14 vs. 16 SEER

[citypaws8]

I am trying to decide between two Trane XLi systems. The 14 SEER is a 2.5 ton unit, the 16 SEER is a 3-ton unit. Either would have a variable speed fan, and both come with Puron.

We have a 1176 square foot duplex with only the main 2 floors cooled, for about 784 square feet. Our current system is just caput, too old, and has never cooled well in the 4 years we've been in the home. We get direct, hot, afternoon sun on very large, single layer glass metal casement windows -- 72 inches wide by 52 inches tall -- in an old, uninsulated brick home with plaster walls (so insulation and new windows aren't coming anytime soon). So here in MD's hot summers, we have needed quite a bit of cooling. We believe the old unit is a 2-ton Rheem.

The 3-ton 16 SEER as we understand it, can work at a reduced 2.5 ton capacity when demand is lower, thus saving energy costs. With a Trane rebate offer, the difference in price is only $500. We were originally sold on the 14 SEER, but the 16 SEER with rebate seems like a good offer on a quality product. Is there any good reason not to go ahead and get the more efficient unit or would it be a waste? It is a starter home for us, but it's in a high-valued real estate area, so no matter how long we may stay, we always consider quality products for our home improvements.

Any thoughts?

Parker in MD

[tigerdunes]

Paws

I assume you are speaking of either the single stg XL14i or XL15i vs the two stg XL16i. These are heat pumps correct? For $500, I would definitely go with the 3 ton XL16i. You will get better comfort/dehumidification plus the extra capacity will help you on heating. One caveat. You will probably have to get your ductwork modiified to handle the extra CFMs. I hope your dealer has mentioned and planned for this. You may want to request a load calculation and think about a window upgrade.

IMO
:)

[pstu]

The two stage action would probably guarantee greater comfort. Sounds like the rebates are giving you a bargain here.

You probably had a not-too-well designed duct system in the first place, because that seems to be true of the majority of houses. One typical problem is leakage in the range of 15% or 25% of all the air blown through them. Another typical problem is insufficient return so that airflow back to the air handler can be choked off, resulting in reduced cooling capacity and sometimes premature failure. Your duct system could be part of today's problem.

Now that you propose to blow 25% or 50% more air through the ducts, it might be a necessary idea to consider replacing the duct system as well. Some highly skilled techs can evaluate, diagnose, and fix duct problems but that would perhaps be too sophisticated to ask for. More power to you if you can find a pro to do this.

But if you just hook up the larger AC to the existing ductwork, it is a crapshoot with a high probability of failure and inefficiency. There is more science to this than most people think. Certainly I would choose the Trane 16i model if the price got this close, but would also expend serious effort into making sure you get a first class install. This is unlikely to be the lowest bid job.

I hope a pro from this board could be close enough to tell you what exactly to ask for, and perhaps to serve you directly.

Best of luck -- Pstu

[BaldLoonie]

WTF?

Someone is suggesting a 3 ton system to cool 784 square feet? Even with an old building, sounds awfully high for what isn't a particularly hot area.

So even you go this size, did anyone check the duct system? If you have a 2ton now, chances are you're gonna need 50% more duct airflow capacity to go 50% in cooling capacity! Tigerdunes is suspicious of this too!

[citypaws8]

Paws

I assume you are speaking of either the single stg XL14i or XL15i vs the two stg XL16i. These are heat pumps correct? For $500, I would definitely go with the 3 ton XL16i. You will get better comfort/dehumidification plus the extra capacity will help you on heating. One caveat. You will probably have to get your ductwork modiified to handle the extra CFMs. I hope your dealer has mentioned and planned for this. You may want to request a load calculation and think about a window upgrade.

IMO
:)
I don't have the product number on the 16 SEER, but XL16i looks right, based on the XL14i originally quoted. They are not heat pumps. This is a straight a/c compressor and air handler replacement.

What sort of duct modifications? More runs? Larger ducts? Larger return?

Parker in MD

[dan sw fl]

I am trying to decide between two Trane XLi systems. The 14 SEER is a 2.5 ton unit, the 16 SEER is a 3-ton unit. Either would have a variable speed fan, and both come with Puron.

... 1176 square foot duplex with only the main 2 floors cooled,
... for about 784 square feet.

Our current system is just caput, too old, and has never cooled well in the 4 years we've been in the home. We get direct, hot, afternoon sun on very large, single layer glass metal casement windows -- 72 inches wide by 52 inches tall -- in an old, uninsulated brick home with plaster walls (so insulation and new windows aren't coming anytime soon). So here in MD's hot summers, we have needed quite a bit of cooling. We believe the old unit is a 2-ton Rheem.

The 3-ton 16 SEER as we understand it, can work at a reduced 2.5 ton capacity when demand is lower, thus saving energy costs. With a Trane rebate offer, the difference in price is only $500. We were originally sold on the 14 SEER, but the 16 SEER with rebate seems like a good offer on a quality product.

