How To Install Aprilaire Humidifier With Duct board Ducting Or Fiberglass Ductwork?

How To Install Aprilaire Humidifier With Duct board Ducting Or Fiberglass Ductwork?

Install Aprilaire Humidifier- Today I’m going to walk you through the process of installing an Aprilaire humidifier with duct board ducting or fiberglass ductwork. You’ll need just a few tools and materials, but don’t worry! I’ll get into that in more detail later on. The first thing we’re going to do is get all of our materials together, which will take about ten minutes. So let’s jump right in!

Install Aprilaire Humidifier- The tools and materials you’ll need for this project include Aprilaire humidifier, drill, measuring tape, level, pencil, straight edge, saw (either hand or power), duct board (or fiberglass), insulation (optional), metal duct strap (optional), and screws (optional).

If you’re using duct board, you’ll need to use either fiberglass insulation or your existing insulation. If you want to be extra safe, it would probably be wise to use insulation as well as a duct strap just in case there’s ever a fire hazard. Now that we have our supplies together, let’s get started!

Step by Step guide

  • Disconnect the furnace from power. I recommend putting on heavy rubber gloves if you’re going to be handling the furnace directly.
  • For a detailed description of how to shut off power at your furnace and install a switch, please refer to the Aprilaire humidifier installation manual.
  • After this is done, remove the old filter and any other materials from within your furnace using a small screwdriver or similar tool so they won’t interfere with our installation work.
  • Remove your furnace cover.
  • Install Aprilaire Humidifier- You’ll need to remove the screws on either side of the humidifier so that you can pull it out and get at it from all angles.
  • I recommend rotating or repositioning your furnace cover so that you can easily slide your humidifier into position. If done correctly, it should slip right in with minimal contact between any surfaces. Here’s a short demo video: (Note: this is for an Aprilaire 400 and not an Aprilaire 600 like we’re using here today.)
  • Install Aprilaire Humidifier- After the humidifier has been installed, replace any insulation you used as well as your metal duct strap if applicable before connecting the wires to power again and running through a “system charge” as per Aprilaire’s installation manual. If you’re using a remote sensor, proceed to the next part of the article now.
  • Install Aprilaire Humidifier- If not, feel free to skip to the “For those who aren’t installing a humidistat” section below for information on how to wire your Aprilaire 600 with an external 24V power supply and control switch.
  • Now that we’ve installed our humidifier let’s talk about wiring it up. Just because ours is hardwired doesn’t mean that it can’t be configured for use as a whole house fan-powered unit or as a stand-alone model with its thermostat.
  • To configure this correctly, we’ll need a 24V AC transformer along with a junction box and toggle switch.
  • First, determine where you want to mount your humidistat.
  • Install Aprilaire Humidifier- If you are using this humidifier as a stand-alone model, I recommend mounting the thermostat on the wall right next to it so that it’s easy to see and access. When configured for use with an individual thermostat, Aprilaire recommends installing a separate switch box that will allow you to toggle between the unit is in cool mode or fan-powered mode with power supplied directly from your furnace transformer. If you’re running your furnace fan constantly instead of having one of these switches installed, make sure that you don’t exceed 1 Amp draw. A 24V 10W lightbulb typically draws around 1 Amp while lit.
  • For those who aren’t installing a humidistat

