The difference in BTUs comes about because HVAC contractors are too lazy to do a proper load calculation. They use their rules of thumb which leads to different sizes.

You started another thread so please post the size of your house. This will give an indication of sizing. If the current sizes maintained the desired temperatures, and the equipment did not short cycle, then that would indicate the current sizes are good.

You are right that spending thousands of dollars more to gain a few percentage points on efficiency does not make sense. You can decide to spend more money that will make you more comfortable. I personally think a 2-stage variable speed furnace is money well spent. If you live in a high humidity area like I do, then a 2-stage AC condenser is also a good investment. Running on the low stage is a little more efficient, quieter, and more comfortable. It is like deciding on cloth versus leather seats in a car. It is all about additional comfort.

The Carrier Comfort series is a basic furnace at the low end of the Carrier product line. The furnace is not as well built as the Performance and Infinity models. If you are planning to be in this house for another 10 years spend the extra money on a better furnace.

A couple of things

Don't make several different threads. Keep posts all in one thread, much easier for everyone to follow.

Have dealers inspected your ductwork system? You have adequate returns on both floors of your home.

I would go 3 ton on outside condenser whether single stage or two stage.

Am Std is equal to and just as good as Carrier/Bryant.

You will need a filter box cabinet for either system. I would not consider the Carrier Comfort quote, too low end.

Ask AmStd dealer to upgrade you to 3 ton model Gold XI series single stage and Platinum XM 2 stage.

Also you will need a two stage thermostat HW Prestige 2.0. Request from AS dealer.

I don't trust your nat gas rate as being all inclusive. You shouldn't either. But not to worry because I will not recommend a DF system. Stay with high end nat gas furnace with high eff AC condenser.

Post back with updated pricing and if you have further questions.

IMO

Sorry for the confusion I caused with the new thread!

The house is a 2 story colonial - 2,052 square feet plus a partially finished basement.
How could I tell if the equipment was short cycling? I have been pretty comfortable with the exception of the second floor is sometimes hotter than the first floor in the summer- mostly addressed with the attic fan. I would not want to spend a lot of money to fix that. It has been a cool summer and not noticeable this year. That is why at least the one contractor that I asked did not think a two stage AC would be a good idea in this house. And why a 3 ton might be a better idea ��" although Manual J apparently says 2.5 ton (100% of cooling load ��" 26389 Btuh), if I understood what I read.

Tigerdunes ��" what is a DF system (which you said you would not recommend)?

Mike ��" I prefer leather seats in my cars! I was not sure I would actually be any more comfortable for the extra bucks since the rest of the house is from 1986.

What should a contractor do to evaluate the ducts (if anything)? The ducts are not insulated as far as I can tell ��" just sheet metal. The house was built in 1986 with a heat pump system only. I converted to gas in 1996 ��" and I was thrilled to be able to do that.

I calculated the cost of a therm by dividing therms used by total cost of gas on my bill ��" cost $1.28 per therm. I pay $13/month as a gas delivery charge whether I use any gas or not. I use about 560 therms/year (heating and cook top only).

Using the same method, my total cost per kWh is $0.14 and I use about 19,000 kWh/year (everything else ��" hot water and clothes dryer, lights, etc).

Contractor #1 did a Manual J and gave me the written report on software letter head (Wrightsoft Right J Mobile).

Contractor #2 did not give me the Manual J but told me that he did it and it shows a total cooling load on the house using R19 insulation in my attic at 22,744 Btu's and a total cooling load at 21,750 using R30 insulation in the attic ��" which is not the same as the Manual J that I have in writing from Contractor #1??? According to Contractor #2, the Gold XI 2.5 ton A/C total cooling load at 95 degree outside temperature and 75 degree inside temperature is 24,400 Btu's. He said he could come back and take a closer look at the house if I would like. His original proposal has a 2.5 ton AC.

Here is the updated pricing from Contractor #2:

Proposal #1 - Supply and install an American Standard Gold ZM-80,000 Btu’s, 97% AFUE efficiency gas furnace and an American Standard Gold XI- 16 SEER 3 ton AC unit:

AC AS 4A7A6036H1, single stage AC
Furnace AS AUH2B080A9V3, 2 stage variable speed
Coil AS 4TXCB036BC3 cooling coil.
Thermostat AS digital programmable thermostat.

Net cost to me $6,475.00

Proposal #2 - Supply and install an American Standard Platinum ZV-80,000 Btu’s, 96.7% AFUE efficiency gas furnace and an American Standard Platinum ZM- 16.25 SEER 3 AC unit:

AC AS 4A7A7036A1- 2 stage
Furnace AS AUHM1B080ACV3 ��" 2 stage variable speed
Coil AS model 4TNCB036AC3 cooling coil
Thermostat Honeywell Prestige 2.0 digital programmable

Net cost to me: $7,925.00

Contractor #3 did not do a Manual J. I asked him for a price for the same Carrier equipment as Contractor #1 anyway. He said he was not able to do that because he did not inspect the work for an Infinity system. He would need to come back and look at the job to provide a price for the Infinity systems. That makes no sense to me because how could he give me a price on this system which was in his original proposal that contained the $4300 system? I had not included this option in my original post because it seemed like not a lot of bang for the extra bucks.