Is there any good reason not to go ahead and get the more efficient unit or would it be a waste? Parker in MD

High estimate/ ball park of sensible load might be 22,000 BTUh ( 43,000 BTU heating) with VERY Poor, old construction ...
R-4 walls, R-13 ceiling with clear, 132 square feet of Single pane glass ( U 1.3, SHGC 0.78).

I would get a quote for an XL19i 2.5 Ton.
XL19i operates at 50% capacity (1.25 ton) using first stage.

At 350 CFM/ton setting, a 2.5 ton V S air handler would have 875 CFM total
which likely is not significantly higher than the existing set-up.

Does your MD utility over a worthwhile rebate for higher SEER replacements?
IF yes, the utility rebate combined with a slightly higher TRANE rebate, the overall XL19i cost may not be significantly different than a XL 16I and performance will be much improved with a more appropriately sized unit.

800 sq. feet may not need > 1.5 Tons (Second stage) in subject residence,
except for ~ 4 hours/day when > 85'F (330 hours / year at Andrews AFB)

What is the age of this residence? I wonder if the infiltation loads are very much higher than one might generally anticipate.

In addition, for MD, I would recommend a heat pump in most cases.
However, a heat pump may not be the most viable option for you at-thi$-time.

[citypaws8]

Thanks for the replies. No, they haven't suggested we need larger ducts, but I certainly will follow-up before making a decision. I have faith in the company; I selected them first, then the system. They came with great references, I'm dealing directly with an owner, and I liked their techs both times they were at the house before.

Also, it is quite hot here in the summer. It's not Texas, but it's not Indiana either, and we get buried in humidity. We have many days in the 90's and with direct sun on the bricks, good a/c is a must, and in most summers it will run non-stop from mid-May through September at least. In warmer summers, we have used it April through October.

The windows are definitely a handicap, but the home has certain historic value, and that combined with other house factors make a window replacement by any owners unlikely, I think, ever.

What, exactly, would a GOOD duct system look like? Ours runs from the air handler in the attic down through closets, etc. to serve the 2nd and 1st floors. We are adding one run to the living room, which is the hottest room and does not currently have a duct. I do know that the ducts on the old system were not properly secured. There was one large duct taped to the air handler end, and the other ducts ran off that, duct-taped to the side, with many leaks, I'm sure. The ducts are round tubing, gray plastic (like Hefty bag plastic) on the outside, presumably insulation/foam inside of there.

The return issue was brought up on our first consultation, but without a good place to put a 2nd one (existing one is at top of open stairs), we were aiming to work with the one we have until signs show we need the 2nd. It won't be impossible to put one in, but definitely a pain, and again, more marks on a historic house. However, that was when we were looking primarily at the 14 SEER.

Parker in MD

[citypaws8]

High estimate/ ball park of sensible load might be 22,000 BTUh ( 43,000 BTU heating) with VERY Poor, old construction ...
R-4 walls, R-13 ceiling with clear, 132 square feet of Single pane glass ( U 1.3, SHGC 0.78).

I would get a quote for an XL19i 2.5 Ton.
XL19i operates at 50% capacity (1.25 ton) using first stage.

Does your MD utility over a worthwhile rebate for higher SEER replacements?
IF yes, the utility rebate combined with a slightly higher TRANE rebate, the overall XL19i cost may not be significantly different than a XL 16I and performance will be much improved with a more appropriately sized unit.

800 sq. feet will not need > 2 tons, except for a couple hours a day when > 89'F ( 100 hours / year at Andrews AFB)

What is the age of this residence? I wonder if the infiltation loads are very much higher than one might generally anticipate.
I will have a better guess on "ball park" load due to "old" wall structure later.

In addition, for MD, I would recommend a heat pump in most cases.
However, a heat pump may not be the most viable option for you at-this-time.
We talked about the 19 briefly, though I hadn't considered it seriously. He was to check to see if it used Freon or Puron. We are trying to stay away from Freon.

I don't think in MD we get energy credits, but the 19 from Trane I think is one of their only models that qualifies for the federal credit of $300.

The house was built in 1940. :-) It's beautiful, just old, with brick, plaster, and no insulation. We have large window exposure on the East, South, and West sides. We considered a heat pump but ruled it out. We have boiler heat with radiators and the boiler also heats the water tank. Here it is considered the warmest system available, and to do a heat pump for even part of the year, we were informed that it would make no sense to keep the boiler to heat the water. So to do a heat pump, we were advised to do a new water tank at the same time. It would have to be electric, and frankly, our water system is great; it's instantly hot no matter how many showers are taken back to back, and electric would be a downgrade. The boiler is original also but with new parts everywhere, including a replaced burner, and we've been told over and over by techs and real estate folks that in our area it makes no sense to replace a working boiler. Just get it serviced regularly, which we do. We definitely need the a/c and want to spend our dollars there. More $$ to do the boiler also may not get recouped by us unless we stay in the house a very long time.

