The big benefit of 2-stage equipment is comfort with some small energy savings. The 2-stage will be quieter and run longer on the low stage. The low stage operation will help reduce the humidity level. When the humidity lower, you may be able to set the thermostat a degree or two higher and still feel comfortable. This results in some energy savings. The reduced amount of cycling also has some energy savings benefit and less wear and tear on the equipment.

I don't understand the logic why a house with leaky windows and below standard insulation won't benefit from a 2-stage AC. The most important thing is to install a true 2-stage thermostat. The thermostat will start the AC in the low stage, then go to the high stage if needed, and then finish the cycle in the low stage as the set temperature is reached.

Thanks for the reply, Mike! What he told me with regards to the 2-stage AC was that his concern would be that during the hotter periods it would run constantly at the low setting without ever reaching the target temperature (due to old house/windows inefficiency ). Sounds like your'e saying that with the proper thermostat, this wouldn't be a concern as the high stage would eventually kick in if that were occurring?

As far as the thermostat goes, I'm guessing my current ecobee3 isn't a "true" 2-stage thermostat even though they say it supports two stages?

Were the models of condenser/coil/furnace recommended with his single-stage quote a "good" solution? If so, what would be the 2-stage equivalent models I should be looking at?

Thanks again!

I have read good things about Ecobee thermostats. I would have to see the spec on the Ecobee3 to see if can control a 2 stage AC. You have to decide whether you want to spend the money on the wifi feature.

"his concern would be that during the hotter periods it would run constantly at the low setting without ever reaching the target temperature"

I get a little concerned when an HVAC contractor makes statements like this. What should happen is the thermostat reads to temperature in the room and compares it with the temperature setting. The AC will usually start in the low stage and then move up to the high stage depending on the temperature difference and how long it has been in the low stage. It should not stay in the low stage for long periods of time if it can't reach the temperature setting. The staging should be done by the thermostat and not the furnace.

I am not an expert on Trane equipment. I believe the XR16 condenser is middle of the lineup. The furnace is an 80% efficiency model. You should consider a 90%+ efficiency model that may qualify for a local utility rebate. Hopefully some Trane experts can give you better guidance.

Has anyone done a load calculation? The outside winter design temperature for the Houston airport is 31 degrees. I question whether you need a 100K BTU furnace. The summer design temperature is 94 degrees which is not that much hotter than what I have in NJ. The 5 ton AC is probably over sized. An over sized AC does not do a good job of humidity removal.

See if you can find a contractor who will do a load calculation. It should be done as part of the quote.

Ameristar isn't made in China. It is made on the same assembly lines as Trane and Am Std in NJ and Texas. It is just a stripped down version of those units with different sales and marketing channels that is targeted at the low-end of the market. If it had been made in China then their furnaces wouldn't be 40" tall still.

You should NOT consider a condensing furnace because you will have to install new combustion air supply and exhaust ventilating and add condensate drain lines.

With your house as you describe it I would recommend a low end system too. Your heat loss will be so high that your system may just run non-stop. If you are planning to make energy efficiency upgrades, then a higher end 2-stage system would definitely be worth it. You are doing yourself a disservice by dumping money into the central unit instead of adding insulation, sealing up ducts, and changing to windows with a higher insulation value. If you take those steps then you will be able to cut down your utility cost, and may even be able to cut down your heating and cooling load to drop you into a smaller input system.

@mike_home: Thanks again for the reply! Both companies that came out when I brought up sizing the system made the same comment of "well, 5 ton is the biggest you can get residentially, so you should stick with that". I hadn't thought of the fact that we were potentially over-sized to begin with, so something I'll follow up on. I'll also be following up with the 80 v 90% furnace options.

Looking at the documentation of the ecobee that I already have, it seems like it should be able to handle a 2-stage system:

Robust Staging Options: ecobee smart thermostats can control up to 2 stages of heating and two stages of cooling (depending on the type of your HVAC equipment). Your thermostat starts by engaging the lowest stage of heating or cooling, and automatically upstages and downstages as needed. A higher stage is only engaged when the current indoor temperature is significantly different than the desired temperature and using a lower stage would not get your home to the desired temperature within the given window of time (i.e. before 5 PM from the previous example). The thermostat automatically switches back to a lower stage as your home gets closer to the desired temperature.

