New system, but high indoor humidity

[CPA Nerd]

Yesterday I had an American Standard system installed in my 2k square foot, 2 story house.

3 ton 16 SEER AC with new coil
80k BTU 80% furnace, variable speed motor
Humidifier
Thermostat

The thermostat shows that the indoor humidity is 62%. It is 72 degrees outside with 30% humidity.

The humidifier is turned off.

The fan is on constant "ON." This is the setting the installer told me I should use in order to keep circulating air and keep the upstairs and downstairs temperatures even or close to it.

They are coming back today to take a look. I am not a professional, so what kind of questions should I be asking? I am fearful, but hopeful, that I won't get the runaround. Prior to installation, the owner himself said the indoor humidity should be between 40 and 50%.

The lowest it got overnight, when air temperatures outside were in the 50s, is 56%.

With my old system I never had a humidity reading on the thermostat, but it sure felt cooler and drier than it did in here yesterday, despite the temperature inside being 71 degrees.

[kdean1]

Was your old system the same size, or even smaller? Was a Manual J load calculation performed to determine what size is actually needed? Equipment which is too big will not dehumidify because it does not run long enough.
It may be as simple as there is not enough load when it is 72° outside to need air conditioning. Only at design conditions (normal highest outdoor temperatures) will the system run long cycles and reach 50% RH. During low load times the best thing is a ducted dehumidifier added to the system.

[CPA Nerd]

Size is the same and a load calc was done. Matches the estimates from two other contractors too.

[Poodle Head Mikey]

Tell them that you want the system adjusted so that the indoor cooling coil operates at at least 30º below the return air temperature / the temperature in the house - which should both be the same by the way.

Operating the indoor blower on continuous may even out the various space temperatures but it will reduce moisture removal. When the outside unit turns off the indoor coil is full of moisture. All that moisture should be allowed still air to drain the water off. By operating the indoor blower on continuous you are re-evaporating all that collected moisture back into the airstream and so back into your house.

PHM
----------

Yesterday I had an American Standard system installed in my 2k square foot, 2 story house.

3 ton 16 SEER AC with new coil
80k BTU 80% furnace, variable speed motor
Humidifier
Thermostat

The thermostat shows that the indoor humidity is 62%. It is 72 degrees outside with 30% humidity.

The humidifier is turned off.

The fan is on constant "ON." This is the setting the installer told me I should use in order to keep circulating air and keep the upstairs and downstairs temperatures even or close to it.

They are coming back today to take a look. I am not a professional, so what kind of questions should I be asking? I am fearful, but hopeful, that I won't get the runaround. Prior to installation, the owner himself said the indoor humidity should be between 40 and 50%.

The lowest it got overnight, when air temperatures outside were in the 50s, is 56%.

With my old system I never had a humidity reading on the thermostat, but it sure felt cooler and drier than it did in here yesterday, despite the temperature inside being 71 degrees.

[CPA Nerd]

Tell them that you want the system adjusted so that the indoor cooling coil operates at at least 30º below the return air temperature / the temperature in the house - which should both be the same by the way.

Operating the indoor blower on continuous may even out the various space temperatures but it will reduce moisture removal. When the outside unit turns off the indoor coil is full of moisture. All that moisture should be allowed still air to drain the water off. By operating the indoor blower on continuous you are re-evaporating all that collected moisture back into the airstream and so back into your house.

PHM
----------

Should I not run the fan continuously? If that's the case did I waste money on a variable speed furnace?

[George2]

Size is the same and a load calc was done. Matches the estimates from two other contractors too.

Where do you live? A 3 ton for a 2-story normally is way too much for a number of reasons. These new higher efficiency A/Cs do not dehumidify as well as your old 3 ton A/C.

The evaporator coils run warmer particularly when the coil is overly sized to the A/C to achieve a higher SEER.

[CPA Nerd]

Where do you live? A 3 ton for a 2-story normally is way too much for a number of reasons. These new higher efficiency A/Cs do not dehumidify as well as your old 3 ton A/C.

The evaporator coils run warmer particularly when the coil is overly sized to the A/C to achieve a higher SEER.

I'm in the Chicago suburbs.

[George2]

I'm in the Chicago suburbs.

