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  1. #14
    Join Date
    Aug 2008
    Location
    Booneville, Mississippi, United States
    Posts
    259
    We sell more dual fuel units than either heat pumps or gas systems. Excellent choice.

  2. #15
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    +1 on dual fuel. I had one before and really liked it on my last house and might put on in again on my downstairs system. With the low airflwo settings Infinity has, the air temps above 35F will be pretty warm.

    Get a load calculation if possible. 4 tons doesn't seem out of line for that size home in that location for AC, but I find that 110k BTU suspect for a home that only need 4 tons of cooling in your climate. I suspect a 90k BTU is plenty even with minimal insulation. But only a load calculation can verify that. You don;t oversized because it's 2 stage. IT defeats the point of having 2 stage (comfort) and you may fidn that it's noisy on hgih stage because your short on airflow. 110k BTU's needs about 1600CFM even in "comfort heat" mode. That's more than than AC will use on high stage with Infinity. On high stage the Infinity AC won't call for more than about 1500CFM.

  3. #16
    First of all, many many thanks to all who replied to my post with excellent advice. Thanks also to SkyHeating for the link to videos.
    I watched a video of a blower door test in another thread; don’t remember off hand who posted it. Very informative. This is an awesome website, a little bit daunting sometimes because there is so much to learn, but awesome all the same.

    I knew someone would ask about a Manual J load calculation (like I said, I’ve been reading the posts on HVAC_Talk for a while). I guess I should have mentioned this in my first post. But here’s the rub: none of the contractors who gave me an estimate said anything about Manual J. They just “sized” the system by reading the numbers off our existing units (more on that in a minute). To be fair, I should say that they all did take a gander at the house.
    Also to be fair, I should mention that two of the three did ask us if we had any real discomfort with our existing system (too hot or too cold), and our answer was no. They all assured us that a new system would provide greater comfort than the existing one.

    Just for your information, that “existing system” is a 25-year-old Kenmore 4-ton A/C and 125,000 input BTU gas furnace. I know, I know, very old and very inefficient. But not only is it still running, it has never failed us, and it does a decent job of heating and cooling the house (albeit for way too much money).

    So once again the question is, what to do? And once again I defer to all of you experts on HVAC-Talk.

    Should I discount the three opinions I’ve had so far because none of the reps. so much as mentioned a load calc. or blower door test?

    If I get additional quotes, should I ask for a load calc. and blower door test? I get the feeling that if you have to ask, then it doesn’t count; a good contractor should know better.
    I Actually did ask one of my three quoting contractors after the fact about doing a load calc. and he assured me that it wasn’t necessary – sorry, but his reasoning kind of went in one ear and out the other, something about the results being unreliable because of too many unknown variables like the R factor for our walls etc.

    Are there any circumstances at all under which a Manual J would not be necessary?

    Also, are designations like “Factory Authorized Dealer” or “President’s Award” (Carrier) any guarantee (or any indication, for that matter) that a company will do the job right?

    And one final thought:
    .
    In response to my last post, Second Opinion wrote:

    “Pay close attention to your third dealers statements in reference to air distribution to the top floor with two stage, and modulating furnace system not being able to deliver air to the top floor. This is one item that gets overlooked when two stage/modulating equipment is installed on existing systems.
    As fare as duel fuel in the Washington Metro area, it is a great choice, if installed and set up properly.”


    If the top floor is, or can be a problem with two stage and modulating furnaces, how do I avoid this potential problem?

    As before, all of your expert insights are greatly appreciated.
    You guys rock.

  4. #17
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by AZag View Post
    First of all, many many thanks to all who replied to my post with excellent advice. Thanks also to SkyHeating for the link to videos.
    I watched a video of a blower door test in another thread; don’t remember off hand who posted it. Very informative. This is an awesome website, a little bit daunting sometimes because there is so much to learn, but awesome all the same.

    I knew someone would ask about a Manual J load calculation (like I said, I’ve been reading the posts on HVAC_Talk for a while). I guess I should have mentioned this in my first post. But here’s the rub: none of the contractors who gave me an estimate said anything about Manual J. They just “sized” the system by reading the numbers off our existing units (more on that in a minute). To be fair, I should say that they all did take a gander at the house.
    Also to be fair, I should mention that two of the three did ask us if we had any real discomfort with our existing system (too hot or too cold), and our answer was no. They all assured us that a new system would provide greater comfort than the existing one.

