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I got the Aprilaire 700M (manual) version because with a smart thermostat, you don't need an outdoor sensor to tell the temperature. The idea is that the relative humidity (RH) inside your house should decrease as the outside temperature also decreases. Otherwise you'll get condensation on the windows and other parts of your home, leading to frost, freezing, dry-rot in your attic or window sills, etc. The Ecobee4 knows the temperature at your location (via Wi-Fi connection) and has a "Frost Control" setting that will automatically adjust the home's humidity level accordingly; no need to use the manual humidistat and constantly change the humidity setting as temperatures change. I've attached a diagram of the exact wiring I used -- even the colors are the same. It took combining about 4 different diagrams that only told part of the story, a call to customer service, an email to an HVAC guy, and bit of trial and error (e.g. I had to learn not to use the HUM connection on my furnace because it's only charged when blowing heat) but my Aprilaire 700M and Ecobee4 now work PERFECTLY together! When I need humidity in my house, my thermostat will turn on the furnace fan and the humidifier to add humidity without heat... as well as with heat, if needed. IMPORTANT Instructions: 1) You DO NOT need to use/wire the humidistat control (dial-a-humidity level) because the Ecobee4 perfectly takes it's place (actually, it does a much better job). 2) You have to know that when you set up your humidifier with Ecobee, you have to tell it that it's a "steam" humidifier, NOT an evaporative one. This is not true, but it will allow the Ecobee to call for humidity even without heat blowing. 3) You need to purchase an extra relay to make the call for humidity without heat to work. Aprilaire recommends the Aprilaire 4851 relay. I'm not convinced there isn't a less expensive relay that will make this work, but I know the 4851 will work. 4) Take note that the G (green) wire needs to be disconnected from your furnace control board. This is according to the 4851 relay instructions. There are a few other oddities with the wiring too, so pay close attention. 5) Be sure to use 18-guage wire for 24 volt purposes (which is all this diagram shows) 6) I used the 2-wire setup for my Ecobee; there is a 1-wire installation, but I couldn't get it to work. 7) I did not need to use the transformer the Aprilaire 700M came with (because I didn't need extra 24v power). 8) When using no-heat with your humidifier, please note that Aprilaire recommends installing the humidifier on the hot-air service side of your furnace plenum, and to use hot water to flow into your 700M. This will allow the water to evaporate better. I'm going to add insulation around my 1/4" OD (outside-diameter) copper tubing (sold seperately needed for installation, with compression fasteners) to keep the water a little hotter. I used a SharkBite valve (Model # 24983A; 1/2" push-to-connect, 1/2" push-to-connect, and 1/4" compression fitting) to tap into my hot water line. The SharkBite fittings made it super easy to install onto my PEX hot water pipe. You may want to use something similar if you don't want to use the saddle valve the 700M came with (which I couldn't, nor did I want to run the risk). I had virtually no plumbing or electrical experience before doing this install, so you can do it too! I've attached a few other photos and the diagram that came with the 4851 relay, and the Ecobee4. I hope this helps! And enjoy your new perfectly comfortable home! p.s. Be sure to go to your electric company's website and look for a rebate on smart thermostats; the two main ones here in Colorado Springs both offer a $50 rebate!!! Free money.