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  • Need advice on Aprilaire humidifier installation

    I purchased an Aprilaire 400A humidifier and am planning the installation. I need to install the humidifier on the return air duct due to clearance to the walls. The electronic controller must be mounted in the return air duct at least 6" from the humidifier.

    I need to mount the humidifier on the long side of the return air toward the wall opening. The bypass take-off duct needs to be mounted above the A/C coil. The bypass duct will need to be at an angle and have two elbows.

    Does this sound like a acceptable installation or am I missing something?

    Thanks!
    Attached Files

  • #2
    Re: Need advice on Aprilaire humidifier installation

    Yep, sounds good to me. If the PVC exhaust were relocated you might be able to install the humidifier on the plenum side above the coil. That's the preffered location but the bypass will work fine from the return side.

    When you go to install the waterline to the unit you should cut in a tee and add a shutoff valve. Using saddle valve for this unit is a bad idea. A 1/4" water filter is a good idea too.

    Comment


    • #3
      Re: Need advice on Aprilaire humidifier installation

      Plumberscrack, you have me thinking - I could reverse the PVC inlet - put the dual elbow at the bottom and see if that provides additional room for the humidifier. The only thing that would prevent that from working is if the bypass duct wouldn't clear the A/C lineset. You are saying that the humidifier will work best if the cartridge unit is installed on the supply plenum right?

      Will the performance be affected noticably if the unit itself is mounted on the return air duct with the bypass from the supply plenum?

      There is already a tee plumbed into the cold water line that is capped off. I have a 1/2" ball valve on hand that I am going to use. I hate those cheesy, self piercing saddle valves... after having one spring a leak on me in my old house, I refuse to use them.

      Thanks for the advice!

      Comment


      • #4
        Re: Need advice on Aprilaire humidifier installation

        If You Dont Want A Major Problem Down The Road.(buying Another Furnance) I Would Not Mount The Humidifier On R.a. It Will Rust Your Heat Exchanger And Not To Mention Your Blower And Motor. It Needs To Be Installed On The Supply Side Of The System. I've Seen Alot Of System's Messed Up Because They Were Mounted Wrong.

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        • #5
          Re: Need advice on Aprilaire humidifier installation

          I don't think I can mount it on the supply side - look at the photo of my installation - the bypass duct won't clear the gas line, A/C lineset, and electrical conduit...

          Even if I could mount the unit on the supply side, the bypass would pull the humidified air over the heat exchaner so how would that be any different than mounting the unit on the return air duct?

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          • #6
            Re: Need advice on Aprilaire humidifier installation

            I posted in this thread the other night before the board had problems. Does anyone have my response embedded in their email notification that they could post for me?

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            • #7
              Re: Need advice on Aprilaire humidifier installation

              Ruudacguy,

              I'd like to know what your thoughts are on this. Thanks!

              Comment


              • #8
                Re: Need advice on Aprilaire humidifier installation

                Alright, I'll try this again.

                Looks like you have a doorway framed in your basement next to the return drop. With the humidifier mounted there, you might have to move the doorway if you ever finished off your basement. If this isnt a concern, then I dont see any problems mounting the unit on the return drop and connecting the bypass to the supply plenum.

                Although, if you did want the unit mounted on the supply, with 2 elbows and 1 6" tto, you could cut the bypass in the 10" side of the drop. You would have to relocate the combustion air intake. I'd cut it loose and place those 2 ells just under the humidifier.

                Looks like your furnace is a NUGM or builders model NTGM. Both are known for primary heat exchanger failures so keep your filter changed regularly. Also, you dont ever want to have to replace your inducer motor. The ICP's are twice the cost of any other brand I service. Probably because they are paying for all those heat exchangers.

                Whats up with the goofy crossbreak on the coil door?

                Comment


                • #9
                  Re: Need advice on Aprilaire humidifier installation

                  Originally posted by Ruudacguy View Post
                  Alright, I'll try this again.

                  Looks like you have a doorway framed in your basement next to the return drop. With the humidifier mounted there, you might have to move the doorway if you ever finished off your basement. If this isnt a concern, then I dont see any problems mounting the unit on the return drop and connecting the bypass to the supply plenum.

                  Although, if you did want the unit mounted on the supply, with 2 elbows and 1 6" tto, you could cut the bypass in the 10" side of the drop. You would have to relocate the combustion air intake. I'd cut it loose and place those 2 ells just under the humidifier.