    Just for your information, that “existing system” is a 25-year-old Kenmore 4-ton A/C and 125,000 input BTU gas furnace. I know, I know, very old and very inefficient. But not only is it still running, it has never failed us, and it does a decent job of heating and cooling the house (albeit for way too much money).

    So once again the question is, what to do? And once again I defer to all of you experts on HVAC-Talk.

    Should I discount the three opinions I’ve had so far because none of the reps. so much as mentioned a load calc. or blower door test?

    If I get additional quotes, should I ask for a load calc. and blower door test? I get the feeling that if you have to ask, then it doesn’t count; a good contractor should know better.
    I Actually did ask one of my three quoting contractors after the fact about doing a load calc. and he assured me that it wasn’t necessary – sorry, but his reasoning kind of went in one ear and out the other, something about the results being unreliable because of too many unknown variables like the R factor for our walls etc.

    Are there any circumstances at all under which a Manual J would not be necessary?

    Also, are designations like “Factory Authorized Dealer” or “President’s Award” (Carrier) any guarantee (or any indication, for that matter) that a company will do the job right?

    And one final thought:
    .
    In response to my last post, Second Opinion wrote:

    “Pay close attention to your third dealers statements in reference to air distribution to the top floor with two stage, and modulating furnace system not being able to deliver air to the top floor. This is one item that gets overlooked when two stage/modulating equipment is installed on existing systems.
    As fare as duel fuel in the Washington Metro area, it is a great choice, if installed and set up properly.”


    If the top floor is, or can be a problem with two stage and modulating furnaces, how do I avoid this potential problem?

    As before, all of your expert insights are greatly appreciated.
    You guys rock.
    If you are having trouble getting air to the second floor, using a modulating or multiple- stage furnace when in low fire you will get even less air to the upstairs. Correct duct design and air distribution is the only way to eliminate the problem.

    A far as the "accalaids" go I would not put to much weight into them as fare as a qualification for an end result. One is strictly sales oriented.

  5. #18
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,735
    I agree with everything here except second opinion may be making attribution error, possibly because he's hvac oriented and not yet moved into building science.

    You don't 'stuff' air around a house. I've never seen temperature imbalance due to not enough fan. I have seen grossly oversized systems installed because of this incorrect assumption, so be careful, because the size you are being quoted sounds too big.

    Historically there are a LOT of reasons hvac guys may lean toward over sizing, so this need lots of power to push air hokum adds another false reason to the 'let's go up a size' argument. If the house is broken, more hvac as solution is an expensive and often seriously regretted approach to treatment.

    The primary problems causing imbalanced cooling are:

    Oversized cooling which quickly satisfies the stat, never getting even the ducts cold so only warm air gets to far rooms. The air may get evenly distributed, it's the btu's that don't make it, having been absorbed by the duct. Just as heat or cool starts to reach the room, the unit shuts off. The cause, too many btu at once, not too few.

    Reverse stack and unsealed attic penetrations - cold air in home drops as it leaks out low, sucking furnace hot attic air into upstairs spaces.

    Other big culprits: Duct leakage, poorly insulated ducts, and poorly placed returns also share some responsibility.

    The GOOD news is modulating equipment overcomes these issues to a significant extent. hybrid takes that a step further by being able to deliver less btu in mild temperatures. A lot of heat all at once, then off, is inefficient, expensive and not comfortable. A little heat, gentle, even and continuous is very comfortable. And surprise, equipment runs continuously, silently, and bills go DOWN!

    If you think you WANT hot or cold air at registers, let me try to reorient your thinking. You don't want to heat up or cool down your house, you want to replace or remove heat lost or gained. As these losses increase or decrease with temperature, equipment that can match those losses is ideal. By running continuously it maximizes efficiency, longevity (on/off cycling reduced), duct gets uniform temperature so far rooms become much more uniformly conditioned, and energy bills drop through the floor.

    Sounds too good to be true but I have a client in your area (NSA engineer) who will vouch for every piece of this, he followed my advice a year ago and can't believe his comfort or energy bill. and this was a HOT summer, right?

