Pricing is very regional (eg V V expensive in NYC, less so in Little Rock AK). The only real way to assess your local pricing is to get multiple estimates. The pricing isn't awful (depending on the complexity of the installation) but they are builder grade units.

Thanks. I'm in the Memphis area, so our prices tend to be in the middle somewhere. I'm hoping to get a second estimate later today.

Why 80% eff furnaces? What thermostats? Any filter media cabinets? Trane evap coils?

IMO

I just got a second quote. This company quoted $18,700. They quoted XR14's rather than XL16's, and they also said I should retain the one 5 ton XR80 furnace I have, no need to replace it. So the quote is $13,300 less, but results in one less new heater, lower SEER and no maintenance or 10 year labor warranty.

The thermostats included in both quotes are Honeywell 5000's. Both companies quoted the 80% eff furnaces. The first company claimed they are more reliable, and the only unit he's willing to include the 10 year labor warranty (along with the Trane 10 year parts warranty). Both quoted Trane coils.

low end thermostats and I don't believe they are true 2 stage thermostats that the XV80 furnaces should have and deserve...a cheap shortcut...I agree that attic location furnaces should be non condensing furnaces like the XV80,...where are the other furnaces quoted to be located?...you need to see the AHRI matching numbers for the systems quoted...I personally would want minimum 15 SEER rated systems....what about the filter cabinets?...

IMO

All four furnaces are in the attic. Two are in a vertical orientation, the other two are mounted horizontally. I'm not exactly sure what a filter cabinet is .... both said they would replace the inlet and outlet plenums.

A filter cabinet is the cabinet you put the filter in.

Pretty sure that T is referring to 4" thick filters that get replaced once a year or so.

The Memphis summer outdoor design temperature is 94 degrees. That is not that hot in my opinion. Can you describe the size of your house and insulation values? I am curious as to why you are being quoted 12 tons of cooling.

Is this house a quad plex or town home (multiple units)? The reason I ask is it helps to determine what your goals may be. (are you renting them, flipping them or what?)

The Honeywell 5000 is a low cost thermostat, but it does have 2 stage cooling as well as 2 stage heat. Provided your structure has the needed wiring to be wired for 2 stage heat or 2 stage cooling. The bigger problem is this thermostat is non-programmable. (you must adjust it manually)

The humidity in Memphis is pretty high. The house is 4500 square feet, and the 12 tons of cooling is what is presently installed. So both companies just quoted on replacing each unit with the same rating. We plan to live here for the long term, so I'm interested in high efficiency. But I doubt that increased efficiency of the 16 SEER is going to pay for itself, relative to 14.

You need to find a contractor who will do a load calculation. If you can't find one, then you either do it yourself, or pay someone to do it for you. I can't imagine you house have a heat gain of 144,000 BTU (12 tons). I think you are oversized by 2-3 tons, but that is just a guess.

Over sized equipment will short cycle and have poor humidity control. In humid climates you are better off being a little under sized than over sized. You will save more on operating cost with a properly sized 14 SEER system, than an over sized 16 SEER system.

Tell your bidders you are prepared to spend the money but you want a properly sized and designed systems. If they are not willing to spend the hour to do a load calculation on a $20K+ installation, then take your business elsewhere.

A rule of thumb (and its only a rule of thumb), is that you need 1 ton of cooling for every 600-800sq ft. That works out to be 6-8 tons (not 12). I wouldn't use this number sight unseen but it does suggest the need for a PROPER load calculation. Oversized cooling in your climate will result in a very cold but clammy environment in your home.

Thanks for the advice regarding a load calculation. I contacted another company that I believe is capable of doing an accurate load calculation. They're coming out early next week. I'm beginning to wonder if I could go from 4 units to two, at a capacity around 8 tons rather than 12 tons. I'd lose some zone control, but maybe dampers could substitute and give me that control?

With the current configuration, do you find your home to be cold and clammy?

heating load calculation needed as well...don't accept that cheap thermostat either.

IMO

I find the humidity to be too high inside. Being cheap, I keep the temp setting high enough that it doesn't feel cold and clammy; it's more lukewarm and damp.

I really appreciate all the advice. I wish I'd found this forum a long time ago. I'll report back after talking to the third company on Monday. They appear to be more technically-focused, so I'm hoping they can provide some better guidance.

The humidity in Memphis is pretty high. The house is 4500 square feet, and the 12 tons of cooling is what is presently installed. So both companies just quoted on replacing each unit with the same rating. We plan to live here for the long term, so I'm interested in high efficiency. But I doubt that increased efficiency of the 16 SEER is going to pay for itself, relative to 14.

