ReplyWho sized the unit? Are you going to add on to the house? It seems pretty big even for a poorly insulated home that size. That will keep the humidity high because the unit will drop the temp like a rock when it turns on then shut off fast.
Regular Guest
Just had a new American Standard ac system installed. It's a 3 ton 13 seer unit in a 1600 sq. ft. brick home built in 1960.
The temperature can be set at 76 degrees - feels fine when the system is running, but shortly after the air feels somewhat humid.
Is the system oversized? We haven't had weather above 90 degrees as yet.
Regular Guest
Who sized the unit? Are you going to add on to the house? It seems pretty big even for a poorly insulated home that size. That will keep the humidity high because the unit will drop the temp like a rock when it turns on then shut off fast.
Professional Member
Several things can be causing this. If you keep your fan in the ON position the moisture that is on the evaporator coil when the unit cylces off will be re-absorbed by the air passing over it. If the condensate pan isn't draining very quickly same thing. A lot of peole prefer the AUTO position during cooling periods.
Secondly, how was the 3 ton size determined? If anything other than manual J, then it may not be right. Was there an A/C unit before this one? What size was it?
Regular Guest
There was a 3 ton unit prior to the new. I don't think a Manual J was done.
Professional Member
Did the old unit do better than the new one with de-humidification?
Did you get a new air handler too or just a new coil over your furnace?
Regular Guest
Yes, I do belive the old did a better job with humidity. I did have a new air handler installed.
Regular Guest
it could be the new higher seer rating, may not be removing the mositure that the old 10 seer did. you may need to lower the tstat a couple of degrees than you did before , and run the fan on a lower speed to do more laten cooling, lower the humidty.
also look up seer rating on this site you might see whats really going on. hope this helps....
Global Moderator
A-S units if on a matched A-S coil have a good latent capacity rating BUT new units do take longer to get to full moisture sucking rate. So you may have gotten by with a 3 ton for 1600 sq ft in the past but may not with today's units. Without doing a load, hard to say if that's oversized but sure sounds like it.
And I sure agree with the advice to not run the blower constantly, put it in auto!
Professional Member
First thing I would do is confirm all the settings for the air handler. If it is a variable speed unit then it can be configured in different ways. Make sure that it is setup for 3 tons and for maximum humidity removal. Call your installing contractor back and tell him of your concerns and ask him to check everything out.
Also, if you don’t already have one, have your contractor install a humidistat (either separately or a new t-stat that is also a humidistat) that will allow more control of your variable speed blower. With a humidistat, the fan speed will be slowed down further to help with moisture removal when the temps are not high enough to call for cooling. It will allow your a/c to act somewhat like a whole house de-humidifier.
Sponsor & Professional Member*
Moisture on the cooling coil slowly re-evaporates back in the ducts and home. 13 seer coils hold 6-8 lbs. of moisture. Re-evaporate 3 lbs. of moisture raises humidity 10%RH.Originally Posted by mchild
Forget the dehumidistat and slow the fan to max the moisture removal all the time. Getting the home dried down during high hours of a/c helps some for evenings and rainy days. Your home will still be too damp during a wet week. If your home gets too dry, let us know.
Dehumidistats can lower fan speed or over-cool. They never "allow your a/c to act soomewhat like a whole house dehumidifier". With a whole house dehu, you get the %rh you set independent of the a/c operation or without any a/c over-cooling. I am tracking a 2,400 sqft home. Remove 3-4 gallons everyday to maintain 50%RH. No ac for weeks now in Midwest. Tring to do this with a/c would be impossible and very inefficient. Whole house dehu and 13 seer a/c cost about the same two speed a/c, but more eff. and comfortable. Dehu TB
Professional Member*
Thanks to TB's posts...
I added a 35-pint dehum in my 1600 SF walkout basement. Setpoint is 55%. Cycles 50 to 60%. Upper level is staying <45%. Couldn't do that last fall without the dehum.
Perhaps you should have read the instructions before calling.
Regular Guest
Is a variable speed air handler necessary for a humidistat?
Professional Member*
No, but it makes it easy to connect one.
Quality and Value Service and Repair
Regular Guest
Thanks to all. This is a great site!
Sponsor & Professional Member*
Thank you for your comment and welcome to first level of the "dehu club". A small inefficient dehu is a start and adequate for low humidity loads. You have unusually low outdoor points for the last 6 weeks. Higher humidity loads are on the way. http://www.weather.com/maps/maptype/...nts_large.html
This site will give you an idea of the moisture loads headed your way. The next level is being able to maintain <50%RH throughout your home with a +70^F outdoor dew point and rain(low or no cooling load).
Another level up-- Most homes like yours do not have adequate fresh infiltration during the summer when compared to winter stack effect. So consider adding 50-75 cfm of fresh air ventilation when occupied to purge indoor pollutants and renew oxygen. This is minimum fresh air according to ASHRAE. This bumps up the dehumidification load. On the wettest day with low/no cooling and +70^F outdoor dew points, you need to remove 60-80lbs. of water to maintain 50%RH. The highest level of the “dehu club” should include 5-6 lbs. of moisture per KW verses the 1-2 lbs./KW of your current dehu. Good start! Watch for the high outdoor dew points. They can get upto +89^F. Dehu TB
Professional Member*
Baby steps, TB. Baby steps.
It may cost a bit more in the long run, but I want to step into the larger ones to actually measure true performance.
Part of the comfort is the 2-stage cooling and Infinity control.
Next step is definitely fresh air intake and a larger dehum.
Perhaps you should have read the instructions before calling.
Professional Member*
I could not disagree more with this statment.
Quality and Value Service and Repair
Professional Member*
Why? Just curious.
Perhaps you should have read the instructions before calling.
Professional Member*
I changed my air handler and had to set the blower as low as it dould go to remove as much humidity as my old 2 ton airpro with a 1/6 HP blower motor.
I am telling you to have the installers check your unit.
Quality and Value Service and Repair
Professional Member*
13 seer have more fins per square inch then ten seer ten seer was an outstanding dehuimidifier dont use small room dehu's they dry a small area and moisture always moves to dry air but it dosent turn corners just goes right through your walls possibly causing mold in the walls. The manual j has to be done before anything and then use either whole home dehu or two stage compressor with variable speed a/h
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