifier to your home's water supply. You’ll also need a saddle valve to tap into the water supply line.
Plumbing Supplies: Teflon tape, and any necessary fittings for the water line connection.
Safety Gear: Always wear safety glasses when working with tools, and make sure to turn off the power to the furnace at the breaker box before you begin.

Having these items on hand will make the entire process much easier and safer. Now that we have all of our tools, let's move on to the actual wiring process.

Step-by-Step Wiring Guide: Connecting the Humidifier to the Furnace

Okay, guys, let's get down to the wiring! This is where the magic happens. Here's a step-by-step guide to connect your Aprilaire 720A humidifier to your Trane S9V2 furnace. Take your time, double-check your connections, and always refer to the manuals for both the furnace and the humidifier for specific instructions. Before we get started, remember to turn off the power to the furnace at the breaker! This is super important for safety.

Locate the Furnace Control Board: Open up the access panel on your Trane S9V2 furnace to locate the control board. The control board is typically a circuit board with various terminals and connectors. You'll need to identify the terminals specifically for the humidifier. These are usually labeled as HUM, HUMID, or similar. Consult your furnace manual if you're unsure where these terminals are located.
Identify the Humidifier Terminals: The Aprilaire 720A humidifier will also have terminals for low-voltage wiring. These are typically labeled as either HUM, HUMID, or sometimes C and R (for common and hot/power). The exact labels can vary, so check your humidifier's manual for clarification. The manual will tell you where to connect the wires.
Run the Wiring: Cut two lengths of your low-voltage wire long enough to reach from the furnace control board to the humidifier. Route the wires neatly, using existing wire runs or creating your own. Make sure the wires are secured and won't interfere with any moving parts or get pinched.
Connect the Wires to the Furnace: At the furnace control board, connect one wire to the HUM or HUMID terminal. Connect the other wire to the C (common) or 24VAC terminal on your furnace's control board. Consult your furnace manual to make sure you are using the correct terminals, as they can sometimes vary by model. It's important to make the correct connection for the humidifier to work properly. For most setups, one wire goes to the HUM terminal, and the other wire connects to the C (common) or 24VAC terminal.
Connect the Wires to the Humidifier: At the Aprilaire 720A humidifier, connect the wires to the corresponding terminals. The humidifier manual will provide the specific instructions. Typically, one wire from the furnace connects to one of the humidifier's terminals (often labeled HUM), and the other wire connects to the other terminal.
Double-Check Your Connections: Before you close everything up, double-check all your wiring connections to make sure they are secure and correctly placed. Make sure there are no loose strands of wire that could cause a short circuit. Review the furnace and humidifier manuals again to confirm the wiring configuration. This is a critical step to ensure everything works properly and safely.
Test the Humidifier: Once you've completed the wiring, turn the power back on at the breaker. Set the humidistat on the Aprilaire 720A to the desired humidity level. The humidifier should activate when the furnace is running. You can verify this by checking if the water panel is getting wet and the humidifier is drawing water. If it doesn't work right away, don't panic! Check the troubleshooting section.

Water Line Installation and Humidistat Setup

Now that you've got the wiring sorted, let's talk about the water line installation and the humidistat setup. This part is just as important as the wiring to ensure your humidifier operates effectively and efficiently.

Water Line Installation

Locate a Water Source: You'll need to connect the humidifier to a cold-water supply. A good option is the cold water line leading to a nearby sink or the water line for the humidifier itself. Make sure it's easily accessible and provides a reliable water supply.
Install the Saddle Valve: Use a saddle valve to tap into the cold water line. Follow the manufacturer's instructions for installing the saddle valve. This valve allows you to connect the water supply line to the humidifier without cutting the existing water pipe. Make sure the saddle valve is securely attached and doesn't leak.
Connect the Water Line: Run a small diameter (usually ¼ inch) flexible tubing from the saddle valve to the humidifier. Use compression fittings to connect the tubing to the saddle valve and the humidifier's water inlet. Apply Teflon tape to the threads of the fittings to prevent leaks. Ensure the water line is properly routed and doesn't kink or get pinched. This can restrict water flow and cause problems.
Turn On the Water and Check for Leaks: Slowly turn on the water supply and check for any leaks at the saddle valve, the fittings, and the humidifier's water inlet. Tighten the connections if necessary. It's crucial to ensure there are no leaks to prevent water damage and ensure proper humidifier operation.