Efficiency doesn't mean much if you're not comfortable. Given your humidity statement it would probably be better to consider 16 SEER equipment that has 2 speed compressor. Realize not all 16 SEER equipment has a 2 speed compressor, this is why you must know exactly what you are buying / paying for.

Increased efficiency is a misnomer in the single speed AC market... all high end equipment is going to multiple speeds. The next step up from 2 speed is 5 speed which is performed by Inverter System. (They are variable speed, but controlled via 5 steps - algorithmic controlled.)

While you gain efficiency by going to this type of system it is not about paying for itself in terms of monetary pay back. It will save you some, but pays you back with much better comfort and much less humidity than that of a single speed AC.

4500 square foot home: No one is going to whip out a 'honest' load calculation in an hour on such a big home. With such a large foot print, easy to make a mistake... how many of these so called load calcs will you get and if you get a different one how will you know it is accurate? (sq ft guesses of footage per square ton do not take into account high ceilings or windows, these 'pretty' features in a home require additional cooling / heating and vary from one home to the next. Given the size of your home, if I had to take a guess I would say you probably have tall ceilings... this home isn't cookie cutter if you know what I mean.)

By going with 2 speed condenser as a minimum requirement, a two or 3 ton over size in a 4500 sq ft home is of no concern because the equipment will run in first stage or roughly 70% of the normal capacity of the equipment. On those days it is really hot that 2-3 ton over size is increased capacity.

Realize no matter what size (in tonnage) you have and even if you get the load calculation completely right for this home, the sizing is actually over sized 90 percent of the time it runs. Heat of the day is 3-6pm - extended heat wave maybe 3-7pm.

In shoulder seasons (spring & fall) the over sizing is even worse. Humidity is independent from temperature. Meaning you could have high humidity and lower temps like 80 degrees. A single speed air conditioner (properly sized even) will cycle very quickly in these kinds of loads.

An air conditioner is a dehumidifier. But it must run to dehumidify. This is what a 2 speed air conditioner accomplishes.

You get even better humidity control from a 5 speed (inverter or variable speed AC) everything is variable speed with these. These are the crème de le crème at removing and controlling humidity within the home. A due to the speeds that they are capable of, sizing is muted. They will always run at the lowest speed needed to match the load of the structure or the zone they control within.

Ray,

It seems every time someone suggests getting a load calculation you come up with every excuse imaginable why the calculation is not needed. Maybe not doing a calculation works for your type of HVAC business. But in many cases a load calculation for a equipment replacement is justified.

An HVAC professional who does load calculations on every installation can turn one out pretty quickly. Maybe it can be done in an hour, maybe it takes two hours. You are right that two calculations may come out with different answers. But as you know equipment comes in discrete sizes. So there is a good chance by rounding up or down, the size of the equipment may be the same. Even there is a big discrepancy is sizing, I tell homeowners to ask the HVAC contractor what design temperatures were used, insulation values (yes I know you don't have x-ray eyes), and area of the conditioned space. That information with the help of this forum has helped many posters determine if the calculation makes sense.

Don't bother responding with one of your long posts. I am not going to debate you about this. On the topic of load calculations we can agree to disagree.

Mike the load calculation was already done. Your thinking is that someone is going to get a load calculation any more right after the house is already built and older equipment is sitting there. What has changed? How long has this equipment sat in this home? But now because we are going to replace it, it is sized wrong? (It's not a new structure is it?)

Your thought is to second guess the builder who had all the R-values of windows, insulation etc. of the home in order to do the calculation?

Yet a contractor coming into a home has to more or less guess at the R values of insulation.

You won't do an 'accurate' heat load calculation in even 2 hours in a 4500 sq ft home measuring home by hand / every nook and cranny. You have no idea what you are talking about.

The idea (on this board and others) is to do a heat load calculation, and then without checking that calculation just run with it. Even though the equipment sizes are sitting right there telling you. (Old Structure. -- New structure by all means do a heat load calc.)

There was a post on this board in which a heat load was done and the equipment was down sized, didn't keep up and later had to be replaced again. So guess again Mike. They are not fool proof. They are a TOOL, for those who KNOW how to USE THEM.

Whether you want to read and / or listen to my 23 years of HVAC experience in actually doing the work is entirely up to you. I can only help those willing to listen to sound advice.

lol

"Mike the load calculation was already done. Your thinking is that someone is going to get a load calculation any more right after the house is already built and older equipment is sitting there. What has changed? How long has this equipment sat in this home? But now because we are going to replace it, it is sized wrong? (It's not a new structure is it?)

