Dehumidifier Advice & Recommendation Needed | High Attic Humidity

[iliveinflorida]

I have having a humidity problem in my attics after getting open cell spray foam insulation.

I am located in Florida. My home is 2 stories and I have attic space on the 1st story and 2nd story.

I have a main attic of 1549sf on the 2nd story.

Then I have 2 small attics of 405sf and 210sf. These 2 small attics are separated by the hvac system in a mechanical room in the middle. All attics have lower overheads.

My home's interior runs at a temp of 69-72 and has 51%-53% relative humidity according to the device I have.

I zeroed out the other devices attached to this gauge and it has humidity in the different attic spaces going up to a max during the day of 70%, 71% & 84% (with a low of 59%, 56% and 60% respectively). We are getting condensation at our air vents on the 2nd floor and are concerned about mold.

I have been recommended to get 3 Ultra Aire 70 pint whole house dehumidifiers. One system for each attic space. So one system will be up in the large 1549sf attic surrounded by duct work but not close to the hvac system. The other 2 will be next to one of my hvac systems in a "mechanical closet" and ducted into the 405sf & 210sf attic space.

Is this what you would recommend? Is it not oversized for the 2 small attics to each have their own 70 pint dehumidifier?

The 2 small attics have the hvac system located between them in the mechanical room. Could one system be ducted to handle the 2 smaller attic areas( 405sf and 210sf)?

What specific installation instructions should I request?

What is the best ways to reduce the noise from these units?

Can these units be used to dehumidify the attic & also the air coming through my central hvac? The attic is my priority but since I am installing so many dehumidifiers I was wondering if I can get some added benefit?

Thank you in advance for any advice or suggestions.

[dan sw fl]

FIRST Alternative:

Set t-stat to 74'F

Use minimal air flow to condition the attic spaces with the existing A/C system

Balance A/C unit to 360 CFM/Ton

[iliveinflorida]

FIRST Alternative:

Set t-stat to 74'F

Use minimal air flow to condition the attic spaces with the existing A/C system

Balance A/C unit to 360 CFM/Ton

Dan,

Thank you for your quick response! I really appreciate any additional input I can get.

The upstairs thermostat is set to 71 this morning and I guess due to the humidity it is too warm (outside 77 degrees 95% humidity). So setting it to 74 seems unbearable.

I thought about attic vents from the duct work to the attic but I wasn't sure how much it would help with the humidity levels. Especially since the humidity levels seem to be so high.

I will have to ask my hvac person if the a/c unit is balanced to 360 cfm/ton. I'm not sure how to figure that out as a layman.

[pecmsg]

Do you really want to pay to condition attic space in Fla?

Insulating the roof is cheaper with a much better return on investment!

[dan sw fl]

Do you really want to pay to condition attic space in Fla?

Insulating the roof is cheaper with a much better return on investment!

Post #1
1st sentence

" I have having a humidity problem in my attics after getting open cell spray foam insulation."


I presume the roof rafters/ truss -deck underside have adequate spray foam thickness.

Attic is semi-conditioned space that should be < ~ 82'F.
REDUCING the temperature of a tightly enclosed space ~ 5'F might
not require more than a nominal air flow rate.

[pecmsg]

Post #1
1st sentence

" I have having a humidity problem in my attics after getting open cell spray foam insulation."


I presume the roof rafters/ truss -deck underside have adequate spray foam thickness.

Attic is semi-conditioned space that should be < ~ 82'F.

Then find where the moisture is coming in from!

[iliveinflorida]

Then find where the moisture is coming in from!

I am having a home inspector come over today with an infared camera to crawl around the attic to see if there are any spots the insulation mixed.

I don't know how "air tight" my home is as doors & windows but we do have a gas range which I know causes humidity.

The showers do vent to the attic so we are not using the fan and using the shower downstairs.

Any suggestions on how to find the source of humidity?

[dan sw fl]

I am having a home inspector come over today with an infared camera to crawl around the attic to see if there are any spots the insulation mixed.

I don't know how "air tight" my home is as doors & windows but we do have a gas range which I know causes humidity.

The showers do vent to the attic so we are not using the fan and using the shower downstairs.

Any suggestions on how to find the source of humidity?

Tell the home inspector to
PERFORM Blower Door Test

https://www.energy.gov/energysaver/blower-door-tests

[pecmsg]

Forget the home inspector and get a contractor that can do a blower door test!

[pecmsg]

I am having a home inspector come over today with an infared camera to crawl around the attic to see if there are any spots the insulation mixed.

