I'm not sure if this helps, but the regulations are changing in 2023. Because of this you want to make sure you get an air conditioner that's manufactured in 2023.

https://www.rheem.com/air-conditioning/articles/what-to-know-about-the-upcoming-hvac-efficiency-and-refrigerant-regulation-changes/

https://www.iccsafe.org/building-safety-journal/bsj-technical/2023-efficiency-requirements-for-air-conditioning-systems-what-you-need-to-know/

meltedviking,

You have a number of things to consider... from what I read about your situation is that you are mostly accustomed to where you use to live versus where you live now.

In the deep south East and Mid-west have fairly common problems with AC related tasks. Things are a bit different for the south west because of desert conditions. The biggest difference in my mind of doing this job for nearly 30 years is humidity.

SEER is now SEER2 as of 2023 and beyond. It's essentially the same as before, just that the calculation is different. Depending on where you live this could have an impact on what you can do. HVAC changes even more starting in 2024 and hard change in 2025 when R410a equipment is banned / restricted etc.

When R410a is eventually phased out they will do this by cost of the refrigerant for most places. Some more green places may restrict the sale of the refrigerant. This restriction is more likely in the far, far west.

So if you choose something now and that something springs a freon leak / R410a leak if you prefer --- you will pay more to fix it. Regardless of brand, refrigerant isn't covered by any warranty.

The efficiency of SEER / now SEER2 courtessy of the white coats to make things more complicated than they were before.... Essentially the bigger the number of the SEER2 efficiency rating the better the efficiency.

Efficiency in general is like that of MPG or miles per gallon on a car. If you rarely drive or drive little the efficiency rating means little. Same with AC. The more you run the AC (lower temp in a hotter climate than you used to live) the more you will save.

The climate you used to live in the north most likely had a 3 month AC use. So going with higher efficiency in the north doesn't lead to any significant savings. However, in the south we run our AC's here maybe as much as 3 times more than the north. Like where I live in Katy, Texas this span of time is closer to 10 months of use.

Typically recommended set points is around 78 by most utility companies because of the threat to bringing down the grid because everyone is blasting their AC, never mind those EV guys and bit coin miners plugging their wares into the grid? yeah plenty of fodder to go around. This is the nonsensical world we live in.

If you have lived at this location for 15 years already that would change things most likely. But you just moved here so the more efficient AC you can buy is your best bet. Typically this will mean full system replacement for most major manufacturers because in this realm the HVAC systems are considered communicating equipment.

While you may not think your set point of 70F is all that low, design temps for most southern areas is 75F. So you are running your AC quite hard at 70F setting.

Design temps for my area 95F / 75F the 95F refers to outdoor temp. So a properly sized system would start to struggle at outdoor temps over 100F for a prolonged amount of time. (It would show these symptoms in the late afternoon early evening before the sun goes down.)

The better way is Inverter (variable speed systems) because over sizing can be detrimental. An Inverter based system will vary the compressor speeds that over sizing is less of a factor to worry about. The system still needs to be sized properly but due to the nature of the Inverter and how it operates it's much less than sizing a traditional AC a ton larger than it should be.

The inverter starts slow, then ramps based on the info it gathers in run time. All manufacturers make inverters most of them are communicating... which add costs. Bosch is an Inverter that is different. No expensive communicating thermostats / proprietary zoning hardware and so on.

The con with Bosch is currently the distributor network isn't all there for some parts of the country. The best of the best in this realm is IDS 2.0 -- Bosch makes lower level cheaper inverters now at the cost of not being as efficient. So any utility savings will be less with those models.

Zoning: There can be a lot of problems initiated by zoning improperly. HVAC zoning is an art form to put cooling or heating where you want it, when you want it and none where it's not needed or don't want it.

Equipment can zone spaces and it's typically much easier to zone a level of a structure with it's own equipment rather than controls / dampers to do this function.

I own 2 homes with zoned systems that I installed. Not to brag, but to tell you this post is brought to you by experience of doing not just talking about it from a perch where I tell other (cheaper labor folks to go do it) --- there are a myriad of ways to do something. I offer different ideas for my neck of the woods in Katy, Texas area.