Your thought is to second guess the builder who had all the R-values of windows, insulation etc. of the home in order to do the calculation?"

A lot of assumptions here, though, Ray. Load calcs weren't done much until the late 1980s. Anything built after that may have had a load calc but more likely just the old 1 ton per 400 sq ft rule of thumb. More recently, (2000+ and in certain states) this has been a requirement for new home construction but there's still a lot of homes with guesswork sizing. I'm not saying a load calc is the be-all and end-all of HVAC but it's the most intelligent starting point.

Well as I said before it's a tool. When you need a hammer you go get a hammer. So I thought I was being clear... as to suggest if a HVAC contractor due to experience see's something that doesn't look right you would use the 'tool' in those instances.

The other problem as it portends to HVAC sizing in previously constructed homes is that if you down size the HVAC system, the duct system is in many cases now over sized.

If you up size the HVAC system, the duct system is in most cases now under sized.

Realize the OP, due to what was said about general rule 600 to 800 sq ft per ton he started to think he could do away with two systems.

(quote) I'm beginning to wonder if I could go from 4 units to two, at a capacity around 8 tons rather than 12 tons. (/quote)

Meanwhile nothing was said about current duct systems to 'serve' these affected areas.

So in a previous built home, when you are discussing 'sizing options'. The conversation isn't just equipment sizing... it's also duct sizing. But, nothing was said about 'existing' duct systems.

If you get the system sizing right and duct sizing wrong... what does that lead to?

As a side note: "Why do you think I asked OP if this was a quad plex or 'multi unit' town home in my first response to this thread?"

Hint: HVAC is not a one size fits all market.

I think we are generally in violent agreement!

;)

Well you have to have a understanding of variances in real estate market.

A 4500 sq ft mansion is considerably different than a normal 1500-2000 sq ft cookie cutter home.

A person who can afford a 4500 sq ft mansion, the builder typically sells via visually stunning features. Many times these visually stunning features are not in tune to being 'energy efficient' like that of a cookie cutter. Because the cookie cutter is of a quality more to cut costs than to sell something.

a 1500 to 2000 sq ft is more likely to have 1 HVAC system or at best 2 systems one for each level.

Because of the scale of the 4500 sq ft mansion and often times spectacular entrances with not only high ceilings but also walls of glass (in some cases) these can add heavy loads not found in a 'cookie cutter' home.

Because the mansion foot print not to mention the selling prices of these kinds of homes air conditioning is more of a commodity than a heavy cost. The builder is dealing with a 'different' type of client. This client wants to be comfortable. If money was no object of discussion wouldn't you want to be comfortable?

When you get into 3, 4 and as large as 5 HVAC systems in a home the equation changes because many times 'some' of these systems may act as staging. They 'may' be intended only to run when the load is heavy enough.

You have to understand, that in order for a system to run... there must be a call. If you have over capacity (staged) what will this do to opposing thermostats in the area? cycle off. Over capacity in this method doesn't harm anything in terms of humidity and so on because you can stage the units to run under appropriate circumstance.

So over capacity is a good thing (when you need it) but can be shut off when you don't need it. You can't really pull this off in a cookie cutter, because it's always the argument about costs.

The other side of this is that a 4500 sq ft home has much bigger chance to host lavish get together with potentially large families. The mansion can hold much more people than a cookie cutter could ever dream about.

Whether you agree or disagree is fine. I've been in similar homes with as many as 5 HVAC systems. Entirely different because of layout and staging options available to this type of structure.

Get others there to help you & try doing a number of individual load-calcs & Sizing's... 12-Tons on a 4500-sf home seems like over-kill; unless you're going to staging units...

http://www.loadcalc.net/

Variable-speed compressors and variable-speed blower are wonderful for humidity control. I live in South LA, very humid. My cooling is generally off all day and comes on in the late afternoon. Indoor temp is generally about 75 when I get home and the humidity can approach 40%. I do have mini splits.

One great thing about multiple systems is that it layers variable speed on variable capacity. If not all of the house is "on" at the same time, you get the HVAC in one part of the home doing some work to do bleed-over tempering the "vacated" part. That is great in times of low demand. You don't want to let is go too far though and run at full-throttle opening. VS systems are in an inefficient operation zone when approaching flat-out operation. They are probably most efficient at less than 50% output.

Another nice thing about multiple systems is that if you want backup generator power, you don't need as much to keep at least part of the home reasonably comfortable. My inverter-driven compressors also have no significant start-up surge which is also a boon in times of utility power failure.