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A little background: I live in Maryland, which has a very humid climate (last night humidity got up to 94%, a couple days ago it was 100%). My house was built in 1984. In August 2012 I had R-49 insulation put in the attic, and had it air sealed, and in November 2012 I got a Trane 16 SEER 2-stage variable speed HVAC system. The humidity in the house has been pretty high recently, reaching highs of around 70% with the thermostat set to 75 and the fan set to ON. Half the doors in the house don't want to close anymore, and some of the wood flooring is sticking up, like it's forming some kind of bubble.
On to my question. To reduce the humidity in my house, should I set the fan to ON or CIRC (circulate, I think it runs 30% of the time) or AUTO?
Thank you very much for any help!
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Last edited by beenthere; 07-17-2013 at 03:51 PM. Reason: Non Pro * member, no warning, caught himself and reported it
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Last edited by beenthere; 07-17-2013 at 03:55 PM. Reason: Non Pro * member
Auto
I suspect that is what happened. Before I had the new HVAC system installed, I read on the internet that it's good to do something called a "Manual J" to make sure it's the right size. I requested that the installer do this because we had just had the attic insulated up to R-49 and air sealing done. The installer said that doing a Manual J would be overkill, it would be better to just put in the same size unit that was being replaced, a 3 ton unit, which all the houses around here seem to have. I deferred to his professional judgement.
I suppose in the future I should insist that the installer do a Manual J first, particularly if I've just upgraded the insulation, to make sure that it's sized correctly and I don't wind up with humidity problems again.
Last edited by beenthere; 07-17-2013 at 03:57 PM.
It's hard to stop a Trane. but I have made one helluva living keeping them going.
Gaius Baltar...cylon traitor!
Auto is best for humid climate operation.
Say hi to Caprica 6...
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
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Last edited by beenthere; 07-17-2013 at 03:55 PM. Reason: Non Pro * member
From the appraisal:
2594 square feet of livable area (1473 above grade)
Type: Detached
Design style: Split Foyer
Attic: Scuttle
Foundation: Full Basement
Exterior
Foundation Walls: Masonry
Exterior Walls: Siding
Roof Surface: Comp. Shingle
It's 2 stories, one a finished basement. High ceilings in the living room. Does that pretty much describe it? I'm not sure what else to say about its layout.
@Shophound
Head Six says hi back
@Random1634
I began setting the fan to ON because I had a problem with the master bedroom being 11 degrees hotter than the rest of the house (73 at thermostat, 84 in master bedroom). This problem predated the new insulation and HVAC system, and is what prompted me to get them last year, along with a hot air return in the master bedroom and a vent on the top of the master bedroom door.
After the insulation was installed, I began running the old (25 year old AC, 8 year old heater) furnace fan on ON in the late summer 2012, and stopped during the winter because it was spreading cold air after the heater turned off. I turned it back to AUTO for the winter.
Installing the new insulation and above-door vents reduced the temp in master bedroom (when thermostat was at 73) from 84 to 82. Running the fan on ON 24/7 reduced it further to about 80. Getting the new HVAC system, with the new hot air return in master bedroom, reduced it further to about 75, nearly eliminating the problem. Of course, now I have the humidity problem, but setting it back to AUTO only increases the temperature to 77-79, still comfortable.
I've been experimenting with trying to get the humidity down for a few days now. Up till last week, I had the thermostat set to 75 and fan ON, and that was resulting in humidity between 63% and 73%. After reading on the internet about how to reduce humidity, I tried setting it to 73 and fan AUTO, which reduced the humidity to between 53% and 63% (63% at night, 53% during day). But when I called the installer who put in this Trane HVAC system, and asked his advice on what I should do to reduce humidity, he told me that switching the fan back to ON would reduce humidity. This contradicted my experience, which is why I decided to ask you guys. The installer also said that getting a whole-home dehumidifier would be expensive and probably overkill.
If you have a Trane VS air handler or gas furnace, your installing contractor (or another heating and AC person) should be able to set the 'ramp' profile of the blower to help with the humidity. Another thought would be to lower CFM/ton fan speed... tends to run a colder coil and condense more water from the air.
