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AC won't stop running...

Posted by tbritt (My Page) on
Mon, Jun 7, 10 at 5:00

My home is 1742 sf, was built in 1968, single level with an attic above and crawl space beneath. My ac has always run more than I believe it should. 3 years ago, I called a local HVAC company to check it for me. They said right away that my duct work needed replacing as it is old and leaking. So, I had a brand new duct system installed. That didn't help.

Last year, I had them return and they said that my unit was borderline for the size of my home. The size of the unit then was 2.5 ton. So, I put in a 3 ton Goodman ac unit. That didn't do the trick.

Two weeks ago, I had Simonton vinyl replacement windows installed. Double pane, low E, Argon etc. That has not helped. Yesterday it was 91 degress here, my thermostat is set on 76, my ac came on at 10:30 a.m. and it ran for 13 hours non stop.

I was told to have the insulation in my attic checked. There is about 6 inches of insulation up there and it is the blown in type. Someone also suggested an attic fan. I have vents at the gable ends, but I do not have any vents in the soffits. They said soffit vents would help with "passive" venting.

Oh yeah, underneath the house is well insulated. I am really frustrated here. I have spent more than $10,000 in the last three years trying to solve this problem.

The only area left to check, is the attic. That has to be my problem....right?


Follow-Up Postings:

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RE: AC won't stop running...

Not a pro here, but 6 inches in the attic is not much at all. Probably the first place you should have put money into though as it is where you get a huge amount of heat transfer. It should be more than 2x deeper than that from my limited understanding. Did you get an energy audit done prior to spending so much $$$? That would have pinpointed your issues and told you where to invest. Is your house (I guess attic at this point) sealed well? Air leakage (between the attic and living space) and lack of insulation in the attic will increase cooling requirements.


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RE: AC won't stop running...

My home was built six years after yours was and the blown in insulation was 8"-10" deep.

1 years ago I had insulation blown in. That insulation is 24" deep and provides R-38 value plus whatever the original insulation provides.

I'm in the MD suburbs of DC and the cost for the additional insulation was $1.00 per square foot.

It made a dramatic improvement in the comfort of the house.


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RE: AC won't stop running...

Thanks for the replies. I have not had an energy audit done. I had never heard of one until a friend mentioned it a couple of days ago. I spoke with a couple of insulation companies today and they said that I need double what I have now. Said it would give an R-30 level of insulation.

I am having 4 companies come out Thursday (my day off) to talk with and get estimates. Two ballpark figures I have so far are, $1100 and $800.


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RE: AC won't stop running...

The attic insulation will make a huge difference. Depending on how the house was built, I've seen many cases where only 6 inches of insulation allowed warmer air to circulate (chimney effect) between the wall studs, especially in single story homes. This would include behind the thermostat. The additional insulation will surely help to minimize that.

You didn't mention whether the temperature in the home was comfortable or not. Sometimes the placement of the thermostat can make a difference. Is the thermostat in a hall way or is it in an open area such as the living room? If in the hall way, do you keep the doors to the rooms closed in that hallway (return air concerns). Do you have return ducts in all the rooms or, is there one return for the whole house? If it's in the hall way, is there a pull down stair way nearby? How high on the wall would you say the thermostat is?Does the unit eventually shut off around 10 or 11 pm and then cycle normally during the night? I think the insulation may greatly solve your problem but, I'm asking these questions just in case you continue to have issues after the work is done, it'll give me and some of the other guys in field here on the forum, some idea where to point you.

There's no way I can judge whether the unit is sized properly for your home without personally doing a heat load calculation and an air balance along with the layout of the home. However, I'm thinking a 3 ton unit could also be marginal. The 2.5 you had, for the square footage you quoted, was undersized.

Let's see where the insulation goes.


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RE: AC won't stop running...

Great questions maryland irisman. The thermostat is in the hallway. It is about 5 feet off the floor. There are 4 doors immediately adjacent to the t-stat. 3 bedrooms and a bath. Those doors are opened about half the time. The attic pull down stairs are in the same hall, above the t-stat. I did notice there was hot air from the attic being pulled in, so I took some duct tape and sealed the crack around the stairs. There is also a minimal amount of air being pulled in through the exhaust fan in that bath.

There are two air returns in my home. One in the hall by the t-stat, the other is in the hall on the other end of the house. I have a brick house. It is similar to a doublewide trailer in the way it was built. It is about 60 feet long by 20 feet wide.

The unit does shut off and cycle better during the night. The way tonage was explained to me was, the unit works at 600 sf per ton. Overall, the house does stay fairly comfortable. It's just, the ac runs all day long without shutting off. If the outside temp is 87 or above, my unit is in for a long day.

BTW, my air handler and ductwork, are underneath the house. The air returns are positioned low on the walls, just above the floor, and so are the air vents.


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RE: AC won't stop running...

I had my first on site inspection and bid today. This company has been in the insulation biz for 41 years. I was quoted a price of $750 for six inches of blown fiberglass. He also strongly suggested adding soffit vents (I have none) to the outside of my home. Thoughts anyone?


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RE: AC won't stop running...

6" of additional insulation blown in doesn't sound like much. What is the R value of that insulation? When mine was done 1 years ago it was 24" deep plus the original insulation. The new insulation equates to R-38.

There are at least a few ways to determine the amount recommended for your area. Google on "Attic Insulation R Value" or similar.

Another way would be to consult your local government and find out what is currently required for new construcion in your town or county. Just a guide in your case.

I paid $1000 for my 1000 Sq Ft attic with 24" deep. You're being quoted $750 for ~1800 Sq Ft at 6" deep. You're paying more per unit volume of insulation, but I suspect that they would not quadruple the price to quadruple the depth of insulation if it were required.

Where are you located? Again, I'm in Montgomery County, MD.


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RE: AC won't stop running...

What kind of venting does your attic have now? If you have vents up high and none down low, you are probably sucking conditioned air right out of the interior of your house. An attic fan would only make it worse.


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RE: AC won't stop running...

Saltidawg, I was told and read online, that six inches of blown fiberglass has an R value of about 19. That plus the six inches that is already up there, should be close to R 38. The man that should be enough. If not, I can always have more blown in. You got a great price for 24 inches! I am in Wilmington, NC. Southeast NC right on the coast. I am five minutes from Wrightsville Beach, NC.

Creek side, My attic has a gable vent on each end of my home. And, as you mentioned, I was told that an attic fan might make my situation worse.


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