No need to close a return, a bad idea. How are you currently filtering your return air? You have returns on both levels?

I prefer authorized dealers. Check Trane website.

IMO

As a general rule can never have too many returns. It doesn't matter if it is high or low in a room that has 8 foot ceilings. You have to question someone's HVAC knowledge if they are telling you to close a return. The only reason to so is if the return is right next to a supply.

The thermostat will control the furnace stages based on the temperature in the room. You do not want the furnace stages controlled by the furnace's control board. The Honeywell you were quoted should do that. The question is how good is the staging algorithm.

I am not familiar with Honeywell's filter cabinet. You want a cabinet that is sturdy and can accept filter you can easily buy.

Yes humidifiers have to be kept clean. It is could become a maintenance headache. A house your size should not need one.

The 59TP5 has a 2-speed blower. The speeds are set at the time of installation.

See if these contractors are listed on the Carrier and Trane web site. You don't have to be an authorized dealer to sell the equipment. Authorized dealers are supposed to be better trained, but even that is no guarantee of a good installation. I would think an authorized dealer would not be proposing a third party coil or thermostat, but then again there are no rules against this.

No furnace board timer or algorithm on the thermostat. It will always go to high stage on a 2 stage furnace regardless whether it is needed or not. You want a true 2 stage thermostat that controls furnace staging based on demand when it is needed. I can't make it any more clearer than that.

IMO

Tigerdunes we are in agreement. By algorithm I mean the control software embedded in the thermostat which makes the decisions whether to be in the low or high stage. The thermostat manufactures don't explain the staging process. We have to trust they are doing a good job.

tigerdunes, by "on demand" do you mean when I manually change the stage on the thermostat every time I feel it is necessary, or it is something more automatic than that?

"by "on demand" do you mean when I manually change the stage on the thermostat every time I feel it is necessary"

No. The determination of using the 2nd stage would be determined by the thermostat based on 'demand', IE, the temperature difference between actual and desired, and the rate of temperature change. If the rate of change is enough at low stage to get from actual to desired in a 'reasonable' time, then the thermostat should keep the system at 1st stage. If the rate is not doing it, then it should increase to 2nd stage.

"As for thermostats, do the manual, non-programmable ones allow me to control stage and blower speed?"

Usually not. Else you'ld be spending all your time doing what the thermostat is supposed to do.

"If not, can some programmable ones run in a manual mode?"

Yes, if you mean can the program be overridden.

Thanks! Great explanation. Is there usually a way to see on the thermostat what stage and blower speed the furnace is running at the moment?

One related thing I can't understand is how variable speed assists with comfort -- specifically with longer duct. I understand how a lower stage will take longer to trip the thermostat, and that allows more conditioned air to travel through the longer ducts. But as far as varying the blower speed, in my mind the same amount of cubic feet of conditioned air is being pushed through, whether it's faster or slower. What am I missing here?

Some thermostats will indicate what furnace stage is currently in operation. The Carrier Infinity controller can do this but only in the service mode. You should able to hear a difference in sound and fell the air speed between the two stages.

The air speed is measured in CFM (cubic feet per minute). Increasing the speed of the motor pushes the same volume of air put in to shorter amount of time. It is like increasing the water pressure on a garden hose. As the the pressure is increased, the water flow rate increases allowing you to fill a bucket of water faster. The garden hose doesn't expand to do this. The higher pressure forces more water through the same hose diameter.

In the past the biggest compliant about forced air systems was that when they turned on you got a blast of cold air and it was noisy. Operating in the low stage minimizes those problems.

Variable speed is better at humidity extraction than single (high) speed. Units usually follow a profile that runs slow and the beginning and ramps up after a few minutes. Slower speed across the coils allows for more humidity extraction.

Weed is exactly correct on the thermostats. The worst is staging controlled by furnace board timer. Second worse is staging by a thermostat's software algorithm. And the best is the staging by the thermostat based on demand. It really is that simple. So be careful when a thermostat specs say it can control up to 3 stages of heat. Algorithm and demand are entirely different. This can be very misleading.

and if interested in a Carrier non Infinity furnace similar to Trane's XV95, that model would the Performance 96 Mdl 59TP6. See Carrier website for details and specs.

