Air Conditioning - Humidifier

I have a humidifier attached to the return on the furnace. 6 inch duct goes from return to plenium. Does this setup cut down on the efficiency of the AC?
I imagine that air is blown from the plenium through the 6 inch duct into the return. Is this good bad or no effect on AC performance?
One more question. Should the return in summer be pulling from floor or ceiling?

Thanks for the help!!

Frank

6in duct should have a damper in it. it needs to be closed. High low return! will not make a big difference. Id close low.

What you have is a bypass humidifier and yes the duct should be closed during cooling season. There should be a summer / winter damper somewhere on the duct which bypasses the airhandler. Newer Humidifiers have these dampers built in. If you don't have a damper, they're not hard to find nor to install yourself.

I really dislike humidifiers that attach to the return. In addition to making your AC run harder, it also causes condensation on your gas heat exchanger. Put a pot on the stove if you really need additional humidification.

This post reflects my own personal bias.

I really dislike humidifiers that attach to the return. In addition to making your AC run harder, it also causes condensation on your gas heat exchanger. Put a pot on the stove if you really need additional humidification.

This post reflects my own personal bias.

Run "harder"? What is that supposed to imply?

If the damper is left open, yes, a bypass humidifier can reduce cooling efficiency, cause liquid floodback (to the compressor) and/or freeze the evaporator coil. The damper should be closed during the cooling season however, so it's not much of an issue.

When a furnace is operating (heating mode), the heat exchanger is way too hot for anything to condense on it. (easily in excess of 500F, well above the boiling point of water at atmospheric pressure - 212F)

Up here, cold winters mean that the humidifier is often calling even when the heat is satisfied, this causes condensation on the heat exchanger. I was serious when I said it was my own personal bias. I've replaced many units with rusted out heat exchangers and would never consider installing one in my own house. There are lots of humidifiers on the market that are designed to attach to the supply plenum and don't add high humidity to the return duct.

Up here, cold winters mean that the humidifier is often calling even when the heat is satisfied, this causes condensation on the heat exchanger. I was serious when I said it was my own personal bias. I've replaced many units with rusted out heat exchangers and would never consider installing one in my own house. There are lots of humidifiers on the market that are designed to attach to the supply plenum and don't add high humidity to the return duct.

Evidently you have dealt with humidifiers which weren't wired correctly.

When wired correctly*, a by-pass humidifier will never have power to open the soleniod valve (flowthrough) or turn the drum (drum models only) when the blower motor is not operating.

*Directly in parallel to the blower, or connected to the Humidifier terminals on newer models which have circuit boards.

A humidifier on the supply plenum can dump water on directly on to the heat exchanger if there's a blockage in the drain line.

Just close the bypass damper and we also tell people to turn the water off to the humidifier for the summer. Cause some fill from a float. ;)