Why a Bigger A/C When Current one Cools Adequately???

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On Sat, 24 Jul 2004 11:03:18 -0500, snipped-for-privacy@webtv.net (m Ransley) wrote:

each), and to get custim made double pane of any ilk would be cost prohibitive. I am considering the semi-reflective film. Up until Isabel the windows were shaded by a huge oak tree. Unfortunately it fell on the family room. Also, unfortunately, it didn't fall on any of the windows

zoning would help. As this was explained to me once the main house was cooled, if the family room still exceed the setting of the secondary thermostat, dampers would shift and the cooling and controlling thermostat would be diverted to the family room. Once it was cool, the system would turn itself off. It would then respond to whichever cooling demand it got, however, the main t-stat system would always attempt to cool the entire house and the secondary one would only work to control that part of the system (isolated) that would cool the family room
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I took out a 6x8ft 1/4 single pane and put in a 4x6 Tri pane , room temp on south exposure went down 20f + in sun. It cost 550 for the glass. It isnt cost prohibitive if you figure your cost to heat and cool. R 1 glass is crap for every 4x4 piece you have the equivilant of a 4" hole in it costing you year around. It will cost but save you maybe 40- 50 a month , every month for all that glass, tinting wont help R value. Awnings help but new glass is best.
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I took out a 6x8ft 1/4 single pane and put in a 4x6 Tri pane , room temp on south exposure went down 20f + in sun. It cost 550 for the glass. It isnt cost prohibitive if you figure your cost to heat and cool. R 1 glass is crap for every 4x4 piece you have the equivilant of a 4" hole in it costing you year around. It will cost but save you maybe 40- 50 a month , every month for all that glass, tinting wont help R value. Awnings help but new glass is best.
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See below inserted, but keep in mind, I have no idea about YOUR situation, as I have not done a load calc, and can not over the net.... Well..I COULD, but it would be pretty hackish.
wrote:

How old is it..meaning, what is the date it was made? Posting the make and serial number will normally tell us.

Again....there are NO RULES OF THUMB...NONE. There are FACTS, and unless someone actually uses them, all the facts are worthless.
Quick example. We started doing EPA energy star homes. The walls are R40, and the ceilings are R60+ Around here, you can normally EXPECT a 2 to 3 ton unit on a home constructed within the last 30 years with about 1700SF...it varies, but you are not surprised when you get those numbers. We did our first ES home, and it was 3500SF.. It took a 1.5 ton unit, and that was pushing the limit. Think about that when you consider the sizing "rule of thumb" bull you got handed.

IF, and thats IF hes using the NEW manual J, the numbers might be off a bit, compared to the old manual J. The new version is a POS, and we havent switched. Wont till its a point of issue. the new ManJ is about 4X as complicated as it has to be, and there is talk that ACCA might be changing it again..just rumors mind you, but it would indeed be nice.

Yup..I can think of one.
It was sized wrong to start with.

No one can "do the math" with that information. If you have the blueprints, with all factors on it, someone COULD do a manual J over the net for you, but you would be foolish to do that, unless you wanted a very, very, very rough idea of if the others are right.

No...no..not always. more to it than that.

Ok..look.
36,000BTU=3 tons. Not all 3 ton units are 36,000BTU.
SEER has only to do with the system, installed in a perfect world, and the amount of power it will use to run, and remove those BTUs from your home.
Higher SEER units, normally have larger evaps, and higher blower capacity. Many times, the humidity removal is lower with a high SEER unit, and it will run longer, or not..depending on the individual situation. This is why in the more humid climates, like you and I are in, that a variable speed air handler, or furnace can be of importance. Slower fan speeds-=more humidity removal.
Higher SEER units, depending on how they are designed, may, or may NOT run longer, or they may. York, the brand I use, has a two CAPACITY, not speed, but capacity outdoor unit. It can reduce start and stop times by as much as 75%. It DOES run longer, and its SUPPOSED to. And yes..they are much cheaper to run as well. Match that to a VS indoor unit, and you wont know the difference, other than in the power bill.
Given what you have posted, let me make a couple of suggestions..
One, get more estimates, two-anyone that does not do a full manual J, or T if you are getting a heat pump, AND a manual D, is wasting your time.
Rules of thumb are out, and actual hard fast calculations are in. Period.

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On Sat, 24 Jul 2004 17:05:15 -0400, "CBHVAC"

Mfgr # 99929 I think it is a Kenmore. It was put in in 1973

home built ~1950

In a private communication it was suggested that I go here: http://tinyurl.com/4plhd consider the house to be one big room and throw in the information to get a "ball park" idea of where the numbers come from and what changes what. Yes, I know this is for a window A/C but the correspondent said it would give me an idea.
SInce I have the house blue prints and know what insulation I have added over the years, in doing some research I have also found this and could spring for the $49 version if it was any good: http://www.hvaccomputer.com/gsizeindex.asp
There is also this, but I am having some problems with compatability, even tho I am using one of their suggested browsers. Am going to try another. http://mrhvac.com/index.html?http://www.mrhvac.com/manualjshort.htm

I got that message loud and clear. I am working with two of the best known installers in the area. Neither really is that interested Again thanks for the interest and help
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royroy wrote:

HVAC Calc Residential is a professional grade heat gain / loss calculator, easy to use and well worth the $49 IMHO. Check out related discussion threads at HVAC-TALK http://hvac-talk.com/vbb/forumdisplay.php?forumid=1 If you want a "free" *but harder to use* calculator you can try the old Lennox calculator (Logic MP) which is available at: http://home.att.net/~alt.hvac/loads.htm
HTH.
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Seems to me that a new, clean, well installed three ton would cool same or maybe better than an old dirty tired three ton.
Things to ask: Are you using a scroll compressor, or piston? Scroll costs a couple hundred dollars more, but is more energy efficient.
Are you using a TXV or an orifice? TXV costs more but is..... you guessed it.
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I just replaced two 12 year old AC units with larger units (I don't recall the size differences between the old and new units). My electricity bills have gone down by about 40-50% over the same time last year, even with larger units. Energy efficiency in newer units is much, much better than in a 12 year old unit; I can't imagine what the difference would be with a 30 year old unit.
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30 year old unit!? All I can picture is the Ice machine the Doc built in the barn on "Back to the Future part III"
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Mark wrote:

compressors with a similar pumping capacity to the newer higher SEER condensers. "Newer high SEER compressors have smaller capacity compressors and larger area condenser coils, perhaps they are trying to match compressor capacities."
Regarding the second post above, perhaps they only went up a half ton, so that the amp draw per btuh would be less than the older units with perhaps more cooling capacity. I have been retired too long to be able to accurately compare all the critical data to the above equations.
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Mark wrote:

probably had similar pumping capacity to the newer higher BTUH & SEER condensers. "The newer high SEER compressors have smaller capacity compressors and larger area condenser coils, perhaps they are trying to match compressor BTUH capacities."
Regarding the second post above, perhaps they only went up a half ton, so that the amp draw per btuh would be less than for the older units but with perhaps more cooling capacity. I have been retired too long to be enabled to fully compare all the critical data to the above equations.
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Doesn't matter, the units are still 3-ton cooling units. If they were not, they would be rated for such.
Do the manual J, make sure they have all the correct data. If it's different than what you have now, something is not computed right!
~kjpro~

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You heard right. It has to run a lot to properly dehumidify the house. A too big unit won't run enough to do that.
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