need trane-specific info

[billsweats]

I have a Trane DY120R9V5V 2 stage furnace with variable speed blower. Max blower cfm is 2100. I am considering purchase of a Trane XL16i split system compressor. If anybody out there has Trane-specific knowledge, I’d really appreciate some help. My furnace manual doesn’t go very far in explaining some details.

1. Blower. In heat mode, my blower has 2 stages. Within each stage, there are multiple blower speed settings (low, lo-med, med hi). For example, in my current setup (lo-med),
stage 1 heat blows 1200cfm and stage 2 heat blows 1850 cfm. If I get the 2-stage XL16i, will my blower be smart enough to throttle back when the compressor is on stage-1 cooling?

2. To restate the same question, if I get a 4 ton compressor and set my cooling airflow dip switches to “normal” (400cfm per ton), then what blower cfm will I see in cooling mode stage-1 and in cooling mode stage-2?

3. Coil. What is the correct coil to get with this furnace/condenser combination? What are the coil box dimensions (length, width, height)?

4. Coil icing. I live in a semi-arid climate (low humidity). Am I correct that this will tend to cause more coil icing problems since I won’t be dumping much latent heat into the coil and therefore the coil will run colder? Is there any way to address this other than run the blower faster? I don’t want the noise from running the blower faster.

Any comments gratefully accepted.

[dan sw fl]

I I am considering purchase of a Trane XL16i split system compressor. If anybody out there has Trane-specific knowledge, I’d really appreciate some help. My furnace manual doesn’t go very far in explaining some details.

2. To restate the same question, if I get a 4 ton compressor and set my cooling airflow dip switches to “normal” (400cfm per ton), then what blower cfm will I see in cooling mode stage-1 and in cooling mode stage-2?

4. Coil icing. I live in a semi-arid climate (low humidity). Am I correct that this will tend to cause more coil icing problems since I won’t be dumping much latent heat into the coil and therefore the coil will run colder? Is there any way to address this other than run the blower faster? I don’t want the noise from running the blower faster.


Blower setting is normally 450 CFM / ton for low humidity climate.

[Airmechanical]

I have a Trane DY120R9V5V 2 stage furnace with variable speed blower. Max blower cfm is 2100. I am considering purchase of a Trane XL16i split system compressor. If anybody out there has Trane-specific knowledge, I’d really appreciate some help. My furnace manual doesn’t go very far in explaining some details.

1. Blower. In heat mode, my blower has 2 stages. Within each stage, there are multiple blower speed settings (low, lo-med, med hi). For example, in my current setup (lo-med),
stage 1 heat blows 1200cfm and stage 2 heat blows 1850 cfm. If I get the 2-stage XL16i, will my blower be smart enough to throttle back when the compressor is on stage-1 cooling?

2. To restate the same question, if I get a 4 ton compressor and set my cooling airflow dip switches to “normal” (400cfm per ton), then what blower cfm will I see in cooling mode stage-1 and in cooling mode stage-2?

3. Coil. What is the correct coil to get with this furnace/condenser combination? What are the coil box dimensions (length, width, height)?

4. Coil icing. I live in a semi-arid climate (low humidity). Am I correct that this will tend to cause more coil icing problems since I won’t be dumping much latent heat into the coil and therefore the coil will run colder? Is there any way to address this other than run the blower faster? I don’t want the noise from running the blower faster.

Any comments gratefully accepted.

1. yes if its wired properly

2. if its wired properly and dip switches are set properly it is smart enough, both hi and low speeds will be 400 cfm per ton!

3. the correct coil is in my trane catalog in the truck, sorry i am too lazy to go get it! i am sure its an 048 something

4. if its installed, wired, dip switches set, and charged properly you wont have coil icing problems with that combination!

5. if your getting a heat pump make sure a dual fuel kit and/or or the proper t-stat is installed!

6. get a qualified hvac contractor!



.

[aircooled53]

Yes the furnace will operate properly as the dip switcheas will be set-up for 1-2tonnage,3-4cfm cooling,5~6 Comfort ^R 7-8 cfm heating..

The only thing you need to consider is a (2)stage thermostat.:cool:

[ampulman]

Regarding coils : While you're looking up that coil info, could I slip in a related question?

I want to replace my furnace and a/c and am considering an XV90. Ran HVAC-Calc since the reps so far have refused or faked it.

