If you've just opened your aprilaire model 600 installation manual, you're probably looking at a project that'll make your home a lot more comfortable during those bone-dry winter months. Let's be honest, nobody likes waking up with a scratchy throat or dealing with static shocks every time they touch a doorknob. Installing a whole-home humidifier is one of those "adulting" tasks that feels incredibly rewarding once it's done, but looking at all the parts and wires for the first time can be a little daunting.
The good news is that the Model 600 is a classic for a reason. It's a bypass humidifier, which means it's relatively straightforward compared to some of the more complex powered units out there. As long as you can handle a drill and aren't afraid of cutting a hole in your ductwork, you can definitely get this done in an afternoon.
Getting Your Tools Ready
Before you even dive deep into the first page of the aprilaire model 600 installation manual, do yourself a favor and gather your tools. There's nothing worse than being halfway through a job and realizing your drill bit is in the garage or you can't find your tin snips.
You're going to need a few basics: a drill (with a good set of bits), a screwdriver, a level, and a pair of offset tin snips. If you've never used tin snips before, they're basically heavy-duty scissors for metal. You'll also need some supplies that might not be in the box, like a bit of extra 1/4-inch plastic or copper tubing for the water line and some 18-gauge thermostat wire.
Having everything laid out on a workbench or the floor near your furnace makes the whole process feel way less chaotic. It also gives you a chance to make sure all the components—the humidifier housing, the water panel, the solenoid valve, and the control—are actually there and didn't get lost in shipping.
Finding the Perfect Spot
The aprilaire model 600 installation manual will tell you that you can install this unit on either the supply or the return plenum. For those of us who aren't HVAC pros, the "supply" is the duct that blows hot air into your rooms, and the "return" is the one that sucks air back into the furnace.
Most people prefer putting the actual humidifier unit on the supply side, but it really depends on how much space you have around your furnace. The "bypass" part of the name comes from the 6-inch duct that connects the humidifier to the other side. So, if the unit is on the supply, the bypass duct goes to the return. This creates a pressure difference that pulls warm air through the water panel, picking up moisture along the way.
Just make sure you have enough clearance. You don't want to mount it so low that it's hard to change the filter (water panel) later, and you definitely don't want it blocking any access panels on your furnace that a technician might need to get to later for a repair.
The Most Stressful Part: Cutting the Hole
I'm not going to sugarcoat it—cutting into your ductwork for the first time is nerve-wracking. You're literally making a giant hole in an expensive system. However, the aprilaire model 600 installation manual usually includes a cardboard template. Use it.
Tape that template to the duct exactly where you want the unit to sit. Use a level to make sure it's straight. If the humidifier is crooked, the water won't flow evenly over the panel, and you might end up with a mess or a unit that doesn't work right. Once you're sure it's level, trace the outline and then take a deep breath.
I usually start the hole by drilling a large bit through each corner of the traced rectangle. That gives you a starting point for your tin snips. Wear gloves! Duct metal is incredibly sharp once it's cut, and it'll slice your fingers before you even realize you've been touched.
Mounting and Plumbing
Once the hole is cut, the housing should fit right in. The manual walks you through securing it with sheet metal screws. After that, it's time to talk about water.
The Model 600 needs a water supply. You'll usually tap into a nearby cold water line using a saddle valve (though some people prefer a T-valve for a more secure connection). Run your 1/4-inch line to the solenoid valve on the humidifier.
Don't forget the drain line! This is a "flow-through" humidifier, which means water constantly trickles over the panel while it's running, and the excess needs to go somewhere. You'll run a plastic tube from the bottom of the unit to a floor drain or a condensate pump. Make sure the tube has a steady downward slope so water doesn't back up and cause a leak inside your furnace.
Wiring the Brain of the System
This is where people often get stuck. Depending on which version of the Model 600 you have, you might have a manual humidistat or a digital one. The aprilaire model 600 installation manual provides several wiring diagrams, and it's important to find the one that matches your specific furnace setup.
In a basic setup, you're basically creating a loop. The humidifier needs 24 volts of power to open the water valve. Usually, you'll wire it so that the humidifier can only turn on when the furnace blower is actually running. You don't want water pumping into the unit if there's no air moving to carry that moisture away.
If you have a modern furnace with a dedicated "HUM" terminal, you're in luck—it makes the wiring a lot cleaner. If not, you might need to use the transformer that comes in the kit to get the right power. Just take your time, use wire nuts, and make sure your connections are tight.
Manual vs. Digital Controls
If you're using the digital controller, you'll also have an outdoor temperature sensor. This little gadget is actually pretty cool. It tells the humidifier how cold it is outside so it can adjust the indoor humidity automatically.
Why does that matter? Well, if it's -10 degrees outside and you have your indoor humidity set to 45%, you're going to get a ton of condensation on your windows, which can eventually lead to mold or wood rot. The digital control prevents that by lowering the humidity target when the outdoor temp drops. If you're using the manual version, you'll just have to remember to turn the dial down yourself when a cold snap hits.
Testing Your Hard Work
Once everything is plugged in and the water is turned on, it's time for the moment of truth. Turn your thermostat up so the furnace kicks on. Head down to the humidifier and check the drain line. After a minute or two, you should see a steady drip or a small stream of water heading toward the drain. That's exactly what you want.
Check every connection for leaks. Feel around the solenoid valve and the water line entry point. If everything looks dry and you can hear the faint click of the valve opening, you've done it.
Keeping it Running
Your aprilaire model 600 installation manual isn't just for the first day; it's also your reference for maintenance. The biggest thing is replacing the water panel. Depending on how hard your water is, you'll probably need to do this once a year—usually at the start of the heating season.
It's a five-minute job. You just pop the cover off, slide out the old crusty filter, and slide in a new one. While you're in there, it's a good idea to make sure the drain hole isn't clogged with mineral deposits.
If you ever notice the house feels dry even though the humidifier is "on," that's the first thing to check. Often, the tiny orifice inside the water line can get clogged with calcium, or the water panel is so filled with minerals that air can't pass through it. A quick swap usually fixes the problem.
Installing the Model 600 might seem like a lot when you first see the parts spread out on the basement floor, but if you take it step-by-step and follow the logic of the aprilaire model 600 installation manual, it's a very manageable project. And trust me, your skin and your hardwood floors will thank you when February rolls around.