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Old 05-01-2012, 08:28 AM   #1
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new system, now more humid than before


I had my HVAC system changed out a month ago and now it's uncomfortably humid and muggy inside my house that I need to run the AC 4°F cooler and the fan set to ON just to be comfortable - so much for energy savings.

My house is 1107sqft. Previously I had a 2 ton unit. The old unit cooled, but would run for 14 hours on a hot day and our electric bill was sky high. In addition, the lights in the house would dim every time the compressor would cycle. Fearing that the old unit would decide to stop working in July or August we got it replaced in April.

Previously I have had more insulation blown into the attic, minimum R-38 and installed an attic vent as we only had soffits before.

In the beginning of April I had a new single stage 2 ton outdoor unit installed, a new gas furnace with variable speed blower, and new evaporator coils (of course). I got a fancy Honeywell Vision PRO 8000 thermostat that is supposed to monitor and control indoor humidity.

Since I had this new system my house has been more humid than ever. RH is constantly above 60%, and ranges from 58%-66%. Yesterday's RH outside was 40%. Once the sun went down it was nicer outside than inside.

The new system cycles much more than the old system. I don't see any error codes indicating a short cycle (but that doesn't mean I'm not missing them). The system will run for a few minutes and then supposedly the fan will slow down to continue to cool the house, up to 3° cooler than the thermostat is set to in order to draw out excess moisture. It is not working as it seems it should. Basically, I could have kept my old system, turned the thermostat to 73° and bought a dozen humidifiers and I'd be in the same place and could have bought a boat instead.

Does anyone have any insight on what the problem might be? Could damaged evaporator coils be causing this?

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Old 05-01-2012, 09:19 AM   #2
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new system, now more humid than before


Sounds like the new system might be oversized and not running long enough to dehumidify the air properly. With that small a place and that much insulation 2T sounds big. Need to be confirmed by calcs...


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Old 05-01-2012, 10:39 AM   #3
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new system, now more humid than before


I will get load calcs and post them here. The thing is, I add the insulation a couple years ago, and was running a 2 ton unit before and didn't seem to have this issue.

I checked the drain outside and there is some condensate coming out, but not what I would expect given the level of humidity in the house. There is a float switch but it hasn't tripped. With the unit running I removed a plug on the drain down the pipe from the float switch where the drain attaches on the indoor unit and it felt almost dry. I can't locate any place where condensate is spilling down into the furnace or over the sides of the unit.

It just doesn't seem to be pulling ant moisture from the air. Would the same size unit that is that much more efficient cause this problem?
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Old 05-01-2012, 11:30 AM   #4
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new system, now more humid than before


Actually, this has become an issue with some units. The first thing to do is measure your temperature drop across the evaporator (inside coil). Try to get as close to the coil without removing any panels as you can. Manually set the temperature so it shouldn't turn off while you are testing, in other words as low as you can and let it run for at least five minutes. Then measure the return air temp at the filter. If you can't get a thermometer in the air flow beside the filter take the filter out, lay the thermometer in the return and replace the filter cover or tape over the opening and leave it for about 3-5 minutes. While that is acclimating find the manuals for your units and look for the efficiency charts and specs and try to find the recommended temperature drop for your system. Most spec a temp drop in the 15 to 25 degree range but you need to find what your system spacs are, not what someone says they are. With the system still running quickly pull out the thermostat and check the reading and write it down. This is the incoming or return air temp. Put the filter back in and replace the filter cover. Now find the closest register to the coil and take a temp reading there. Again allowing it to be in the airflow for at least 3-5 minutes. If you need to, take the register out of the duct so the thermometer gets the full airflow. When it's time pull the thermometer out and quickly take a reading and write it down below the return air temp. This is the supply temperature, subtract it from the return temperature and this will give you your temperature drop. If it isn't within the range spec'd in the chart or text something is wrong and needs to be addressed. If it is, further work will need to be done. From this point you will need to consult with the installing dealer. This issue needs to be addressed quickly because with humidity levels like this mold is a very real possibility. This has become an issue with the new super-insulated, super sealed house. You may find the only two alternatives open to you will be either a whole house dehumidifier or a heat recovery ventilator commonly called an air exchanger. Neither are inexpensive but your health is at stake here. My vote would be for the air exchanger which will give you a constant supply of fresh air to the house and help with indoor air balance. Good Luck.
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Old 05-01-2012, 11:39 AM   #5
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Thanks, I will follow your directions and ensure the temperature drop is within specifications.

My concern with an air exchanger is that since I live in the south (Tallahassee), the RH outdoors can be > 80% for weeks at a time day and night in July-September. I wouldn't think I would want to keep bringing that air in.

