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Question DetailsAsked on 9/10/2011

My heat pump does not remove humidity from my house effectively and the humidity level stays around 80 %. Is this an HVAC issue?

I have had an environmental person come in and the first thing he said was "This house is too humid," and he showed me the percentage on his hygrometer. Water condenses in the duct work and has actually dripped out onto the floor in the laundry room. I wonder if it is dripping inside the walls. The humidity has caused rust on the grill work and staining of the ceiling around the grill in one room. My HVAC Company tells me that my hygrometer has to be wrong, but I disagree. I don't use the humidifier on my unit during the winter so that doesn't add to the problem. I live in a townhouse and have an attic fan. I have seen ads for radiant insulation for the attic. Would that help by making the contrast between the heat outside and the cool inside less dramatic? This is a very frustrating problem and in the heat of the summer, the downstairs closet and area under the foyer have a musty smell. Have installed a sump pump. No water inside the house.

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2 Answers


First off, your ac contractor should be able to tell you in a heartbeat exactly what you relative humidity is in the house, But it doesn't take a genius to know you have a humidity problem if you have water condensing on your duct and onto the floor. The question is if the problem is just in the equipment room or throughout the entire house. I'm assuming this is a summer only problem. It sounds like you have a restriction in your ductwork. If you notice where the condensation stops on your ductwork, that may be the point of the restriction. If it's strictly above and on the furnace you probably have a plugged evaporater coil.The variables would this a new problem?...are you getting the same air flow you always have?...Is you living space comfortable?...Is the problem only in the hvac room?...If so is the duct insulated in the unconditioned space?...There are many variables I can't see from my laptop!..This ain't rocket science, so you may need a new contractor, but your problem isn't some thing that can't be fixed. It sounds like a restriction in air flow..Good Luck!

Ralph Little

Little Heating & Cooling Co. Inc.

Haymarket, Va

Answered 9 years ago by ralph little


I'm sorry to hear about your problem. Let's go back to the basics. If the problem is happening in the summer time when the air-conditioning system is running...I would suspect it's the A/C unit! It's a little hard to define what you're dealing with exactly without doing some diagnostics but I believe you have an oversized air-conditioning unit based on what you stated in your post. If this is a fairly new A/C installation, the contractor may not have performed a load (calculation) analysis to determine the proper size for the structure. An improperly sized unit would have a terrible time removing the humidity from your house. A properly sized unit needs to be sized to first remove humidity and then condition (lower) the air temperature. That's why equipment sizing is so important! In an improperly sized unit the internal refrigerant never reaches btu capacity, so you never get it's true cooling capacity and efficiency ratings. If your bills are extremely high during the summer months when the A/C is running and the humidity level never goes below 50%, you can bet this is your problem. Your only option is to replace the unit with a properly sized one. The water condensating on the outlet registers and ductwork is a result of the cool (not cold) air traveling through your ductwork-lowering the temperature of the humid air around it on the outside. It's lowering the temperature of that air to its dew point. The moisture wrings out of the air on to the colder surfaces. This happens because the air-conditioner cannot condense this moisture at the evaporator coil.


Answered 9 years ago by Stans HVAC

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