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  1. #1

    Question 2-Stage Gas Furnace to 1-Stage Gas Furnace setting

    Just had our HVAC contractor replace a 22 yr old Carrier single stage 92 efficiency gas furnace with a Carrier Performance 95 2 Stage ECM gas furnace. Currently using the old t-stat, Honeywell Chronotherm III (single stage). The contractor wired the furnace board to run off of the 1 stage t-stat.

    We have a two story colonial with finished basement. Total space with basement 3300 sq feet. Average insulation. Reside in Central Maryland. We leave the t-stat set at a given temp and don't use the programmable features. Use to, but don't anymore.

    If I understand correctly, the 2 stage furnace has a low stage and high stage burner...I'm thinking lower BTUs and higher BTUs. The low stage kicks in when the temp difference is nominal and the high stage kicks in when the temp difference is significant.

    I'm not pleased with the system calling for heat as it goes to the low stage for heat 99% of the time since we don't do the programmable (i.e., a dramatic change in setting). I've notice the house is cooler....at least it feels that way. Kind of reminds me of the heat pump days in our townhouse. Just never got warm.

    So (finally), my question is....can the furnace be wired/programmed to skip the low stage and run on the high stage.....without having to set the t-stat up X degrees to get the high stage to kick in? I would prefer to feel that roasty toasty blast of heat the way our old system ran. I know there are all the trade offs of economy and efficiency. I've read so many HVAC forums on 2 stage gas furnaces and 1 stage vs 2 stage t-stats that I have a headache and my eyes are red. LOL

    Point is I've tried to learn and do my homework. I appreciate everyone's input.

  2. #2
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    Yes, it can be set to operate as a single stage.

    Sounds like it wasn't set up right when installed though. Could be under fired in first stage.
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  3. #3
    Join Date
    May 2008
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    If you have enough wires have the thermostat changed out to a 2 stage and get the most out of your system.If not go to a wireless thermostat, worth the money.

  4. #4
    Beenthere - I'm wondering about the set up too. What does it mean "under fired" in first stage? I assume I know but would appreciate your explanation. Thanks.

    TwincamDave - Why a wireless tstat? Any suggestions on brands (wireless & non-wireless)? If I do switch out the tstat, I'd like to stay with Honeywell...been happy with the Chronotherm III and Honeywell's are considered good. Looking at the Pro Vision 8000 series. Comments?

  5. #5
    Join Date
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    Quote Originally Posted by heatingstuff View Post
    Just had our HVAC contractor replace a 22 yr old Carrier single stage 92 efficiency gas furnace with a Carrier Performance 95 2 Stage ECM gas furnace. Currently using the old t-stat, Honeywell Chronotherm III (single stage). The contractor wired the furnace board to run off of the 1 stage t-stat.

    We have a two story colonial with finished basement. Total space with basement 3300 sq feet. Average insulation. Reside in Central Maryland. We leave the t-stat set at a given temp and don't use the programmable features. Use to, but don't anymore.

    If I understand correctly, the 2 stage furnace has a low stage and high stage burner...I'm thinking lower BTUs and higher BTUs. The low stage kicks in when the temp difference is nominal and the high stage kicks in when the temp difference is significant.

    I'm not pleased with the system calling for heat as it goes to the low stage for heat 99% of the time since we don't do the programmable (i.e., a dramatic change in setting). I've notice the house is cooler....at least it feels that way. Kind of reminds me of the heat pump days in our townhouse. Just never got warm.

    So (finally), my question is....can the furnace be wired/programmed to skip the low stage and run on the high stage.....without having to set the t-stat up X degrees to get the high stage to kick in? I would prefer to feel that roasty toasty blast of heat the way our old system ran. I know there are all the trade offs of economy and efficiency. I've read so many HVAC forums on 2 stage gas furnaces and 1 stage vs 2 stage t-stats that I have a headache and my eyes are red. LOL

    Point is I've tried to learn and do my homework. I appreciate everyone's input.
    Could you please define in greater detail what you mean by "I've notice the house is cooler....at least it feels that way". Everywhere in the house it feels cooler? While sitting in your favorite chair it's cooler? The air coming out of the registers is cooler? The furnace quits running before the temperature in the house is what you set the thermostat too? As our trade's purpose is to supply comfort it is always important to understand what you, the customer, feels is not comfortable.


    By using the old thermostat and your description of how the furnace is operating, what is happening is when the thermostat calls for the furnace to run there is a timing function that determines how long the furnace runs on low fire. After a certain amount of time has passed and the thermostat is still calling for heating, the furnace will change into high fire until the thermostat is satisfied. So yes, it is a function of temp difference but decided by time not temperature.


