We have two of these units installed in our home that don't seem to be working properly.

We're located in eastern Tennessee. We have a dual fuel system to cover the main portion of our home. This consists of an American Standard heat pump and furnace, plus the Honeywell DH90 dehumidifier (and a Honeywell humidifier as well). The house is split into three zones. We have Honeywell VisionPRO IAQ thermostats in all three zones but the dehumidifier can only be set from the primary thermostat which is located in the basement level. We were told that the unit will actually operate based on the average humidity level of all three zones but we know no way at present of verifying that.

We also have a completely separate HVAC system to cover a studio space located above our garage. This has an American Standard heat pump plus the Honeywell DH90 dehumidifier. This is a single zone controlled by the same type of Honeywell thermostat.

For the past two weeks our local daytime temps have been in the 90s with high humidity, dropping to the 70s at night. We have the dehumidifier set to maintain a relative humidity of 50%. The actual humidity readings we're seeing, however, range from highs of 62% to 64% during the hottest part of the afternoon, down to as low as 38% around 11:00 p.m. (and for all we know it may drop even lower overnight). Our thermostats are set at 78 degrees, which is quite comfortable for us provided the dehumidifier is doing its job.

One of our main reasons for purchasing the dehumidifier units was so we could maintain a stable level of humidity, but we're seeing fluctuations of 24%to 26% in a single day. The units cannot seem to keep up with humidity during the day, but they don't shut off when they reach the set level at night, either. Our installer had no answer for why this was happening and was going to research the problem (these are the very first whole-house dehumidifiers he has ever installed), but now he is simply not returning our calls.

Is this large of a fluctuation in humidity levels to be expected? Isn't this bad for our wood floors, woodwork, etc.? Is there a solution?

We'd greatly appreciate any insight the experts here could provide.