It all boils down to cost. 2 stage is better in every way, it just costs more. Run away from anyone who recommends a single stage system because "the 2 stage systems are unreliable, can't get parts, etc, etc".

Air conditioning systems need to deliver occupant comfort. In Phoenix, AZ, relative humidity averages less than 50% in each month of the year. Accordingly, the task for an air conditioning system is lowering the temperature (sensible heat load) and not so much the relative humidity (latent heat load.) A single-stage system would be well suited for the purpose. That said, a multi-stage system will produce a more consistent comfort level and will reduce wear and tear on the compressor when air conditioning loads are less than peak loads.

Phoenix is a desert. The primary 2 reasons 2 speed AC's exist is better dehumidification function. The secondary reason is efficiency.

Because humidity is the least of your concerns in Phoenix, a 2 speed AC would be over kill in my opinion for Phoenix. The part supply problem is a problem that effects all brands to various degrees. It is more common for a two speed AC unit to be controlled by a control board.

The control boards are mostly made in China or Mexico none are made in USA any longer. So as you can imagine every brand is effected by this and the problem goes far deeper than control boards. Sometimes certain types of motors etc.

Choosing a single speed unit, regardless of brand you "could" be faced with the same problem.

What are the odds you will need a control board? They don't fail that often, but I did run a call just yesterday in which the control board to the two speed AC is beginning to fail. That part is not available (Amana unit)

The wait currently could be 2 weeks to a month or longer. *no promises made to when the part you need will show up. Why? these are factory and supply chain problems that span the globe.

Assembled in USA? what does that mean... the parts were shipped in and workers assembled a mostly foreign made unit here in USA.

----------- two speed or not for Phoenix ----------

I think this decision is more for adequate cooling for all year. In some periods of the year running in 1st speed will be all you need. The efficiency might pay for itself if the cost difference between single / 2 speed units are close in cost. Depending on utility rates and other factors this might take a decade or more to recoup the cost.

The refrigerant any unit uses this year is right at the cusp to begin phase out. Depending on a variety of issues concerning R410a phase out, the China / Mexico part availability syndrome may be referred to as a pic-a-nic.

So the argument to choose or not choose is far more confounding right now than you can possibly imagine. That's my opinion and I live it everyday.

I have a 4 part mini series going on my You Tube Channel that explains the coming R410a phase out. Each part is roughly 30 min long. The fun begins in 2024, maybe sooner than that if new equipment with new refrigerants make it thru this supply chain hoopla.

I'm sure I'll add to this mini series in the coming months / year or so as things develop.

Contrary to popular myth, refrigerant is not covered by any manufacturer warranty. They consider it a consumable, even though the system is a sealed system.

"I have a 4 part mini series going on my You Tube Channel that explains the coming R410a phase out."

The series needs to come with a warning to anyone who invests two hours to watch it. At the end of the series you will know as much as the narrator knows about the subject, but you will have lost a fair number of IQ points in the process.

Everyone has an opinion Charles. If you disagree with mine, I am fine with that.

Some people only want to be told what they want to hear.

If that's you and your opinion, you won't like what I have to say and I am perfectly fine with that.

As always your mileage will vary.

Given this house is located in Phoenix, there is a high probably the condenser is at least 4 tons, and likely to be 4.5 or 5 tons. A single stage 5 ton system means every time the unit turns on you are getting about 2000 CFM of air flow cycling on off every time. That is a lot of air flowing through duct work which is probably under sized. If the duct work is under sized a 5 ton condenser may only have 4 toons of cooling performance. The large amount of air flow happens at night and during the cooler parts of the year when you don't need as much cooling.

With a 2-stage AC, the low stage can cycle on and off to maintain the temperature. It is quieter and you don't get the blast of air. The cycle times are usually longer which improves efficiency and reduces operating costs. I think the extra comfort is worth the extra cost.

I have a two-stage packaged heat pump. I really like it because I could set the stage one blower speed lower than that of stage two. That made the system nearly inaudible when operating in stage one which is nearly all of the time. My unit is Heil, an ICP brand most of whose units are nearly identical to Bryant and Carrier units but are less expensive. Be sure to shop around; installers' prices for these products vary dramatically in my experience.

