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  1. #1
    Join Date
    Mar 2010
    Posts
    80

    Adding second system and general issues

    I am a homeowner trying to sort out the hvac issues in our home - have had a few contractors out to look and want to vet some recommendations and questions.

    Home is from 1986, new england, about 2200sq ft downstairs and 1200 upstairs - loft ceilings everywhere. 5 year old Carrier infinity ECM furnace and 5 ton 14 seer compressor. upstairs is offset from downstairs and farthest bedroom might be one story up and 80 feet away from the air handler. Hardly any airflow there.

    In Summer, AC needs to run for hours to cool from 78 down to 72; maybe one degree an hour and that is downstairs, upstairs is hot, maybe 4-8 degrees above downstairs depending on room. In winter, heat downstairs is good, but upstairs ranges 2-4 degrees cooler than downstairs, but heat situation is definitely better than cool. House is well insulated.

    Contractor did measurement and when system called for 2000CFM, measured 1200 CFM with 0.5 static; he then found some foam insulation in the blower and system went up to 1700CFM, 0.8 static (limit of blower - not running efficently). He suggests no more than 3 tons downstairs due to ductwork sizing.

    Computer model he ran says 6.1tons for house with about 4 downstairs and 2 upstairs; but given the way model works and some high foyer areas that retain heat, suggests 3 ton downstairs and 2.5 ton upstairs (is this slightly undersized based on computer model? Is such ok?).

    So, recommendation is downsize (rebates for this) downstairs unit to 3 tons.
    Install heat pump and new ductwork upstairs at 2.5 tons.

    Does this all sound reasonable?

    Other contractors had similar suggestions, but were not as scientific about it all.

    Lastly, any thoughts on exposed spiral ductwork high up in loft style bedrooms? (easily solves some duct run issues).

    Thanks.

  2. #2
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,977

    Arrow Start With Reducing Home's Heat-Gain

    Six ton is a lot of cooling & airflow.

    You won't need that much tonnage, because they/you should be able to greatly reduce that figure!

    Depending on the layout, the heat near the ceiling should be left undisturbed, it acts as an insulator to heat transfer into your home.

    If possible, don't recirculate & remove the heat from that air near those high ceilings!


    There is a proper sequence when buying new equipment, that starts with reducing the whole house heat-gain.

    After that work is completed, then a Manual J heat-load calc should be performed, then equipment sizing & a manual D duct system performed, so the proper airflow is delivered to each room, at an ESP of static pressure with well sealed ducts @ 0.5"-IWC.

    Your existing units may not have been delivering enough airflow or the ducts were leaking, etc.

    Also, low static pressure readings are meaningless as to airflow if ducts are leaking air; test the actual CFM being delivered to the rooms!

    Tell us what major city in your state you live near or in. - Darrell

  3. #3
    Join Date
    Mar 2010
    Posts
    80
    Near Boston.

    On first floor, much of the heat can be left near celling (although there are ceiling fans we have tried off and on). Unfortunately, the house is quite open plan including up to the second floor where heat sits in living space.

    I've been told by a few contractors that number of ducts (few), size (small) and overall distance from air handler (large) simply prohibits adequate airflow to second floor bedrooms. Not to mention lack of any meaningful second floor returns.

    We did try to install an inline duct fan for one duct in the MBR - it really helped, but overall cooling rate for house is even lower and other bedrooms still do not fare well (they are linearly arranged and far from the MBR).

    Of course, the other issue is having only one zone and having to heat the whole house for either main living or bedroom use.

  4. #4
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    Quote Originally Posted by udarrell View Post
    Six ton is a lot of cooling & airflow.


    There is a proper sequence when buying new equipment, that starts with reducing the whole house heat-gain.

    Darrell
    What he said. All solutions are not necessarily mechanical solutions, although if all you sell is mechanical equipment that's what you'd prefer the customer to think.

    If you leave your back window and front door open on a 5 degree day you will be uncomfortable even if your equipment can maintain 72 at the thermostat.

    Fix the house and you may not have to fix ductwork or add a second system. Throwing more equipment at a corn crib costs $ in equipment and energy, but does not guarantee much more comfort.
    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.

