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  1. #1

    One versus two HVAC systems for a 2 story house

    I am currently looking at replacing my 25 year old HVAC systems in order to get the Federal tax credit. I have two systems, one serving the first floor and the other serving the second floor. Each has a Carrier 100,000 BTU furnace, a Carrier 3 ton high efficiency air conditioner and a Aprilaire humidifier. There are two thermostats with the first floor one in the front of the living room just around the corner from the front hallway and the second floor one in the upstairs hallway. The two thermostats are almost vertical from each other.

    My house is also 25 years old and is located in the Chicago suburbs. It is two stories with about 3200 square feet of living space with 1950 on the first floor and 1250 on the second floor. The front of the house faces east. The living room is on the north side of the house and is 325 sq. ft. (13x25). The family room is on the south side of the house and has a vaulted ceiling. It also has three glass French doors, two skylights which face west and a fireplace. The family room is 400 sq. ft. (19x21).

    The 2 furnaces are located next to each other by the wall in the basement around the center of the house. The air conditioners are outside. I recently found out that the cold air duct work runs between the two furnaces so that whenever either furnace turns on, all of the cold air returns on both floors are pulling in air.

    I have two heating/cooling problems. The family room is always about 3-5 degrees hotter or cooler than the living room. It is hotter during the summer because it is fully exposed to the east afternoon sun. I think the vaulted ceiling is making it colder during the winter. The air flow to both rooms seems to be about the same.

    The problem on the second floor is that the four bedrooms are 2-5 degrees warmer/colder than the hallway. I believe the upstairs hallway is being warmed by the downstairs. Right now it is 68 in the downstairs hallway and the upstairs hallway and only 65 in the master bedroom. The other problem is that if we turn down the first floor thermostat at night, then it gets too hot in the bedrooms because it is colder in the hallway. There is a heat vent in the downstairs hallway that has a weak airflow and there is a cold air return in the upstairs hallway that doesn’t seem to have any air flow.

    I had four people out from both Carrier and Trane to give me estimates for new systems.

    One Carrier guy recommended replacing the two furnaces and A/C’s with just one of each and use three zones (living room, family room and 2nd floor). The system he recommended is
    1 Carrier Infinity ICS furnace - 100,000 BTU
    1Carrier Infinity System 17 air conditioner – 4 ton, 17 seer
    3 Infinity thermostats

    The Trane guys recommended:
    2 Trane XV-95 furnaces – 60,000 BTU or one at 60,000 and one at 80,000
    2 Trane XR-13 air conditioners – one 3 ton (upstairs) and one 2.5 ton (downstairs)
    2 Honeywell IAQ thermostats to be put in same locations as old thermostats

    I personally like the Carrier system because it has a top of the line furnace and A/C and attempts to resolve my family room issues. Trane as a good furnace but the A/C is one of their cheapest and isn’t Energy Star. They claim the two stages and variable-speed will resolve my heating/cooling issues but I cannot understand how it can heat up a room that is 67 when the thermostat is set for 70 and it is in a room that is 70. I also don’t understand how it will stop the 1st floor temperature from influencing the upstairs thermostat. I also don’t understand why you have lower BTU furnaces and lower tonnage A/C’s serving the first floor when it is almost twice the size of the second floor which would get the bigger units. The prices for the Carrier and Trane systems are about the same.

    I am about ready to forget the tax credit and just wait until next year to deal with this because I am totally confused by this. By the way, the Carrier rep was the only one that went in every room of the house and did a load calculation. I am just afraid that going from two of everything to one of each with a 3 zone system may cause even more problems. I would greatly appreciate any suggestions that anyone has.

  2. #2
    Join Date
    Apr 2008
    Location
    TEXAS
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    1,701
    my personal preference is always two seperate systems for two story homes. it sounds like the trane guy was quoting less efficiency to take the sting out of buying two systems. so you are not looking at apples to apples. i would get a load calculation before pulling the trigger on any system. one guy is saying one 4 ton and the other is total 5.5 tons. a load calc will tellyou who's closer to the mark. good luck.
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

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  3. #3
    Join Date
    Oct 2003
    Location
    Washington
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    No-brainer. 2 systems.

  4. #4
    Join Date
    Jul 2006
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    6,447
    As i type, im on my second floor and my first floor is basically off.

    Better control of temperature and my utility bills.
    You sure are cocky for a starving pilgrim.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,709
    While the first floor may be larger. It has no heat loss or gain in/from its ceilings that are covered by the second floor.

    On the Trane system. They can add remote sensors to the bedrooms, so that it senses the temp in the bedrooms instead of the hallway. Ask the Trane dealer about it.

    I'd also ask the Trane dealer about upgrading to 2 stage A/Cs. This will improve your cooling comfort.

    The redundancy of 2 systems. is never better appreciated. Then if you have one system go down during the hottest or coldest time of the year. And you don't have to call a tech out on a weekend.
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  6. #6
    kenney t Guest
    Quote Originally Posted by seatonheating View Post
    No-brainer. 2 systems.

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    You posted , 3 Infinity stats,so I assume 3 separate zones.

    I prefer zoning over two systems. Less to maintain and eventually replace, 3 versus two zones,better comfort room to room,different set back temps per zone,etc.,etc..