My guess is the estimates you got were free... but you're here in this forum board because none of them could explain to you exactly why or give you complete options as to what you could do to solve this problem of yours.

There's more than one way to do it... but explanation of exactly what you are buying? Usually it's along the lines of "trust us" when none of them has built any trust. It's one thing to get a free quote it's quite another to show up and fix problems.

Don't kid yourself new equipment can and do have problems... outside of cost what ever you decide you need to be sure the contractor you choose will be there to pick up the pieces if things don't go as planned. (while it's rare, it does happen and usually goes south due to money)

In 30 years most of the time the excuse I hear is "hey we got a good deal on this so and so a few years ago and now it's not working we had the installing contractor out here 20 times and he can't fix it."

Communicating systems usually drop into "error code hell" within a few years. This isn't to suggest a traditional system can't go into this realm, but it typically takes a decade or more and normally much easier to fix.

This long winded story probably won't help you much. The nature of this business is in person by a skilled person... not a salesman that is not skilled in fixing anything. Their job is to sell. Getting an engineer to your home, then they send the cheaper crew to install the machine. Not saying you can't do it this way and have success... but how will you really know?

95F-100F outside and too hot inside. That's about it. If it's 90 degrees for an hour in the north and 50F at night how hard is it to cool a house to 70F? Illustrations like this to show you what you may be up against.

I service the Katy, Texas area.

"SEER is now SEER2 as of 2023 and beyond. It's essentially the same as before, just that the calculation is different." Nope. It's not the calculation that's different-- it's a change in the testing protocol. SEER2 ratings are based on performance testing of systems at 0.5" w.c. versus 0.1" w.c. for SEER ratings. That's a five-fold increase in static pressure. It's intended to provide a better indication of how HVAC systems will perform under real-world operating conditions. That's a good thing in my opinion.

"HVAC zoning is an art form to put cooling or heating where you want it, when you want it and none where it's not needed or don't want it." Residential HVAC has been evolving since man first chose to live in caves to get out of the weather. It's not an "art." HVAC design is pretty straightforward (mostly prescriptive) design. That said, it requires a level of design competence beyond that of most HVAC contractors and certainly beyond that of most HVAC replacement contractors.

I realize you live in the southeast and the concern is about cooling. I am curious what is the plan for heating. Is it heat strips only or are you considering a heat pump.

He said he didn't think a zoned system was necessary, and that if it tends to be hotter upstairs (where we sleep), we could just move the thermostat to the top level. He recommended a variable speed system and said we could just leave the fan on low at all times.

You can move the thermostat, but it doesn't fix the problem of maintaining a uniform temperature throughout the house. If you set the thermostat to be 70 degrees in the bedroom upstairs, then the lowest floor may fall to 65 degrees. Zoning should be seriously considered. For a 3,000 square foot house I would recommend installing two separate systems. Most HVAC contractors are not skilled in installing zone with a single 5 ton condenser. I am also skeptical your duct work is large enough to handle the air flow required for 5 tons of cooling. This is another reason two smaller units makes sense if it fits the budget. Running the air handler 24/7 on low speed is not a good idea in a humid climate and do little in keeping temperatures even throughout the house . It also can consume a lot of electricity.

You can purchase a condenser manufactured in 2022 as long as it meets the SEER2 requirements for the Southeast region for a 14.3 SEER2 rating. There will be a sticker stating this on the side of the unit. Your quotes should be stating SEER2 ratings and not SEER. It is very confusing and I suspect contractors will use this confusion to their advantage. A variable speed will provide better humidity control compared to a single stage unit.

I would recommend you find a contractor who will do a load calculation. Oversized equipment will be more expensive, nosier, and not be as effective for humidity control. If you want the bedroom to be 70 degrees at 40-50% humidity, then that should be the indoor design temperature for the load calculation.

Austin must think he gets paid by the hour for his comments. All those words without answering any of the questions asked.

I appreciate all the comments. As someone who tends to be longwinded himself, I can empathize with Austin (although i did laugh out loud at your comment, Elmer)

Mike, re: your skepticism about the duct work, would it help to know we already have separate duct networks running from the unit to the different sections of the house? i.e. ducts going directly upstairs and ducts going directly to th bottom floor. Im not sure if im describing it correctly, and that may be normal anyways.

