Full Humidifier Education

Here are most of the tools needed to install this humidifier. The meter is helpful and should be used if you have one, but we have included a simple way to be sure the power is off further on. The 1/4" nut driver, a small pocket flat head screwdriver, adjustable wrench, pliers, 1/4" tubing cutters and sheet metal cutters are a MUST. A hammer will come in handy for starting a hole in the sheet metal with the edge of a screwdriver.

Remove the blower door and see if you have a Printed Circuit Board. If you have a Printed Circuit Board look to see if there are terminals marked HUM (stands for humidifier). If you have this terminal we will now need to find out if this terminal is supplying 24 volts or 120 volts. We will come back to this photo a while later.

Did you find a HUM terminal? Also look at the wiring diagram usually found on the inside of the blower door or on the manufacturers instructions if you have them.
If you found a terminal marked HUM - go to your local Wal - Mart and pick up a cheap Volt/Ohm Meter or at least a 120 volt circuit tester as shown below. This tester costs $1.44 and can be used all over your home! The one in the photo was found in the Hardware section near the electrical extension cords. Wal Mart scan number is 3207601693. A cheap Volt/Ohm Meter will be able to read 24 Volt, 120 Volt and 230 Volt circuits and will be a much better investment for this project and you will have it for future use!

Here we plugged the tester into a normal home receptacle to show how the tester is used. This tester checks 120 volts and can't be used in an electric dryer or electric range receptacle as they are using 220-240 volts which will destroy the tester. Also 24 Volts will not make the light come on. Notice the red light has come on indicating there is 120 volts to this receptacle.

Here can see below, some more warnings from the manufacturer.

Open the box and make sure everything is there and not damaged when the unit arrives. There should be the humidifier itself complete with it's water panel, a bag of hardware, a transformer, an instruction template and a humidistat. Report any damage to the carrier immediately.

Dismantle the humidifier down to it's shell.

This shot shows where we had to move the flexible conduit to one side to make room for the humidifier on the return drop.

Take the instruction template out of the box and tape it in place in a level position where you want it on your return drop. Be sure you give enough room to service the unit in the future. NOTE: These units can mount on the return drop ( the vertical duct beside your furnace )or supply plenum. Don't mount the unit on the air conditioning coil however since it will impede air flow to the AC coil AS WELL AS the humidifier. The return works MUCH better. Below we are marking the cut out hole for the humidifier using the template. This hole is about 9 7/8" wide by 12 3/4" high and must be level. See the attached PDF file at the bottom of page for a better view of both sides of the template (the scanned image could not be fully scanned).

Start a small 2" long hole at some point on the black line by holding a flat head screw driver at a steep angle ( about 30 degrees ) and striking it with a hammer a few times. See the shot below. Worth Noting: If you have Duct Board plenums we suggest you use sheet metal and reinforce the hole you cut out with about a 3" metal frame which you will have to build. If you build a "U" type of frame it will fit over the duct board giving support on the outside and inside of the duct board. It would also be a good idea to take the weight off of the duct board by supporting the Humidifier itself with metal straps such as plumbers strap or at least mechanics wire.

Using a pair of sheet metal cutters ( available at Home Depot or Lowes ) cut out the remaining hole. Be sure to wear good leather gloves and safety goggles, as sheet metal will give you a nasty cut and metal chips in the eyes could blind you!

If you have cut the hole square and correctly, the humidifier shell should sit exactly in place.

Screw in (6) 3/4" long # 8 plated sheet metal screws. If you have a cordless drill with a hex nut driver, the job will be much easier, if not, you can do it manually with a long nut driver of the correct size, but be prepared to get irritated as it will take a lot of pressure and time!

Re install the black water panel water tube to the water panel. NOTE: it goes in the round hole and stops when it hits the black stopper. Snap the water panel in place, making sure you have the drain stub in the correct hole in the bottom. Worth mentioning is you can make the air discharge from the opposite side of the humidifier by removing the drain and turning the cover 180 degrees and re installing the drain on the other end. See the instructions that comes with the unit if you need to do this.

