House insulation question

[solocam_aggie]

Thought I had it all figured out, until chatting with my AC buddies. They said I need to be concerned with spray foam insulating the house causing condensation to build on windows. They said that making the house too air tight with a unit that doesnt have a dehumidifier can cause this. Anyone else who has sprayed their house had this issue?

I've already purchased my outside unit (5 ton), and it sounds like a unit with a dehumidifier is higher than Giraffe ______

My plan is to spray 3 exterior walls, then batt the wall dividing the shop and living (barndo). Im not sure what to do on the ceiling. The roof is already insulated with big batts. Im debating between just batting the ceiling, or doing blown insulation myself. Any thoughts?

[solocam_aggie]

TTT

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[12RingKing]

Interested as well, I hadn't heard that yet. Quite a few guys in here suggest foam insulation...

[pyrobow]

I have a 2800 sq ft conventional home. Sprayed Exterior and bottom of roof deck. I have not had problems with condensation. Over 10 years old.

[Kgert]

Anytime you use spray foam the a/c needs to be designed in accordance. Yes spray foam will create a tight home thus resulting in less air exchanges. Your a/c is a dehumidifier in itself. Less air exchange, higher humidity. What I normally see is a unit designed around EFL when paired with spray foam. Fresh air intake along with a humidistat so the unit will not only kick on based off of temperature, but also humidity levels. There was some talk in the building industry that linked premature coil failure with spray foam also. Just do your research and talk to both HVAC guys and a foam rep guy.

[mjhaverkamp]

I went with open cell foam, we have tall ceilings with several return air, the home is 3400 living, highest electric bill has been 112.00, no problems with anything, really liking the foam.

[stuntriderant]

Fresh air ventilation.

[elliscountyhog]

Hvac person that knows how to deal with foam house will know and set it up and it's a great thing to have! I have done numerous foam houses. Heat load calculation is a must!

[mjhaverkamp]

Hvac person that knows how to deal with foam house will know and set it up and it's a great thing to have! I have done numerous foam houses. Heat load calculation is a must!

My ac guy measured every window before he designed our system, works great.

[Rat]

Not a problem if the HVAC system is sized, designed and installed correctly. You will need to bring in outside air though.

The best designs use an ERV to both act as the exhaust for the home (bathrooms, utility rooms etc) and as a fresh air heat exchanger for the air coming in.

Second best is using a demand ventilator/damper system that uses a timer to allow the correct amount of outside air in according to the ASHRAE standard.

Last best is using a straight motorized damper system so the outside air damper is only open during a call for cooling/heating.

I have done hundreds of foam houses, both open and closed cell and never had single problem with condensation in the walls or on the windows.

It is critical that the house be balanced, that the amount of exhaust air equals the amount of outside or make up air. The main problem is usually the kitchen hood. Generally the kitchen hood is not tied in to the outside air system, so when it runs (and some of them can move over 1600 CFM of air) this puts the house into a negative pressure which causes all kinds of problems. Ensure that the kitchen hood is balanced with the correct amount of makeup air and that the total exhaust air is equal to the total amount of outside air being brought in.

This is where a load/loss calculation is needed; that much outside air adds quite a bit of load to the home. The HVAC system will need to be sized accordingly to handle this load as well.

Any HVAC contractor worth his salt can do this. If you get the goat stare when asking about it hire a third party consultant (I know a few who are very good if you need names) and hold the contractor to the recommendations of the third party engineer.

[bowhntrmatt]

How have you already sized and purchased a unit without even knowing your insulation values?

Unless you are building a monster barndo, 5 tons is probably way big if it is spray foamed.
I just got finished designing a system for a 3600 sq ft single story home that was encapsulated and it only required 3 tons of cooling. The big thing that can be different on an encapsulated house is matching the system to the sensible/latent heating load.

[Keg]

We built our steel home 8 years ago.... 5-6 inches spray foam in walls and 8 inches under roof.... We have never had condensation or sweating of windows....

[orlybow]

Just crack open a window a little bit...[emoji41]

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Por favor!...No mames güey

[Mike D]

Hvac person that knows how to deal with foam house will know and set it up and it's a great thing to have! I have done numerous foam houses. Heat load calculation is a must!

This!


"An honest government has no fear of an armed population".

[tps7742]

The comments above on the "correct" hvac installation is the key from talking with people and the research I have done on this matter. We are using spray foam on our present house build and believe me I am old school but decided on allot of the modern advances used these days.