IMO

The thermostat will change stages based on demand, but the decision process of when to change stages is controlled by its embedded software. The current room temperature, and the desired temperature are inputs to the algorithm. Some thermostats will also use the outdoor temperature as another input in the decision making process. Others may store a history of how long it took to raise the temperature during the last set back period.

The algorithm can be very complex, or it can be very simple. I have never seen a thermostat manufacturer publish the flow chart of the software. I could be wrong, but I have never seen a thermostat where you can turn off the algorithm. Some may allow you to switch from comfort to more efficient, but the thermostat is still going to make the decisions based on its software.

My understanding is in a dual fuel system, the thermostat could control 3 stages of heat if there was a heat pump and a 2-stage back up furnace. I thought some of the better Honeywell thermostats have this ability.

tigerdunes, I've eliminated the Trane vendors because they should have matched the Trane coil in the original quote. I still haven't received a call back for a quote with a matched coil. Additionally, one of the Trane vendors quoted that 80K BTU furnace and in our conversations seemed to be of the more-BTU-equals-better school of thought.

I'm leaning toward Carrier Vendor 1. I got the best impression from them when they came for the estimate visit. Unfortunately, Carrier Vendor 1 can't provide the 59TP6. As far as they know, it isn't available in the Baltimore region. Two local Carrier dealers listed on the Carrier website, however, are offering this furnace. That likely means this vendor isn't an official dealer. Is that a huge issue?

I agree with mike_home, that "on-demand" vs "algorithm" can be
confusing. Both are algorithms, one is based on temperature
(on-demand), and the other likely timer-based. I wasn't able to find a thermostat that will allow me to turn off the algorithm and just say, e.g.,: "Run the furnace at Stage 1, Speed 3 until desired temperature is reached." The "on-demand" style is close to this, but it's still making algorithmic decisions on what stage/speed to run the furnace/blower. Also, mike_home is right in that it's impossible to get Honeywell or Carrier dealers to tell me if their thermostats are "on-demand" style. How can I tell?

Carrier Vendor 1 also told me staging and blower speed are controlled by the furnace control board, not the thermostat. That was a bit alarming. I will be discussing this with the vendor again. Unfortunately, I will have to sort through this myself because even the dealers from Carrier's website couldn't answer my questions. When I called Carrier to ask, they said talk to our trained dealers. I said I did, but you didn't train them well enough.

First, I know staging can either be controlled by the thermostat or furnace, but what about blower speed? Is that always controlled by the furnace or can the thermostat also control that? Is it possible to have a situation where the thermostat controls the staging, but the furnace controls the blower speed?

(Below, I assume, yes, a thermostat can control both staging and blower speed.)

Second, can a thermostat control staging/blower speed on a Carrier Perfomance 59TP5 furnace? (I.e., are there 2-stage furnaces where you are forced to use the furnace control board?)

Third, just to be 100% sure, can the Honeywell Pro 5000 thermostat control staging/speed on a 59TP5 furnace? The 59TP5 is multi-speed, not true variable speed.

I appreciate all the time you guys have invested in helping me. I apologize if it sounds like I'm asking the same questions over and over again.

"Is it possible to have a situation where the thermostat controls the staging, but the furnace controls the blower speed?"

Yes. Pretty much all the time.

But I'm aware that there are more advanced systems where the thermostat communicates with the furnace and fan speed is 'negotiated'. I think 'dehumidify on demand' systems to this, allowing the thermostat to set a low fan speed while cooling to remove more humidity.

My Trane system does not do this. The thermostat says 'ON' or 'OFF' for the fan. The fan speed varies via the control board.

Thanks, weedmeister. Finally starting to make some sense of things.

"Carrier Vendor 1 also told me staging and blower speed are controlled by the furnace control board, not the thermostat."

I believe most furnace manufacturers set the furnace at the factory to be controlled by the internal control board. The installer has to change the board settings to allow the thermostat to control the staging. Many installers either don't know how or are too lazy to do this. I would be worried if Carrier Vendor 1 does not know how to set up a 2-stage thermostat.

In AC mode, the thermostat may be slow down the blower if it detects high humidity. It is a small change in air flow. I big change could cause the coil to freeze. However in heating mode the blower speed is constant for each stage. Lowering the blower speed could cause the furnace to over heat and shut down. So either the furnace or thermostat controls both staging and blower speed.