My heating needs would be served by a High Efficiency unit of between 75,000 (such as a Rheem MOD) or 80,000 BTU input (XV90) at design temp (refining my study seems to favor the Trane providing an ample safety factor.

With regard to a/c, my ductwork is sized for 3 tons and at this stage, I would not consider any changes. The current 3 ton unit was somewhat less than adequate, I believe due to a less than ideal sensible heat capacity. My study indicates a sensible gain of 26,745 and latent of 3744 at design. I would like to have a sensible capacity of about 31,000 BTU to be able to handle the extra hot days.

Question: Does Trane Brand or approve any oversized coils for use with a 3 ton XL1Vi that would provide the above capacities? Thanks.

AM

[dmctechtrainer]

I agree with Airmechanical...get a qualified contractor who can assist with the selection and setup of your equipment. Especially the multi-stage products like the 16i, which is by the way 70% capacity on first stage and 100% capacity on 2nd stage.

[billsweats]

thanks for the info. Very helpful. I would appreciate
if someone could come up with the coil info (model #, dimensions).

I agree with the comment about finding a competent tech. The
question is, HOW. I have had 3 guys come out and bid, and none
of them seem to know much about HVAC, or at least to show it.

They ALL are pushing me into a 5 ton compressor, whereas my load
calcs show that 3 tons will carry me easily. That, BTW, is why
I am interested in the XL16i. It is a way to finesse the sizing
question to some degree by going 2-stage. I'm willing to bet $$,
BTW, that if I get a 4 ton XL16i, it will NEVER call for stage-2, unless
I am overcoming a large setback.

So, I feel that I need to really know my stuff so I can figure out
who is a hack and who isn't. I'm not trying to cheap out, BTW, I just
want a quality installation.

[lbf]

Bill, it sounds to me that you're on the right track to get a good contractor. You're getting some knowledge of your own and your asking questions. Talk to friends who have had success with someone and try them. Trust your instincts, and your BS smeller. To answer some of your questions, yes the furnace is "smart" enough to slow the blower during 1st stage, it will be 80% of high stage. You will see that 1st stage compressor capacity is 70% of high stage so you will actually get a very slight change in your sensible heat ratio. Ampulman, Yes Trane makes several "oversized" coils that will match up to that unit. You can go to ARI's website to find out which ones. Try asking these questions of the contractors your interviewing, they should be able to tell you these things as well as us. Good Luck.

[pstu]

Bill, would you allow me to ask you why you need to research the coil model on your own, vs. asking a tech whose job it is to recommend a match? I understand your concern for some of your questions, I deeply empathize with the difficulty finding a pro you can trust, but a couple of questions sound like you are trying to manage too many details. I know that isn't what you want to hear, but sincerely feel this is the case and believe you could improve quality and lessen effort by not managing some things directly. I will offer help where I can.

There is a technical manual that goes with your Trane furnace called "SERVICE FACTS". My tech gave it to me, maybe yours can get you one. My furnace is the Trane variable speed AUD-080-R9V4K, it has performance details on page 13: Airflow, wattage, temperature rise, and DIP switch settings. These last should be regarded as powerful information, capable of causing equipment damage with the wrong kind of mistake.

Airflow can be selected as low-med-high for each stage of heat, with varying temperature rises. My AUD080 VS air handler will raise or lower its torque to keep airflow nearly constant between 0.1 and 0.9 inch ESP (backpressure, measured in inches water column). I observe the 5-ton counterpart has more variability, but it's still flat between 0.3 and 0.7.

Separately, my AC airflow can be selected for 2.5, 3.0, 3.5, or 4.0 tons (The TUD120 is good for 3.5, 4.0 and 5.0). For each of *those*, airflow can be chosen as low-med-high, corresponding to 350, 400, or 450 cfm/ton. You should be able to work with any AC size in this range and airflow will be essentially correct, plus you have low-humidity and high-humidity options.

Your concern about coil icing -- I want to ask the pros, is that a common hazard in dry climates? I just don't know and am a little curious about that.