I talked to several of the contractors about two separate systems, and it doesnt seem feasible. For one thing, it would almost certainly push the cost above what we can spend. and then i dont think we have great space for a second indoor unit.

As to the heat, i will have to ask. i just know what we have now is what laypersons would refer to as a ”furnace”. powered by natural gas.

One specific follow up question - would you say it would be better to be slightly undersized vs oversized?

Independent supply ducts for the floors will allow easier implementation of zoning. If you were to get two systems, the one for the upper floor can be located next to the other unit on the lower floor. The returns don't have to be independent. It takes skill and planning to install a single 5 ton system to supply the proper amount of air when only one zone is calling for cooling. The two independent zone simplies the installation, but it costs more money at the time of installation. The two smaller independent unit operate more efficiently in my opinion.

In a humid climate it is better to be slighlty undersized. Longer run times allows the air to dry out and not over cool the air.

Where in the Southeast are you located? I was not expecting your house to have a gas furnace. Did any of your quotes have a gas furance included? Quotes should have equipment model numbers, if they don't they are incomplete.

Base on the details you provided so far, I am not sure I like any of the quotes. I say this as I ignore the prices and concentrate on the type of system and equipment being proposed.

I’m in Atlanta. Believe it or not, it does get cold enough for a gas furnace from time to time.

they did quote equipment model nos. for the furnace. or two of them did at least. the contractor who recommended the 5 ton = Trane TUD2C100A

First, get heating and cooling load calculations done. In your hot, humid climate, you DON'T want an oversized system. Replace the condenser, coil and furnace. If the third estimate included the furnace, that's a pretty reasonable price, the others are on the high side. If you can spring for it, get a two stage heating and cooling system - they work better with zoned systems than single stage - it will work on low speed most of the time and when it needs high speed, more of the zones will probably be open.

The TUD2C100A is a 100K BTU furnace with a 80% efficiency. The winter design temperature is about 23 F degrees. This seems over sized. The size was probably chosen to be compatible with the 5 ton condenser. This is likely also oversized. The Atlanta summer design temperature is about 91 degrees.

Hi, Meltedviking,

In my opinion, any HVAC replacement contractor worth his/her gauge set would have recommended performance testing of your existing system to include air flow and duct leakage testing. The tests aren't difficult nor are they expensive to perform. At least one state (dare I say California) requires duct leakage testing prior to any HVAC equipment replacement. Deficiencies indicated by either test should be remedied as part of the replacement work and may result in smaller replacement equipment or at least more efficient operation.

Most residential HVAC systems operate at negative conditions, so the credibility of the contractor who wants to add some returns rates a couple of notches higher than the others, in my view. Reducing the outdoor/indoor pressure differential reduces air infiltration, and, in turn, reduces the heating and cooling load.

Regarding "over-sizing" and "under-sizing" systems, both terms require some some qualification. Residential HVAC systems designed to comply with the 2018 International Energy Conservation Code (IECC) are designed to provide comfortable conditions 97.5% of the time. So systems designed per code will be intentionally undersized 2.5% of the time; i.e., they won't be able to heat or cool to setpoint. For Atlanta, your indoor design conditions are 72 F maximum in heating mode and 75 F minimum in cooling mode. Outdoor design conditions (97.5%) are 22 F winter d.b., 92 F summer d.b., and 76 F summer w.b. temperature. It's important to include the wet bulb temperature so the latent (moisture removal) load can be calculated.

Your home has three levels-- each of which will heat up/cool down at a different rate. If the rates differ enough (as I suspect they would be in a home configured per your description,) installation of a zoned system is indicated. The design of zoned systems is neither "art" nor black magic provided there is a design professional responsible for the design. The issue with sub-zoning a single system into three zones is the turndown capability of the system. By way of illustration, let's say all three zones have equal heating and cooling loads and only one is calling for heating or cooling. The system needs to be capable of operating at 1/3 of its total capacity or less. Single-stage compressors and single-speed air handlers won't cut it. They'll apply 100% of the cooling capacity, rapidly cool, and poorly dehumidify the spaces. You'll need a multi-stage/variable speed compressor and a variable-speed air handler. Any contractor who recommended zoning of a single-stage, fixed-speed system should be shown the door.