                  Looks like your furnace is a NUGM or builders model NTGM. Both are known for primary heat exchanger failures so keep your filter changed regularly. Also, you dont ever want to have to replace your inducer motor. The ICP's are twice the cost of any other brand I service. Probably because they are paying for all those heat exchangers.

                  Whats up with the goofy crossbreak on the coil door?
                  Thanks for the advice! The doorway is 48" wide so when I finish the basement, I'll probably reduce the doorway opening by 12" on the furnace side so I can use a 36" door.

                  I thought about relocating the combustion intake but the electrical conduit to the furnace, the gas supply line, and the A/C lines are still in the way. I think the easiest thing would be to mount the humidifier on the return duct.

                  The Heil furnace model is NUG9100FHB1 - The vent motor was replaced a few years ago - before I bought the house but I'm now concerned about the heat exchanger failure rate... The house is 10 years old - how long do the heat exchangers typically last?

                  The goofy bends on the coil door were my mistake... I replaced the A-Coil last September because the capillary tubes were rotted. The original A-coil was installed sloping away from the drain and the capillary tubes sprung a leak due to being submerged in water... I installed a new coil and wanted to be able to remove the door for inspection without cutting it apart so I lined the seam along the centerlines of the A/C lines. The door was a little flimsy (but probably fine...) so I added the bends.

                  I'll probably install the humidifier tomorrow. One last question: There is a 6" diameter duct that is vented to the outside and terminates about 18" from the floor along the outside wall. It is an air intake but all it appears to be doing is dumping cold air into the basement... The furnace has its own air intake so what's the other intake used for?

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                  • #10
                    Re: Need advice on Aprilaire humidifier installation

                    Originally posted by khe View Post
                    One last question: There is a 6" diameter duct that is vented to the outside and terminates about 18" from the floor along the outside wall. It is an air intake but all it appears to be doing is dumping cold air into the basement... The furnace has its own air intake so what's the other intake used for?
                    That was combustion air for the original furnace. You could get rid of this providing the water heater has enough air.

                    Comment


                    • #11
                      Re: Need advice on Aprilaire humidifier installation

                      Originally posted by SAVIMAN View Post
                      I Would Not Mount The Humidifier On R.a. It Will Rust Your Heat Exchanger And Not To Mention Your Blower And Motor. It Needs To Be Installed On The Supply Side Of The System. I've Seen Alot Of System's Messed Up Because They Were Mounted Wrong.
                      Its a bypass humidifier. So regardless where its installed there will be some humidity passing through the furnace. Aprilaire bypass humidifiers have been around for quite some time and have not had any problems with exchangers or blowers. They don't put out enough humidity to affect the furnace or its components. On the other hand, mist humidifiers you don't want mounted on the return.

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                      • #12
                        Re: Need advice on Aprilaire humidifier installation

                        That's whay I thought - I'm going to mount it on the return air side.

                        Ruudacguy, does my furnace serial # fall within the range of the defective heat exchangers you mentioned? If so, how long do they typically last before they go out?

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                        • #13
                          Re: Need advice on Aprilaire humidifier installation

                          There was a transformer included with the humidifier and the instructions state not to hook it into the blower motor leads or premature failure of the components will result.

                          My furnace has a "HUM" terminal on the controller board and I plan to measure the amp draw on the output side of the current transformer. If the humidifier (requires 10 VA) combined with the furnace draw does not exceed the VA rating on the existing transformer, I see no reason to install a second transformer for the humidifier. Does that sound correct or am I missing something?

                          Comment


                          • #14
                            Re: Need advice on Aprilaire humidifier installation

                            I'd just wire into the HUM terminal. This will energize the humidifier circuit (up to the point of the humidistat) generally within a few seconds of energizing the 'heating relay'.

                            I've seen plenty of low voltage humidifiers wired to "C" and "W", but I just dont like it. If theres a hum terminal, I think it should be used.

                            One more note on your furnace: Some of them did not come with low voltage fuse protection. If theres a 5amp fuse on your circuit board, youre good. If not, check for an inline off the red secondary transformer wire. If there isnt one there, add one.

                            Wheres the pics?

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                            • #15
                              Re: Need advice on Aprilaire humidifier installation

                              There's a 3 amp fuse on the controller board so hopefully, that is OK. Before I started hooking everything up, I measured the voltage on the HUM terminal of the controller board and it was 120V! I am glad I didn't assume it was 24V or I would have been buying some replacement parts...

                              If I use the HUM terminal, I'll need to add the transformer inline with the humidifier solenoid.

                              I'll have to get a picture of the installation posted in the next couple of days - hopefully, nothing will make you guys laugh.

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