a/c or insulation issue?

[hotinthesouth]

I have had this problem for the last 3 years. I live in N. Alabama and when it hits about 90 and a little over my in room temp. rises about 5 degrees above set point and finally levels off about 8:00 pm and plays catch up the rest of the night and does fine in the morning all the way to about lunch time and then it starts rising again. I have had tech after tech check it and they all say it is doing the best it can and is charged correctly. I live in about a 1950 sq.ft. house that is a ranch style house with a 3 ton unit. It works great up to about 88-90 degrees. I check my filter regularly and have my coils cleaned regularly. However, in my attic, my ceiling joints are exposed and the insulation in some places only comes about half way up the ceiling joints. My question is if I have more insulation blown in and get it all above my ceiling joints, would that make a significant difference?
Any help is much appreciated!

Thanks

[Shophound]

Has anyone evaluated your ductwork for leakage? If you've had tech after tech consistently state the charge is normal, then I'd start looking elsewhere. Insulation can help some, but if your ducts are leaking, no amount of insulation will solve a loss of system capacity by way of duct leakage.

If you have ducts in the attic, and they are leaking, they affect your comfort as follows:

Supply ducts: air leaking into an attic is not returned to the blower. This air must be made up from somewhere. Any leak in your house from outside will be this source. This source of air will be hot (and humid if you live in a muggy climate). You will be paying to cool this air along with the air in the house, and at the same time you'll be throwing some of this air right back outside. Not good.

Return ducts: If in attic, it will suck in hot attic air and add an unnecessary load to the cooling coil. It will also cause the house to be pressurized, which will force your cooled air out through gaps in the house construction.

[hotinthesouth]

I have a crawl space and all ducts are under the house. If I had a duct leak it would be messing up all the time wouldn't it? The air coming from the registers are cold and works well up until about 92 degrees then as temp rises outside the temp. on the inside rises as well that is why I thought it might be an insulation issue.

[Shophound]

Here's something to consider...download HVAC-Calc from this site and carefully read the directions to perform your own heat load calculation. Once you successfully perform this calculation, the software can be directed to break down your heat gain and loss figures into sources, such as windows, ceilings, walls, etc. What this data can do is help you guide your decision making processes for insulation, windows, etc.

As it is it sounds like your attic insulation may be marginal and you're experiencing "temperature swing" as the day becomes hot. Also, as outdoor temperature climbs, the condenser is able to reject less heat at the very moment it needs to reject more, especially when temperatures climb into or past the mid-nineties.

You may also want to consider adding a radiant barrier beneath your roof decking. Radiant heat from overheated roof decking is the primary source of attic overheating.

[rohalon]

http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation _table

alabama is recomended as r-38 for cieling insulation, sounds like you have r-19 or less.

As already said, make sure there is no air leaking from the ducts. Adding insulation and sealing up any drafts will only help, how much I can't really say from here.

[cem-bsee]

do you know where U live?

I have 2160sf trilevel & can cool with less than 1 ton, until temp over 95F, then full --
but I have shade
but I have joists covered

yes, joists in attic need covering with insulation -- at least 2" -- if you have more blown, have enuf to allow for settling.

BUT, have holes caulked or foamed around the pipes & wires coming into the attic first
have ALL seams & joints & holes sealed in the ductwork, boxes with mastic
have boots caulked to the subfloor
put pvc over dirt, leaving 4" of masonry exposed to look for termites
seal the crawl vents