"The primary 2 reasons 2 speed AC's exist is better dehumidification function. The secondary reason is efficiency."

Two stage systems are not more efficient than single stage systems.

Hi all! Thank you so much for your responses. So the price difference is 2500 dollars between a single stage and a two stage lennox unit. With that being said, I am gathering that a two stage unit is better then a 1 stage unit but a 1 stage unit would do the job? Does a 2 stage unit tend to last longer? Does the 2 stage unit also leave some humidity in the house?

Hector, I live in a near by state, hot and dry. We have 3 large Trane a/c units, the upstairs one is 2 stage (others are variable). I would never go back to 1 stage! The quietness, you barely notice that it's on, cools down a large addition very well! (we didn't really need the 3rd one but wanted a separate control for the bedrooms only).

I am gathering that a two stage unit is better then a 1 stage unit but a 1 stage unit would do the job?

Yes a properly sized and installed single stage AC will keep the house cool. The typical indoor design temperature is 75 F degrees.

Does a 2 stage unit tend to last longer?

The 2-stage should have less on and off cycles. This helps reduce wear and tear, and it may last longer. No real data on this. It will cost more to repair.

Does the 2 stage unit also leave some humidity in the house?

The 2-stage AC does a better job of reducing humidity if it is properly sized.

Two stage systems are not more efficient than single stage systems.

This one is up for debate. The AC uses more energy on start up until it reaches steady state operating conditions. So the longer less frequent cycles of a 2-stage AC should be more energy efficient. The other thing to remember SEER testing of 2-stage systems is done in the low stage. The SEER ratings come out higher. So they appear to be more efficient under lab testing conditions.

Two stage systems are not more efficient than single stage systems.

Current entry level AC systems are 14 SEER in the south. 13 SEER in the north.

There isn't a manufacturer that I know of that makes a 14 SEER or 13 SEER ----- 2 speed AC unit *currently as you can buy it now* so you realize I am not saying 15 years ago. Because there were 2 stage units at 14 SEER ----20 or so years ago. LOL.

The higher the SEER the "more likely" it is a 2 speed unit. Entry level SEER ratings are going up. There will still be single speed AC's once the new ratings take shape next year.

The work of the compressor determines a good part of efficiency. Certainly there are other things beside that. If the compressor is only working at 70% it burns less energy than a single speed at 100%.

SKTN77a, If you can find a modern day 13 or 14 SEER rated unit that is a 2 speed please post your info. I'd be more than happy to admit I am wrong. (I'm talking about a model that is *advertised* as being 13 or 14 SEER, not one that hits those numbers due to configuration issues.)

If your argument is over the SEER rating itself? Let it be known.

If you look at any manufacturer website product listing you will see all 2 speed condensers at the top end, just below Inverter tier group. Even Goodman has an Inverter AC now.

Inverter efficiency is geared again toward the work the compressor is doing. Less work, better efficiency.

For those who may not understand efficiency:

If the compressor + cond fan pulls 15 amps while running in 2nd stage, but pulls 10 amps in 1st stage and first stage runs 90% of the time. That means 10% of the time it pulls 15 amps.

If a single speed compressor + cond fan pulls 15 amps all the time that will cost more to operate = less efficient. It must do 100% of the work every time it runs. In cooler periods you likely don't need 100% of the work.

However, this is only 1 thing that determines how well your efficiency will be. It makes little sense to concentrate on this one thing (power consumption) and then do nothing else like duct work, insulation, proper line set sizing, proper refrigerant charge etc.

------- The realm above 2 speed AC is Inverter ------

Modulation of the compressor can save up to 50% of the energy costs (consumption of energy) compared to that of a 14 SEER single speed unit. (current minimum efficiency in the south)

It wouldn't work any different for a desert type installation. The one benefit an Inverter would have in this desert type situation is the additional capacity boost of 30% when it gets really hot there. Due to the lack or need of dehumidification for the desert it would need to be "configured" for that climate.

There's more than one algorithm to accomplish that. Because of that it's another advantage for the Inverter going forward.

