HVAC system 20 degree rule

HI. I recently did a major overhaul on our house in Atlanta, due to a fire last summer. My house is about 2500 sq.ft. and the sub contractor put in a 4 ton unit with three zones. We are having a great deal of difficulty getting the temperature to be below 78 degrees, especially on hotter mid ninety afternoons here. the AC guy says the best you can expect is a 20 degree difference on a hot day from the outside temperatures. Is that right? We had a 3 ton unit previously that kept us at a comfortable 70 (brrr) all year. Oddly enough, the zones furthest from the unit keep a cooler temp more consistently. Any advice? Thx Beth
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Someone on another board mentioned this same thing last week. Is this some kind of nationwide excuse used when the contractor installed a system that was too small ?
--
JerryD(upstateNY)



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Try telling that to the people in Phoenix when it hit 118 a couple weeks ago.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
beth wrote:

Load of bunk. If this were true the food in your freezer would be thawing....
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
beth wrote:

Something's got to be wrong if your old 3-ton unit was adequate.
I'd have a blower door and load analysis done on the house to see how the numbers come up. You might also get a thermometer and read the temperatures going into and coming out of the AC at the closest register (after it's been running constantly for maybe 1/2 hour) to see if the differential is in the right ballpark. Did they tell you the capacity of the air handler in cubic feet/minute? You can have someone do calculations given the humidity, temperature differential and air handler cfm's to see if you're roughly getting what you should out of the system.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In Arizona it can be 120 degrees outside and plenty of houses and buildings are 70 degrees or so inside!
Might want to have another company look at your system. Maybe they did not install what you paid for? Something is fishy here.
If you can, post the brand and model of your 4 ton unit (read label on unit) here along with the square footage of your house. One or more of the experts here should be able to tell you if this is in fact a 4 ton unit.
"beth" wrote in message

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bill wrote:

OK, Sorry for the delay in responding. I really appreciate all the list suggestions. It is a Copeland Scroll version of a unit made by Goodman Manufacturing company out of Houston, tx. the model number is #CLJ481-C. I hope this helps. IN the meantime I am having the a/c guys come back out to do the temp. comparisons. The unit is running almost constantly to attempt to reach a cooler temp, and there is a significantly higher temp near the ceilings. Thanks again!! Beth
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Searching on the internet I found that this is in fact a 4 ton unit...
Page 14 or search the text for CLJ481 http://www.midbec.com/Document%20HVAC%202005.pdf
So it would seem that the unit is not working properly if you in fact had a 3 ton unit which worked OK previously.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
beth wrote:

The 20 degree rule applies to the difference between the air at the return and what's coming out of the registers. I'd _guess_ there is either something wrong or you have a very poorly insulated/leaky house. 4 tons for the avg 2500 sq ft house should be good.
--
Art

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm no A/C expert but even I know that four tons for 2500 sq. ft. is too little. I've come to believe that the rule of thumb (for standard eight foot ceilings) is one ton for every 400 sq. ft. I think you're a couple of tons short.
--
"New Wave" Dave In Houston



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In south Florida the rule of thumb is 600 sq ft per ton. If the A/C is oversized then it doesn't run long enough to remove the humidity.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
It was 102F outside the other day (not counting the fact there was also high humidity, which apparently made it feel like 117, and the A/C happily kept the house at 72F. I have a 2 tonne air conditioner, total condition space is 2000 sq ft with 8ft ceilings well sealed.
PS. I also have a heat recovery ventilator and didn't need to switch it to recirc or having to run any additional dehumidifier, the A/C removed any extra humidity the HRV might have been bringing in.
David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I had a similar problem after a new install. Installer came back three times. Finally found freon leak under the insulation.
--
remove one of the @\'s unless you are a spammer.
"beth" < snipped-for-privacy@comcast.net> wrote in message
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I have an even better one. My ex moved into a trailer when she moved out last summer, one without A/C. She had a new furnace & A/C installed last Nov. This spring she finds out that the A/C apparently doesn't work.(NO cooling at ALL!) After several calls to the installer, she finally gets a response that turns out to be a different outfit responding to the call as a favor to the original co. since they are going belly up. After about 45 min. of trying to get some freon into the system since it is showing all the symptoms of being low, one of the guys decides to check something really stupid. It seems that compressors come pre-charged, and there is some sort of valve at the intake and output that needs to be opened when the system is being charged during install. You guessed it - they had not been opened yet. As soon as he started to open the valves heat started coming off of the heat exchanger and she was in business. Guess that's why the original outfit was going under!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Good point! You would assume that someone installing something would test it after installation to be sure everything is working properly, etc. However I have worked for many companies which have "that one new employee" who never does anything right, will not be sure everything is working before leaving, etc. So if you get a bad "luck of the draw", might get one of these guys installing something for you.
Usually the repair guys are well trained - experienced and can resolve these problems. The installation department has the new employees typically. (Sometimes a boss will keep sending the same installer out in an attempt to educate him so he will do things right in the future... "You will keep going out there until you get it working" is the thinking.)
"tim" wrote in message

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I had the exact same situation as Bill. A new installation of an A/C unit, the air that was coming out of the registers was not very cold, and it seemed that no matter how long we ran it, the house would not cool down much.
As time went on (for a couple of weeks) it got worse and worse until the A/C did no good at all. We called the contractor who found a leak in the freon. He fixed the leak, and the problem was instantly solved. Night and day difference, we had no problem (even on very hot days - 100+) cooling the house to below 70. Took less than an hour of the contractor's time.
One additional note - we had the same problem again a few months later; a different leak in a different area. After they fixed the second leak, we had no further problems.
beth wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.