It sounds like you need more air to the second floor.

I would stay with 1200 cfm and look for contributing issues. Don't overlook possiable duct leaks. The windows can be helped alot by heavy drapes,solar screens,awnings or operational shutters.

How well was the old system performing before it went down hill? Were any duct changes made with the new installation?

How large are the first and second floors? What thermostat setting are you using? Where are you located?

Located in central NJ - weather right now is 90 degrees and about 60% humidity. Supposed to get hotter as the day goes on.

Unfortunately, I don't remember how it felt last year, I didn't pay much attention to it because I just figured it was a builder-grade system and I would someday replace it. However, I do know I kept the house at 76 then and generally remember feeling OK. I REALLY wish I did now though. No duct changes, only the outdoor compressor, Indoor Furnace, and attic sealing / Insulation.

Tried an interesting experiment - not sure what to think....We went out last night and since we weren't home I bumped the thermostat up to 78. Came home, and I forgot to re-adjust it before bed so it sat at 78 all night long. Woke up this morning and set it back to 74 around 7am. By 7:35, the stat was reading 74 degrees, but the upstairs thermometer didn't move and was still at 81. So I bumped the stat down to 72 - it's now 8:50 and it just turned off. Is it weird that it only took about a half hour to drop 4 degrees, but over an hour trying to get an additional 2? Even though the system has been ran non-stop since 7am, the RH is still reading 59% (both the downstairs stat and separate gauge read the same so I know it's accurate. I would think the RH should be lower since it's been running so long now? CFM has been running at 1200.

The upstairs wall thermometer I have is now showing 76 degrees, but our previous thermostat (not that old) I have on the table is saying 79. Both are in the upstairs common area.

Our upstairs is weird - it's basically an 100 sq ft half octagon common area with the one side having 6 doors (4 bedrooms, closet and full bath), and the other side being open to the stairs and the 1st floor foyer. The stat is located in the 1st floor foyer.

There is one 22" square ceiling return (8" tubing centered inside) in the "common" area but no supply. Each bedroom has a return (same size as the common), with 1-2 supplies (12x6) pending on the bedroom size - with the exception of our master which has 5 supplies including the master bath. Am I better off keeping all these doors closed or open to the common area?

Sorry for the long reply.

To sum up my questions:

- Is it normal to have 59% RH when it ran for over an hour and a half non-stop?

- Am I better off leaving the bedroom doors closed, or open to the common area knowing there are no supplies in the common?

- Is it more cost effective to run the thermostat at 74 degrees and cycle more often, or at 72 and let it run more continuous?

- Why did it only take just over 30 minutes to cool down 4 degrees, but over an hour to cool down an additional 2?

- I try to keep the stat warmer during working hours when no one is home (from 74 degrees to 80) but I have a feeling that it makes it work harder in the evenings. Even though the stat satisfies easily on the first floor foyer, it takes a few hours of running to get the second floor slowly re-adjusted. Would I be better off leaving it at 74 degrees 24/7? I assume this would be more expensive though?

- I have soffit and ridge venting in the attic, I was told turning on the attic fan would not make it any better and be a waste of money because no heat should transfer down from the attic due to the air sealing and added insulation. The attic is fairly large ("A" frame - 10' from floor to peak and runs the entire house. The attic fan is a single 1600 CFM fan if it matters. Any truth to this?

You didn't state how large you house is. I assume you have a 3 ton AC for the whole house? Was a load calculation done?

The outdoor design temperature for central NJ is 90 degrees. The typical indoor design temperature is 75 degrees. This means that a system exactly sized for your house would run continuously at these temperatures. It hit 95 degrees yesterday and your system would only run for 13 minutes. That is the reason the humidity is so high. The fact that the AC comes on after 7 minutes means there is a lot of heat infiltration. Most likely though your windows and doors. The sealed attic with the R49 insulation is not helping much.

Keep all the bedroom doors open. The air has to flow from supply to the common return. It is going to take several hours of continuous running to bringing down the humidity. But if you have leaky windows you are fighting a losing battle.

I would think slowing down the blower, and closing one or two vents on the first floor would allow the AC to run longer and balance the floor temperatures. Setting the thermostat back during the day is a good way to save money, but it doesn't help to lower the humidity.

Oops, sorry. Our house is approx. 2,500 sq feet, SW facing and NO shade. I've never known the system to run non-stop, even the old system didn't do that on hot days, but the previous unit was a 4-ton. My direct neighbor and I had the same guy install the same unit at the same time, so I believe he had the load calc done at his house, and he used it for mine since we have literally identical houses. Almost all of our other neighbors over the past couple years have been fitted with the same size (4 ton) unit, so far we are the only two we know of that were downgraded to a 3-ton unit. Which I actually think is a good thing.

FWIW - There is the same size return in each bedroom as the hallway area return which is why I was questioning closing or opening the doors.

Ever since the thermostat turned off at 72, I noticed it's now cycling again. I haven't timed it, yet but it seems to be on a similar cycle as yesterday. I tried slowing down the blower yesterday to 1050 CFM, but it seemed to make the second floor feel warmer then when it's at the 1200 CFM. Plus, the run times were a little longer, but not that much - definitely not continuous.

I'm home today - and now that the unit cycled a couple times at 72 it's reading 54% RH which is why i'm wondering if i'm shooting myself in the foot by putting it on a timer while at work setting everything off-balance.

Just trying to find that "sweet spot" between energy savings and comfort.

Are you sure you only have a 3 ton condenser? Have you checked the model number? I am a little skeptical that you cool a 2500 sq. foot house when it is 95 degrees outside.

