So, everyone states that you need a ton more cooling & one says 2-Ton more or a Five ton.

Did each one tell what you existing blower & ductwork would support? If so, how did they make their determination(s)?

No one did a manual J heat-gain calc, or offered a 3.5-Ton system with the ductwork & blower matched to its' requirement? Have a manual J calc done!

Well, you could consider going say 50 - 50 between those systems tonnage ratings & the actual Btuh rating of the compressors. Also go by the EER Rating of the equipment rather than the 82-F SEER Rating.

There could be a lot of reasons why the 3-Ton was not pulling the sensible temperature down, to say 75 or 76-F.

There is a lot you can do to reduce the air infiltration, the solar radiant heat load, etc., so a 3 or 3.5-Ton would do the job without installing larger ductwork.
udarrell _ 2007

Here is a link that might be useful: udarrell.com

udarrell - the 2nd service guy said I would be getting a new AC unit outside, and a new attic system (not ducts, because the 4T unit could use the same ducts). I am leaning towards the 4T 21 SEER infinity system, but still would like more feedback.

No one did a manual J, just walked the house, took measurements in the house and in the attic. The house is definately hot, as it was 100 hear, and all the rooms upstairs were 80+ degrees.

All of them agreed that the 3T unit was way undersized for the amount of space and cooling requirements (74-75).

21 SEER is BS. SEER ratings are determined at 82 degrees outside air temp. These ratings will drop like a rock at Texas summer temps of +100. EER (Energy Efficiency Ratio) is taken at outside air temps of 95F which is more in line with real world temps. This is why Darrell told you to check EER and not SEER. 21 SEER uses a dual speed, or variable speed, compressor which can run on low when outside temps are not that high. You need a unit that can crank out the cool air to beat the Texas heat.

How well-insulated is the attic in your home? Adding more insulation, sealing up ductwork leaks, and reducing air infiltration makes a huge difference in cooling requirements with 100 degree outside air temps.

Best of luck.

There is a post now on HVAC-Talk.com titled "Summertime in Texas". Talks about adding a radiant heat barrier in the attic to reduce the cooling requirement. Check it out.

It is 100+ degrees here in La. also.
Hot & Humid!

You may not know that hvac is designed to lower temp
20 degrees, so on a 100 degree day...indoor is 80 degrees,
This is all the system can achive.

Oversizing your system is a problem..short cycling, high relative humidity, less comfort and shortened life cycly of system, Bigger is not better.

Invest in a stand alone dehumidifier (about $200 @ lowes/hd) You would be suprised at the comfort it provides.

Radiant barriers are a benefit in our climate.
Florida Solar Energy Center has excellent info, and they
are info only. Don't sell products.

Sealing ductwork with mastics, adding insulation after sealing penetrations ...all these things are necessary.

It is only going to get hotter & is worth the investment.
Have your home tested (blower door test) to isolate these
leakage sites. There are several energy raters in Texas.

Best of luck, and it is HOT here also!!

"You may not know that hvac is designed to lower temp
20 degrees, so on a 100 degree day...indoor is 80 degrees,
This is all the system can achive.

Sorry, have to disagree with you on that one......I don't know to many people who would be comfortable with 80 degrees inside at 100 degrees outside, myself included. If that were true, people living in arizona w/ 110 degrees outside would only have 90 degrees inside....by your numbers...

I agree with Jeff. Maybe he's confusing the 20 degree difference in outside/inside temps with the 20 degree "split" temp which is the difference in the temp of the air just before the evap coil minus the temp of the air just after the evap coil. 20 degree split temperature is indeed accurate for a good system on a low humidity day.

Two weeks ago had a 105 degree day in Baltimore with 50% humidity. Most of the other days in the week were mid 90's with high humidity. On the 105 degree day, the new 14 SEER Goodman heat pump ran for 8 hours and 40 minutes and kept the house at the 75 degree setpoint easily. On the other mid-90's days, the unit ran for about 6.5 hours and kept the house at the 74 degree setpoint. If my unit ran non-stop like I read in some posts, my house would be a meat locker.