  5. #5
    Join Date
    Mar 2010
    Posts
    80
    I completely get the 'fix the house first' approach and we have done as much as possible. Well insulated, windows shaded, skylights shaded or tinted, trees in all the right places. We have definitely reduced summer heat gain - particularly shading certain skylights. Nonetheless, we still need to do more.

    I am actually curious as to the effect of the increased airflow (1200-1700 when the contractor unblocked the blower) this season. Perhaps would be wise to get into this cooling season a bit before making any moves.

    If all else has been done to the house and otherwise, can anyone comment on the suggested approach (downsize compressor on main system to match ductwork and add dedicated heat pump system upstairs).

  6. #6
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    You have a new and good hi-eff. furnace. The A/C eff. is okay, particularly for New England area.
    I would recommend finding someone who can make sure your ductwork is correct and then add zoning.

  7. #7
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    Do you remember your blower door number after you finished doing "as much as possible." Knowing that and your square footage goes a long way toward finding what wall your sizing dartboard is on.

    And I think your implication that you may see how things operate now you've unplugged your unit makes a lot of sense. Taking notes on operational challenges helps point the building scientist in the right direction.
    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.

  8. #8
    Join Date
    Mar 2010
    Posts
    80
    The ductwork going upstairs is (I am told) inadequate even if zoned - at the max static pressure due to duct size and distance, we will not get enough airflow upstairs.

  9. #9
    Join Date
    Feb 2010
    Location
    The midwest.
    Posts
    663
    Quote Originally Posted by dbbarron View Post
    The ductwork going upstairs is (I am told) inadequate even if zoned - at the max static pressure due to duct size and distance, we will not get enough airflow upstairs.
    If you can't improve the ductwork, can you add a second A/C system only (if the heat is okay)?
    If you need some additional heat, you can add elec. to the new air handler.
    There are a number of ways to solve your problems.

  10. #10
    Join Date
    Mar 2010
    Posts
    80
    FYI - here is my gas usage for heating. Also have gas pool heater and hot water (not dryer); so non-winter months for gas usage.

    Tstat on 63 during day and 68-70 at night.

    03/08/10 2881 AMR READ 31.9 32 223.0
    02/04/10 2667 AMR READ 26.1 29 261.0
    01/06/10 2417 AMR READ 25.2 30 254.0
    12/07/09 2171 AMR READ 45.0 31 127.0
    11/06/09 2047 AMR READ 48.5 32 104.0
    10/05/09 1946 AMR READ 59.6 27 35.0
    09/08/09 1912 AMR READ 63.9 33 75.0
    08/06/09 1839 AMR READ 64.8 29 67.0
    07/08/09 1774 AMR READ 63.0 33 105.0
    06/05/09 1672 AMR READ 59.4 29 35.0
    05/07/09 1638 AMR READ 51.9 31 77.0
    04/06/09 1563 AMR READ 40.3 31 147.0
    03/06/09 1420 AMR READ 31.2 28 198.0
    02/06/09 1227 AMR READ 20.7 30 279.0
    01/07/09 0956 AMR READ 29.8 34 247.0
    12/04/08 0717 AMR READ 38.8 29 148.0
    11/05/08 0573 AMR READ 48.4 30 95.0
    10/06/08 0481 AMR READ 59.7 31 21.0
    09/05/08 0461 AMR READ 64.5 29 27.0
    08/07/08 0435 AMR READ 0.0 30 21.0
    07/08/08 0415 AMR READ 64.6 32 122.0
    06/06/08 0297 AMR READ 57.9 31 65.0
    05/06/08 0235 AMR READ 49.8 32 100.0
    04/04/08 0138 AMR READ 37.0 29 174.0

  11. #11
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    Quote Originally Posted by dbbarron View Post
    The ductwork going upstairs is (I am told) inadequate even if zoned - at the max static pressure due to duct size and distance, we will not get enough airflow upstairs.
    How was this determined? Did they perform a duct "score"? Did they do room by room heat loss and heat gain? Did they match the room losses to the delivery available? How far off were the rooms, and which rooms were off? How far away from enough are you, 10%, 20%? Did they measure, leave, then come back with the calculations? Did you watch them calculate? Did they just magically tell you "not enough?"

    Do they just want to sell you what's easy and "get 'er done"...

    I found this great report. Look at airflow analysis on page 8/9 to understand how this analysis SHOULD look! Really helps to understand the size of the challenge when you make decisions.
    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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