re: Brand new AC and vents in living room are leaking badly

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The house is elevated and we are having insulation done under the home this week. The jumper in the return in the living room came back good on tests. At the end of the day, he says the humidty in the house is high - and it is. We are going to re-evaluate after the insulation in the flooring is done. I also purchased a dehumidifier hoping the conjunction of both helps eliminate the issue.

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Any buckling going on with your wood flooring?

With floors that old, I'd be worried that the closed cell foam is going to cause flooring issues. I hope not, but Paul Lagrange always has people calling into his home improvement show because of buckled floors after sprayed insulation. I'd want to get the HVAC issues figured out first in case you need to add any returns or whatever else under the house. Probably too late at this point.

Hmmm...I see what you mean. Did a little research on this and see a potential pitfall. What would be your counter? I can still cancel the insulation...but something would still be needed. When I say HVAC has come twice and said everything is working 100% I don't know what else to do.

I just called a company about an encapsulation instead....they said their best plan/option would be approaching $20k with a French drain/pump under the crawl space to remove moisture, dehumidifier under the house, and their plastics/insulation for the lattice, HVAC and conduits. So, about five times the price of the foam insulation.

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I get the sarcasm here

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No sarcasm intended…I would be extremely dissapointed. You bought what many would consider a dream home on the beach, installed a brand new HVAC system, and now you are having to deal with this.

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Now I am trying to decide if it's the best route. Found this piece from LSU and am reading it now. LINK

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Very good article. Paul LaGrange is basically residential building forensics expert who for all practical purposes identifies the causes of issues that you are having. I think he is based in Slidell, he’s the type of person you should hire to identify causes to your issue(s) and solutions to the problem. Here is his website LINK. He has a weekly 2 hour call in radio program Sat morning on WWL 870 - much it dealing with your type of issues. He’s fond of saying 80% of his time is spent crawling through attics and crawl spaces trying to find causes of issues that you are describing for your house.

You have a unique issue that house is historical. I’m not saying that you don’t have an issue with the new HVAC, but I could equally believe that are being truthful in saying the HVAC is operating according to specifications and other issues are in play, i.e., because of its age, the house is very leaky as it relates to air infiltration. You could be a rare case where the HVAC is undersized, almost never happens but then very few own historical homes.

What size is your HVAC, tons of cooling capacity, and how many square feet of house are you attempting to cool?

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Now I am trying to decide if it's the best route. Found this piece from LSU and am reading it now. LINK

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That is the best guide out there, and has been for years for explaining the potential dangers of high humidity and air conditioning in homes with crawl spaces. But, if you notice they do not give a definitive fix to the problem. They would be liable if you followed their recommendation, and it exacerbated your problems.

I've seen situations where spray foam is used and it helped, and I've seen the opposite occur as well. Open cell is generally recommended for under subfloor use, but it's a crap shoot as to your result. You might get lucky, you might not.

One guy installed exhaust fans with hygrometers built in to turn them off and on automatically. It worked for him. Not so for some others.

It's very frustrating, but each home with a crawlspace is a slightly different situation due to so many variables that can be involved. Narrow crawl space ( under 2 feet), lack of enough vents and improper placement of same, morning sun, evening sun, excess ground moisture, poor air flow under the house due to plantings around perimeter, irrigation of flower beds running back under house resulting in standing water, too much forced air flow, lack of insulation in the house walls, leaky roof, windows or fireplace, clogged gutters, excessive low temperatures being kept by tenants so they can sleep at night (I've seen thermostats set at or below 65° continuously because the wives are having hot flashes).

I have watched floors buckle within two months into a situation where they tent up a foot or more and "pop". Once you begin changing things in a house where things have been at a harmonious balance for years, you can start getting unintended consequences.

I would start with getting more opinions on that new air conditioner you had installed. That is where this all began, and I would think it might save a lot of pain down the road.

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4 tons, 2,000 square feet, vaulted ceilings throughout.

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Poorly insulated and leaky, raised house. The unit is too small.

Do you have an exhaust fan or fans that run a lot? If so your home is negative and you are drawing in outside, humid air.

Grilles don’t leak. They sweat when the air is moist and the temp on the grille reaches Dee point. The water you see came from the air inside your home.

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Poorly insulated and leaky, raised house.

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I bought the most expensive insulation option I was given for the attic. The subfloor is bare for now as I make a decision.

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Do you have an exhaust fan or fans that run a lot? If so your home is negative and you are drawing in outside, humid air.

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The air inside the house is humid, but it is not illogical to agree the lack of subflooring allows elevated amounts of moisture to enter thus causing the AC to suck up that high moisture and circulate it all day.

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4 tons, 2,000 square feet, vaulted ceilings throughout.

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That’s helpful. Basically it’s the old 1 ton of HVAC per 500 sq ft of conditioned area “rule of thumb” that been around since the 1970s, when many “identical” tract houses were built and that number was pretty accurate for many houses at that time.

Sadly far too many HVAC firms still adhere to that number, sometimes it is right, often times it wrong as not all houses are equal in regards to orientation, insulation type & amount, sealing/air infiltration, windows, etc., etc., etc. The correct way to size HVAC cooling tonnage for house would done via manual J, S and D. In many areas of the USA a manual J heat-cooling load calculation is required by code before permits would be issued to install a HVAC.

Here is table of HVAC tonnage size put together by guy in FL who sizes HVACs using manual J, S, and D for a living. He refers to it as as a “best guess” table in the absence of manual J calculations. The numbers in the table are square feet of conditioned area pet 1 ton of cooling. Note he took into consideration age of home from the past, into the future, and the insulation & air tightness of house (thermal envelope quality) in 7 broad categories that he describes in the footnotes.



You have 100+ old historical house, assume the house is “poor” to “average” in terms of air tightness & insulation - of course I understand you have made significant improvements to the house to better insulate it, and additional improvements will continue to be made.

This table might suggest your HVAC is undersized, not saying it is of course, but it is something worth discussing with the HVAC contractor if indeed your new HVAC unit is functioning properly. But the table shows 1 ton of HVAC could be required per 300 sq ft for one house, and 1 ton per 1400 sq ft would perfect for another home. In the absence of a manual J heat-cooling load calculation and blower door test to determine air filtration of your house anything regarding HVAC sizing is going to be a guess.