I don't know how "air tight" my home is as doors & windows but we do have a gas range which I know causes humidity.

The showers do vent to the attic so we are not using the fan and using the shower downstairs.

Any suggestions on how to find the source of humidity?

Moisture can still be drawn into the attic!

The exhaust fans MUST be addressed!

[iliveinflorida]

I presume the roof rafters/ truss -deck underside have adequate spray foam thickness.

Attic is semi-conditioned space that should be < ~ 82'F.
REDUCING the temperature of a tightly enclosed space ~ 5'F might
not require more than a nominal air flow rate.[/QUOTE]

I will have my inspector check the thickness of the spray foam but at the attic entrance they put a measuring stick in the foam and it shows 6".

The chart below doesn't paste well but this was yesterday. Peak attic temperature was 83.8 degrees without accounting for the thermometer being a couple degrees off. So it doesn't look like I am meeting the < 82'F. However, I do have low attic space so it was always hot (and thus the spray foam insulation). If the thermostat is set to 71' do you think adding some registers in the duct work will cool the attic enough? You probably can't answer this without being hands on. But how would I find out? Seems a cheaper fix then adding a dehumidifier.


Yesterday had a high of 90' and low 75' and humidity around 90%

Temp/RH
Interior Attic 1 Attic 2 Attic 3 Outside
7:14am 69.1/51% 70.7/70% 72.7/56% 71.5/60%
12:52pm 69.4/52% 80.3/61% 74.9/65% 72.8/84%
4:05pm 70.6/55% 81.5/70% 79.3/71% 83.2/76%
6:53pm 70.3/53% 83.8/61% 80.8/67% 82.8/71%
9:27pm 71.4/51% 83.4/59% 79.6/62% 76.2/68% 80/86%

[iliveinflorida]

Moisture can still be drawn into the attic!

The exhaust fans MUST be addressed!

Thanks for the advice! I will have a roofer come out after the hurricane to work on venting the attic fans out of the house. Also get a blower door test. It's my understanding this will show if the insulation is keeping my house air tight & if air is coming in the doors & windows. Is that correct?

[iliveinflorida]

Tell the home inspector to
PERFORM Blower Door Test

Thanks for the advice! I will get a blower door test. It's my understanding this will show if the insulation is keeping my house air tight & if air is coming in the doors & windows. Is that correct?

[pecmsg]

Thanks for the advice! I will get a blower door test. It's my understanding this will show if the insulation is keeping my house air tight & if air is coming in the doors & windows. Is that correct?

It will show how much infiltration the home has. Visual as well as Smoke tests will determine where things can be tightened!

[iliveinflorida]

Thank you again! This is all over my head.

[teddy bear]

I have having a humidity problem in my attics after getting open cell spray foam insulation.

I am located in Florida. My home is 2 stories and I have attic space on the 1st story and 2nd story.

I have a main attic of 1549sf on the 2nd story.

Then I have 2 small attics of 405sf and 210sf. These 2 small attics are separated by the hvac system in a mechanical room in the middle. All attics have lower overheads.

Sounds like a retro open cell spray foam on the roof deck?? Are all of attic vents sealed? What is the roof materal? Heat from the sun drives a small amount of moisture through the roofing and vapor barrier/deck/foam into the attic, "Building Science Corp" research. The moisture builds up. The colder you keep your home, the more moisture is attacted to all the cool surfaces. Also lowering the temperature in the home raises indoor %RH. When was the attic spray foamed? Did the a/c run time change? What was the moisture condition before the insulation was added? %RH in the interior of the home?

My home's interior runs at a temp of 69-72 and has 51%-53% relative humidity according to the device I have.

I zeroed out the other devices attached to this gauge and it has humidity in the different attic spaces going up to a max during the day of 70%, 71% & 84% (with a low of 59%, 56% and 60% respectively). We are getting condensation at our air vents on the 2nd floor and are concerned about mold.

I have been recommended to get 3 Ultra Aire 70 pint whole house dehumidifiers. One system for each attic space. So one system will be up in the large 1549sf attic surrounded by duct work but not close to the hvac system. The other 2 will be next to one of my hvac systems in a "mechanical closet" and ducted into the 405sf & 210sf attic space.