------------- To the OP --------

So the price difference is 2500 dollars between a single stage and a two stage lennox unit. With that being said, I am gathering that a two stage unit is better then a 1 stage unit but a 1 stage unit would do the job? Does a 2 stage unit tend to last longer? Does the 2 stage unit also leave some humidity in the house?

For a desert climate the 2 stage is more about efficiency or cost to operate it.

What is your utility rate per KWH?

$2500 more isn't too bad, but it might take you a decade or more to recoup that.

What is the efficiency of the single speed you are comparing the 2 speed against? What is the equipment size in tons? If you are comparing a low 2 speed offering against a higher single speed offering -- the single speed would be better. (The answer is it DEPENDS we need more info)

Because this only about efficiency and Inverter is even better in that regard / if you plan to stay at this house for 15 years or more? A comparison of that cost wouldn't be out of the question in my opinion.

Air conditioners last approx. 15 years national average. Hotter climates / maintenance issues / who works on the equipment / can all have an influence on how long or short a unit may last.

It doesn't matter if it's single speed or two speed, they all break.

I just ran a call yesterday from an R22 condenser I installed for a customer back in 2010. I haven't been to their house since 2014 for a maintenance check. The thing has run for 8 years without so much as a blip. You know what she told me?

I have never let any one near this unit, except you. I can tell you though in all honesty it rarely works out like this all the time. Some homes are nothing but trouble, trouble, trouble. So this is just an odd ball 'ac service' example story of mine.

"If the compressor is only working at 70% it burns less energy than a single speed at 100%."

This statement, while true, needs some clarification. A compressor operating at 70% is operating at reduced capacity compared with one operating at 100% capacity. So while its drawing less current, it's also producing a lower cooling rate than the single-stage unit. So it needs to operate longer to meet the cooling load. The way a multi-stage or variable speed compressor reduces energy consumed is by reducing the number of start/stop cycles compared with a single-stage compressor (starting current requirements are greater than running current requirements.)

All true Charles. Desert application has it's own set of problems. It's normally arid and dry so dehumidification which is often used as a selling benefit for 2 speed and inverter systems in other climates might be at a detriment for an arid climate.

The inverter has additional algorithm to aleviate some of those concerns. A two speed doesn't really offer any benefit other than potential lower electrical usage.

I'm estimating a pay off of around 17 years for a 4 ton 14 SEER vs 16 SEER two speed at 15 cents per kwh at 75 degrees inside for my climate which doesn't get quite near as hot-hot the heat way more in the form of humidity.

If the OP chimes back in provides more info, it may become more clear. I have no experience in the desert.

If the efficiency of the systems compared is the same 16 SEER single speed vs 16 SEER 2 speed then the single speed wins the day. We need more info.

If you could get an inverter for marginally more than the 2 speed, that could be the better buy. Provided you live there for 15 years or more and depending on what your utility rate is.

Hi all!! Thank you so much for taking time out to respond to my post. Wow! I appreciate it. So the two stage unit would be 16 seer 3 tons and the same would be for thr single stage unit. I did have another company come out yesturday and thet advised against a two stage unit. He said in our climate which is easily 100-115 degrees in the summer with low humidity puts a lot of strain on the unit. He mentioned something about the coolant being split between to pipes and trying to operate when it's 110 outside would add strain. He also said if I don't choose him, who ever I go with, he would still not recommend a two stage unit.

In regards to rate Per kilowatt, I am not sure how to find that, but my most expensive bill is 220 dollars for the month keeping the house at 73.

I am sort of leaning towards a single stage unit now.

My other dilemma which u can post in a new post is what contractor to choose. Both have great reviews. The first option would be a lennox merit 16 seer 3 ton or a trane xr16 16 seer 3.5 ton unit for less with an authorized trane dealer. My question and I can add a new post for this would be to go 3.5 tons or 3 tons. The lennox dealer is recommending against a 3.5 ton unit. The trane authorized dealer is recommending a 3.5 ton unit. My home is 1310 square feet , south exposure, the garage is on the west side along with two windows to the kitchen which get blocked a bit by the neighbor. Neither did any formal test, just a math calculation.