Here we have the water panel installed.

Now we will attach our 6" metal elbows and make a connector to join them together. Put one elbow on the humidifier flange and attach it with 2 sheet metal screws. NOTE: don't use the crimped end of the elbow on the humidifier as it will hamper the operation of the damper if you don't have specialty tools. Once you have the elbow on the humidifier, turn the elbow until you have it lined up with where you want the other elbow on the supply trunk or plenum. Wear gloves and safety goggles! Using a marker, mark out the new cut out on the supply trunk or plenum. Of course your installation will call for different amounts of metal than ours.

Cut the hole for the next elbow out. Wear gloves and safety goggles!

Now notch the elbow on the crimped end. (We didn't use the crimped end because we have specialty tools that you won't have). We have a notching tool to notch the elbow but you can do the same thing with the metal cutters. Keep the notches close if you want a neat installation with minimal air leaks. You then bend one flange in and the next flange out and so on. Wear gloves and safety glasses! You can then straighten the elbow and while reaching through it, insert it in the hole you just made in the trunk or plenum, start bending the flanges over from the inside. Good practice says to shoot 3 screws to hold the elbow on the duct, in fact it is a code, however it won't be going anywhere if you cut the hole right.

With both elbows installed, turn the elbows and take a measurement for the connector that will be installed next. We cut ours 5 1/2" long which will be a bit difficult to fit in but will result in a tight, neat and air tight joint. If you cut the metal from a new 6" duct leave the crimped end so you won't have to crimp it like we had to. We were working with scrap duct. A crimping tool was actually used but we are showing how you can do it with needle nose pliers but it won't look as well. The ducts snap together at the seam. Wear gloves and safety goggles!

Here we have the cover back on and the duct work done.

We seal our duct air leaks with mastic made for H.V.A.C. people, but you can use foil tape or grey duct tape available at Home Depot or Lowes. The mastic doesn't look good but it will not come apart over time as with tape, and is a code in our area.

Next we have to cut a hole in the return trunk to mount the Humidistat. Make this hole 3" x 4 3/4". The hole should be at least 6" before the return air gets to the humidifier so that we don't sense moisture from the humidifier when it is running. We like to keep it 1' away. Below we have the humidistat pre wired as it is much easier than trying to hook up the wires once it is installed ( you will need the small pocket screwdriver here ). Since our furnace had the HUM terminal it makes the wiring simpler. The humidistat terminals marked 24 volts have a long (2) conductor thermostat wire run down to the Printed Circuit Board in the blower compartment. ( Route these wires safely away from the blower and the filter if your filter is in the blower compartment ) It doesn't matter which color wire goes to either terminal. The H terminals of the humidistat have a short section of wire that will reach the yellow wires on the humidifier. It doesn't matter which color wire goes to either terminal. NOTE: we use the manual mode resistor rather than the automatic out door sensor since we feel it puts the control in the home owners hands instead of the computer. READ THE INSTRUCTIONS CAREFULLY since there are certain settings that have to be set depending on which humidifier you have and if you are going to use manual or auto mode. Also remember to put the manual sticker on the face plate if you will use manual mode. You will need the small pocket screwdriver to work on the humidistat terminals since they are tiny.

Here we have mounted the humidistat and put the manual sticker on, as well as configuring the internal switches. READ INSTRUCTIONS!

These pictures show wiring information on the transformer.

As shown, mount the transformer at the Printed Circuit Board making sure the metal panel cover won't come in contact with any wires. The white wire on the transformer goes to Neutral and the black wire goes to the HUM terminal. Remember, we are powering this transformer with 120 volts and ONLY if the blower is running in this installation. We will be showing another way to install the wiring if you don't have the HUM terminals, but you will need to use the A50 relay. If you get confused, use the A50 relay and follow the instructions and pictures on the next set of pictures. You can't go wrong with the next set of pictures and it will work fine even if you DO have the HUM terminal. We have only shown the above pictures to keep you from having to buy the A50 Relay but as we have said, if the above has confused you go by the next set of instructions.