Coil identities -- is there a reason you want to manage this directly? Is there going to be a physical fit problem, are you aiming for the best SEER, or what? The simple answer is just ask your Trane tech to look it up in his publications. But that is not the only way, you can also go to http://www.aridirectory.org/ari/ and look up tons of tech details yourself. You will find there are a small number of coils rated as a match for the 4.0 ton XL16i and your furnace which I shortened to "TDY120":

4TXFH063AS3 -- 16.00 SEER, 48,000 BTUH total capacity
4TXFH054AS3 -- 15.50 SEER, 46,500
4TXCD061BC3 -- 15.25 SEER, 46,000
4TXCD050BC3 -- 15.00 SEER, 45,000

You may note that Trane proudly advertises higher SEER ratings which can only be obtained by a specific combination of coil and condenser, the top is only available in a smaller size. As far as I know all other manufacturers are the same way.

My own coil is a TXH041 coupled with an Allegiance 18 (nearly same as XL19) and I have found a Trane document called "Split System Cooling Product and Performance Data". I have not been able to locate it online for the XL16 series, but have for the XL 14 and XL19. If you can locate it, this book will list tons of Trane coil, furnace, and condensor models. It will give sensible and total capacity for 4 outdoor temps, 4 indoor wetbulb and 4 drybulb temperatures -- providing answers similar to part of Manual S. I really admire Trane for publishing such info and do not know whether other manufacturers do as well.

Hope this helps -- Pstu

[billsweats]

Ptsu –

Thanks for your interest. First of all, let me just say, “Guilty as charged”. What I mean by that is that in my career (which has nothing to do with HVAC, btw) whatever problems I might have had were due to my tendency to micromanage. So, you got that one right. Along with that aggravation, my bosses got systems that worked right, were on time, and on or under budget. In the end, my customers loved me, my bosses appreciated me, and many of my subordinates disliked me. Oh, well.

Thanks also for the pointer to the “Service Facts”. I have the same document for my furnace and it is very useful.

My concern about coil icing is because one of my objectives in this-here exercise is to end up with a system which is as quiet as possible. I figured the installer would set things up for 400cfm/ton, but I also figure that at 1600cfm total, I will be able to hear the airflow. This is my sole motivation for the 2-stage XL16i, and I thought I would also try out the 350cfm/ton setting, also. I started thinking about potential problems, and it seemed to me that the evaporator coil would run warmer in a damper climate, and therefore one potential problem if I cut the airflow to 350cfm/ton might be coil icing. Hence, my question. I might add that what really got me going was that the "service facts" says that dry climate airflow is 450cfm/ton, and I was wondering why. It is pure speculation that dry climate coils run colder and hence require larger airflows to keep them from freezing up.

My questions about the coil size are because I am worried that some installers might be tempted to install a smaller coil. My existing heating system was installed in 2002. At that time, I completely redid all my ductwork, plenum, etc. At the time, I asked the installer to put in a coil box, so that adding a/c in the future would be a simple drop-in. In 2002, I knew *nothing * about a/c. Well, sure enough, the guy screwed me by putting in a small coil box that won’t accept a 4-ton or a 5-ton coil. Fool me once, shame on you; fool me twice, shame on me. I just want to make sure I’m comparing apples to apples with my bids. Of the 3 bids I have, only one has specified a coil (?!). I figure there are actually 2 coil issues – first the SEER (or EER), i.e. cooling efficiency. Second, I suppose it would be possible for the coil to obstruct my heating airflow enough to cause the power consumption on my blower to increase appreciably.

What I want for my system is a quiet, reasonably efficient system. I agree that it would be vastly preferable to specify that to the contractor, and let him do is job. The problem is, I have tried that now with 3 contractors, and they all have bid 5 ton condensers. If I let them have their way, I would have a cooling system that would blow at 2000cfm. It would be neither quiet nor reasonably efficient. By the way, the price for this mis-design would be as high as $8500. At the end of the day, then, I am responsible for my system, and the only way I will get a bad system is if I let them sell me one. I’m just not going to let them do it.

In 2002, when I re-did my heating system, I had a bunch of guys who wanted to drop a 2100cfm blower on top of my existing ductwork and call it a day. In the end, I had to resort to drawing up exactly what I wanted and then attach the drawing to the bid. I got 3 bids. These guys to one degree or another all gave me the old “customer is always right” wink-wink you are a dumb *&^%. What I had drawn up was a duct system that would match the blower at 0.1inch pressure on the supply and 0.1inch pressure on the return. It is EXACTLY what I wanted, and it works beautifully.

