Feli,

As I stated in the other thread you started on this subject, you need to address the duct issues. A variable speed furnace is not a magic cure for weak air flow to rooms which are the farthest from the furnace.

If you can get the Carrier Infinity furnace for an additional $2100 ($8800 vs. 6700), then I say go for it. Is the dealer offering the Carrier rebate? It should be $150 for the system you described.

You have been quoted 2.5 and 3 ton condensers. Is this the same contractor? You need to make sure you are getting the correct size. If you do move up to 3 tons then the duct work has to be sized to handle the additional air flow.

If you do get the Carrier 3 ton condenser, then you must get at least a 3 ton coil. The coils you listed are 2 and 2.5 tons. Ask the contractor to review this. He should be able to provide the AHRI number showing an approved match of furnace, coil, and condenser. You can verify this yourself by going to the AHRI directory web site (ahridirectory.org).

Thanks, Mike. The dealer offering option #3 gave us two choices:

- return duct work with vents; 3 ton Carrier Perf. 16 #24ACC624 air conditioner; Carrier 80% efficient furnace #58CVA070-12; Evaporator Coil #CNPV3014; Thermostat #SYSTXCCUIDO1 for $8800 after $150 rebate (16 SEER)

- return duct work with vents; same air conditioner as in option #1; no furnace; no thermostat; Evaporator Coil #CNPV2417 for $6700 after $100 rebate (14 SEER)

Both have same warranty; 1 year labor; 5 year manufacturer's warranty on parts; 10 year manufacturer warranty on compressor.

This is the only bid so far where the company has wanted to do the duct work. The other companies just wanted to sell new equipment.

Do these look like the right coils for these systems? Is the new Carrier Infinity furnace really better than the Trane XB furnace I currently have? Thanks for your help.

The 24ACC624 air conditioner is a 2 ton unit. The correct model number is 24ACC636. Evaporator coil CNPV3014 is a 2.5 ton size. The correct model number is CNPV3617.

Below is the AHRI listing for the 3 ton Carrier condenser, coil, and furnace you are considering:

3656312 Active Systems COMFORT 16 PURON AC CARRIER AIR CONDITIONING 24ACC636A**30 CNPV*3617A** 58CV(A,X)070-12 32800 12.00 15.00 1 RCU-A-CB 255

Are you sure the contractor said he was quoting a 3 ton AC? Either you misunderstood, or he is pulling a fast one on you.

The Trane XB is a basic builder's model single stage furnace. The Carrier Infinity furnace with the controller is superior in comfort and performance.

If the funds are avaialbe, I would consider getting a 95%+ efficiency furnace and a 2-stage AC condenser. You may qualify for additional rebates which will help offset the additional costs.

I recommend getting a 4 inch media filter and the Carrier 10 year labor warranty. Carrier provides a 10 year parts warranty in the equipment is registered within 90 days.

Thanks for the information. Yes, the written quote says "3 ton air conditioner" and then lists #24ACC624". How much more do you think a 95% efficiency furnace and 2 stage AC condenser might cost in the Carrier line? My understanding is the Carrier furnace would be two stage, so you are saying that the AC unit should also be two stage? None of the dealers we have talked to would break down the price of the AC/coil/furnace -- they all give one overall price, but I am curious, would duct work usually be a pretty large component of the total price? And do you think it is a problem that we are only doing the supply, and not the return? Thanks for your help.

You need to get the correct model numbers on your contract. There should be no confusion about this. I would be suspect of a contractor who makes this kind of mistake on a quote.

If you get the Carrier Infinity furnace and controller, then you can upgrade to a 2-stage AC. If you were to upgrade to the 24ANB7 condenser with the same furance, the Carrier rebate would be $1100. Increase in the rebate should offset most of increase cost of the better equipment. The 2-stage condenser is nice if you suffer from high humdity in the summer.