Get out someone that understands indoor air quality... they should be able to help you.
GA-HVAC-Tech
Your comfort, Your way, Everyday!
GA's basic rules of home heating and AC upgrades:
*Installation is more important than the brand of equipment
*The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
*The value of comfort, over the long term; leave economic choices behind!
Choose your contractor wisely!
If your two stage system runs in low stage most of the time, you are probably not getting enough air to the master bedroom, although you note considerable improvement since insulation, new HVAC, and added return air.
What might be a next step is an air balance on the ducts. If you have rooms or entire zones that are too cold when the a/c runs, you might be able to reduce airflow there so air into the master bedroom increases. This is best done with manual dampers at the supply take-offs near the trunk vs. throttling air at a supply register.
One other possibility...give Six a little rest...she may be heating up the place too much!
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Here is the equipment I had installed:
Trane 2 Speed 3 Ton AC Condensing Unit Model # 4TTX6036G1000A
Trane 21" Cased Evaporator Coil Model # 4TXCC044BC3 with TXV
Trane XV80-80% 2 Stage/Variable Speed Gas Furnace Model # TUD2C100A9V5
Trane Digital Two-Stage, Digital Programmable Thermostat Model # TCONT802A
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Last edited by beenthere; 07-17-2013 at 03:55 PM. Reason: Non Pro * member
Random1634, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.
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Okay, tomorrow I will be calling my installer to see if they can send someone with experience at improving indoor air quality to adjust the ramp profile of the blower in order to help with the high humidity.
Shophound, I can't really tell which stage is running, the thermostat doesn't display stages, just cool on or heat on. When I was having the insulation and new HVAC put in, I tried to see if someone could improve the airflow to one of the two registers in the master bedroom which has very little airflow (my neighbor has the same problem in his register in the same exact location, must be a design defect of these houses), but it turned out to be impractical. No dampers anywhere to be found, and going looking for them would have involved disassembling lots of ceiling and/or floors and added expense. The master bedroom is quite comfortable at 77-79 (with fan on AUTO), though, especially with the ceiling fan running.
Though maybe if I tell Six to put on more clothes, that will help
Now we have a paradox... Running the fan continuously will aggravate a humidity issue... yet; running the fan continuously will help a temp variance issue.
If the tech can help the humidity issue with the ramp profile and/or lowering the fan speed... then perhaps you could set the fan on circ (which runs it about 1/3 of the time when the system is off).
Now I would not go to the extreme of having 'six' dress more...
GA-HVAC-Tech
Your comfort, Your way, Everyday!
GA's basic rules of home heating and AC upgrades:
*Installation is more important than the brand of equipment
*The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
*The value of comfort, over the long term; leave economic choices behind!
Choose your contractor wisely!
Ok, a contractor arrived to look the system over. He was one of the gentlemen who installed it. I explained the issue with him, the system runs briefly then turns itself off, but doesn't fully dehumidify, just gets the temperature down to what's listed on the thermostat, and that we've been having problems with doors not closing and wood floors popping up. I told him that I thought perhaps it was oversized, because before we had it installed, we added lots of additional insulation and did air sealing. I requested that he adjust the ramp profile or the fan speed in order to make sure it stayed on longer in order to reduce the humidity enough. I made sure to act polite and cheerful, and not at all aggressive or demanding.
He didn't believe that the system was oversized. He said that perhaps the humidity reader wasn't giving an accurate reading, because I had it located in the master bedroom. He relocated it to the main air return duct, between the master bedroom and the second bedroom on the 2nd floor, which he said would give a more accurate reading. When it was located in my bedroom, it read 56%, later on I checked it again at its new location, near the main air return duct, and it had increased to 60%.
He instructed me to set the temperature at the thermostat to 73, and hold it there, and maintain the fan on AUTO, and said that a good humidity level is about 50%. He said that if, on Monday, the humidity issue still persists, to call him back and he'll come back out. He did not adjust the ramp profile or fan speed.
What temp do you normally keep the thermostat at.
Ordinarily, 75, fan set on ON
Since I've been trying to deal with the humidity, 73, fan set on AUTO