The thermostat can control the staging and blower speed on the Carrier 59TP5. On any multi-speed furnace, the speed taps are selected one time at installation on the control board. After that that the thermostat selects which one to the two blower speeds will be used.

With an "on demand" thermostat, how does the thermostat decide when to switch to stage 2? From my discussions with a vendor, if the desired temperature hasn't been reached after a set amount of time, the furnace will switch to stage 2. Does such a case still fall under a furnace controlled by an "on demand" thermostat?

What you described is staged timing which is usually done by the furnace control board. The thermostat decides when to switch to stage 2 and back to stage 1 based on the algorithm built into its software. Some thermostat may go directly to stage 2 in the case of ending a set back period where the programmed temperature is 6 or more degrees than the current room temperature.

Sadly, when it comes to thermostats, I've found education level low for installers of all three brands: Rudd, Carrier, and Trane. I've been accused of "not trusting us" and been told to "stop believing what you read on the Internet", among other things. Pretty much everyone thinks the furnace control board is the optimal method. "You can't do better than the manufacturer." "Yes, the thermostat triggers the furnace when the temperature drops below your target. It's on demand." I have installers recommending to connect an outdoor thermometer to the thermostat when the furnace board will ultimately be in control!

Fortunately, I've found one installer who's interested in what I have learned here. But I will have to help him out.

Could someone please provide a specific model number of a generic thermostat (like from Honeywell) that is on-demand?

Honeywell YTHX9421R5051 Prestige IAQ 2.0 Thermostat... but if going Trane say XV95 then their 824...if Carrier Infinity furnace, then Infinity Controller....

Thank you, thank you! I'm going Ruud, but I was unable to find a Ruud thermostat. Just realized the corresponding thermostat will probably be labeled "Rheem".

Oddly, almost everyone here prefers generic thermostats as opposed to the manufacturers' models. Not sure what the deal is with that.

What model Ruud furnace?

U96VA0702317MSA

U96VA0602317MSA

The first one is what is recommended by the installer, a 70K BTU unit. I am pushing for the second one, a 56K BTU unit. I would assume the same thermostat would work with both. I am waiting on an energy efficiency company who will do a true Manual J for me and let me know if 56K BTU is okay. I got a bit nervous because 56K is a bit less than 60K. Just want to be sure.

Here's Ruud's web page for that furnace.

The specification sheet there recommends an EcoNet model number UETST600SYS. I found a spec sheet for a RETST600SYS, which may or may not be the same thing. I can't find anything specifically stating the RETST600SYS is a true 2-stage thermostat.

tigerdunes, the Honeywell YTHX9421R5051 is discontinued and has been replaced by the YTHX9421R5085WW. Do you know if the updated model behaves the same way? I can still get the discontinued model on eBay.

"However in heating mode the blower speed is constant for each stage."

Does this mean 2-stage Variable Speed systems are in practice 2-stage, 2-speed systems? If so, what's the advantage of Variable Speed over Multi-Speed assuming both have an ECM motor? (Or was that statement only meant to describe a Multi-Speed system?)

That statement is describing a multi-speed furnace.

A variable speed furnace should be able to change the RPMs of the motor in order to keep a constant air flow. It also allows you to change the speed of the blower from the thermostat if that feature is supported. A multi-speed furnace does not have these features.

Okay, now I think I get it. I always thought of Variable Speed as: If it's taking too long to heat up the house, run the blower faster. But that's actually remedied by going to a higher stage. Once it's reached the target CFM, the Variable Speed motor will stay more or less at a constant RPM. But that RPM could be different at different times depending on many factors. Now it makes sense why furnace boards are usually handling the Variable Speed component.

Kinda mostly. Increasing the airflow does not result in more heat necessarily. But there is a target flow based on BTUs being delivered. And that will increase with activation of the 2nd stage of the compressor. The other part of Variable speed is that there can be a profile such that the speed is low as the evaporator is heating up, then the blower can ramp up to the desired target speed. It can also ramp down after the target temp is reached extracting the extra heat from the evaporator (same thing for cooling).

On a single stage furnace with a multi speed blower motor whether ECM or PSC type motor, the speed is fixed but can be adjusted usually low, med, med high, or high. These speeds are usually marked as CFMs/ton.