It's all about system sizing, condition of the a/c unit, ductwork, house size and type, and insulation.

I have to vent for a moment. I am so tired of hearing that you must not (under any circumstances) oversize. The humidity issue and short cycling... Well, isn't humidity only a problem when you oversize and your unit short cycles? Seems the easy solution for that horrible dilemma is to simply set your Tstat lower so you do not short cycle. I know that is a politically incorrect assertion. I hate to burst the bubble of so many out there who adopt the 20 degree rule, but if I want to have 5 tons for 1,500 square feet with huge ducts and more than enough supply and return registers, why is that the end of the world? Why can't you decide on the tonnage, insulation... first (if you want to get to 65 degrees on a 110 degree day), then build your duct work around that? I know that is an ignorant question, and is probably unreasonable, but I am willing to take the heat. I would rather have a $400 electric bill at 74 dergees than be sweating at 80 degrees for 200$. No offense. I value all responses.

Garyg is on target, high SEER is no solution to extra hot climates & especially in high hot humidity zones.

Additionally, your initial upfront costs will be above most budgets, all but eliminating any payback over the life of the units. (I could be much tougher on 18to 23-seer systems, but will hold off.)

Man - garyg, those New model 14-seer Goodman's just proved to you & me that they can perform, huh! Never listen to the nay sayers' when it comes to other AC brands that they don't sell.
----
If you want efficient performance:

I am first & foremost, for reducing all sources of the heat-gain rate to every extent possible!

I like the longer cycles with excellent design engineered airflow distribution at the terminal level of the occupants, say between 50 & 75-fpm.

Other low cost means should be used to keep the air moving at those velocities, at the occupant area & level, while the AC unit is between cycles!

"That will maintain the 'Human Comfort Level' at little cost to the consumer user."

In respect to a room TH, first I want "a temp differential more than one degree & no cooling anticipator."

If you want higher SEER you need 2 to 3 degrees or more differential with a low percent Relative Humidity, at 50% RH you should always have a Human Comfort Zone of from 78-F down to 75 or even 74-F.

"The Human Comfort Chart" shows an even wider spread - see link.

This temperature differential TH will allow even a somewhat oversized system to have long enough run cycles to get the humidity down.

With the new reduced heat-gain the unit will be off longer, & this combination will lower the electric bills & raising the SEER level.

Remember, they used to think it was necessary to keep the temp within one degree using a cooling anticipator TH combo.

Most of the 6 & 8 SEER units were over-sized & the ductwork & air distribution was not up to standards.

We should always level with the user consumer & provide them with the choice of savings or a one degree differential with poor air distribution & ductrwork shortcomings.

Therefore, when installing the new high SEER units if we want efficiency of performance, we all need to do considerable Retro work on the Air Side of Air Conditioning.

I have NO quarrel with eths, or anyone wanting something else, - after they have heard (our points), that is their call . udarrell _ 2007

Here is a link that might be useful: udarrell.com

"Man - garyg, those New model 14-seer Goodman's just proved to you & me that they can perform, huh! Never listen to the nay sayers' when it comes to other AC brands that they don't sell."

Darrell - thanx for the kind words. I spent a lot of time researching the 14 SEER Goodman with scroll and TXV. At an installed cost of $3500, I think I did very well. If it lasts 10 to 15 years, I'll re-post and give myself a pat on the back.

I firmly belive in the last line of my last post: "It's all about system sizing, condition of the a/c unit, ductwork, house size and type, and insulation."

Take care.

Well folks, after 6 contracts, the winner looks to be the 21 SEER, 15EER 4T infinity system. 2 of the contracts actually said I was getting a GREAT price on the system (8700 installed) that they would recommend getting that.

Everyone agreed my insulation, duct work, and vents were in order, just my 3T unit could not do the job in Texas. The only debate was either a 4T or a 5T. I have not gotten a price from the guy for the 5T. I am contacting him in the AM.

