I purchased an aprilaire 700, and I plan to install a 15a electrical outlet on the furnace right where the electrical comes in. If I first feed hot wire to outlet, and then feed off outlet to furnace, what is the best way to install the transformer? Can I just double up and twist the hot wire together on one of the terminals? Also, can I just sit this on top of the outlet box or should I try to put it inside the furnace? Thanks!



  • You should have a service switch at your furnace, where is that? – ThreePhaseEel Dec 8 '16 at 3:09
  • Generally you can't use flexible cordage for fixed equipment, NEC 400.7. – Harper - Reinstate Monica Dec 8 '16 at 7:37
  • The service switch for some reason is across from the furnace. This is a new construction house i just moved into. It's all conduit, and then is flexible conduit tubing leading to furnace. So i couldn't use that to put a box at? The conduit does come out and bend down at the ceiling before going into flex. Can i put it right there? I just thought it would look cleaner this way. I will edit question to show picture of furnace. Thank you. – eaglei22 Dec 8 '16 at 13:44
  • @Harper, what is considered a, "flexible cord" ? I am using a flexible conduit.. is this the same thing? If not, what prompted the citing of the article. Thank you. – eaglei22 Dec 8 '16 at 21:18
  • @Harper -- the Aprilaire 700 is cord and plug connected for its 120VAC needs. – ThreePhaseEel Dec 8 '16 at 23:26

If I were in your shoes, I'd use a small box (a handy box with a blank cover is A-OK) placed at the rigid to flex junction and supported from a metal hangar strap attached to the ceiling (vs. mounting boxes to the ductwork, which isn't such a hot idea) to hold the "tap" connection to the furnace power wires, and then run a flex (or a MC cable, your pick) over to another strap-suspended box that mounts the transformer (as 24V HVAC transformers generally mount directly to a box) and a single 120VAC outlet for the humidifier's power cord.

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  • Thanks ThreePhaseEel. I had gotten some further advice which allows me to circumvent the transformer by placing the wires differently to feed off the voltage thermostat. So I may give that a try. Furthermore, Can I place the box right where the flex conduit goes into the furnace? I was going to do that until I read what Harper wrote about it being against code, but now I am thinking he was referencing something else due to misinterpretation. That way it will just mount to the body of the furnace rather than the actual duct work. Unless you still think that's a bad idea. – eaglei22 Dec 8 '16 at 23:43
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    @user1794106 -- there should be a box at that point anyhow, but yes, you can put the tap-box where the flex goes to the furnace (although that'll make for having to run a big, long length of flex conduit or MC out to the receptacle for the humidifier). – ThreePhaseEel Dec 8 '16 at 23:45
  • Okay. The humidifier has a pretty long cord. I was just going to use the tap box with a single outlet regular receptacle or possibly a single outlet GFCI and just neatly run the cord to there then. So that way I minimize the work involved adding the outlet. I just want to avoid the cord dangling across the ceiling to get to another outlet. – eaglei22 Dec 8 '16 at 23:49

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