Is the occupied space 1549 + 1549 +405 + 205 = 3,700 SQFT. total? A UA 70H should handle the large attic.
The home needs a minimum of 100 cfm of fresh make-up air to purge indoor pollutants and renew oxygen during calm weather. I would suggest an Ultra-Aire 98H for the home and have 2-4" dry supply ducts to the small attics with a damper in each 4"supply for minimizing the amount of dry air to each attic.
The a/c air flow should be re-adjusted to provide 73-75^F, <48%RH during the heat of the day without any dehumidifier assist. This is important. <300 cfm per ton of a/c. This warm the a/c ducts/grills a little warmer and less prone to sweating. Also the warmer will condense less moisture in the exterior surfaces that migrate into interior space. Getting to 74^F, 48%RH should as comfortable as 70^F, 53%RH. Critical to have the UA 98H dry air supply be connected to the a/c supply ducts with a return to the dehu from the open part of the home. Also the fresh air duct connected to the dehu return with a balancing damper.

Is this what you would recommend? Is it not oversized for the 2 small attics to each have their own 70 pi dehumidifier?

The 2 small attics have the hvac system located between them in the mechanical room. Could one system be ducted to handle the 2 smaller attic areas( 405sf and 210sf)?

What specific installation instructions should I request?

What is the best ways to reduce the noise from these units?

Can these units be used to dehumidify the attic & also the air coming through my central hvac? The attic is my priority but since I am installing so many dehumidifiers I was wondering if I can get some added benefit?

Thank you in advance for any advice or suggestions.

Possibly your contractors suggest will work fine. Seems like a little over kill on the small attics and not not enough drying on the home.
Regarding noise of the units, always better to hang the units from the trusses. You will need a safety pans with float switches. Use flex duct around the dehus. If noisy, surround the dehus with 3/4" plywood boxes.

I would like to here your comments on my questions.
Keep us posted.
Regards
Teddy Bear

[iliveinflorida]

This is a retro open cell spray foam on the roof deck. The attic vents should be sealed. I am having it inspected to confirm.

The roof is 40 year architectural shingle that is 13 years old.

The attic was just sprayed 8/19-8/20. I didn't think to take records of %RH before spraying but we always had a humid 2nd floor. Right now the 1st floor has a 49% RH with attics at 55%, 62% and 91%.

The home is 3800sf heated & aired.

I have a 2.5 ton hvac for the upstairs which is a smaller space & has the spray insulation. I believe I have a 3 or 4 ton for the 1st floor.

How can I tell if I am getting a min of 100 cfm of fresh make up air into the home?

I would suggest an Ultra-Aire 98H for the home and have 2-4" dry supply ducts to the small attics with a damper in each 4"supply for minimizing the amount of dry air to each attic.

I'm not sure if a dry supply duct from the main attic can reach the smaller attics. Unfortunately I have low overhead with a lot of duct work so it would take a really small person to make it to the edge to find out. I will discuss with my contractor. Thank you for your input!

Critical to have the UA 98H dry air supply be connected to the a/c supply ducts with a return to the dehu from the open part of the home. Also the fresh air duct connected to the dehu return with a balancing damper.

My contractor wasn't going to duct any fresh air in on the 3 dehumidifiers. Is that an issue? Is that something easy to fix in the future if needed?

Possibly your contractors suggest will work fine. Seems like a little over kill on the small attics and not not enough drying on the home.
Regarding noise of the units, always better to hang the units from the trusses. You will need a safety pans with float switches. Use flex duct around the dehus. If noisy, surround the dehus with 3/4" plywood boxes.

Thank you again! I really appreciate the install advice.

I assume if I go with my contractor plan of the 3 dehumidifiers you still recommend "The a/c air flow should be re-adjusted to provide 73-75^F, <48%RH during the heat of the day without any dehumidifier assist. This is important. <300 cfm per ton of a/c. This warm the a/c ducts/grills a little warmer and less prone to sweating. Also the warmer will condense less moisture in the exterior surfaces that migrate into interior space. Getting to 74^F, 48%RH should as comfortable as 70^F, 53%RH."

[teddy bear]

Thanks for the advice! I will get a blower door test. It's my understanding this will show if the insulation is keeping my house air tight & if air is coming in the doors & windows. Is that correct?

This will prove that when the wind blows your home leaks air. During calm weather like evening and many hot days in FL, you need fresh air ventilation.
You have enough into to show the need for supplemental fresh air during calm weather and making the suggested mechanical changes. If after all of the adjustments, you have excess moisture, a blow door will find the big leaks. To me this home looks fairly air tight during calm winds. You just need an a/c ajustment to remove more moisture during peak cooling loads and some supplemental dehumdification in the attics and home during low sensible cooling loads and high outdoor dew points.
But whatever, keep us posted. It is a interesting project that we will all learn from no matter.
Regards
Teddy Bear