On a seperate note - what do people do with the systems they deinstall? I have a perfectly working (just undersized) 3T TRANE unit now. Do I sell it? does my a/c guy just take it?

any ideas?

Keep it and sell it or your heating contractor will.

Quote: Well folks, after 6 contracts, the winner looks to be the 21 SEER, 15EER 4T infinity system. Two (2) of the contracts actually said I was getting a GREAT price on the system (8700 installed) that they would recommend getting that.

Everyone agreed my insulation, duct work, and vents were in order, just my 3T unit could not do the job in Texas. The only debate was either a 4-T or a 5-T. I have not gotten a price from the guy for the 5-T. I am contacting him in the AM.

On a seperate note - what do people do with the systems they deinstall? I have a perfectly working (just undersized) 3T TRANE unit now. Do I sell it? does my a/c guy just take it? Any ideas?
===============================
I would NOT take their word for the duct sizing!
If they talk you into 4 or 5-Ton I am betting you will need an entire new duct system.

Even if the ductwork, filter rack(s), diffuser, etc., handled 3-Ton it will NOT handle 4 or 5-Ton!

The linked page below is for Heat Pump duct sizing or 450-cfm per ton. I prefer that sizing over 400-cfm per ton as ou never know when you will install a Heat Pump system.

Measure the ducts & the filter rack(s), also get the flow rate of the diffusers!

The entire system has to be perfect for a high 21-SEER to deliver its rated Btuh & 15-EER. udarrell _ 2007

Here is a link that might be useful: udarrell.com

"On a separate note - what do people do with the systems they deinstall? I have a perfectly working (just undersized) 3T TRANE unit now. Do I sell it? does my a/c guy just take it?"

Tx Heat

I agree with UDarrell about the ductwork. The Infinity is a high end system that does not tolerate an undersized ductwork system.

What is your electric rate? Is this an AC or heat pump system? Why not a HP system?

As far as old unit, I would give it to a church or perhaps Habitat for Humanity and take a tax deduction.

IMO

Dude..what is all the debate for? Your choice is real easy. Get the Carrier Infinity 17 SEER system, 4 ton and get an attic ventilator (powered) which will drastically reduce the heat load on your living space on the second story. Add about 6 inches of insulation in your second story attic. By doing the above you will: (1) save a few bucks by not getting the Infinity 21 (which isn't really 21 SEER anyway except for one model with a matched coil 2 ton if you look at the ratings on the Carrier site) (2) Qualify for a FEDERAL TAX CREDIT for adding insulation and ANOTHER federal tax credit for purchasing a high efficiency HVAC system with an "advanced fan" (ECM blower) Also Carrier has a rebate through select dealers right now and/or your utility company may have incentives too! (3) You will be getting a positively superb, "best money can buy" system with 4 tons of cooling for the really hot days, 2 tons for milder days (4) Unmatched humidity control. This unit has no less than 42 patents on it. I installed the Infinity system myself w/ air cleaner, uv lights, and infinity furnace in a house that I sold and I think this system was the best product I ever owned.

Also, as an aside here unrelated to your air conditioning woes---did you know you could couple that Infinity unit or your other air conditioning unit to a desuperheater which will heat all the hot water you could use for free? (check out trevor-martin.com)--Also, you would effectively raise your SEER rating to about 20-23 and literally turn off your hot water heater because that Infinity unit (or your other condensing unit) can use waste heat which would normally be expelled into the air to heat 80 or more gallons of hot water per day? This unit would cost about $700-$1000 installed (perhaps more if you have a long run to your water heater). As long as that upstairs AC is running, you would be producing free hot water, increasing the efficiency and life of your condensing unit, reducing the head pressure on your compressor, AND lowering your electric bill in the process. For six months a year you could literally turn your water heater off! This unit would pay for itself in energy savings rather quickly. (I would be willing to bet you are running the AC upstairs in the spring and fall too at times bc I am sure it is hot up there even when it isn't hot outside) However, you may find that this desuperheater would be better to add to your other condensing unit with R-22 refrigerant which has much higher discharge temperatures (produces more hot water). The 410-A systems have higher pressure but lower discharge temperatures. If you do get a desuperheater and add it to your new Infinity system--make sure you get the unit which is rated for 410-a (Trevor Martin makes such a unit specifically designed for 410-a/Puron). Ask a knowledgeable contractor. He or she can tell you what is right for your specific situation.