@capedude: I appreciate the reply! I don't want to paint the picture that my house is super inefficient. While our windows are old, our older (now failing) system did not run constantly during the hot summers, cutting on/off at a relatively good clip. I would imagine a more efficient system would do better. Also, we plan on living in this house for 10+ years, adding new windows along the way. I wouldn't want to purchase a lesser quality system knowing that we'll be improving the house along the way in these other areas.

Also, I don't want to brand-bash with regards to Ameristar. I only know what I've read and what some others have stated. Everything I've read is that with the exception of their furnaces, all Ameristar products are made in China:

http://www.sanantonio.ac/blog/category/us%20made

That being said, since I already know I'll be spending a good chunk of money with this replacement, I want to make sure I do things "right". That includes ensuring I get something that's good quality/reliable and also has all the features I want now and would be able to benefit from in the future as well.

Replacing equipment with the same size because "that is what you already have" is bad practice. Most houses don't have the correctly sized duct work for a 5 ton AC. The size needs to verified.

Adding condensate lines and new exhaust and venting for a condensating furnace is done everyday. It will cost more money, but it is a good investment in my opinion if you plan to live in your house for another 10+ years. You should also avoid low end systems.

I could be wrong, but I don't think American Standard has manufactured any HVAC equipment in NJ for many years.

@dcernosek If you are living there that amount of time, then I'd agree that it is smarter to go with a better system. I'd say it would be far more important to consider a furnace with variable speed than a furnace with condensing. The ECM motor itself will save you a lot of power, and it will give you a lot of flexibility to add things cheaply like continuous fan mode to improve your IAQ.

Also, in general for your area I'd advise putting your money into cooling (ECM as pare of that), not heating. Consider that in Houston, at a 65F balance point, in the last 12 months you averaged 3659 cooling degree days vs 965 heating degree days. Basically your system had to deal with over 3.5x as much cooling load as heating load. A higher seer unit, variable speed compressor, a heat pump are all things that would greatly benefit someone in your area. A heat pump would probably cover most of your heating days itself, and the furnace could just be saved for the coldest days.

When I was living in Houston I could remember counting the days when it felt dry. Even if I didn't feel cold I would feel disgusting because of the humidity so I'd run my AC non-stop most of the year. Having a system with the tech to address the humidity would be the most important thing for me.

I would advise that you have some other manufacturers systems quoted as well. I like Trane/Am std AC, but their furnace tech (with the exception of the S9V2) is the oldest in the industry at this point.

I wouldn't get an Ameristar either (except for my rentals), but I can't find any evidence of where they are made. Importing them from China would be very strange since it cost to much to ship and the style is uncommon over there. The reason that HVAC isn't made in China is the shipping cost, since you are shipping a big box with a lot of air inside it.

@mike_home that is a mistake. American Standard (which is the exact same product as Trane) makes all of their furnaces and most cased coils in their factory in Trenton NJ. They have 1100 union manufacturing workers there. Condensers are made in Tyler Texas. A few items are/were made in Mexico, but they are moving MFG around all the time.

American Standard and Trane compressors are made in Mexico, this is common knowledge. With that said, installation and service after the sale are two most important ingredients to any residential based Air Conditioning installation.

Properly installed 2 stage AC's will dehumidify much better than single stage systems for the simple reason they run longer. There is much confusion on this topic. The key here is that the system has to be set up properly. If a company is trying to get you away from one versus another it is most likely due to the inability they have to diagnose problems with them.

Operation of 2 or more stages when set up properly: Initiation starts and system starts in stage 1. What determines if it goes to stage 2 is typically based on time and controlled via the thermostat. You don't even have to think about it. In some situations the system may run continuously in 1st stage, not because of anything bad but because this is the load on the home. If this load increases the thermostat recognizes it and turns on stage 2. If the thermostat dictates that cooling is too much it may revert back to 1st stage or cycle off completely.

If you have more than 2 stages: there are a couple of different varieties. Some require specific controllers, some work with regular two stage thermostats and then use algorithmic logic that dictates which stage the unit will operate in.

Thanks for the comment, Austin Air! By the way...I see that you're in the Katy area and unfortunately don't service my neck of the woods (Meyerland/Bellaire). First, I hope you stayed dry over the last couple of days. Second, do you know any good/trustworthy guys/companies that service my area that you'd recommend?