In 2007, what I want is a cooling system that will carry a sensible load of 28kBTU. This corresponds to 2pm on the hottest day in our history. Nobody will bid it, because they are afraid that it won’t cool the house. They’re wrong. But I understand, because they are used to poorly insulated houses with poorly insulated, undersized ductwork. They bid 5 ton systems because that’s what they’re used to. OK, I understand, and am actually mildly sympathetic. But I’m not sympathetic enough to let them install a system that roars from the ducts and which short-cycles. So, we’ll compromise. I’ll buy a 2-stage 4 ton unit. They’ll get their 4 tons per the cookbook. I’ll get 2.8 tons on the first stage. It might kick on to the 2nd stage once in the next 10 years. But, we’re getting close. I figure that if we can get the coil sizing right we’re almost home free.

I say almost because (I am not making this up), 3 out of 3 guys bid the electrical run based on matching the wire gauge to the Trane breaker spec. Problem is, the run is 160 feet, so the IR drop is excessive. OK, wink-wink, the dumb *&^% customer is always right, we’ll run larger gauge wire.

I do truly appreciate your interest in my design problem. I apologize for the rant.

[Engineer-Gal]

One good thing that has evolved from the Energy Efficiency hikes in the past few years has been the advent of installing TXVs on just about every combination of appliances (except for Goodman...). With a properly sized unit/coil and proper refrigerant charge--you should avoid nusiance ice/frost.

As far as heat transfer... remember that more energy is transfered in latent heat change of state than in sensible heat rise... Every application needs to have a period of sensible heat elevation above the boiling point of the refrigerant to protect the compressor while obtaining the best efficiency out of the coil.

As a rule of thumb and a fact... it's better to undersize a unit than oversize it.

Someone mentioned the ARI website... great place to obtain facts about coils and other appliances. The SEER rating is only one component of a system and can easily be diminished if only "part" of the system is as tested.

Installation can also be another concern... for evern 1% away from ideal refrigerant charge of a system you pay 1% more in electric (up to 20%, then then the curve changes).

I am curious how you calculated your whole house load?

[billsweats]

Engineer-Gal-

I did my energy calcs as follows:

known R-values. Derate conservatively. ex R30 ceiling, use R22

known attic temps. Derate conservatively. ex. 145F attic

known crawl-space temps. Derate conservatively.

known areas.

Multiply.

Here’s the excel data. Sorry about the formatting.

no attic fan tgt 75
area avg R outside T delta T heat load
ceiling 2500 22 145 65 7386 ceiling
walls 1680 11 105 30 4582 walls
windows 400 2 105 30 6000 windows
floors 2500 5 80 5 2500 floors

20468 subtotal house only

U factor supplies 100 80 35 3500 supply energy loss
U factor returns 78.5 145 70 5495 return energy loss

29463 total house incl duct loss
2946.318 add'l 10%margin

32410 total heat load

with attic fan

tgt 75
area avg R outside T delta T heat load
ceiling 2500 22 125 50 5682 ceiling
walls 1680 11 105 30 4582 walls
windows 400 2 105 30 6000 windows
floors 2500 5 80 5 2500 floors

18764 subtotal house only

U factor supplies 100 80 35 3500 supply energy loss
U factor returns 78.5 125 50 3925 return energy loss

26189 total house incl duct loss
2618.864 add'l 10% margin

28808 total

[Engineer-Gal]

billsweats,
there are a few more factors that are entered into the equation that may be why your contractor has specified a larger unit...

The "formula" -- if you will -- for calculating Q Specific and Q Latent (also known as a Manual J Calculation) takes into consideration the orientation of your house (N,S,E,W) and the heat gain from orientation with windows doors, how many heat generating appliances you have, how many people occupying the space, the door sq ft area, fireplaces (loss), roofing material and color for deflection, aggregated weather data, etc... there's no short method for the calculation other than using a program to crunch the numbers instead of actually doing the math (which I had to do longhand in college!)

I think you have a very strong foundation--and might suggest something that I've had to do (since I'm a woman) is sometimes act 'stupid' when with a contractor. I'd ask them for a manual J and compare their numbers with yours. Also, my Father is a Mechanical Contractor and if he thinks that a customer is "high maintenance" they jack up the price :)

Some states actually require a Manual J to be performed on all new or existing installations.

You could be right on the money with your calcs... but it should NOT be unreasonable to ask the contractor (whom you're about ready to drop thousands of dollars with) to provide you with this level of detail.

If your unit is sized correctly (they always say...) on the hottest day of the year, it is not uncommon for it to run 23 of the 24 hours of the day.

I hope this helps...

