A) The coil should be flush to the furnace for a replacement, so yes, I would ask the dealer (in fact this jumped out right when I saw the quote--I couldn't imagine 17.5" for a 100k 5-ton furnace).
B) Upsizing the coil isn't uncommon for more efficiency and sometimes capacity.
C) Usually significant revisions. I don't even see a 4TWX5048B1000A as even existing... the 4TWX5048A1000A should be the model I believe.
D) Probably either didn't note the need for an upgraded wire for a heat pump or didn't notice. Outdoor temp sensor is an option.
E) Possibly...

7/8" x 3/8" is the right size for the R410A 4-ton XL15i. Flushing the lineset in this case would probably be ideal.

Other thoughts:

1. Sizing is important. The fact that one dealer is quoting a different size is something to think about. Was a proper load calculation done to determine sizing of the furnace and A/C?
2. Honeywell's VisionPRO IAQ thermostat is a better thermostat for this system. It can slow down the blower to dehumidify on demand. The 802 can't do anything to dehumidify, and the 803 can overcool up to a point. Same touchscreen interface. 800 thermostats are just rebadged VisionPRO 8000 series thermostats anyway.
3. Contractor 1's setup is not an ARI-rated match. I believe the 4TXCC coil is right (21" width). Go with an ARI-rated system as coil and condenser matchups only do not show the potential efficiency and capacity of an ARI-rated match, which takes into consideration the furnace as well. That furnace with the 4TXCC060BC3 coil provides 11.7 EER, 14.0 SEER, and 8.6 HSPF. Ask the contractor for an ARI certificate of his matchup--I don't think he'll be able to provide one that includes all components. Contractor 2: same problem--need a 5-ton coil with this matchup. None of the contractors proposed nominal 5-ton coils.

Good luck.

Yikes! We are getting ready to install two Lennox XC-16 and one XC-21 compressors each linked G60V Variable Speed Gas Furnaces and we are not going to use any additional dehumidification devices. I have three unused VisionPRO TH8320U1008 stats that my contractor said they would work fine with the variable speed blower in the respective air handlers.

I might be missing something basic here, but as I think might be implied above, please confirm that all versions of the VisionPRO 8000 series, including the TH8320U1008, "can't do anything to dehumidify?"

Many thanks...

The TH8321 VisionPRO can overcool (up to a point) to dehumidify. The VisionPRO "IAQ" YTH9421 can slow the blower down to dehumidify on demand (best way in my opinion). The TH8320 can't do anything. I'd personally step up to the IAQ thermostats for such a high end system, critterdoc. Also, do you live in a climate where heat isn't used very often, hence the 80% AFUE furnaces? Great systems. Good luck.

Glad I visited this forum! We live in the New Orleans area, and there are a number of months where we need heat to fend off several months miserable cold wet weather. Rarely does it ever drop below freezing but the winter months can be raw when the wind is blowing, the humidity is high, and the air temp is hovering in the mid to upper thirties.

The rest of the story is that I bought this bizarre house in '74 from a lunatic dutch architect who built if for himself in '72 - one of the dumbest things I ever did. 4,400 feet of original ponding coal pitch roof totally died 10 or so years ago and we have lost the battle to hold back water. So, we will soon begin the adventure of going down to lumber and rebuilding from the deck up. Unfortunately, if we slope the roof we destroy the character of the house. It appears that fate may have smiled upon us because the commercial company that built the roof on the Louisiana Super Dome has made me an sweet offer which I likely won't refuse. One of their proposals is to apply a seamless sprayed on Bayer Polyurethane roof [SPF] which will *require* high end A/C systems to control humidity inside of the house. I have not coordinated the final details of the A/C System and the roof system yet, but I do know that the dehumidification capacity of the modern high end HVAC systems with variable speed blowers was something the owner of roofing company indicated was essential for the SPF roofing system.

The cost of the TH8321's is nothing on the scale of what this job is going to cost. I bought them on Ebay for 80 bucks each before the roofing guy entered the fray. I think the HVAC contractor told me that Lennox's top shelf thermostat was approximately $150 each but that more or less went to the wayside for the time being when he thought the TH8321s might work...as did a Trane contractor when I asked him also about the TH8321s.

I suppose I am having a hard time understanding the relationship behind variable rate blowers, thermostats, and humidity control. If there is an online reference you can point me to on that topic I would appreciate it.

But for now please tell me:
1) if any of Lennox's t-stats would be equal to or better than the IAQ YTH9421 in dehumidifying by slowing the blower speed and are they in fact one in the same internally.
2) How effective is the variable speed blower contyrolled by an IAQ or the equivalent Lennox t-stat, in comparison to throwing Humiditrols into the mix?

If dehumidification is your goal, you better double check that those systems were sized properly! Proper sizing is key for dehumidification, even with dual-stage systems.

The TH8321's don't take full advantage with the ECM blower's ability to slow down to dehumidify. Are these the thermostats you have? (I thought you mentioned TH8320).

I'm not sure of an online reference for that matter, but I can tell you that there are what I would call "experts" on this matter at HVAC-Talk.com. Some of them could probably answer your questions better than I can. I am a member there as well.

