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  1. #1
    Hello-

    I am looking at a near future upgrade/redesign of my system and wanted to get your opinions on it:

    House is 2500 sq feet. two story, 40 yr old. pretty leaky, in atlanta area

    Currently have
    3 ton gas furnace in crawlspace and 4 ton condenser outside ( I know it's mismatched I would assume it has been setup this way due to lack of space in crawlspace - original 40 yr old furnace is still there rusting)
    current system is about 10 yr old - Goodman

    duct work is all aluminum mostly insulated with a couple of runs on outside walls. Mostly in crawlspace

    each duct seems to split and go to one room downstairs and then way up into one room upstairs. So each room upstairs has a separate duct.

    return vents are in every room as well.

    Current issues are:
    * 2 bedrooms upstairs get very little air flow (farthest from the furnace and smaller furnace???)
    * several vents have varying levels of heat (probably insulation)


    I am considering the following options:


    1. Put a new heat pump + air handler in attic and run new duct runs for 2nd floor. Close off old ducts and effectively split the system in two zones. One upstairs and one downstairs. 2 ton unit should be fine for upstairs and would replace old ac condenser with 3 ton unit and effectivly match up the furnace to 3 ton for the first floor? I would also need to do some electrical work to support the 2nd system.

    2. upgrade to dual fuel - which brings up another question. How hard will it be to upgrade? I have not been able to find exact steps. I know that I would need to replace condenser with heat pump, new thermostat..anything else? Then upgrade to zoning via someone like arzel. about 4-5 zones using current ducts. this is new option I have not figured out costs yet. Advantage of this option is reuse of existing ductwork, more control via zoning. I would probably end up getting 4 ton heat pump and plan on replacing 3 ton furnace with 4 ton (hopefully newer version are smaller so they would fit. or going away from gas altogether??

    Thanks a lot in advance.





  2. #2
    Join Date
    Jul 2005
    Posts
    648
    To upgrade to dual fuel, the condensor would be replaced with a heat pump. You would need a different t-stat that would determine (using an outdoor temp sensor) when to cut out the heatpump and bring on the furnace. Keep in mind there are so many variations with different equipment and appication as far as staging goes. Depending on where you live and the price of electricity it might be cheaper to go straight heatpump with electric strip heaters. You're doing the right thing by doing some homework first. One bit of advice though. Make sure the contractor does a heat loss calc.

  3. #3
    Join Date
    Nov 2001
    Posts
    1,874
    Call a compnay with a long history in the city you live.
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    Which have you done ?



  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,286
    Originally posted by president69

    2500 sq feet
    two story
    40 yr old
    pretty leaky
    in atlanta area

    duct work is all aluminum mostly insulated with a couple of runs on outside walls. Mostly in crawlspace

    return vents are in every room as well.

    I am considering the following options:

    1. Put a new heat pump + air handler in attic and run new duct runs for 2nd floor. Close off old ducts and effectively split the system in two zones. One upstairs and one downstairs. 2 ton unit should be fine for upstairs and would replace old ac condenser with 3 ton unit and effectivly match up the furnace to 3 ton for the first floor? I would also need to do some electrical work to support the 2nd system.

    I would probably end up getting 4 ton heat pump and plan on replacing 3 ton furnace with 4 ton (hopefully newer version are smaller so they would fit. or going away from gas altogether??
    Use 16 SEER/ ~ 9 HSPF heat pump only for Atlanta
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Mar 2004
    Posts
    1,042
    First we have to effectively isolate the different questions. Right now they are getting dangerously jumbled together.

    Question #1 is sorting out air distribution- ductwork, zoning, and perhaps the question of one system versus two. In the end that's often hard to decide without seeing the house firsthand.

    Question #2 is sorting out how much heating and cooling capacity needs to go where. The only way to determine that properly is using a Manual J load calculation. Undersized systems don't do the job; avoiding that risk without doing careful calculations yields a tendency to oversize. Oversized equipment doesn't produce good comfort, humidity control, and never achieves its efficiency ratings. You can get a top-notch HVAC company to do one for you, but they may not want to give away their engineering services without a purchase contract being signed. If you're a bit technically savvy, you can do your own calculation. I (as a homeowner) did my own using HVAC-Calc software, as sold on this web site for $50 (see the red tab above) and got excellent results, as far as comfort, efficiency, etc. My numbers agreed closely with the calculation my contractor ended up doing on his own for comparison. Incidentally, determining whether to use one system or two is best done while looking at the results of such a load calculation. Then you know how much conditioning is needed where, which tells you how much airflow is needed where, which can tell you which duct runs are adequate and which aren't; it also tells you what size equipment is needed, and based on the sizes available, you can decide if one system or two will do. Don't assume that any such care was applied in sizing or installing your original system, as the chances of that are very small.