[billsweats]

Engineer-Gal:

thanks for your interest. Yes, I know that to some degree
I'm digging my own grave here as a "high maintenance" customer.

My problem is, I have had 3 bids, and no one did a load calc. No
one *asked* about my insulation. No one *asked* about my
ducts. No one *looked* at my windows.

When I asked, in all 3 cases I got an answer that they use 500 sq ft
per ton. That's it.

So, I'm kind of between a rock and a hard place.

Nonetheless, I really appreciate your interest.

Regards,

Bill

[dan sw fl]

Engineer-Gal-

I did my energy calcs as follows:
known R-values. Derate conservatively. ex R30 ceiling, use R22
known attic temps. Derate conservatively. ex. 145F attic
known crawl-space temps. Derate conservatively.
known areas.

Multiply.

Here’s the excel data. Sorry about the formatting.

with attic fan

tgt 75
area avg R outside T delta T heat load
ceiling 2500 22 125 50 5682 ceiling
walls 1680 11 105 30 4582 walls
windows 400 2 105 30 6000 windows
floors 2500 5 80 5 2500 floors

18764 subtotal house only

U factor supplies 100 80 35 3500 supply energy loss
U factor returns 78.5 125 50 3925 return energy loss
26189 total house incl duct loss
2618.864 add'l 10% margin

28808 total

Where is the Solar Radiation load for the 400 Square Feet Window area?
Depending on the S.H.G.C. (S.C. / Shading Coefficient * 0.87), Internal & External Shading, locale and the window orientation,
one needs to add > 8,000 BTUh & < 20,000 BTUh.

[pstu]

Billsweats, I invite you to rant at me and I occasionally will rant at you, I highly appreciate it that you collect facts and think rationally. A couple more facts for you: I went up into my attic and measured my Trane TXH041 coil at 37.5 by 22.5 inches, and a 2nd system has an Aspen coil at 36 by 17 inches.

I think 3 contractors is not enough. You have gotten 3 bids all right, but what's lacking is the process of qualifying. 500 sqft/ton is stupid although it may work OK in some climates. But you are in N. California are you not (put some info in your profile, for mutual benefit)?

I say it is *not* conservative to choose the hottest day of the year for design conditions, nor an attic temperature which has never been seen. This is consciously constructing "garbage in" for the model, I cannot help wondering what is the difference between that and fibbing about your window area. Or about your house size. I am feeling the strong urge to say you have talked to 3 mediocre guys in a row. My experience has been to talk with 6 companies before I finally settled on one that is content to let me specify many things, with a little discussion and the background philosophy of "if you are happy then I am happy". I appreciate that to the extent that I frequently emphasize my eagerness to pay extra when I get extra.

I have wound up being more of a designer than I want, but try not to push it to the Nth degree. A testimonial to my nerdiness: I have found a couple NOS Dwyer Model 25 red-oil manometers from Ebay, and permanently installed brass nipples to the return and supply plenums -- actually the transition between air handler and coil -- to monitor ESP. I was motivated by reading about how the Carrier Infinity control monitors ESP as a way to signal the actual need for filter change. My tech accepts this (though others felt threatened) and tells it to the counter guy when he buys parts, nobody else seems to be doing this. These Dywer units are low tech and cheaper than a Magnahelic gauge, you can find them as a commodity on Ebay.

You can find what I stereotype as "Goodman Hacks" which will install what you buy, can you not? If so then why not what you select? I have Trane brand but would happily accept Goodman if it came with the right workman. It might take a little searching, but the guy who sometimes "rents his body" to DIY-ers might be able to work with you if he can have good craftsmanship. I suggest when you find the right guy, a time-and-materials pricing so he will feel no pressure to cheap out.

Have you thought about sidestepping the big problem and going to a ductless mini-split AC instead? You have an interesting project to say the least.

Best of luck -- Pstu

[pstu]

...
If your unit is sized correctly (they always say...) on the hottest day of the year, it is not uncommon for it to run 23 of the 24 hours of the day.

I hope this helps...

Please allow me to ask what you mean by this! Do you mean running for 23 hours non-stop, or having just some cooling call in all but one hour in the day? How did you arrive at this information? Have you ever observed this happening?

It does not seem plausible to expect a high duty cycle in the nighttime hours between midnight and dawn. To me the "run all the time" phrase begs to be interpreted as over a 1-3 hour period. I agree there is a matter of defining one's words, that standard Manual J parlance has not done here.

