Wiring Aprilaire 700a to Honeywell EIM and Furnace

mk5tdi

http://www.discountfurnacefilter.com...structions.pdf

My furnace terminals pic (note the HUM terminal with 0.5A @ 24VAC)



Honeywell EIM pic



I purchased Aprilaire 700 automatic that came with an outdoor sensor humidistat and separate 24vac transformer.

I also have a Honeywell EIM, Prestige IAQ 2.0 Thermostat with ourdoor air/humidity sensor that I plan to install today.

What I want to be able to do is use the EIM, the Honeywell outdoor sensor and the Prestige IAQ to control the humidifier and not use the Aprilaire Humidistat and the outdoor sensor, can I do that?

Lets assume that the Honeywell system is wired to the furnace and is working correctly.

Now in order to add the humidifier, do I need to use a separate transformer?

What is the reason to use a separate transformer, is it only if you use the Aprilaire humidistat and the aprilare outdoor sensor because the outdoor sensor requires constant power to figure out what is the outdoor humidity even when the humidifier isn't running) or is there another reason?

I am thinking of running the wires as following:

One of the brown wires to the UI1 terminal on the EIM
Other brown wire to the Comm24vac terminal on the furnace
And run a wire from the HUM terminal on the furnace to the UI2 terminal on the EIM

Is that the best/proper way to wire in my case?

beenthere

Wire in the Aprilaire's transformer to a 120 volt source. Then run the one of the wires to the EIM's HUM terminals. From the other hum terminal to the humidifier, and then its other wire back to the transformer.

mk5tdi

Ok thanks.

Here is what my Furnace Installation Guide says:
Humidifier (HUM)
A quick-connect terminal (HUM) and screw terminal (COM
24v) are provided for 24v humidifier connection. (See Fig.
34.) HUM terminal is energized with 24v (0.5-amp
maximum) when gas valve is energized.

Is there a reason why I should not use the 0.5A 24VAC HUM terminal and Com 24VAC terminal on the furnace instead of the new transformer? I thought the only reason for using the provided transformer is because the Aprilaire humidistat and the Aprilaire provided outdoor sensor needs to be always ON but I plan not to use them in my case.

I was thinking about wiring it like this:

Yoyizit

You may also need a sail switch to control the humidifier.

Make measurements on your install to use for later troubleshooting.
I was surprised to find that my perfectly functioning humidifier solenoid reads 17 vac, down from the nominal 24v. That is one humidifier transformer with lousy regulation.

mk5tdi

17vac @ standalone separate transformer or @ furnance HUM terminal?

I tested the voltage at the HUM terminal yesterday and its 24 volts, isn't that a dedicated transformer for humidifier?

beenthere

No sail switch needed. Anyone that knows how the IAQ stat works knows that.

beenthere

The hum terminal on teh furnace board, gets its power from the furnace transformer. Its not for powered humidifiers.

mk5tdi

if the fan on the powered humidifier is plugged into a desperate power outlet? Besides the fan, what makes if different then non Powered?

beenthere

Non powered only energize the solenoid. Yours has the additional relay to run the fan. While small, it tends to use power, and can be enough to overload the furnace transformer.
A 40 VA transformer can only operate so many things.

mk5tdi

Thank you for helping me understand the reasoning, that's the info I was looking for.

I will install new power outlet from the beaker panel for the fan and the transformer.