Same weather as the QCA. The problem, I'm sure you're experiencing, is the A/C doesn't run long enough to do the job properly. A smaller system would have done a much better job.

Everyone sizes (mistakenly) to the old, existing A/C..............BIG mistake as you are now learning (the hard way.)

What I've learned from people is that after they have "moved-up" to higher efficiency A/C, they need to run the A/C 6-8 degrees cooler than their old system to achieve the same comfort.

[pecmsg]

Yesterday I had an American Standard system installed in my 2k square foot, 2 story house.

3 ton 16 SEER AC with new coil
80k BTU 80% furnace, variable speed motor
Humidifier
Thermostat

The thermostat shows that the indoor humidity is 62%. It is 72 degrees outside with 30% humidity.

The humidifier is turned off.

The fan is on constant "ON." This is the setting the installer told me I should use in order to keep circulating air and keep the upstairs and downstairs temperatures even or close to it.

They are coming back today to take a look. I am not a professional, so what kind of questions should I be asking? I am fearful, but hopeful, that I won't get the runaround. Prior to installation, the owner himself said the indoor humidity should be between 40 and 50%.

The lowest it got overnight, when air temperatures outside were in the 50s, is 56%.

With my old system I never had a humidity reading on the thermostat, but it sure felt cooler and drier than it did in here yesterday, despite the temperature inside being 71 degrees.

How old of a structure, have any improvements been made, Windows, doors, insulation?

[George2]

How old of a structure, have any improvements been made, Windows, doors, insulation?

Excellent point that I forgot to ask......you know there probably have been some energy efficiency steps taken over the years.

[pecmsg]

Excellent point that I forgot to ask......you know there probably have been some energy efficiency steps taken over the years.

Look into a whole house dehumidifier. Cheapest solution.

[BaldLoonie]

The variable speed blower can help with humidity control 2 ways. With the right thermostat, it will slow down if the thermostat says it is too humid. OR you can run what AS calls Comfort-R, a slow ramp up of the blower to get the coil cold fast and start dehumidifying more quickly.

What's the stat set at? At 72° out with low humidity, the unit won't be running much so won't dehumidify much. Especially if you keep it a ways above 72.

[martyinlincoln]

Your AC isn't going to run hardly at all when it's 72 out. You need a dehumidifier in mild damp weather. When it get 80-95 out the AC will take care of it.

[teddy bear]

A lot of good info so far. The biggest problem is that you now know the %RH. put a piece of tape over the meter. Just kidding.

Fan "auto" mode during short cycle cooling loads you will have the problem quick evaporation back to the home.
The setup of a/c is everything. True bigger coil retain more moisture and do not remove as much moisture.
Unless your installer sets up the coil to be as another poster said "30^F colder" than the return air temperature.
Have your tech slow the blower enough to get a <50^F dew point cold air from the cooling ducts. Your a/c will maintain <50%RH during +40% cooling cycle.
Bet as another poster said during low/no sensible cooling loads and high outdoor dew point plus the moisture from the occupants, you will need a small whole house dehumidifier like the Ultra-Aire 70H.
No a/c cooling --no dehumidification.
Wait for some significant cooling loads before raising hell.
But then you got the instructions.
Keep us posted.
Regards Teddy Bear

[CPA Nerd]

Thanks for all the great comments.

I spoke with my contractor. Here are the cliff notes:

1. The thermostat was slightly off calibration. Once calibrated properly, humidity was actually about 4-5 degrees lower than I thought.

2. As many of you said, with these mild temperatures (high 70s high today) there simply isn't enough run time to dehunidify the home as much as we'd like.

3. He said as temperatures warm up, I will see lower indoor humidity as the AC runs more.

4. He says in summer, 50 is ideal humidity. 35 in winter. Right now as I type this, it's at 53. Even before he recalibrated, the highest it displayed today was 58. Much better than yesterday's 62.

5. He recommended a basic dehumidifier for the basement so that damp air is not cycled from the basement to the rest of the house. Makes sense to me.

I am comfortable with the recommendation and discussion with him today.

[teddy bear]

Thanks for all the great comments.

I spoke with my contractor. Here are the cliff notes:

1. The thermostat was slightly off calibration. Once calibrated properly, humidity was actually about 4-5 degrees lower than I thought.