Model number on the outside unit is RA1436AJ1NA. Thermostat is programmed to a 3-ton unit too.

Yesterday it was 95, today it's about 90 last I checked, but it's also only 10:30 still.

I moved it back to 74 degrees and within 15 minutes it rose up to 74 and started cycling back at that temperature. I didn't want to run at 72 all day because of energy costs... I was just trying to add some additional run time to get the second floor re-conditioned.

FWIW when the guys did the final blower door test, they told me the numbers were a lot higher then they expected in a good way, they sounded surprised - not sure if that means anything?

Thought I'd give another update. I took a wall thermometer / humidity gage and put it on the steps across from the thermostat at the same height and noticed that it was reading consistently 76 when the thermostat was reading 74.

I found an adjustment on the stat and adjusted it to match the thermometer and it seems to feel a little better now.

It appears 74 was really 76 and 72 was actually 74. This makes more sense why it took so much longer to cool down to 74 being 90 out. It still cycles at 74 even though it's 90 out though.

I put the thermometer in upstairs hallway and it's been reading 2-3 degrees different on average which I guess is average.

Quick humidity question though:

When the A/C is running the stat shows RH around 57%, but as soon as the AC shuts down for 10 or so minutes, the RH drops down to 52% - why is this? I checked with the manual gauge and it seems to be close to the same readings. I put the manual gauge on the actual supply vent while mid-cycle and it read 58%.

The humidity gauge in the thermostat is probably not very accurate and overly sensitive. Every gauge is going to have slightly different readings. There are YouTube videos available to show you how to calibrate your device.

I don't understand why running your AC so long and the humidity is still in the upper 50s. With the very hot and humid weather we just had my AC was running long times and the humidity in my house was about 40%.

What is the humidity level in the basement? If the basement is very damp, then you may want to get a portable dehumidifier to lower the humidity. You will feel more comfortable and you may be able to raise the temperature in the house a degree or two.

I'm not sure either. Our basement is fully finished and in the past 5 years we've lived here I've haven't seen any moisture. I haven't ever seen or heard the sump pump go off either (even during hurricane Sandy!)

I believe the new furnace vents and takes air in from the side of the house via PVC piping - maybe that has something to do with it?

I have also have outside PVC exhaust and intake. This is not the cause. Have you measured the humidity in the basement?

I put the gauge in the same area as the HVAC in the basement and it showed approx. 57%. A little earlier it showed 55% on the first floor near the thermostat.

I think the basement is contributing a big part of the humidity of the house. You could install an vent and return in the basement and attempt to dry out the air. This has worked well in my house.

Another way would be to install a dehumidifier. You can get a cheap one in Home Depot or Sears, or purchase a much more efficient and expensive one such as the Santa Fe brand.

Interesting... The basement is 1300 sq ft of all finished space. Would only one help the entire basement? Would adding return vents to the basement starve the second floor returns?

I have 2 supplies in the basement now, but no returns. I keep them closed because they dump a lot of cold air that I'd rather channel upstairs and the basement is generally colder anyway.

That is the drawback of using the AC to lower the humidity in the basement. It becomes too cold. You are also stealing some air flow from the upper floors.

A 70 pint unit from a big box store should be sufficient. You want to set it up so the condensate either into a drain. Otherwise you will be emptying the bucket every day.

Well, I wasn't trying to use the AC to dehumidify the basement, I have the vents closed completely off.

If I get a portable unit, where should I place it?

Hard to explain, but the HVAC and HWH are in a walk-in closet wishin another larger finished 300sq ft closet in my basement. Should I put it in the same closet area as the HVAC? I have a decent size spot to the left of the unit in there.

Is it OK to run the drain hose into the existing condensate pump so it pumps to the sump with the AC?

You can put the portable unit anywhere in the basement. Moisture will pass through sheet rock. You may want to initially keep the closet door open. It will take several days to bring the humidity down. Having it drain into existing condensate pump should work well.

You may have a basement that is dry but the surrounding ground holds a lot of moisture. Check the drainage outside. The ground should needs to be sloped to drain water away from the foundation. Can you see the foundation walls behind the finished wall? Check to see that the concrete blocks are not wet.

In certain areas I can, it's a solid concrete foundation but I've never seen wet spots. The concrete is exposed in the HVAC room and that's always dry. Times I've had to remove small patches of drywall I've never seen any moisture either.

The entire basement has a French drain system that leads to the sump, but as I said earlier I've never heard or witnessed it running since we've lived here.

As far as the grounds, most of the water leads to each fence then runs down the center between the houses and into the street. The side yards are always soaked because of this but not along the foundation.

I'll see if the humidifier makes a difference. I can always return it if it doesn't. Would it be worth looking into a supplemental whole-house dehumidifier that attaches to the unit? Is that even a thing?

Found this one online at HD and it appears to use 1,500 watts? Yikes! These things use that much energy?

If that's the case, I think I may stick to my 54% and deal with it? I don't want to run the electric bill sky high...

Here is a review of the Delonghi DD70PE.

This review measured the power dissipation to be 655W at 50% humidity with fan set at high. This is what I would expect. I don't understand why the one page spec sheet says 1500W. Even at 655W it is expensive to run.

This unit has a built in pump which you won't need if you are going to use an existing condensate pump. You can buy one without a pump and save some money.

This seems to be a good web site for dehumidifier reviews. You can also watch reviews on YouTube. The review says there are better options than the Delonghi.

The Energy Star site used to tabulate dehumidifier efficiency the last time I looked. Most of them were pretty much the same. If you want high efficiency, you need to pay a lot more upfront.