If it came to it could maybe a reinstall down to a 1.5 ton do the trick?

.... Still waiting for the load calcs to get emailed.
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Old 05-01-2012, 12:12 PM   #6
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Check to see if your coil get cold enough while the system is running. If it is not easy to get into there, do the test mentioned by GarryE and also hand touch the outside condenser large pipe to see if it is very cold.
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Old 05-01-2012, 12:57 PM   #7
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Yes, the OP should do the tests. But he said he was getting the house 4 degrees cooler even though the unit wasn't running very long. So that is one indication that it seems to be working properly. The old 2 Ton unit could have well have been underperforming hence the longer run times for it.

BTW, I grew up in Pensacola, so I know all about the humidity down there. It can be pretty stifling and stay like that for much of the year.
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Old 05-01-2012, 01:20 PM   #8
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Probably not the best idea to speculate about which system may or may not have been performing to par without actual run times.

OP, time the system's cycles, how long it runs and how long it is off before starting again and then again, how long it runs. I'd be willing to bet it's not 10 minutes.

I'm going to have to believe that a 2 ton is too big since you've tightened the envelope with blown in insulation. Shorter runs times equals less dehumidification equalling "icky sticky" air.
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Old 05-01-2012, 02:13 PM   #9
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Holy Humidity Batman! I didn't realize you were in Florida, I'm with Doc and Raylo 32, it's probably short cycling so yes, it gets cool but it doesn't run long enough to dehumidify. That pretty much narrows it to either a smaller outside unit or whole house de-humidification. Still no cheap fix.
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Old 05-01-2012, 02:26 PM   #10
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Exactly! Having grown up down there and seeing how the warm fronts and the Bermuda high pump the moist air up the east coast in the summer, I tell everyone here in MD that the Gulf of Mexico is the mother of all humidity.


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Old 05-01-2012, 02:30 PM   #11
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which model of the visionpro 8000 series do you have?
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Old 05-01-2012, 03:00 PM   #12
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Quote:
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OP, time the system's cycles, how long it runs and how long it is off before starting again and then again, how long it runs. I'd be willing to bet it's not 10 minutes.
That sounds about right. With the thermostat set at 76° & RH at 45%, I am at 73° and 65%. That level is pretty much maintained all day. Once the temp gets to 74° the low speed fan kicks on, runs for less than 5 minutes until it reaches 73° attempting to reduce RH. It may be anywhere between 5-20 minutes before it cycles on again depending on how many times the front door is open, how many people are inside, what appliances are running, etc. But even with the low speed fan the house cools quickly.
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Old 05-01-2012, 03:26 PM   #13
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In order to simplify the OP I left some information out that may be relevant. My house is off-grade with a 2 ft crawl space underneath that is dank, damp, and often musty. There is no vapor barrier between the subfloor and crawlspace and it is not insulated.

When the unit was first installed the evaporator coil was accidentally pushed too far back when the tech connected the ductwork. The indoor unit is installed upright in a tight closet and once installation was complete was impossible to see.

This caused the back of the coil to hang over the furnace resulting in condensate to run down behind the furnace. The condensate dripped for about 12 days on the floor of the air return directly below the furnace. The floor of the air return was carpeted, which allowed the water to drip and collect without knowledge.

The installer came out and found the problem, reinstalled the coil on top the furnace and reattached the ductwork. They also removed the carpet in the air return. Under the carpet, above the plywood subfloor was a sheet of particle board. The particle board act like a sponge soaking up all the water. The particle board was removed and only the plywood subfloor remained. The plywood appeared dry, but could have absorbed some moisture. I asked that they put ductboard down over the plywood and seal it, but I wanted to make sure all moisture had been drawn out of the plywood first. They were going to come back a week later to seal the air return. In fact, they are coming Thursday to complete this.

So I have 3/4" of unsealed plywood between the air return and the musty dankness that is my crawlspace. Do you think the moisture in my crawlspace is being continually drawn into my house?

Even if the moisture was being drawn up though, wouldn't the system only draw as much as it could handle resulting in no moisture being removed from the house, but not adding any to it? I suppose if no moisture is removed though, it will accumulate and continue to increase. Anyway, does it sound like my humidity problems are the result of an oversized unit or an inadequately sealed air return?
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Old 05-01-2012, 03:28 PM   #14
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Originally Posted by hvactech126
which model of the visionpro 8000 series do you have?
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new system, now more humid than before-1335900384664.jpg
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Old 05-01-2012, 03:38 PM   #15
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A better thermostat to have used would have been the VisionPro IAQ which could have been wired to slow down the blower for extra dehumidification. The thermostat you have can only run the a/c past the cooling setpoint by up to 3 degrees. It does nothing to slow your blower down.

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