Heating, Air Conditioning, Fridge, HVAC/Aprilaire 400 install help



Hi Jim, I'm in search of someone to help talk me through an Aprilaire 400 whole house humidifier install on my furnace. I"ve sorted the install into 3 parts. My first question is the location. Due to limited space and no floor drain I chose the 400 model. You see in the picture to the left the 6" round tie in to the furnace supply, the furnace sits directly underneath. To the right is the cold air return where I plan to mount the humidifier. Above this I plan to mount the humidstat. Does this plan look good to you?

Furnace is a Lennox SLP98UHV heat only system. I have an old Honeywell round thermostat with only two wires, R & W. My biggest problem is with the wiring but first things first. The install and plumbing are easy so once I get that set maybe we could get into how to wire. Hope you can help!

Hi Linda, I think I can help you with this. According to the install manuel the humidifer mounts on the supply duct. I have seen them mounted the way you have it laid out though, so I think you will be ok.

To make the round cut easier I would use a "right hand cut" tin snips (green handle). I think you have a good plan going.

Let me know if you have any other questions. I'll be here.  

Heating, Air Conditioning, Fridge, HVAC

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Jim S.


I can answer questions on gas or electric furnaces, ac units and heat pumps. I don't work on boilers,chillers,or home appliances.


I have been in the HVAC trade for over 35 years. For the past 15 years I have owned my own business. I am semi-retired so I can answer questions in a timely manner.

I attended trade school for 5 years on weekends and evenings. This was very hard to do, but well worth it!

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