It's actually those couple hours a day that we are trying to perfect. In the old system, we were getting only 10 degrees of cooling once the temp went over 85 and the sun came out.

Parker in MD

[pstu]

I believe the Trane 19i series is totally R-22 Freon, your proposed 16i is totally R-410 (Puron). FWIW the 1st stage on the 16i should be 67% of the total, so it will behave as a 2-ton unit on 1st stage and 3-ton on 2nd stage.

I am curious, are your ducts attic or elsewhere? Are they flex ducts or hard metal? Good sealing is mandatory for good performance, unless ducts are in conditioned space. The problem you and many others face is, the cooling BTUs (tons) delivered to the supply registers, will be a fraction of what is on the nameplate. Many times when you need more cooling, the real necessity is to reduce those losses -- the common thought is a bigger AC which sometimes is a poor solution or none at all.

People like to think of AC as an appliance. Sales people like to sell an appliance, it needs minimal manpower and brainpower once plugged in. The biggest problem I see is, any house which has air ducts doesn't have an appliance but a custom engineered system. It could be engineered well or engineered badly, but you cannot think plug-and-play like an appliance.

Gloomy but I think it will help -- Pstu

[beenthere]

I would look real close at that duct work.

3 tons to cool less then 800 sq.

You may have more air leaks then you thought.

[coldking]

I doubt that flex duct is insulated. Flex duct straight from air handler isn't a sign of good duct design. I would definitely have the duct work addressed no matter what system you choose.

[citypaws8]

I would look real close at that duct work.

3 tons to cool less then 800 sq.

You may have more air leaks then you thought.
Many thanks to all. They are coming back out to shore up these decisions. My understanding of the 16 SEER 3-ton unit is that it has two stages and in the first stage it operates as a 2-ton unit, which is what we currently have. So it would only operate at 3 tons during peak times, and technically, I guess if we address the duct work then we may never need the 3 tons. So the 2.5 ton 14 Xli is still on the table. The 19 suggested by someone is more than we wish to pay right now, even with rebates and tax credits.

Parker in MD

[tpa-fl]

Even 2 tons for that space still seems a bit high... but I've never seen the place, so it very well may be warranted. 3 tons for that space is totally overdoing it unless you've got something serious going on in there. Hydroponics, perhaps?

The only time I use anywhere near 250sqft/ton is in high-density electronics rooms and even then it's a special occasion. The only one I can think of off-hand is a room which houses 24,000 watts' worth of audio amplifiers + the 480v->240v split phase transformer for them. Even then, it takes running the amps near flat-out to come close to the capacity of the 3 ton AC system.

[kevinmac]

If you are not going to use the 2 stage for what it was designed for why buy it! It's just a waste of money. Configure the system so it runs on first stage for 85 to 90% of the time and the second stage kicks on to play catch up. Use a variable speed airhandler to provide the comfort throughout.

[pstu]

So Kevinmac, are you saying the smaller XL16i would be a better choice? The OP says they have inadequate cooling already, they want to make their comfort better somehow. As a homeowner I can see why 99% of people translate that into upsizing their AC. They may overlook important factors such as duct sealing, but you cannot blame them for lack of AC expertise.

When you say "Configure the system so it runs on first stage for 85 to 90% of the time", can people actually do that? I don't know how and would like to hear how it can be done.

Best wishes -- Pstu

[tpa-fl]

If you are not going to use the 2 stage for what it was designed for why buy it! It's just a waste of money. Configure the system so it runs on first stage for 85 to 90% of the time and the second stage kicks on to play catch up. Use a variable speed airhandler to provide the comfort throughout.

I'm well known for upsizing units and getting away with it... and there are times when installing a system that runs 1st stage 85-90% of the time...but those aren't the typical situations. Those situations are for things with widely varying heat loads, such as large solar gains from entire glass walls or where the homeowners do a large amount of entertaining and/or run the air con with their windows and doors open. That's when 2-stage REALLY shines. Proper ductwork, especially in the latter example, to make air curtains, is even more important in installations like this. I've seen many $3+ Million homes where they didn't get it right.

[citypaws8]

Even 2 tons for that space still seems a bit high... but I've never seen the place, so it very well may be warranted. 3 tons for that space is totally overdoing it unless you've got something serious going on in there. Hydroponics, perhaps?

The only time I use anywhere near 250sqft/ton is in high-density electronics rooms and even then it's a special occasion. The only one I can think of off-hand is a room which houses 24,000 watts' worth of audio amplifiers + the 480v->240v split phase transformer for them. Even then, it takes running the amps near flat-out to come close to the capacity of the 3 ton AC system.
Interesting. I can't explain the differences regionally, I only know that here in MD, 2 or 2.5 tons is the standard size put into old rowhomes and duplexes.

Parker in MD