I've talked to a few more AC contractors since I've first posted...all highly recommended in some form or fashion. One of them (the most expensive one) is recommending a 14 SEER, single-stage unit (American Standard 4A7A4060 condenser, 4TXFH063 coil, AUD2C100B9V5V furnace). When I asked about both a 16 SEER and a 2-stage unit, I received the following responses (paraphrased):

* A 16 SEER option would only achieve a 14.5 SEER AHRI rating, while a 14 SEER option would get a full 14 SEER AHRI rating, so the extra cost for 16 SEER wouldn't be worth it.

* Your home’s cooling load is already at the full 5-ton capacity. The full 5-tons will be used to cool the home during most of the year. The 2-stage systems are more efficient because they are capable of running at “low stage” most of the time and only kick into “high stage” when needed. In your case, since the load is already at 5-tons, a 2-stage system will end up running in high stage most of the time, which negates the efficiency acquired from the 2-stage operation.

These guys have definitely been the most thorough and responsive of all the other contractors, but their explanation on the 2-stage systems seems to contradict a lot of what I've been reading elsewhere. I get their point on the 14 SEER vs 16 SEER, but I guess am confused about whether there are alternate 16 SEER configurations that would get higher than a 14.5 AHRI rating.

Yeah I'm high and dry thankfully, the roads are a mess up here so traffic delays will likely be a nightmare for a few weeks if it can stop raining more a while to let us dry out.

I think part of the problem you're getting is the manufacturer dealer you are using. You see Trane and American Standard are mostly one in the same. They force contractors that use them to exclusivity deals meaning they can't offer other options that are made by other manufacturer's. If they went behind Trane / American Standard and offered these solutions they would probably get chopped off at the knees. The other part may be that they pre-purchased equipment to get better pricing and they have a lot of that equipment in stock from the past year. That is about the only rhyme or reason why I think they are probably telling you these things, because they are totally inaccurate.

Certainly any 5 ton system SEER rating will diminish when it is operating in 2nd stage, but in terms of running in 2nd stage usually this will only be in the hours of heavy loads. Typically between 3pm and 6pm. Certainly if we get a heat wave it may run more in 2nd stage during longer spans than those times above.

You can easily prove this to yourself when you watch the weather forecast on TV. Pay attention to the highs and lows of the day. Notice that lows are over night (usually) and the highs aren't hit until around 3pm-4pm usually. Well if the average low in summer is around 70 degrees there is far less load on the home than the high of 95 degrees or more. In other words a two speed AC system will most likely run in first stage for hours outside the 3pm to 6pm window. Which means 1/8 of the day it runs in 2nd stage... unless a heat wave or you're cranking settings etc.

The flip side is that because the system has 2 stages it runs longer in 1st stage... during all this time it is removing humidity. Lower the humidity and you feel much more comfortable.

When deciding make sure the system is a 2 stage with a 2 stage thermostat minimum. SEER ratings are tricky because you could have a 17 SEER single speed air conditioner. The single speeds are the ones not worth it because you don't get the dehumidify punch from those... they are either on or off.

Realize it's not only just about efficiency it's also about comfort.

The SEER rating is based on the combination for condenser, coil, and furnace or air handler. Change one component and the SEER rating changes. The condenser by itself has no SEER rating, however condensers are designed so they can achieve a range of SEER ratings when connected to the other two components. So if you want to achieve a SEER rating of 16, then in addition to the condenser, you may have to change one or both of the other pieces of equipment.

SEER ratings are optimized for the 3-4 ton sizes which are the most common. You rarely see the highest SEER rating in the 2 and 5 ton sizes.

Your house requires 5 tons of cooling on the days when the outside and indoor temperatures are at the system design limits. Any lower outdoor temperature, or higher indoor temperature makes the cooling load lower. So on a mild day you don't need 5 tons of cooling. This when the AC would be operating in the low stage. Any cooling done at night would likely be in the low stage.

Most houses don't have the duct work or filter size needed to support 5 tons of cooling. Your contractor needs to verify they are sized correctly.

So far all of the contractors have said that the ductwork looks good for 5 tons of cooling. One even said that they were a bit oversized for 5 tons, whatever that means.