Install An Aprilaire Humidifier


  • Install Aprilaire Humidifier- If you’re not installing a humidistat, the Aprilaire 600 can be configured for whole-house fan-powered mode or hardwired with an external 24V power supply. To wire it up, find the black and white wires coming out of your furnace (usually these are located near the blower).
  • Remove the connector from each wire and twist them together then attach a male spade connector to each one.
  • Install Aprilaire Humidifier- Take your transformer and cut off the power cord close to the transformer. Strip off about 1/2″ of insulation from each end of the new wire then twist them together and attach a female spade connector to each one.
  • Do the same thing for your toggle switch if you plan on using one.
  • Attach the black wire from the furnace to the common pin and attach a female spade connector to it. Attach your black wire from your transformer (with a male spade connector) and attach another female spade connector to that one as well. Finally, connect power from your switch or 24V AC transformer if you plan on wiring this up as a whole-house unit. (i.e., not for connecting it to an external thermostat). If you’re putting this in as a whole-house fan-powered unit, take care not to exceed 1 Amp draw at 120 VAC with the lights turned off lest you blow a fuse or trip a breaker. If you have halogen lamps installed throughout your home, be aware that they draw far more than the standard 1 Amp.
  • Install Aprilaire Humidifier- Once you’ve hooked everything together, attach your new power cord to the transformer and feed it through the tab (or not if you’re installing it as a whole-house unit) before reattaching your cover to make sure that it’s weatherproof before powering on your furnace again.
  • Install Aprilaire Humidifier- Now let’s talk about how to wire up our humidistat. Power is supplied directly from the 24V AC transformer so all we need to do is tap into its output using some cabling then cut off their connection with a switch box.
  • Install Aprilaire Humidifier- Start by finding an area where you want to install your humidistat. I chose right next to my furnace because I won’t have too far of a run from the unit itself to my thermostat so I have easy access to it.
  • Install Aprilaire Humidifier- To install a junction box, you’re going to want to drill two holes on either side of the wall large enough for your wires that lead into and out of it. For this to be weatherproof, you will need a junction box with a built-in gasket around its opening. Make sure that whatever wire comes in through the top is protruding out enough so that when the cover is placed back on, there’s an inch or two sticking out at each end allowing plenty of room for all your cables. After drilling your holes, secure your new box in place with sheetrock anchors then feed both ends of these cables into the box (you might need to use some Teflon tape or a pipe thread compound on the ends if they’re not self-sealing as you don’t want any sort of gas, smoke, or fumes getting into your home from poor sealing) and tighten down their screws.
  • Find an appropriate location for where you’re going to install your humidistat near your furnace. Drill a hole through which you can feed both cables so that it can reach the area where you’ve installed your new junction box with the gasket around its opening.
  • Attach a male spade connector to each wire going into and out of this box then attach a female spade connector to your 24V power supply wire which will be powering up both your probe and humidistat then attach another female spade connector to the other end of the power supply.
  • Install Aprilaire Humidifier- Now go ahead and solder these connections, but remember that you want them to be weatherproof so DO NOT use your soldering iron for long periods as you don’t want any sort of gas, smoke, or fumes getting into your home from poor sealing. If you can see the bare wire inside the connection after it’s been soldered together, make sure you cover it with either electrical tape or a heat-shrink tube. Only remove a small amount at a time otherwise you’ll nick through to the copper beneath which will no longer be safe to use come winter! Once all your wiring is done, close up your drywall holes and attach your humidistat wherever you’ve chosen to install it. Of course, if you choose not to wire the probe and only go with a separate wireless model, feel free to skip all this wiring jazz and just place your humidistat where you want it then plug in both components using an appropriate extension cord or two.
  • Install Aprilaire Humidifier- Once everything is wired up, cover the back of your junction box with some sort of plastic covering so that nothing can get into it from behind. I used one of those tubes meant for electrical wiring but anything would work fine given that there are no moving parts inside anyway.
  • Now let’s install our new furnace filter grille by first removing the old one from its housing. If you have a fiberglass filter as I do, then this is a simple process that only requires you to gently push up on it from one end and pull it out towards the other. Install Aprilaire Humidifier- However, if your filter has been in place for quite some time, now’s a good idea to take those old-fashioned metal pleats from its sides as they may have accumulated dust over the years which could drop back into your furnace or even break off and fall into odd places where it can cause damage. Just carefully remove them without tearing any of the paper backings inside and discard them properly.
  • Install Aprilaire Humidifier- Now slide your new filter grille right into place being careful not to snag anything on the housing itself. That should be everything! Now just turn your furnace power switch back on wait about ten minutes for everything to properly warm up and enjoy the fact that you’ve just saved yourself a ton of money this winter by not having to turn your thermostat down anymore!


Install Aprilaire Humidifier- With the money this filter grille and humidistat will save you, you can come out of this winter in much better shape both fiscally and temperature-wise. So between now and next year’s heating seasons, be sure to check these items monthly to ensure that your HVAC system is running as it should.

Install Aprilaire Humidifier- If you notice anything unusual (such as discoloration on exposed metal parts or exposed wires), make sure you turn off your furnace power switch immediately then consult a professional! Also keep an eye out for any strange smells emanating from your vents or open flames coming from them when they kick on, because if either of those things happens, again, turn off the power switch immediately then a service technician! And just like that, you’re now an educated homeowner who knows how to properly take care of their heating and cooling system.

Does Aprilaire Make Carrier Humidifiers?

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