Question 1: I have tried to check into this myself, but I am still unsure of whether or not Lennox's ComfortSense 7000 (the new one) can slow down the blower. This is something to ask the Lennox dealer you are "dealing" with.

Question 2: Not sure what you mean by "humiditrols," but I do know that the VisionPRO IAQ YTH9421 comes recommended for humidity control with its superior ability to slow down the blower to dehumidify. This is what I would want if I were going for such a high-end system, if Lennox's thermostat couldn't achieve the same thing.

I'm curious: Why are you getting one XC16 and one XC21, rather than 2 of the same?

Thanks so much for getting me started pondering the relationship between different t-stats and variable speed blowers. That added investment sounds worth it's weight in gold over time. Is installation of a VisionPRO IAQ YTH9421 and matching it with any given upscale A/C system a simple task for a reasonably experienced installer?

Question: I'm curious: Why are you getting one XC16 and one XC21, rather than 2 of the same?

I have the same question. I'm guessing it is because the house is complex in layout, shaped like a large "H" with three "zones" that each pass air into the large central living room. The contractor for the Lennox proposal is out of town until next week and we will talk quite a bit more getting me ramped up in the planning process but I'm leaning towards selecting three XC-16s at this point in time.

The other thing I am concerned about is that the house has always been cooled by one 4-ton and two 2-ton units and it has always cooled well except for one room, in the 4-ton zone (the one we spend most time in) that is like a blast furnace in the summer because of a wide expanse of westerly facing uninsulated glass and clear underducting. I suspect that Lennox guy upsized the 4-t unit to 5-t because there is no way that we can increase airflow to that room without structurally busting the crap out of the house because there is absolutely no attic and the space between the ceiling and the deck for the roof is filled with sprayed in foam in the early 70s. Now that I'm considering the need for humidity control with a polyurethane roof, I'm thinking that we might be better off keeping the big unit at 4-ton so that it will be active for longer periods of time and we can deal with the "blast furnace window" by removing it and rebuilding with something which transfers far less heat which needs to be no anyway.

Humiditrol is Lennox's add-on dehumidifier device.

The VP IAQ should be installable by a competent installer if he reads the installation instructions carefully. It requires quite a bit of setup.

That's good that you're getting Humiditrol systems. The VisionPRO IAQ may be able to control this system for dehumidification, or it may require the use of one of Lennox's thermostats to properly control. Definitely something to check with the contractor beforehand. As far as airflow goes, it could be as simple as installing/adjusting balancing dampers in the ductwork.

Did this contractor perform a Manual J load calculation to determine sizing? Something to ask him. Many don't do them, but it's the best way to size the system.

Critterdoc,

I just checked Lennox's engineering handbook (I'll attach below), and it looks like Humiditrol is NOT supposed to be used with zoning and REQUIRES Lennox's touchscreen thermostat. I am unsure of whether or not Lennox's thermostat can slow down the blower, but it's very possible that it can. You'll have to talk to your contractor about it as I don't know. Are you planning on zoning all of your systems? You may not even need the Humiditrol if the systems are properly sized with on-demand humidity contrl with the thermostat. They will run in an efficient low-stage most of the time removing humidity. Hope this helps.

No manual J load test to date, but the original install and replacement of parts including compressors and furnaces over the years was done by my best ever and trusted friend who was an HVAC contractor now retired to the country too far from here to handle a job of this scope. I don't know if Woody ever did a formal test, but he has long been confident that the 4-2-2 combo was what we needed with that relatively old technology. I'll ask all of the contractors who submit proposals for a load test, but none of the three that I've spoken with thus far have mentioned it.

I am *not* planning to add Humiditrol to the mix unless it is absolutely required because I'm a bit on the old side to be heavily re-mortgaging the house and the total expenses to do what we need to do now will put a big chink in our available resources. Neither the roofer nor the HVAC guys suggested the need for dehumidification beyond that which the new hi- efficiency systems provide.

Please define "zoning." I had used the word in quotes to generally refer to three parts of the house each supplied by it's own compressor and furnace/coil- with some of the airflow from each being shared with the central living room which has no system of it's own. Perhaps "zoning" is something far different.

When we speak of "slowing down the blower" relative to humidity control, is "variably slowing down" an all or none thing, or can I assume that some t-stats are more precise about when and to what degree they "progressively" slow down the fan; and do some use a more effective algorithms in determining what the blower speed needs to be at any given time?

Also, is variably controlling blower speed strictly controlled my the t-stat or is this function operating in concert with on-board sensors and electronic controls that are built into the air handler itself?

...hope I'm no wearing out my welcome here with all these newbie questions! You've been a terrific help and I very much appreciate your time and advice.

Doc

Zoning: Running separate "zones" or separately conditioned areas off the same system. This is done using dampers, a zone control panel, and separate thermostats.

I suppose you could call zoning having more than one system as well.