So, it sounds like it's fairly unanimously agreed that a 2-stage condenser paired with a variable speed furnace would offer the greatest efficiency + comfort level. What are your thoughts on the contractor's configuration from above with a single-stage condenser paired with a variable speed furnace? He had commented that the variable speed furnace would help with cooling performance along with humidity control. Is this a valid way of increasing comfort while avoiding the upfront cost of a 2-stage condenser? I'm just trying to narrow down all of the configuration options right now without making my head explode...

The main supply trunk for a 5 ton AC needs to be a 20 inch round duct, or an equivalent rectangular duct of about 300 sq. inches. A 5 ton AC requires 2000 CFM of air flow. To support that you need about 1000 sq. inches of filter are. Typically you would use two 20X25 inches filters on the returns. Anything less you are undersized in my opinion.

The AC air flow needs to be in the 350-400 CFM per ton. So the air flow for the AC could go as low as 1750 CFM. Not sure how this is done if you don't buy a communicating furnace and thermostat. Even if you did, it is not much of an air flow reduction so the humidity control is not going to be as good as a 2-stage AC system.

Main supply trunks are typically not used in residential, these are more typical in commercial type duct systems that need to distribute more air farther for better distribution (more people = more complaints). It's not saying you couldn't do it in residential but due to space that is not the norm in residential systems. (Katy- Houston and so on.)

Air flow is certainly important not only for proper operation but also efficiency as well. But on a two stage system that air flow "room" mostly comes into play when the system switches to 2nd stage.

dcernosek, You could put in a single stage AC with the variable speed furnace and gain a humidity "function". But like I said before the devil is in the details. A "function" is completely different than true humidity mode of a 2 stage AC.

Because a single speed 5 ton system is going to deliver the majority if not all of the 5 tons every time it kicks on, where typically a 2 stage will only deliver about 40% of that cooling in first stage. This is why the system runs longer thus pulling more humidity out of the air. This is also the most energy efficient mode of operation (1st Stage).

I often use the car analogy because you go thru cars much more frequently than air conditioners. You could focus on buying a car for great gas mileage and later after a long trip find that it's uncomfortable wish you had bought a more comfortable bigger car, that would probably use more gas. The difference between a car and air conditioner is you buy a air conditioner typically only for comfort. Each and everyone out there has different visions of what true comfort is.

Another analogy is TV's - you remember the old standard definition TV's, then digital, then HD, then super HD and next is 4k I think. Each revision is a more buttery look for your eye balls. This is more or less what the HVAC industry is beginning to go thru. It is more or less called "load matching". In other words eventually the HVAC system will be so smart that it will run continually to match the load on the home, what ever that load may be up to the maximum amount of cooling or heating of the system.

I think you should take a consultation from expert who will suggest you what will work better for your home keeping in mind all pros and cons. In my case HVAC service Bergen county NJ will be of great help to me while getting the best HVAC system for my newly built home.

So far, these are the 2-stage condenser/variable furnace configurations I've been quoted (by two different contractors):

AHRI #8232313

Trane XL18i 4TTX8060A1, 4TXFH064AZ3, TUD2C100B9V5

~$12000

AHRI #8232166

Ruud UA17 UA1760AJ2, RCF6021SEAM, U802VA100521MSA

~$12000

I've requested quotes for single-stage compressor/variable speed furnace from those two companies, but have yet to hear back. The third company is the one who I referenced a couple of posts ago and recommended that config with a 14 SEER:

AHRI #?

American Standard 4A7A4060, 4TXFH063, AUD2C100B9V5V

~$14500

Right now I'm waiting to see the price difference in the single-stage compressor/variable speed furnace configs from the first two companies. I'm still trying to find another AC contractor as well as all three have said various things that don't necessarily jibe with what I've heard from you guys and other sources on the internet.

Any thoughts on the above quotes and this general plan of attack?

Folks who know the part numbers better than me will chime in, but the Trane and American Standard are the same units, or at least should be.

I think the Trane listed is a 16 SEER while the American Standard is 14 SEER. The Trane/American Standard furnaces listed are indeed the same though.

I believe that at this point, all I can legally say about this discussion on this thread is that I believe and it is my professional opinion of over 20 years in the HVAC field that there are better choices available.