2. As many of you said, with these mild temperatures (high 70s high today) there simply isn't enough run time to dehunidify the home as much as we'd like.

3. He said as temperatures warm up, I will see lower indoor humidity as the AC runs more.

4. He says in summer, 50 is ideal humidity. 35 in winter. Right now as I type this, it's at 53. Even before he recalibrated, the highest it displayed today was 58. Much better than yesterday's 62.

5. He recommended a basic dehumidifier for the basement so that damp air is not cycled from the basement to the rest of the house. Makes sense to me.

I am comfortable with the recommendation and discussion with him today.

Good comments from your a/c guy except one.
The actual moisture contact in your basement air the same as the main floor.
Here is how it works, your air handler mixes and circulates all the air in your home.
Your basement is 5-7^F cooler than you main floor.
Every degree that you cool the air, raises the %RH 2%RH.

75^F, 50%RH, a 55^F dew point main floor
67^F, 60%RH, a 55^F dew point Basement
<55^F, 100%RH, a 55^F dew point Sweaty duct
This is all the same moisture content 66 grains per lb. of air
A good a/c tech should know this.
He is right about one thing, you should have a small whole house dehumidifier in your basement. I suggest an ULtra-Aire 70H serving your basement and the entire home.
Get a good %RH meter and check the %RH throughout your home and next to the a/c T-stat.
Amazon <$10
Keep us posted on your %RH as we go through the different weather systems and your a/c control of %rH.
Regards Teddy Bear

[CPA Nerd]

The last few days, the indoor humidity has been between 52-54%, with outside air temperatures around 70 for the high.

It has been very comfortable in the house. I can't get over how the temperatures upstairs are the same as downstairs. With our old single stage system it had always been a large temperature fluctuation.

[CPA Nerd]

The last seven days, indoor hunidity has been at 60-61%. Outdoor highs have been 72-79 degrees.

My 30 pint dehumidifier in the basement that I bought three days ago is running continuously and not showing a reading below 60%. It started at 65%. Should I get a larger unit?

Another important question: With the fan of the blower motor continuously on, what speed should it be at? It's at 50% now. Would turning it down be helpful? If so, should I leave it at the same speed in winter?

[teddy bear]

Your AC isn't going to run hardly at all when it's 72 out. You need a dehumidifier in mild damp weather. When it get 80-95 out the AC will take care of it.

Here is good advice. A/c only removes moisture when runs for an hour. The first 15 mins. the coil/pan loads with 1-2 lbs. of moisture, then moisture starts tripping down the drain. At the end of the run, the moisture on the coil/pan evaporates back into the home.
During low/no sensible cooling. resulting short cycles, no moisture is removed.
During rainy weather, not moisture is removed by any a/c. Do not pay any attention to the %RH meter or get a small whole house dehumidifier. A word of caution, during significant cooling cycles, the a/c must be able to maintain 50% RH without the help of a dehumidifier. A dehumidifier will not fix a lazy a/c.
A properly setup a/c coupled with a correctly installed whole house dehumidifier will get <50%RH all the time.
Hot weather headed to Chicago!
Keep us posted.
Regards Teddy Bear

[CPA Nerd]

Here is good advice. A/c only removes moisture when runs for an hour. The first 15 mins. the coil/pan loads with 1-2 lbs. of moisture, then moisture starts tripping down the drain. At the end of the run, the moisture on the coil/pan evaporates back into the home.
During low/no sensible cooling. resulting short cycles, no moisture is removed.
During rainy weather, not moisture is removed by any a/c. Do not pay any attention to the %RH meter or get a small whole house dehumidifier. A word of caution, during significant cooling cycles, the a/c must be able to maintain 50% RH without the help of a dehumidifier. A dehumidifier will not fix a lazy a/c.
A properly setup a/c coupled with a correctly installed whole house dehumidifier will get <50%RH all the time.
Hot weather headed to Chicago!
Keep us posted.
Regards Teddy Bear

Thank you. We have hot weather coming this week, so it'll be a good test.

Independent of that, any thoughts on whether I should try a larger dehumidifier unit in the basement since it's only getting it down from 65 to 55?

Also, is 50% a good speed for the blower fan to constantly run or would something lower be better for general humidity levels? What speed is generally recommended?