    4000 sf. He got the 60,000 infinity mod and 2 ton vna, replacing a 120,000 btu furnace and /4 ton ac.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #19
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,543
    We do a LOT of dual fuel heat pump systems and I have one in my house! My heat pump heats home down to about 25 and below that the 95% gas furnace takes over. I also have a programmable thermostat that most will not recommend however I have additional controls that keep the 1st stage heat (heat pump) on longer during re-heat of the home. Works great and have had zero problems with either. My last home also had a dual fuel (sometimes called hybrid) system. It basically keeps the heat/cool bill under control, and the outside thermostat can be adjusted if you want more gas furnace and less heat pump. Or we can simply switch over to total gas heat from the thermostat. Great system!

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,167
    Quote Originally Posted by second opinion View Post
    If you are having trouble getting air to the second floor, using a modulating or multiple- stage furnace when in low fire you will get even less air to the upstairs. Correct duct design and air distribution is the only way to eliminate the problem.

    A far as the "accalaids" go I would not put to much weight into them as fare as a qualification for an end result. One is strictly sales oriented.
    I find that Mod or 2 stage get more air upstairs. Since they are not forcing as much air to come out the first floor registers.

    In low fire, the blower is slowed and the static is much lower.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #21
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    +1, longer run tiems and low static will always even out temeprature imbalances. Also factor in that at low air velocities, convection will become more of a factor, so warm air will want to rise, and the inertia of hte air is less prevalent, so supplies located at the end of a trunk, will not get disproportionately more air than when velocity is higher. Similarly, you don't get somewhat of a venturi effect on supplies located in the middle of a main trunk. At high velocities. Also, after a turn, whre air gets turbulent on the inside of the cirve and "packs" to the outside, depending on velocity, it can take up to 10 pipe diameters in distance for air to even out and become more laminar again. This is a common issue with the installatin and location of many types of mass flow meters for example.

    SO while air pressure is measured "statically", air moving through ducts is quite dynamic. Those dynamic effects are minimized at lower velocities.

    THe only problem you cna run into at very low velocities, is depending on size of registers and type of grills, you can get poor throw and air mixing in the room. But you have to be pretty low for that to be a problem.

  9. #22
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,669
    I would say that they are going out on a limb saying a new unit will keep you more comfortable as the old units seemed to cool very well. Yes the new systems do burn less energy
    We really need change now

  10. #23
    Join Date
    Oct 2004
    Location
    The Zone
    Posts
    392
    I have dual fuel and have it set to operate below 35 degrees.
    I'm on propane in the country and it saves a gob of money.
    Heat pumps can last as long as A/C units.
    It's Hammer Time!

  11. #24
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Don't be afraid of the Duel Fuel system. My parents has it in their home, and it's very comfy there.. I think it's set up to switch over to gas when it's down to 20˚.

  12. #25
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296
    Quote Originally Posted by AZag View Post

    I knew someone would ask about a Manual J load calculation (like I said, I’ve been reading the posts on HVAC_Talk for a while).

    I guess I should have mentioned this in my first post. But here’s the rub: none of the contractors who gave me an estimate said anything about Manual J. They just “sized” the system by reading the numbers off our existing units (more on that in a minute). To be fair, I should say that they all did take a gander at the house.

    Also to be fair, I should mention that two of the three did ask us if we had any real discomfort with our existing system (too hot or too cold), and our answer was no. They all assured us that a new system would provide greater comfort than the existing one.

    Just for your information, that “existing system” is a 25-year-old Kenmore 4-ton A/C and 125,000 input BTU gas furnace. I know, I know, very old and very inefficient. But not only is it still running, it has never failed us, and it does a decent job of heating and cooling the house (albeit for way too much money).

    Should I discount the three opinions I’ve had so far because none of the reps. so much as mentioned a load calc. or blower door test?

    If I get additional quotes, should I ask for a load calc. and blower door test?
    I get the feeling that if you have to ask, then it doesn’t count; a good contractor should know better.
    Are there any circumstances at all under which a Manual J would not be necessary?
    Manual J is not necessary if you know the exact output of the existing unit?
    Do you have a data logger to monitor ALL the parameters necessary to correlate equipment performance and heat/cool requirements?

    CFM, room temperature, supply air temperature and dew point, room relative humidity, outside temperature
    over an EXTENDED period

    Window replacement is enough of a reason to KNOW that the old unit is oversized.
    You have provided the answer to your own question.

    Blower door and duct blaster test are recommended if one wishes to have a realistic expectation of energy usage.

    80,000 BTU/ hr would be my W.A.G. for a heating load, but an appropriate Manual J would give one real confidence in
    arriving at a sufficiently acccurate load.
    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

  13. #26
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,735
    AZag, any updates?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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