3rd floor AC humidity issues

We’ve been running a brand new installation whole-house HVAC for about a month now, and having issues with high humidity on the top floor. It’s a traditional forced air system, with one unit for each of three floors. The basement and parlor are working perfectly, but even though the third floor can get the temperature down, the humidity can be upto 65%. You can feel the air get heavy as you walk up the stairs. Each unit has a humidifier fitted, so we can humidify the hot air in the winter, and each floor has a Nest2 thermostat. The installer refused to have anything to do with the Nest thermostat, and we ended up with an electrician calling a Nest authorized HVAC installer to install the humidifiers and set up the thermostats. I’m concerned that somewhere in the mix of people setting this up, we have some inherent problem in the third floor system that is causing the high humidity. Sould I be concerned with 65% plus humidity on the top floor on 97degree days, or is that to be expected in NYC in a house with two skylights up there? Should I get a second opinion from an HVAC installer that knows how to install the Nest correctly? If so, any recommendations?

newoldhouse

in Heating and Air Conditioning 12 years ago

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thenets | 11 years and 9 months ago

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Hey newoldhouse I don’t know if you are still looking for someone reliable to help you out with your new nest system, those things are pretty cool looking huh. If you think you would require a second opinion call up the boys at Tameer Inc. You can reach them at 516-858-0555 or check out their website at www.tameernyc.com. Hopefully you have the issue resolved already but if not do try these guys out. Best of luck!

brucef | 12 years ago

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Verify the condensate drain, it should be a steady trickle in these temperatures. Does running the fan 100% of time fix humidity? Skylights, depending on angle etc plus the heat bearing down on roof can add a lot of heat to the space. Do you have a cock loft that is well insulated? if your three units are similarly sized, that doesn’t sound right. Top floor has to remove a lot more BTU’s.

curated | 12 years ago

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Something is not right if humidity is so high. Also the Nest thermostat has no bearing on your issue. We install Nest thermostats on every job and other then the higher cost for the thermostat itself and wifi connectivity they are no different than any other thermostat.

steam_man | 12 years ago

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Yes. The humidity is an immediate issue. 60% is the upper threshold of where mold growth will begin. If you have multiple humidifiers you may want to examine the placement of those units. It is possible that based on your duct layout and the placement of the humidifier, you have more humidity being pushed into the 3rd floor. Of more concern is why you would be humidifying the air in the summer! Something is not right here. -SteamMan

ellenlourie | 12 years ago

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AC load consists from latent and sensible load. Sensible is load having to do with actual temperature change in the space. Latent load has to do with removing of moisture from space, which do not change air temperature. Thermostat has nothing to do with your problem. It is either condensate removing piping layout or undersized AC system. Keep in mind that roof and skylights put additional load on the AC system. If you have cold and humid conditions look into piping, if it is hot and humid, system is undersized. Did your contractor do manual J load calculation?

newoldhouse | 12 years ago

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I already had one call out with a shrug about he Nest settings and advice to run the fan constantly. What I really want is the confidence to know that the humidity issue is a real problem. That will allow me to take the necessary steps to fix it. Right now I’m in limbo, relying on the different advice from many parties that it’s all OK. I don’t think it’s OK, based on the fact that the other two floor are perfectly air conditioned. So I look to the forum for some moral support. Or a reality check.

ellenlourie | 12 years ago

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Don’t you have warranty on this installation?