    Yes, low fire means less BTU's, but it also means less air is being moved by the furnace through your duct work. This can in some cases cause comfort issues. The why is usually specific to the house. You lived with and became used to how the old furnace made the house feel for many years. This "comfort" was just not due to the furnace, it was also very dependent on the entire house, the duct work, the types and locations of the registers, where your furniture is placed, where you spend time in the house and you and your perceptions of "normal".

    Yes, the furnace can be wired to go right to high stage. It will still be a 95% efficient furnace and you will still be seeing the advantages of the electrical savings of the ECM motor.

    Once this is done and you've rested your eyes you might want to research why you felt the difference. You might find that maybe your duct work is located in a very cold area and on low fire the slower air was cooling off on it's way to the registers making the air coming out of them cool and uncomfortable. Maybe insulating your duct work could save you on your heating bills. Read about the benefits of having your forced air system balanced. All this means is that each room requires X amount of heat and your system delivers that X amount by delivering X amount of air to that room. Balancing of your system gets the right amount of heat to the right spot.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  6. #6

    2_Stage Gas Furnace to 1-Stage Gas Furnace

    Firecontrol -
    Comfort is subjective I get that. The comparison is based on old furnace comfort vs new furnace comfort. There is a definite change to a cooler feel with the new system. I have taken temperature readings with a digital thermometer that has a base station and a wireless remote. The temp at the thermostat will read X while rooms on the first floor read X-2 degrees and rooms on the second floor read X-3 degrees. The readings are taken over several days to determine consistency. The duct work only has individual dampers in each floor register. The individual dampers are all open as in the old furnace. There are no main dampers on the duct work at the furnace. Everything with the duct system is the same in the new system as the old system.

    Another reply suggested the system setup may be under fired in the 1st stage. I don't understand and would appreciate feedback on that.

    And with the new 2 stage system being controlled through the furnace and not the 1-stage tstat, I understand the staging is a timing setup not temp setup. So would switching to a 2-stage tstat have a positive impact? If so, any suggestions on what tstat? I would lean toward a Honeywell Pro Vision 8000 series.

    Learning that less air is being forced through the ducts on 1-stage is reassuring as that is definitely what I perceived. Now I know it's not my imagination.

    Thank you in advance for any advice -

  7. #7
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    Most 2 stage furnaces (almost all of them are VS drive) operate at around 70% in low stage and 100% at high stage. This includes the gas firing part operating at 70% as well as the blower operating at 70%.

    Most houses ductwork (how the air is delivered to each room) are not done right, rather done cheaply... builders find granite counter tops and SS appliances sell better than quality heat and AC).

    The ideal set of circumstances is for the heat or AC cycle to run longer... thus circulating the air more thoroughly. Your old furnace blew 'hotter' air, yet it was not as efficient with fuel (even on high, the new furnace will not blow as 'hot' air)... this is the trade-off of newer furnaces... you can thank the govt for that one...

    If it were me, I would just get used to the 'feel'... and after a while you will not notice it. If you really want it to feel more like the old one; then your installing contractor can change some things and make it run on high all the time. Some will disagree, however IMO you will save a small amount of fuel if you operate 2 stage... just it will feel different until you get used to it and do not notice it anymore.
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  8. #8
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    I hear this complaint a lot from homeowners. "My house feels cooler with my new 2 stage furnace". I have had a few who noticed an increase in fuel consumption too.

    Most of the problem can be due to what Beenthere mentioned, most of them come badly underfired in low stage from the factory. If the technician is not proficient in the use of a combustion analyzer (optional training, not very many contractors take it), it will not get corrected upon install. Under fired simply means there is not enough fuel entering the burners. This also increases fuel consumption, sometimes dramatically and also increases the chance of the heat exchanger failing prematurely.

    I have corrected many of them by tuning low and high stage correctly if the furnace has a variable speed inducer. Some of them have single speed inducers and those get locked into high fire since there is no way to tune it properly but to lock it into high fire.

    You need to find a technician that has training in tuning furnaces with combustion analyzers. They should be able to make that furnace more comfortable for you.

    Is your duct system in the basement? Or is it in a completely unconditioned space such as the attic or crawlspace?

  9. #9
    Churckcrj - The duct system is in the basement.

  10. #10
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    Quote Originally Posted by heatingstuff View Post
    Beenthere - I'm wondering about the set up too. What does it mean "under fired" in first stage? I assume I know but would appreciate your explanation. Thanks.