Here are most of the tools needed to install this humidifier. The meter is helpful and should be used if you have one, but we have included a simple way to be sure the power is off further on. The 1/4" nut driver, a small pocket flat head screwdriver, adjustable wrench, pliers, 1/4" tubing cutters and sheet metal cutters are a MUST. A hammer will come in handy for starting a hole in the sheet metal with the edge of a screwdriver.

Turn the thermostat up to 90 degrees and put the selector on heat if so equipped. All we are trying to do is to get the furnace to turn on. Now go to your main electrical panel and find the circuit breaker which controls the furnace and switch it to the off position. The furnace should now be shut off. In the case of our meter below, it would be reading zero volts.

Your gas furnace should have a junction box, which is where the main power is brought into the furnace from the main electrical panel. In our case, the power is brought in on the left side. Our junction box cover had a 1/2" knockout available to install the transformer on, your furnace could be different, but you will need to mount the transformer in some manner and route the black and white wires from the transformer safely into the junction box. Remove the junction box cover. Inside the box you will find a black and a white wire coming from the power source. The black wire is supplying 120 volts to the furnace and the white wire is the neutral wire. The 2 wires on the transformer are also black and white. Simply remove the wire nut (our wire nut is orange, yours may be a different color) from the black wires and join our transformer black wire to them and re-install the wire nut. Do the same with the white wire to the white wires in the junction box. Pretty simple - black goes to black, white goes to white! Just be sure the wire nuts are tight and making good contact and that there are no copper strands from any wires hanging out of the wire nuts that can touch metal. Under no circumstances should the transformer be wired into a direct drive blower motor leads - you will ruin the motor from current back feeding through the motor windings! Wire the transformer only as shown! Re install the junction box cover.

Pictured is our transformer which has been wired into the furnace junction box. We have re installed the junction box cover. The brown jacketed wire is a 2 conductor thermostat wire which can be purchased at Home Depot or other supply house. How much you will need will depend on your particular installation. Our installation took 3 pieces of (2) conductor thermostat wire each being 10 feet long, or in other words 30 total feet of wire. Plan your layout before you buy wire so you don't run short, remembering to take bends into the equation. The red and white wires in the picture are hooked to the 24 volt terminals which are then run to the humidistat terminals marked as 24 vac or R & C on the newest Aprilaire Humidistat, which we will show you later.

Pictured is the A50 Relay installed on the white wire that goes to the blower motor. The white wire to the motor is the " Common " wire. Some motor manufacturers use purple for the " Common " wire but this is very rare. Simply remove the screw from the metal clip, remove the clip from the relay, insert the white motor wire in the metal clip, re install the clip and the screw. Now the humidifier will only run if the blower motor is running. The A50 Relay is a current sensing relay, so if the blower isn't running the humidifier won't come on. This is to keep the humidifier from soaking the return duct and bottom of the furnace which will lead to rust on the equipment and damage to the motor from moisture! One of the yellow wires that come out of the relay will go to the humidistat and the other will go to the solenoid of the humidifier. The wiring details are spelled out in a simple diagram that comes with the humidifier and the A50 Relay. Just take your time and double check the wiring to the diagram. Relax - it's easy!

Next we have to mount the Humidifier to the cold air return duct. Pictured is the Aprilaire 600 with it's evaporative pad removed. The sheet metal has been cut to allow the Humidifier to sit LEVEL. A template comes with the instructions to help you cut the hole to the exact size and level. Simply level the paper template and draw around the edge of it as shown below. Be sure to wear gloves and wear safety glasses! 6 sheet metal screws hold the humidifier to the duct. Note the adjustable damper on the left of the humidifier, it stays closed for summer operation and open in winter. The humidifier is marked winter and summer, most humidifiers make you fabricate a damper in the duct!

Once you have marked the return drop with the marker, hold a flat head screwdriver at about a 30 degree angle and strike with the hammer to start a hole for the sheet metal cutters. You'll need a slit about 2" long.