IMO

tigerdunes, I got part of a response from you in my email, but somehow it was deleted here. Unlike Trane and Carrier, Ruud spoke directly with me over the phone and answered my questions. The reason I was after the Honeywell YTHX9421R5051 is because you confirmed it takes into account rate of change. The EcoNet does not; it uses low stage if temperature difference is 1 degree, otherwise high stage. However, Honeywell couldn't confirm if their thermostat works well with this particular furnace. In case there are proprietary commands in the furnace communication-- and frankly because I don't want to read installation manuals anymore -- I'm just sticking with EcoNet for now. I can always switch later if some particular nuance is annoying me. (Honeywell also has Delta T sensors, which is kind of neat.)

Let me check with my Ruud/Rheem expert.. The model furnace you have selected is not a communicating furnace. I think the HW Prestige 2.0 is your best choice. Hold off till I reply back.

IMO

I really appreciate you doublechecking that this model furnace is in fact a communicating furnace, and that the EcoNet is my best choice.

I read pretty much all those specs/docs. I was interested to see how the short cycling protection works, especially since AC units are always oversized, but couldn't figure that out. Other details like what happens in constant fan mode when the heating/cooling kicks in (e.g.,does it slow the motor and then kick in), I'm just giving it a rest now.

Installer is nifty guy, he can modify the 70K BTU to be 60K BTU by replacing the gas valve or some such!

Is a communicating AC required for "dehumidify on demand"?

Outdoor temperature sensor connects to furnace, not thermostat. I guess furnace communicates outdoor temp to stat. Are outdoor sensors useful in single fuel setups?

Why not get a heat pump, instead of AC, keep the furnace and go dual fuel?

"Is a communicating AC required for "dehumidify on demand"?"

I would say, "probably". On a furnace blower that can change speed it would be a good thing since the stat will tell the blower to run low while the AC is working. For a system that doesn't have a way to tell the furnace to run slow, the thermostat would probably cool below the setpoint by X amount in order to achieve a lower humidity.

"Are outdoor sensors useful in single fuel setups?"

probably depends on how 'smart' the furnace is. Possible that if the outside temp is 'very low' the furnace will start at it's highest BTUs first rather than waiting to see how fast the setpoint is being achieved. Certainly useful for heat pumps.

"Installer is nifty guy, he can modify the 70K BTU to be 60K BTU by replacing the gas valve or some such!"

I don't think you want someone to be modifying the gas valve on your new furnace. This could be potentially dangerous.

What is your definition of a communicating AC? Communicating to me means information is traveling in both directions, and the communication is in the form of digital data.

There are 2-stage thermostats like the Honeywell Vision Pro series that have a cool to dehumidify feature. You can set the humidity level you want and the thermostat will run the AC until the humidity setting is satisfied. The thermostat may over cool the room by 3 degrees in order to achieve the humidity level before turning off. You need a variable speed blower with some communication in order to slow the speed down. Cool to dehumidify works well with 2-stage equipment.

Outdoor sensors are good for multiple stage equipment. The furnace and AC have no "smarts". They do whatever the thermostat commands them to do. The smarts are built into the thermostat. The outside temperature is another input to the software algorithm the thermostat uses to determine how long to stay in each stage, when to stage up or down, etc.

If you are buying a modulating furnace and multiple stage AC you must buy a communicating thermostat in order to make use of all the features. There is no standard in the industry on communication so you are basically forced to buy the manufacturer's thermostat. It is unfortunate but that is the current state of things as of now.

I'm slightly wary of drilling more holes through the house. (Recent blower door test showed some holes I thought I had sealed well were still leaking.) Would you guys consider the outside temperature sensor important enough to install in your own homes?

That is a hard question to answer. The thermostat manufactures don't explain how the outside temperature data influences how the staging will be performed.

The size of the hole to pass the wire is small. Seal it with silicone and there should be no air leakage.

By "silicone", do you mean something like this?

Yes, it comes in clear or colors. You can buy it at Home Depot or Lowes.

I was told the old heat pump we are replacing has eight wires, so they can just use a couple of those for the thermometer since the new A/C won't need all eight. No need to drill extra holes. Just updating in case anyone was curious. Thanks for all the help guys, really.

One thing I wanted to record for future information seekers: The new, efficient 96% furnaces -- at least my Ruud/Rheem one -- are condensing furnaces. This means they output water like your AC coils do in the summer. Where I live, by code, this condensate is not allowed to drain to the sewage. Usually you have to send it to the sump pump.