    TwincamDave - Why a wireless tstat? Any suggestions on brands (wireless & non-wireless)? If I do switch out the tstat, I'd like to stay with Honeywell...been happy with the Chronotherm III and Honeywell's are considered good. Looking at the Pro Vision 8000 series. Comments?
    May not be inputting as much gas as it should. this will cause the supply air to be cooler then most people like. And can give you a cool draft feeling making the house feel cooler then it is.
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  11. #11
    Thank you all for the feedback and most importantly the resulting sanity check.
    I'm going to proceed with two things -
    1) contacting a qualified carrier technician to eval the stage one cycle to see about adjusting the settings (btu and time) a bit higher and shorter respectively; and
    2) insulation eval of the attic just in case there can be some improvement there; I don't believe this will be significant but it can't hurt to cover all my bases.

    After these two actions, I'll let the system settle in on me and then decide if I really want to go with a straight 1-stage system again. BTW, I've read from a lot of HVAC folks that studies show the 1-stage systems do provide better heat and are consistently more cost effective. Seems counter intuitive in today's technology, but could in reality be accurate.

    Again, I really appreciate everyone's 2-cents. After accomplishing a steep learning curve on the topic, it was nice to have this forum to bounce my thinking around.

  12. #12
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    Quote Originally Posted by heatingstuff View Post
    Firecontrol -
    Comfort is subjective I get that. The comparison is based on old furnace comfort vs new furnace comfort. There is a definite change to a cooler feel with the new system. I have taken temperature readings with a digital thermometer that has a base station and a wireless remote. The temp at the thermostat will read X while rooms on the first floor read X-2 degrees and rooms on the second floor read X-3 degrees. The readings are taken over several days to determine consistency. The duct work only has individual dampers in each floor register. The individual dampers are all open as in the old furnace. There are no main dampers on the duct work at the furnace. Everything with the duct system is the same in the new system as the old system.

    Another reply suggested the system setup may be under fired in the 1st stage. I don't understand and would appreciate feedback on that.

    And with the new 2 stage system being controlled through the furnace and not the 1-stage tstat, I understand the staging is a timing setup not temp setup. So would switching to a 2-stage tstat have a positive impact? If so, any suggestions on what tstat? I would lean toward a Honeywell Pro Vision 8000 series.

    Learning that less air is being forced through the ducts on 1-stage is reassuring as that is definitely what I perceived. Now I know it's not my imagination.

    Thank you in advance for any advice -
    Switching to a 2-stage tstat would not improve what you're experiencing because by it's nature a 2-stage thermostat will bring first stage on at X°'s below set temperature and then the second stage X°'s cooler than the first stage. On the digital stats you can set this difference fairly close, but you still would be probably looking at no closer than 1 degree. So if you wanted it 70 in the house the second stage wouldn't kick on until it potentially dropped to 69 or 68. If your other thermostat turns the furnace on and off and it's accurate I'd suggest saving your money if the only reason you are contemplating changing it is to resolve the differences in temperature in different parts of the house. A simplified description of a thermostat is it's nothing more than a temperature controlled switch that turns the heat on and off. It can't resolve issues that are not related to the temperature sensed at the location it's mounted.

    I didn't see where you said if the new furnace is the same BTU input (on high fire/second stage) as the old furnace or different. If the new one is the same, then even on high fire the air flow on the new furnace can be different (and in most cases less) than the old furnace. The old furnace had 3 or 4 different speeds that the blower could run at (amount of air it moved) and that was hard wired by the installer. The new furnace's blower speed is controlled by the electronics in the furnace. The control is programmed to run the blower at the speed needed to achieve the manufacturer's recommended air flow across the furnace in low and hire fire respectively. I said this because, I suggest you set the thermostat 5° above what the temperature is in the house. This will, in time, bring on the high fire and maximum blower speed. Once this happens go around the house and see if the air coming out of the registers is what you remember with the old furnace as far as the force of the air. If it's less, than you should get your duct work (dampers) balanced for how the new furnace operates. This can only go so far because of the 2 stage/speed that the new furnace operates at. It's one of those "balancing acts" where you find what is the happy medium between the two different conditions.

    As far as the temperature of the air coming out of the registers with the new furnace (even on high fire) compared to the old furnace, this was more than likely going to be different no matter what kind of new furnace you put in. What I think is happening is that the new furnace (in low fire) is showing you things that need attention in your duct work like balancing and possibly insulation.

    This is just another step in evaluating what's going on so that you can make an informed decision as to how to proceed.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  13. #13
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    A Honeywell IAQ will bring on the first stage heat before the temp drops 1 degree, and also bring on the second stage before the temp drops a degree.
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