    Here's some pics of a zoned furnace,hybrid heat system;

    http://hvac-talk.com/vbb/showthread.php?t=156408


    Them them you ant it to b installed like this! lol

  8. #8
    Join Date
    Aug 2009
    Posts
    1,127
    There is something to be said for the redundancy of two systems, but plenty of arguments against as well. Twice the chance of a failure for one. Half your house will be without conditioning in the case of a failure, I doubt that would impact your decision to call a tech for service on the weekend or a week day. Nor would I base a purchase decision personally on that one weekend service scenario (unless I'm in the space shuttle - then triple redundancy is the standard).

    Three zones will keep your house at a more even temperature than a two furnace (only two zone) system. You will also be able to program each system for setbacks in temperature when those zones are not in use during the day or night. That potentially will save you a significant amount of energy depending on your home usage patterns.

    The Carrier guy did a load analysis. That is a huge plus. Some Carrier dealers have a 100% satisfaction guarantee as well for one year. If you are dissatisfied for any reason, they will pull the system and give you a 100% refund of your money. Ask him about this. If so, it means he trusts his design and installation to pass this very high criteria, your satisfaction.

    The Trane two furnace design will work exactly as well as your existing systems. If you are happy with how things currently work, that is a good choice. It cannot fix room your room imbalances, no matter how many thermostats are installed.

  9. #9
    As posted by Smittyii
    "i would get a load calculation before pulling the trigger on any system. one guy is saying one 4 ton and the other is total 5.5 tons. a load calc will tellyou who's closer to the mark. good luck. "

    The Carrier rep had a handheld device that he held up to a wall and shot a laser beam across the room. He went to every room in the house and did this. I assume he was measuring the length and width of each room to use for his Manual J calcs. He left some notes with some numbers. It said Size BTU +95deg -10deg. It then said Manual J and under it were two columns. The first column had 100K 64K 42K then there was a line and then 86K. The second column had 36K 32K 20K and then the line and then 47K. At the bottom of these numbers, he had 48 - 4 ton. I guess that is how he came up with the size.

  10. #10
    Quote Originally Posted by zachhvac View Post
    As i type, im on my second floor and my first floor is basically off.

    Better control of temperature and my utility bills.
    I tried doing this in the winter by turnib down the first floor stat. The problem was that as it got colder on the first floor, it also got colder in the second floor hall where the stat is. The result was that rooms on the second floor were getting too hot.

  11. #11
    Join Date
    Jul 2004
    Location
    Massachusetts
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    6,829
    Quote Originally Posted by Confused2474 View Post
    The Carrier rep had a handheld device that he held up to a wall and shot a laser beam across the room. He went to every room in the house and did this. I assume he was measuring the length and width of each room to use for his Manual J calcs. He left some notes with some numbers. It said Size BTU +95deg -10deg. It then said Manual J and under it were two columns. The first column had 100K 64K 42K then there was a line and then 86K. The second column had 36K 32K 20K and then the line and then 47K. At the bottom of these numbers, he had 48 - 4 ton. I guess that is how he came up with the size.
    Hmmm. If he didn't measure the windows and sliders, he didn't actually do a load analysis, just a square foot size. That doesn't qualify as a Manual 'J' calc. If he did measure all the glass, skylights, etc. then you should be okay. I'd be curious as to what type of duct changes the Carrier rep is quoting. And how is he proposing to access the opposite floor? In other words, where are the ducts being run to accommodate the 2nd floor if the unit is on the 1st floor or basement or vice versa if the unit is in the attic?

    There are still many questions to ask before committing to a job. And be advised that the Federal Tax Credit applies to any $5,000 expenditure for qualified Energy Star products. It's 30% of the $5,000 = $1,500. You could insulate, buy a new refrigerator, put in new windows or any combination of these to get the $5,000 qualifying expense.

    In the future there may be lots more money available, if the U.S. Congress can ever agree on what should be put into the Home Star program. More important than the small FTC, however, is your comfort. If you make a mistake on sizing and/or ducting, you'll be living with that mistake for many, many, years. So shop very carefully. Decide whether you want a Rolls Royce, Mercedes Benz, Avalon, Toyota or Yugo. All the comparable systems and prices are out there and since you're not as well versed in buying HVAC systems as you are in buying automobiles, make sure you do plenty of homework.

    Follow the suggestions in the attachments and you should be able to make a very informed decision with which you'll be happy, for many, many, years.
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    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  12. #12
    Join Date
    Oct 2010
    Location
    Chicago
    Posts
    36
    Not only Carrier and Trane qualify for the tax credits. I'd shop around a little more. Definitely 2 systems, unless you have the money to do a re-ducting of your home for the sake of in depth zoning.

    Edit: I see you are in Chicagoland area, have you tried your local contractors? We sure are blessed with plenty. They can suggest a wide range of brands to meet your needs.

  13. #13
    Join Date
    Jun 2010
    Posts
    152
    I've owned both. 2 story with 1 system and 2 story with 2 systems. 2 is much better.

    I would recommend 2 systems and dual stage heat. Get a load calc to get the correct numbers but you currently have 200K BTU of heat and 6 tons of cooling. OMG. I have a larger house in texas and I have 4.5 tons of cooling.

    2 stage heat allows for a low heat setting that takes longer to heat up and lets the heat get to more places before it shuts off. You still have a high setting if it is extremely cold or heating up from a low temp.

    I say again if you want to be comfortable get a heat load. You can get the software from this site for $50. http://www.hvaccomputer.com/main.asp

    If you don't know what kind of windows you have or insulation just pay someone to run.

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