Not every thermostat can slow the blower down. As far as how much the blower slows down, while I'm not 100% sure, I believe the extent to which the fan speed is decreased depends on the specific air handler. Usually I think you're looking in the 80% of cooling CFM range. The thermostat would have to send a signal to the air handler to dehumidify on demand. Some air handlers can slowly ramp up their speed (specifically Trane's Comfort-R feature on their 4TEE air handlers) to remove humidity.

Here is one of Lennox's dehumidification ramp profiles (when system is starting up):

"Profile A − Motor runs at 50% for 30 seconds, then at
82% for 7−1/2 minutes, then at 100% (if needed) until
demand is satisfied. Once demand is met, motor runs at
50% for 30 seconds, then ramps down to stop."

No problem. Hope to hear an update from the original poster of the thread soon as well.

doctorvac at hvac-talk.com (http://www.hvac-talk.com/vbb/showthread.php?p=1872105#poststop) said: "I would highly reccomend the lennox comfortsense 7000 stat over the honeywell iaq. It is designed to run your system and provide dehumidification."

Thanks for the referral. hvac-talk like a smart place but first impression is that those guys flame good!

Critterdoc,

I see you posted over at HVAC-Talk. I suggest you open your own thread there and ask all of your questions about the ComfortSense 7000 that I was unable to answer (i.e. can it slow down blower, etc.) and how the ComfortSense 7000 compares to the VisionPRO IAQ. This will give your concerns more attention. Tacking your concerns on to an old thread may or may not gather great responses. Good luck!

Done deal. Thanks for your encouragement.

>> Hope to hear an update from the original poster of the thread soon as well.

Hi, still here. :)

Yeah, so far, none of the contractors have proposed a 'mismatched' coil and condenser. One said 5/5, but all the others have been 4/4 so far.

No load calcs yet. One contractor said he'd do it if there were a commitment to go with them. So if they commit to dropping their price and changing some of the equip to match better proposals from others, then we may have something.. :) [unfortunately, although they had a polished sales presentation, their bid missed a couple elements with regard to equipment, including the low voltage wiring and the mismatched coil size (width)]

I did see that the 4-ton XL15i requires the 7/8" x 3/8", so looks like I'm good. (phew)

A contractor on Friday also said I'd need additional wiring to hook up a heat pump outside, so looks like it was missed by the one proposal.

I think this has been asked before, but is the TL900 the same as the VisionPRO IAQ?

I have two more contractors coming Monday, so after that will hopefully have all the information I need to start discussing it further with 1 or 2 and start negotiating equipment and price details.

On related topics:
There have been other differences in proposals, with some suggesting/including a replacement condenser pad, some not. I currently have what looks like an interlocking plastic condenser pad. Doesn't appear damaged, although may be slightly out-of-level (will be checking to make sure). Surrounded by bushes that I keep in check, and mulched w/ weeding done when needed. I understand concrete is the best option, but doubt the pads being included in some of the bids are much better than what I have. I'll be doing my own check to confirm what I have would fit the new condenser/heat pump.

And, some are including an Electrical Disconnect/Fuse rewiring, some not. There's currently a disconnect (no fuse) connected to a 40amp double pole circuit breaker. One guy told me "that should be enough, but if it isn't and it trips a lot, we'll fix it free of charge" or something to the effect; which I'm not sure whether it's a good deal that he's not trying to sell me something I don't need or a caution flag that he doesn't know if it's sufficient.. The XL15i documentation says "Min Cir Ampacity = 30" and "Max Fuse Size (Amps) = 50", so I'm not sure whether that means the 40amp circuit breaker is sufficient or not.

"I think this has been asked before, but is the TL900 the same as the VisionPRO IAQ?" -- I thought so initially, and it may be. However, I think this thermostat is more geared toward Trane's ComfortLink II compatible systems. You'll have to ask your Trane contractor to make sure or just go with with IAQ.

The coil size difference isn't really a mismatch, but it's common practice to get an ARI-rated match at a higher efficiency. Looks like the setup you're looking at would likely use a 5-ton coil. If any contractor quotes a 4-ton coil, ask for the ARI reference number and actual efficiency numbers.

The pad may or may not need to be replaced, but it's not a bad idea, since it is a replacement.

I am not an electrical pro, so you'll have to go by yours and your contractor's best knowledge. Or perhaps someone here can comment on this. It's never easy when one contractor tells you something and another tells you something different--I understand.

I cannot find the TL900 on Trane's website. Are we talking about the XL900 instead or am I missing an entire t-stat? If it is in fact the same as an IAQ I would sure like to know.

My bad; I should've typed XL900.

I live in NJ and am considering installing a pair (2 zone) of Lennox XC14 A/Cs along with a pair of Lennox G71MPP furnaces. My contractor tells me that the Honeywell Vison Pro 8000 stat is functionally the same as the Lennox CS 7000. I'm not installing any external dehumidification equipment for the A/C side and am only concerned about proper control of the modulating gas valve and normal AC functions.

On a secondary note, there's rumors floating around that you cannot do setbacks with a modulating furnace - however, I talked directly to Lennox Cust Support and they say the furnace will simply transition to high burn to catch up and then work normally after that - can anyone confirm this by experience?