This means your sump pump will be running in freezing weather. You will get patches of ice in the area where your sump pump discharges. Plan accordingly. Also, any leveling issues in your sump pump discharge PVC could be exposed. If your discharge PVC runs adjacent to a walking area, make sure you have no small cracks in the PVC. Easy to ignore in summer, dangerous in the winter.

When it snows, usually it's not "freezing enough" to discover these issues. But when your sump pump discharges in 17 degrees weather, it's a different story. I.e., if your sump pump only runs in freezing weather when it snows, you may have been issue free for years; but you install a condensing furnace, and BAM, you are in a world of trouble. Trust me, I learned all this the hard way. Came at night a few hours after furnace was installed and fell hard. Fortunately, all my pieces are intact. (Or at least as much as they were before.)

Acidic condensate from condensing boilers is normal neutralized by a device that percolates it through calcium carbonate (limestone chips). After that it can go down the drain. I had always assumed that it is handled in the same manner from furnaces.

The above post by OP anontemp is correct. But it should be noted that this is nothing new. High efficient condensing furnaces have been around for years and as far as code goes, this can vary from different governing authorities. Dealer should be experienced in best method to discharge condensate with little to no risk.

TD

ionized_gw, the way it was explained to me, even with a trap, you have an issue with sewage backing up into the HVAC equipment (?) and also preventing the trap from drying out. If you have condensate in both cooling and heating seasons, probably not an issue with drying. You could also have the condensate drain upstream of an "active" trap, etc. But since there's a lot of variables involved, some places code just says you can't do it. Some places it's okay. Even in my case, my HVAC guy sounded like draining to sewage was no issue, but his subcontractor who came to address the issue said it was against code. I have a DIY relative who reads code for fun (or so we tease him), told me right away it's against code in my area.

tigerdunes, just this was something I didn't see prominently written anywhere and, more importantly, not a single person mentioned it to me even in passing. I felt it should be pointed out more. In certain circumstances, I could even see it being a deciding factor between different levels of efficiency.

I agree that this was a failure both by dealer and myself. High efficient condensing furnaces are just that plus usually waste gas is vented out of the side of the house from a crawlspace or basement location. Same is true of the condensate sometimes with the help of a condensate pump. You know what they say about making assumptions. Sorry for your trouble but otherwise I hope you are enjoying your new Rheem furnace. You did get a media filter cabinet installed as well?

IMO

Oh, no way, a failure by you, someone who's helping folks in your spare time?! No way! (I hope you were joking.) By "not a single person mentioned", I meant like installers when they came to give estimates, not anyone here. No trouble, it's all a learning experience. Yes, I had a media cabinet installed, but it was a Honeywell. I
couldn't convince my installer to get the official Ruud cabinet.

I wouldn't even call the condensate issue a failure necessarily by my installer, because he is right that my sump pump should work in freezing weather. Just these furnaces still aren't common in my area, so I'm surprised there aren't more words of caution out there. (In fact, my emergency handyman who came out that night cause I thought something had burst -- services rental properties as his full-time job -- turned to me and said "I haven't seen this before but your furnace is discharging water.")

My installer is considering a condensate pump and there's a slight issue where the outdoor temp isn't being read. But overall, I'm super happy with my 96% Ruud and EcoNet thermostat. The thermostat tells me whether it's running high or low stage, I've been told I'm spending too much time with it. I can't thank everyone here enough. In the end, I was able to find a great HVAC team. It's been quite the adventure. I'll post pictures soon. The duct work is a masterpiece, everything was turned 90 degrees because otherwise code required I create a service opening in the wall.

Glad to hear that you are satisfied overall...and that you installed the Honeywell filter media cabinet...

TD

I am glad that you are getting away from the sump pump for acidic condensate removal. I'd be afraid that the the pump metal would be attacked and fail pretty quickly. I understand the difficulty in making sure that the trap is kept watered with current code requirements. I understand that things have changed a lot with trap requirements in anything other than very conventional sinks/appliances. I recall reading that floor traps have become difficult to install according to requirements. Even with heating and cooling both providing water, in an mild temperature area with long periods of little or no HVAC activity, a trap could dry out.