I have placed a data logger in a supply duct and obtained a fairly accurate measurement of when my single stage AC turns on and off through a typical Houston area summer. My weaker of two systems has been observed to run 239 minutes non-stop on one occasion, it maintains temperature but has very feeble pull-down capability. It only rested for an entire summertime hour when there was a thermostat setback, then at 4AM when recovery began it would run well over an hour non-stop. My idea is the cooling load *should* be very low in the 2AM-6AM time frame. This compressor unit was diagnosed to have leaky valves and replaced this year.

That same data logger measured 75&#37; duty cycle only (with an outlier exception or two), during each hour in the peak summer days of the year. When you measure 3-4 hour periods the duty cycle falls off considerably. This is from Houston area and we have a lot of days which resemble the Manual J design condition of 94F with high humidity. From that I estimate the 3.5 ton AC is moderately oversized, that a hypothetical 2.75 ton unit would just reach 100% duty cycle in one hour. That sounds like a comfortable sizing to me, consistent with the broad goals of ACCA Manual J. Getting into multi-hour 100% duty cycles, sounds risky to me and I would hesitate to jump into that with actual equipment and my own money.

Let me submit an alternative goal: to have non-stop running for more than one hour during peak time of day, but not much over two hours. That is what I understand would be compatible with Manual J design goals. What would you think of that?

P.S. I often speak of "HVAC guys" as if there were zero women in the field, I know this is not literally the case but have not been called on it yet. I hope you will tolerate this choice of speech as an idiom. No disrespect for women in the field is implied, I have seen the engineering field progress from 99% male to about 70/30 and the newcomers are very impressive professionals.

Best wishes -- Pstu

[mchild]

pstu,

Drop me an email using my user name at simiusa dot com. I have something to send you that I think you will find helpful.

[billsweats]

Designer Dan-

thanks for the guidelines on solar radiation load. That in fact may bump my load up. For what it is worth, my house faces WSW, and the west wall has a large overhang (photo attached). From about 11am until about 5pm in the summer, I have no windows which are directly illuminated by the sun.

Thanks,

Bill

[Engineer-Gal]

I think if you look at the manual J load calcs... and follow them, then on the extreme hot day in the summer, yes, your unit will run practically all day long to satisfy the cooling call.

Unfortunately, most contractors have developed a precedent for oversizing. It doesn't just happen in the AC market, it happens in hydronics... WAFs as well.

Bill-- I might suggest that you get some more estimates as well. You don't need to hang your hat on only Trane. Look at the ARI data on matched coils and condensers... Most units today have Copeland Scroll compressors. Copeland makes a 2 stage and a variable speed compressor that might work for your application. Emerson even touts that their scroll can better control the humidity in the space in tangent with the indoor circulating plan.

[pstu]

>>If your unit is sized correctly (they always say...) on the hottest day of the year,
>>it is not uncommon for it to run 23 of the 24 hours of the day.

You are talking about the extreme hot day in the summer, being rather more extreme than the design day. Do I have it right?

Let me add more observation of runtime. Before I got the data logger, I measured with a stopwatch and found a peculiar pattern. The AC would run for just about 55 minutes in an hour, meet setpoint, then be off for the minimum 5 minutes the circuitry allows. As soon as that 5 minutes is up, a new cooling call is initiated, and it too will run for close to an hour. The resulting duty cycle is 55/60 or 92&#37;.

I submit this pattern of behavior pretty clearly proves 1) sizing is adequate to meet setpoint, and 2) it has basically zero excess capacity. These measurements reflect something close to the design day, not an extreme day. Yet using a data recorder this system was observed to have a 100% load factor based on one hour, and a 73% load factor based on the most intensive four hour period. That is my reason for being skeptical that any system capable of maintaining setpoint, will run 23 hours non-stop. If indeed that is what you said and meant.

Regards -- Pstu

[tpa-fl]

My problem is, I have had 3 bids, and no one did a load calc. No one *asked* about my insulation. No one *asked* about my
ducts. No one *looked* at my windows.

When I asked, in all 3 cases I got an answer that they use 500 sq ft
per ton. That's it.

That's an easy one -- get more bids! There have to be more than 3 HVAC contractors in your area.

[pstu]

Billsweats, I recommend you not overlook this thread, especially post #11:

http://hvac-talk.com/vbb/showthread.php?p=1467729#post1467729

Hope this helps -- Pstu