    #3. Desirable system efficiency and fuel source. Heat pumps with electric backup are cheapest to run in the Atlanta metro. Dual fuel looks about the same as a traditional AC + furnace, but the AC can run in reverse (the old name for a heat pump was "reverse cycle air conditioner") to provide heat in mild to moderately cold weather. The difference in an AC and a heat pump is a few extra controls, switches, valves, etc.; making a system work as dual fuel takes a new thermostat. Gas-only heat is leaving a lot of people in this area crying in their beer now; don't bother with it. Electricity is going to stay comparatively cheap in this area because our juice comes almost exclusively from coal and nuclear, not natural gas or oil.

    Switching to all-electric can be a good choice, but you will need stout electrical service and a 200 amp breaker panel in most cases (maybe 150 in a condo or small/efficient house). Then you run a big 240V circuit to where the furnace is now, and put an air handler in its place. The AC gets replaced with a heat pump, and you need (common theme here) a new thermostat. Everything else would stay about the same. Trouble is, if it's hard to pull a big wire from the panel to the existing furnace location, or your electrical panel isn't up to snuff, you probably won't save enough on energy bills in the long run to cover the upfront cost of switching to all-electric. The equipment itself is actually cheaper, but all the extra wiring needed to make the switch can sour the deal.

    Incidentally, in this area we pay over $200 a year in base charges for the privelege of having natural gas service at all- before you use any gas- so don't put yourself in a position where you're only using gas for hot water. At that point have your gas meter turned off and go ALL electric. Electric water heaters do cost more to run than gas ones, but the difference is small enough that the $200 a year I just mentioned will more than cover the difference.

    If it's the case that switching to HP+ electric backup isn't practical, dual fuel is still a good choice. You're stuck with the base charges, but at least you don't use a lot of gas during heating season. The heat pump does so much of the heating that it's not even worth spending extra for a high efficiency furnace; it really only gets used on the coldest few days of the year. If you do get dual fuel, insist on a heat pump with a "demand" defrost system. Simpler defrost control systems cause a lot of unnecessary defrosting, which interrupts heat pump operation and makes the furnace run in milder weather than is really necessary.

    Variable speed is good to have for best comfort, whether your indoor equipment ends up being a furnace or an air handler. Two speed outdoor equipment is nice, but in my book not as important to have. Don't skimp on the thermostat in any case, because that's the brains behind the whole system, and more and more there are more complicated decisions to make than the traditional "heat or don't heat".

    As for efficiency of the heat pump, our utility costs are moderate. It's tough to justify going for top of the line efficiency based on the economics alone. Middle of the road efficiency is better suited to the area. If you want top of the line comfort, quiet, etc., or if you just have a green streak, though, you know what you have to do

    #4. This one isn't a question- get rid of the 40 year old furnace no matter what!

    [Edited by wyounger on 02-22-2006 at 09:58 AM]

  6. #6
    Thanks for all the replies. Wanted to clarify, since I think I made it sound too complicated.

    2. I am planning on having manual J done.
    3. I've considere moving to an all electric solution and I will probably switch to it gradually as my gas heater is relavely new and I have an expensive gas stove (previous owner install). I have 200amp service to the house and I am pretty sure that the breaker panel is rated for 200 amps. running cable would be relatively straightforward since it would go from garage to crawlspace.
    4. I think I confused you. I have a mismatched 3 ton 10 yr old furnace in crawlspace and next to it old rusting 4 ton unit that is 40 yr old. The reason is that the door to crawlspace is too small to take out the old unit and they just left it there.

    5. TO simplify my original question. What do you think is better/cheaper/easier : one big system with dampers for zoning or two small separate systems?



  7. #7
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,800
    Better-two smaller systems. In the event of a failure, you still have the other system.

    Cheaper-Probably one big system with zone control. Depending on what needs to be done to modify current duct system.

    Easier-Hmmm crawlspace vs. attic. Again, depending on duct modifications, probably the single unit.
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