Thank you all. Can you do performance testing when the ac unit isnt functional? Ours appears to be shot. i suppose you could still run the fan and test the airflow?

Yes, if the air handler works you can test the air flow rates and the duct leakage.

I've also talked with my dad, who is a general contractor. He has far more knowledge re: HVAC than I but is by no means an expert. He said he didn't think a zoned system was necessary, and that if it tends to be hotter upstairs (where we sleep), we could just move the thermostat to the top level.... He also said there was no reason to go too high seer wise, as it likely wouldn't end up being a financial benefit in the long run.

meltedviking,

For the record a lot of my post was covering these specific points mentioned above. But naturally you would have to actually read it. (It's a forum board, even after me telling Mr. Fudd and others repeatedly to read... they still lack this skill.)

To add there are plenty of things I don't know for a job that is done 100% in person and those responding except for me don't actually do the work. The OP failed to state where they actually live in the very first post. But I am supposed to guess? Anyone can guess and many parrot the wrong information as Mike_home demonstrates in spades....

You can purchase a condenser manufactured in 2022 as long as it meets the SEER2 requirements for the Southeast region for a 14.2 SEER2 rating.

Mike_home is a home owner in New Jersey. He doesn't do HVAC either. He's a home owner with too much time on his hands.... obviously not enough time to parrot correct information though. Minimum efficiency is 14.3 SEER2 for a hot climate like Georgia and a desire to cool to 70F for a home you just moved into?

If you expect utility rates to plummet sure go ahead and buy a minimum efficiency unit.

Zoning is an art form: Those like the builder fail to do it right even after they spout the code book to make themselves look so keen.

The reason zoning is an artform is that too many like to cram it into spaces that are barely large enough to contain the equipment. They say hey you need to take the equipment out of the attic and cram it in a closet so it's within the thermal envelope of the house.

When a zone system is calling for one area that area may need 600 cfm of air, where as a system whole the air produced is 2000 cfm for a 5 ton system in full throttle.

But you only need 600 cfm. 600 cfm is all that will fit thru the duct that is calling. So they've come up with marvelous ways of bleeding air thru other zones to alleviate the pressure. If you choose that usually a builder who chooses it because then he can blow smoke for a period of time to wait out the typical 2 year warranty the builder gives out. The builder won't parrot that though. How many builder systems do you need to see before you realize a builder is just a squack box?

The builder hires sub contractors to do the work: he said so right here (click to enlarge)

More equipment and no zoning:

This is the better way, but then there's the more money clause. There's the need for even more real estate needed to house the equipment. There's more maintenance to be done, there is more things that can break and ultimately you're going to one day have to replace that equipment again.

One advantage for having 2 separate HVAC systems is if one system is broken, the other may still be operational so you're not completely without AC. But that comes at a cost. Remember at your set points you are running these systems hard in a hotter climate than what you moved from. The more you use it, the greater the chance of breakage. The more you use it... the more efficient it should be or you pay the utility company. You don't get out of paying for comfort in a hot climate.

There was a time that people said: I just wish the HVAC guy would be honest with what they tell me. But the gimmick is hard to get around for some. (gimmicks are tricks to sell you for reasons sometimes that aren't entirely clear... why those who don't do HVAC get involved in these discussions.

Most of these characters on this board in particular live in more mild climates than you... 3 months and done type AC use. --- climate reasons are often not thought of. Even your father didn't realize why higher efficiency is beneficial for your particular climate /situation. This doesn't mean I never sell a minimum efficiency unit here... the comments made about such fit your specific situation. You just recently bought the house.

This is a job that is done in person... what you are actually able to do versus what might be more practical?

(enthusiasts goals are what? If you can live with that answer then go ahead and take their advice... in 2024 HVAC *begins* to change again unless someone sues the government. Fun times in HVAC.)

I service the Katy, Texas area.