AC Carrier Infinity 21 series two-stage 24ANB136A003 with a 3.0 ton cooling capacity
Furnace Carrier Infinity 98 modulating gas furnace 59MN7080V17-14
Coil Carrier Infinity all aluminum N series vertical evaporator coil with an insulated jacket CNVP3717ALA with a 3.5 ton cooling capacity
Thermostat Carrier Infinity touch series WiFi SYSTXCCITNO1A
Mechanical Air Cleaner: model #:EZXCABCC1020
Power fan humidifier model #: HUMCCSFP1016

Net cost to me after rebates and discounts: $8,465.00

So one stage or 2 stage AC? 2.5 or 3 ton unit?

Carrier or American Standard?

Contractor 1 (5 year labor warranty through him), Contractor 2 (I think the 2 stage AC option might not be a good idea - 2 year labor ��" not sure if that is AS or him), or Contractor 3?

What do you think of the Carrier 10 year labor warranty through Carrier?

And thanks for your input! There were fewer choices 18 years ago. I am glad I am not sitting here with no heat doing this.

I like AmStd just as good as Carrier.

If you have confidence in the load calc for cooling, go 2 1/2 ton single stage, 3 ton for two stage AC condenser.

On AmStd, quote #1 will require two stage thermostat like the HW Prestige 2.0 I recommended.

For quote #2, it should be same furnace as quoted in quote #1, not the furnace dealer quoted. Ask for price to reviewed and updated. Cooling evap coils need to be reviewed by dealer for best application and best performance/ efficiency numbers in AC cooling.

All systems whether Carrier or AmStd will require a filter media cabinet.

DF stands for dual fuel, furnace with HP and I don't recommend.

I will be unavailable for any comments for around 6-7 days minimum.

Hope this helps.

Good Luck
IMO

Short cycling is when the equipment go on and off for brief periods of time.

"I calculated the cost of a therm by dividing therms used by total cost of gas on my bill ��" cost $1.28 per therm. I pay $13/month as a gas delivery charge whether I use any gas or not. I use about 560 therms/year (heating and cook top only)."

You service charge comes out to about $.28 per therm. You are actually paying about $1 for each therm which is what I would expect. You should switch over to a gas hot water heater. The pay back would be fairly quick with a conventional tank.

"Contractor #2 did not give me the Manual J but told me that he did it and it shows a total cooling load on the house using R19 insulation in my attic at 22,744 Btu's and a total cooling load at 21,750 using R30 insulation in the attic"

That is an interesting calculation. Upgrading to R30 only saves 1000 BTUs of heat gain.

If Contractor #2 calculated a 2 ton cooling load, why is he proposing a 3 ton AC condenser?

"Contractor #3 did not do a Manual J. I asked him for a price for the same Carrier equipment as Contractor #1 anyway. He said he was not able to do that because he did not inspect the work for an Infinity system."

I don't understand this statement. Infinity systems need properly sized duct work the same as all other Carrier equipment.

I am always suspect of contractors who say a 2-stage AC might not work well in your house. I would like to understand the physics behind this.

Carrier is not longer offering 10 year labor warranties. You have to get it from a third party. It is a good investment providing it is reasonably priced.

Here is the updated quote from the American Standard contractor:

Supply and install an American Standard Platinum ZV-80,000 Btu’s, 96.7% A.F.U.E efficiency gas furnace and an American Standard Platinum ZM- 16.25 S.E.E.R 3 ton air conditioning unit for your home.
1- American Standard model AUHMB080ACV3 ��" 2 stage variable speed gas furnace.
1- American Standard model 4A7A7036A1- 2 stage air conditioning unit.
1- American Standard model 4NCB036AC3 cooling coil.
1- Honeywell Prestige 2.0 digit programmable thermostat.
1- Copper Line set.
1- Composite pad.

Net cost to me: $7925.

Other than the 2 stage AC, is this apples to apples with the Carrier bid? Is the Carrier equipment a reasonable price for the equipment? Anything else I should consider?

It is getting chilly so I better make a decision.

Thanks.

Before I take the time to give you any detailed analysis, you should know the Carrier and AmStd quotes while similar are not apples to apples particularly the furnaces.

The Carrier is a two stage high eff model while the AmStd is a high eff modulating model. These modulating models allow for better comfort in small increments between a 40-100% range of BTU output. And if interested, AS dealer did not quote the proprietary thermostat control for full functionality of this furnace. If you are looking for a closer AS equivalent to the Carrier furnace, that would be the Gold ZM(identical to Trane's XV95 furnace).

So you need to advise back the direction you are leaning toward.

IMO

This post was edited by tigerdunes on Fri, Sep 19, 14 at 16:01