Once you start cutting the sheet metal be sure to wear gloves. As you cut with one hand use the other hand to gently pull out on the metal - the cutting will go much easier! See below.

Here we have mounted the shell of the humidifier with 1/4" x 3/4" sheet metal screws. A cordless drill with a 1/4" hex head bit will come in handy, but you can use a nut driver instead.

If you have mounted the transformer in another place than in the furnace of course your thermostat wire will be a different distance than ours. The hole that has to be cut in the duct for the humidistat to sit in is " about " 3" x 4 3/4". Wear gloves and safety glasses.

Next start running 6" sheet metal elbows and duct to the SUPPLY trunk. Remember this humidifier is a by pass type which by passes return air to the supply air.

A 6" hole will need to be cut in the SUPPLY duct. A 6" elbow is then connected to complete the duct installation ( SEE BELOW ). Our installer has already run the humidifier duct and taped any air leaks which is pictured to his right in the picture. We are only showing him cutting another 6" hole that he is running some extra supply ducts to a room in the basement that our customer also wanted installed.

Didn't we say wear gloves???

Completed hole.

Here is the Saddle Valve that comes with the humidifier which we have installed to the cold water line. The saddle valve is self piercing once the line is connected, simply screw it all the way in and then back it out all the way. Check for leaks around the small nuts. It humidifies better if installed on the hot water line but will plug with minerals quicker. Be sure the black seal is installed correctly and sandpaper the copper or there will be a water leak! These saddle valves will not work on any tubing except copper! If you have P.V.C. pipe you will need to find a valve that will accept the 1/4" tubing. Now connect the 1/4" copper water line and ferrule fittings and run the line to the humidifier solenoid on the side of the humidifier. Cut the copper line square with a tube cutter which can be purchased at Home Depot. Some companies use 1/4" plastic tubing, we believe you will be MUCH better off with copper!

Here we are tightening up the other end of the water line to the humidifier and leak checking for water leaks.

Here we are running a 3/4" P.V.C. drain line which goes to the black fitting at the bottom of the humidifier. This drain then runs to a floor drain or a condensate pump if you don't have a floor drain. We feel it looks a lot more professional with P.V.C. and it will not plug up like the tubing will, however most of our competitors use plastic tubing since it is quicker and cheaper. Alternately, you can run a 1/2" inside diameter clear plastic tube available at a hardware store or Home Depot. If you use the plastic tubing you should use a clamp to hold it in place.

Here we have finished the secondary wiring and have installed the manual jumper. ( There will be a total of (3) thermostat wires coming out of the humidistat and going to the furnace bottom, and back to the humidifier itself. This humidifier can be installed in either computer controlled automatic mode or manual.

Re install the pad, black water feed tube and install the front cover. Turn the water on and open the damper (winter). Turn the circuit breaker back on, start the furnace and turn the humidistat to test to be sure it is working. Recheck for water leaks. Set the humidifier to 35% as a starting point. Read the operating instructions.

Our furnace and humidifier are running! Annual maintenance should include being sure the pad has been changed and that water flows through the solenoid and out the drain line. The strainer and orifice should be changed annually, but will depend on your water conditions as to how often it has to be done. Usually 35% should humidify quite well, but follow the instructions in the owners manual that comes with your unit and you will have a trouble free system for years to come!

The pictures below will show another Humidifier installation on another 90% furnace which we want to show other ways of sealing air leaks you may encounter. In this shot below we are sealing small air leaks with Duct Mastic which is available at Home Depot if you choose to use it. Aluminum duct tape works but doesn't have the long lasting quality of the mastic.

Here is the completed installation on this on the installation job.
NOTE: Notice the purple material on the pipes. This is a primer which is applied to the pipe and fittings first, then P.V.C. glue is applied. A twisting motion is used to seat them together. They are then held tightly together for about 30 seconds, as a hydraulic action will try to push them apart otherwise.

Here is the actual template that comes with the Aprilaire 600.