"You can purchase a condenser manufactured in 2022 as long as it meets the SEER2 requirements for the Southeast region for a 14.2 SEER2 rating." Mike wasn't advocating the purchase of the lowest acceptable SEER2 equipment. He was responding to an earlier post where the poster claimed that HVAC units are required to be manufactured in 2023. They don't. But they need to meet the minimum SEER2 rating as Mike correctly stated.

"Zoning is an art form..." You frequently suggest the required skill level and experience to perform the job of an HVAC mechanic are more than they are in the real world. Installing residential HVAC equipment properly isn't rocket science; it's mostly a matter of following installation instructions. Ditto for troubleshooting. You'd like us to believe you're an "artist" because you don't cram equipment into less that the required space?

The SEER2 requirment or lack thereof depends upon where you fall on the map.

HVAC isn't rocket science... but for some it might as well be. You're a builder aren't you Charles?

Even you said it yourself more or less yourself. Remember?: click to enlarge.

Rocket Scientists everywhere are laughing out loud.

Yes, Ray, the SEER2 rating required depends on geography. The OP shared his location, from which the requirement for SEER2 rated equipment of 14.3 or greater can be determined. It's not art, it's simple reading comprehension. Maybe the same level as Jethro Bodine.

My aplologies for incorrectly stating the current minimum SEER2 rating for the Southeast region. I have corrected my previous post. In the Southeast region where the outdoor temperature is often in the mid 90s the EER2 rating becomes a better guage of efficiency in my opinion.

The OP will be best served by a multi-stage/variable speed system--any of which will put them, well, comfortably above the minimum SEER2 required rating.

So i ended up having another company out. Guy my realtor (whom i more or less trust) has worked with for 20 years. He said installing a second system would be a far better option than a single zoned system. He recommended a 3 ton unit for the two lower floors and a 2 ton for the upstairs. He pointed out that we could install an indoor unit in out attic and would just yave to cut a slightly larger access/install a pull down ladder/door. the duct work on our top floor is already built into the ceiling, so we could patch the upstairs unit directly into that. He has to ball park but said it’d be $15k to $16k for everything. 2 outdoor units, 2 furnances. and i believe he aaid a heat pump for upstairs. plus reworking to duct work to accomodate the 2 systems.

Installing two separate systems is a perfectly reasonable approach which gives you two independent zones of control without the added complexity of zone controls. If the budget allows, you'll be well served to install a multi-stage/variable-speed system for the 2nd floor to enable improved indoor relative humidity control.

The two independent systems is the best approach for controlling the temperatures of the upper and lower floors. It removes a lot of the risk compared to a single system with zoning controls. I didn't appreciate the duct work for the upper floor is located in the attic. I assume the contractor has proposed installing an air handler with a heat pump in order to avoid running a gas pipe to the attic. It is a good solution for your climate.

The price of $16K seems low for what he has verbally quoted. Get a detailed list of equipment and everything that will be included in the installation.

The contractor didn't quote anything. He gave a ballpark estimate of the cost to furnish and install two systems without providing specifications. That underscores the OP's quandary: the lack of a uniform set of specifications and plans provided to all contractors precludes the ability to comparison shop on price. It also requires the OP to sort through the pros and cons of various alternatives without the technical knowledge and skills required to do so.

He sent me formal quotes today. He just ballparked in person.

Anyone have thoughts about just installing a single system with no zone damper. I am leaning that way at this point.

Do you mean a single system for the lower floors without a zone-control damper or a single system for the entire home with no zone dampers?

How does the ballpark estimate compare to the formal quote? A single system with no zoning will cause uneven temperatires on each level. It is difficult to estimate the amount of the variation. You will have to decide if that is acceptable.

Anyone have thoughts about just installing a single system with no zone damper. I am leaning that way at this point.

It will be less comfortable, harder to control temp thru out the house because heat rises and cooling falls.

So the lower levels will be too cool in order for the upper levels to be bearable. If your goal is still 70F like you said earlier in the thread it almost certainly spells trouble, unless all you do is stay on lower level during summer or get your body acclimated to a warmer temperature.

Moving the thermostat will not help this situation. Thermostat wars break out if you have others in the home living with you. The battle is always either too hot or too cool.

It's not saying you can't do it... just to help you understand the performance of your system if you decide to go this way with a single system and multiple levels in the home.