Honeywell DH90 Whole House Dehumidifier

[MandJ]

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.

[beenthere]

Incorrect sizing. Incorrect installation, or set up.
You may need to call in another contractor.

Yes, its bad for your hardwood floors.

[paul42]

Are you using the visionpro thermostats for your humidity measurments?

Are you sure that the humidifier is staying off?

As a bandaid approach until a real fix is found, I would turn the water off to the humidifiers to see if that helps.

[perrybucsdad]

I'm confused about something. If someone has a central cooling system, why would you need a dehumidifier as I thought the AC did all the dehumidifying?

[beenthere]

An A/C can only dehumidify while its running. If it has a poor latent capacity. It will cool the temp quicker then it removes humidity.

In a basement, there is not a big cooling load, so an A/C will cool the area to quick to remove enough moisture.

[MandJ]

I'm not sure what size units were put in, but we did have load calcs done for the house by a PE (this is new construction), so if I find out the unit size the PE would be able to tell us if they were correct, right?

As far as installation, how should the dehumidifier be hooked into the supply/return for the system? Seems like there was some discussion and confusion about this on the part of our installer. The two units were initially hooked up differently and then one got changed, but I wouldn't be surprised if both were incorrect. The studio unit has already been replaced once as well.

Yes, we are using the VisionPRO thermostats to tell us what the current humidity levels are, as well as to set the level we would like.

I'm pretty sure the humidifiers aren't running, but it's definitely a good idea for us to double-check that. The thermostat allows us to set relative humidity separately for the humidifier and the dehumidifier and to turn simply turn either unit off completely.

We don't like having a really cold house in the summer, which is what we'd have if we relied solely on the AC to remove the humidity. We're quite comfortable at 78 or 76 degrees with 50% relative humidity and we couldn't achieve that in this climate without the dehumidifier.

[pstu]

Unsure whether this is a productive question, but how hard would it be to measure the dehumidifier condensate output for a day?

[beenthere]

It may be miswired.
It could be that the IAQ is not configured right.

There are several ways it can be installed. One is of coursed connected to the duct system.

You can measure how much condensate it is remmoving. But if its low, without knowing how long it ran, you won't know if its under performing, or if it isn't receiving a call to run when it should.

[MandJ]

Good idea, but that would be difficult. The condensate pipe goes right into the drainage system for our gutters and downspouts.

I'm wondering if it would be worthwhile to purchase a few humidity gauges to measure the actual relative humidity at various places around the house in case the thermostats are wrong. The only thing is, I knew right away the humidity was too high when I walked in my studio the first time -- I could feel the stickiness. That's when the thermostat said it was 64%.

[beenthere]

What zone control panel are you using.

[teddy bear]

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.

Judging from the low evening %RH, the dehus must continue operating below their set-point. The range of humidity will not damage wood and is less than the winter/range.
There is both dehumidification and humidification controls on the Honeywell stat. A simple mix-up in wires could account for the dehus not being controlled. The dehus must be operating continuously to achieve low %RH over-night when the a/c is not operating.
Check to confirm that the a/c fan is in the "Auto" which reduces the %RH levels during high cooling loads. Duct leakage when the a/c fan is operating, a not cold enough a/c cooling coil, and excess fresh air ventilation could account for high day time humidity. Have A/C contractor contact the Honeywell Rep for assistance to resolve the problem. Regards TB

[MandJ]

What zone control panel are you using.

Honeywell EnviraZone in the house.

There are no zones in the studio -- 900 sq. ft. separate from the house, on it's own system but no zones necessary. That's where the humidity fluctuations are the worst. There is a Honeywell Equipment Interface Module.

I'm thinking we really should have someone more knowledgeable than our installer come and take a look at our system, but how can we be sure to find someone who really knows about this stuff? Our installer seems to be just that -- a bare bones installer who wanted to put all our ductwork in the unconditioned attic until we nixed that plan. Is there any kind of professional designation or the like that we can look for? We're located just outside Knoxville, TN.

[MandJ]

Check to confirm that the a/c fan is in the "Auto" which reduces the %RH levels during high cooling loads. Duct leakage when the a/c fan is operating, a not cold enough a/c cooling coil, and excess fresh air ventilation could account for high day time humidity. Have A/C contractor contact the Honeywell Rep for assistance to resolve the problem. Regards TB

A/C fan is set on Auto. We also had a duct blaster test run and that came out okay. I've now also turned the humidifier setting to Off on both thermostats to see if that makes any difference. I notice that I cannot set the regular ventilation schedule on the thermostats. I can only set it for a one-time ventilation. The manual says the regular ventilation schedule is set by the installer, so it sounds like we should ask him what he set it for (if we ever hear from him again). What might be considered an excessive level?

That's exactly what our installer said he was going to do -- talk to his Honeywell Rep. Only problem is that now he is not returning our phone calls. Makes me think he heard something he didn't want to hear, like perhaps incorrect installation. Our dehumidifiers are connected into our ductwork (not a separate system), but maybe not the right way.

[beenthere]

Try finding a contractor thru Honeywell.
Select product, and enter your zip.

http://yourhome.honeywell.com/Consum...torLocator.htm

[MandJ]

Try finding a contractor thru Honeywell.
Select product, and enter your zip.

Ahhh, thank you! That's very helpful.

[teddy bear]

Here a wiring diaghram for t-stat/dehu. Regards TB

[MandJ]

Here a wiring diaghram for t-stat/dehu. Regards TB

Thanks. This is very timely. Our general contractor finally got hold of the HVAC sub today, and he was muttering something about hoping he hadn't "got those two wires crossed" He's supposed to come out tomorrow to check things out.