bottom line--Your outlay for desuperheater and new infinity system, insulation and power vent==$11,000.00

Tax credits and rebates may reduce your "net cost" to $9500. Benefit gained--free hot water 6 months or more per year AND 72 degree second story with 50% relative humidity with 100 degree outdoor temp!

A typical increase in efficiency of your a/c system with desuperheater installed and running is 10-15%.

You can expect an energy cost savings over your present equipment by about 1/3 or so (without factoring in the desuperheater)

Typical cost to add that much insulation to your attic--50-60 cents per square foot.

Typical cost for a power attic ventilator (installed) $250-$400.

You can insulate your attic yourself with a free rental of the blower from any Home Depot store. All you have to do is leave a refundable $500 deposit via cash or credit card. Present cost for the insulation itself is about $9.00 for every 40 square feet. You would need about 50 bags which would cost about $425-$450. Or you can have a contractor do it for about $900.00 +/-

The other thing you MAY want to consider is getting a geothermal heat pump system. It would cost about $12,000 installed but it would have a built-in desuperheater which could heat your hot water for you year round. Carrier makes such a unit that uses puron refrigerant with a two speed compressor that can have SEER ratings of up to 31 in some cases. Typical installation is a little slower but it can generally be accomplished in 1-3 days. Hope this helps and good luck!

Holy cow man. I am just re-reading you post. Your house is only six months old? No sane contractor is going to tell you this when they stand to gain $2500 in profit-- but why not try a powered attic ventilator first for a $400 investment. (get a good one--not the budget model) Then if that isn't enough add insulation and/or a radiant barrier. On a 100 degree day, your attic is a good 130-150 degrees without a power vent. Ridge vent isn't enough, believe me. You could still get a tax credit for adding the insulation if the power vent wasn't enough. Why lay out all that cash when you can just reduce the heat load and accomplish the same purpose? Do you have some shades on your windows?

I have a hard time believing that 3 tons isn't enough in a new house for 1895 square feet unless you have (1) an overheated attic, (2) too much radiant heat gain or inadequate insulation. Insulation, radiant barrier and power vent is my prescription. I would almost be willing to wager $500 on you having a 76 degree 2nd story on a 100 degree day if you put in a power attic vent, add insulation and/or a radiant barrier. You don't need 4 tons of cooling in 1895 square feet of space unless your ductwork is not connected or you have an overheated attic or insulation that is inadequate.

My home is 5500 square feet. 1794 square feet on the second story. R-30 insulation in the attic, R-19 in the walls. I have a 2.5 ton unit for that second story. Before I installed the power vent--I had the same problem you did. We had 103 last week here in DC/Northern VA and my second story was a cool 74 degrees. Before I installed the power vent it was a sweltering 78-80. I have two units-a 3 ton for the basement and first floor and a 2.5 ton for the second story---total of 5 1/2 tons of cooling. Of course, there is almost no heat load for the finished basement so 3 tons is enough to cool over 3000 square feet of space (for the 1st floor and basement)

You could add a desuperheater to that unit as I mentioned in my other post and you would increase the capacity of the unit by 10-15%. Hope this helps. Ken

As I mentioned in another thread...4 tons would barely be adequate here...especially for upstairs. I believe his contractors...and would listen to them carefully.

According to ARI, my system isnt really 21 SEER, it is 16 SEER, so how can they get away with marketing it as 21SEER?

ARI # 1076821

As I stated in a few posts above:
"21 SEER is BS".

Your true operating costs are based on the Energy Efficiency Ratio (EER). Many high-SEER systems don't match the 12 EER of a 14 SEER system.

"so how can they get away with marketing it as 21SEER?"
- They lie. Buyer beware.