Humidistat Setup

Mount the Humidistat: The Aprilaire 720A comes with a humidistat that you'll need to mount in your home. The humidistat senses the humidity level and signals the humidifier to turn on or off. Mount it in a central location in your home, away from drafts and direct sunlight. A hallway or living area is usually a good choice.
Set the Humidity Level: Adjust the humidistat to your desired humidity level. Aim for a comfortable level between 35% and 50% relative humidity. Setting the humidity too high can lead to condensation and mold growth, while setting it too low won't provide the benefits of humidified air.
Calibrate the Humidistat (if needed): Some humidistats allow for calibration to ensure accurate readings. Refer to the humidistat's manual for calibration instructions. Accurate readings are important for proper humidifier operation.
Monitor the Humidity Level: After the humidifier is running, monitor the humidity level in your home to ensure it's within the desired range. Adjust the humidistat setting as needed to achieve the desired humidity level.

Troubleshooting Common Issues

Even with careful wiring, things don't always go perfectly the first time. Here's a guide to help you troubleshoot some common issues you might encounter:

Humidifier Doesn't Turn On:
- Check the Power: Make sure the power is on to both the furnace and the humidifier. Verify that the breaker hasn't tripped.
- Verify Wiring: Double-check all wiring connections, especially at the furnace control board and the humidifier terminals. Ensure the wires are securely connected and properly placed.
- Test the Humidifier with a Jumper Wire: If you have a multimeter, you can test the HUM terminals on the furnace control board to see if they are outputting 24VAC when the furnace is running. If no voltage is present, the furnace isn't sending a signal. You can also try using a jumper wire to connect the two terminals on the humidifier to see if it starts running (this bypasses the furnace control signal).
- Inspect the Humidistat: Make sure the humidistat is properly wired and set to a level that calls for humidity. Try adjusting the setting to see if it triggers the humidifier.
- Check the Water Supply: Make sure the water supply to the humidifier is turned on and that the water line isn't kinked or blocked.
- Check for a Faulty Solenoid Valve: The solenoid valve in the humidifier controls the water flow. If it's faulty, the humidifier won't get water. You may need to replace the solenoid valve.
Humidifier Runs Continuously:
- Check the Humidistat: The humidistat might be malfunctioning and constantly calling for humidity. Try adjusting the setting or replacing the humidistat.
- Inspect the Wiring: Make sure the wiring isn't shorted or crossed. Check for any loose connections that could be causing the humidifier to stay on.
- Check for a Stuck Solenoid Valve: If the solenoid valve is stuck open, water will flow continuously. You may need to replace the solenoid valve.
- High Humidity Levels: The humidity level in your home might already be high enough. Verify the accuracy of your humidistat and adjust the setting accordingly.
No Water Flow:
- Check the Water Supply: Make sure the water supply to the humidifier is turned on and that the water line isn't kinked or blocked.
- Inspect the Solenoid Valve: The solenoid valve may be clogged or faulty. Clean or replace the solenoid valve.
- Check the Water Panel: If the water panel is clogged or damaged, it won't absorb water properly. Replace the water panel.
Furnace Won't Start:
- Double-Check Wiring: Ensure that you have not disturbed any of the furnace's original wiring. Any incorrect wiring can cause issues with the furnace's operation.
- Review the Manuals: Refer to both the furnace and humidifier manuals for specific troubleshooting tips. The manuals often provide detailed diagrams and solutions for common problems.

If you're still having problems after trying these troubleshooting steps, it's always best to consult a qualified HVAC technician. They can diagnose the issue and ensure your system is working correctly. Don't hesitate to seek professional help if you're not comfortable working with electrical components or if the problem persists.

Conclusion: Enjoying Comfortable Humidity

Alright, folks, you've made it! Wiring an Aprilaire 720A humidifier to your Trane S9V2 furnace might seem like a daunting task, but hopefully, this guide has made it feel more manageable. Remember to take your time, double-check your connections, and always prioritize safety. With the wiring complete and the water line connected, you're well on your way to enjoying the benefits of a properly humidified home. From preventing dry skin and reducing static electricity to protecting your furniture and improving indoor air quality, a humidifier can make a big difference in your comfort and well-being, especially during the dry winter months. Now go forth and conquer the wiring, and enjoy the comfort of properly humidified air!