I don't know how much more the 95% furnace will add to the price. I am going to guess in the $1500-2000 range. The reason it gets expensive is the installation becomes more difficult since the venting must be done through the side of the house. You have to determine whether this is even feasible with your set up. The more efficient furnace may qualify you for a local utility rebate. You should investigate this possibility.

Contractors will not break down the prices of the equipment. You may get a separate price quote for the duct work. The contractor should measure both supplies and returns. An undersized return is just as bad as an undersized supply. The furnace can only push out only as much air as it receives.

Thanks, Mike. You were right about the incorrect tonnage. The company said that was a mistake on the quote, and that they planned to install a 2 ton AC system, not 3 ton. Our current system is 2 ton. They said the return ducts are fine, but they will be replacing the old floor duct system with a new supply duct system in the attic using "insulated flex ducts." I am concerned because in several rooms where we currently have two registers in the floor (in front of each window), they are proposing installing only one vent in the ceiling. Does this sound right?

Is the plan now to install the duct work in the attic? One vent may be enough depending on the size of the room. It should not be a big issue adding second vent from the attic. The right way to do this is by a calculation and not guessing.

Is the contractor confident a 2 ton unit will is sufficient for your house? It seems marginal to me. A load calculation is the only way to verify this.

I am thinking of going with the company that has proposed installing the duct work in the attic, plus switch out the equipment. So currently, I have:

2 ton carrier AC unit ('91)
3 ton ADP coil ('06)
80,000 btu trane xp 80 furnace ('07)

The proposal from company #1 that I am thinking of going with is for:

2 ton carrier perfom. 16 #24ACC624
66,000 BTU (80% efficiency) furnace #58CVA070-12
2 1/2 ton coil (#cnpv3014). Cost w/ duct work $8800

I had another company propose to put in a 3 ton carrier system, with a 3 ton coil, and 2 stage variable furnace, 70,000 btu. The cost for this (no duct work) would be $9300.

I am leaning towards going with the company that will provide equipment and duct work for $8800, but I am wondering:

- why am I going from a furnace with 80,000 btu to a furnace with 66,000 btu? Is more btu's better?

- is the use of insulated flex duct and metal splitter boxes standard in attic installations? Are there any downsides or upsides to using this? Durability, noise?

When you talk about calculations, are you talking about a "manual j"? I have asked various companies about Manual Js and have been told that they are like $600, there are too many factors that are unknown like wall insulation, and that a similar calculation was done when the house was constructed ... so I get the sense they are not basing their estimates on such a calculation.

More is not better when it comes to HVAC. An oversized furnace or AC will short cycle. This lowers the overall efficiency and comfort level.

Insulated flex duct is standard in attic installations. I am not the attic duct expert, but I believe people have recommended R8 ducts for attics.

The Manual J calculation is the calcualtion to determine the heating and cooling requirements under worst case design conditions. A company may charge upfront for the service, but then give you a credit if you sign a contract. If your exterior walls have 2X4 construction then the insulation would be in the R11-R13 range. The attic insulation can be determined by inspection. The biggest unknown is the number of air changes per hour. This can either be measured by doing a door blower test, or make an estimate based on how tight the windows and doors look. In any case there is no excuse not to do a load calculation.

Also included in the calculation is number and position of windows (relative to sun), shade trees, ceiling height.

A variable speed blower will do a great job with humidity extraction. It is worth having.

An oversized AC unit will short-cycle and make your house feel clammy.

I have 2 air conditioners from Goodman. They make some great air conditioners. Energy efficient, quiet, remote and neat functions like auto on and off after the room cools down but most of all they are reliable. One of my first purchase out of high school was an air conditioner from Sharp and it has ran the same as it did 8 years ago.

Cant add much but my advise...
-Look out for Goodman air conditioners as they make some of the best
-Bigger is not always better but still at least get a 8,000 BTU as your room cant be that small
-Make sure it has on and off fictions or "energy saver"

Here is a link that might be useful: Goodman Air Conditioner

http://acrightsize.com/files/10_reasons_why_oversizing_persists.pdf