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Central Air Q's for the HVAC Peeps--UPDATED W/Quotes

Post in 'DIY and General non-hearth advice' started by thinkxingu, Dec 4, 2011.

  1. saladdin

    saladdin Feeling the Heat

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    Mine is not one of them. 1.5 year old and anything under 45ish and it struggles to keep the house at 70 and runs nonstop. House is tight and insulated to the hilt.

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  2. woodgeek

    woodgeek Minister of Fire

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    Dude, sounds messed up. There are a lot of mistakes and design errors that the installer can make--have somebody competent fix it and put it to work.
  3. Highbeam

    Highbeam Minister of Fire

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    Exactly, your heat pump is either undersized or broken. 45 degrees was easily warm enough in the 80s.
  4. thinkxingu

    thinkxingu Minister of Fire

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    Feedback on these numbers? All include a single return and no electric (my friend will be doing). I think we're now leaning away from heat pump, which looks to be more like $1000 more when you add cost of HP, wiring, returns, etc.

    Trane Heat Pump 13 SEER XR13 and TAM7 variable speed air handler $7213.00
    Trane Heat Pump 13 SEER XR 13 and 4TEC3F24B or Equivalent TAM4 multi speed Air Handler $6820.00
    Trane AC XB14 14 SEER and TAM7 variable speed A.H. $7263.00
    Same Condenser as above but with TAM4 A.H. $6980.00
    Trane AC XB 13 SEER condenser and TAM4 A.H $6735.00
    Trane AC XB300 13 SEER Condenser and TAM4 A.H. $6575.00 (Compared with YORK AC YCJD 13 SEER Condenser and AHR24 multispeed A.H. $6475.00)


    S
  5. woodgeek

    woodgeek Minister of Fire

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    I assume all the quotes are the same tonnage....

    I went for the variable speed blower, and am glad I did. The system cycles on ans off a lot, and the variable speed blower allows a slow ramp up and ramp down on each cycle that makes the unit operating noise less noticeable. I'm a kinda light sleeper, and I always wonder when I wake up in the early AM if it is because of me hearing the unit cycle on and off? While we're on the subject, don't put the compressor outside a bedroom window.

    SEER 13 is the lowest commonly installed, but I would guess your AC needs in NH are pretty light, so it would be hard to make the $$ back in reduced operating costs--did you ask for the price difference with a higher SEER unit?

    As for the heat pump, it really comes down to how you currently heat during the shoulder season....if you are burning scrounged wood exclusively, and enjoy that shoulder season effort, then don't get a HP. If you're running oil backup in the shoulder seasons, and switch to wood or wood supplement in the real cold, OR if you buy your wood, that I think the HP has a decent ROI. The HP above 40°F will be cheaper per BTU than any source other than NG or scrounged wood, and the latter only depending on the value of your time.
  6. woodgeek

    woodgeek Minister of Fire

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    So, they want to add more returns with the HP system than for the AC system? Weird. The cfm and return size should be a function of the tonnage only, and I thought you are talking the same size.
    Are the AC systems for a 'high velocity'/small duct system? I don't know about those, but I was leery of the air noise.

    When I researched it I got all this info that you can't heat with ceiling registers (in an attic retrofit), etc. My registers are all just where they would be for an AC unit (ceiling) and no problem. At the mild temps where the HP would run, I can't see it beng a problem at all.

    On the return.....I already discussed this, but talk to them about it. The SOP is 1 sq ft of return per ton, and my guy did that initially....and it was way too loud. Also I wanted to use a near-HEPA filter at the return, as we all have allergies, and the 1 sqft/ton rule makes it hard to run anything but a 'see through' filter (that exists to keep large lint from clogging the system, not to actually filter the air). I upsized 25% from the SOP, a LOT quieter, and can run a near-HEPA 1" filter no problem (changing it according to a 30-day run timer in the tstat). I use one box of 6 filter per year ($100), you would use half to a third as many.
  7. thinkxingu

    thinkxingu Minister of Fire

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    woodgeek,
    I've been having a side conversation with another member and it was mentioned that unless I put a return lower that I would just be sucking up warm air--given that the place the central return would be going is the warmest part of the home--weird, but definitely noticeable--it seems to make sense that it would be cycling the same warm air.
    As for what we heat with: all electric baseboard, with the wood stove on weekends/vacations. BUT, given the insulation and thermostats, it's not nearly as expensive as you might think: we pay just over $200/mth for an all electric house.

    Thoughts?

    S
  8. woodgeek

    woodgeek Minister of Fire

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    All I can say is that I have a multistory house with a return at the top of a central staircase, and all my registers are also in my ceilings, and I don't have a problem, and I run down to 15F, not 40. There is a little stratification (warmer near the ceiling than the floor), but not really noticeable to me. Of course, I did run some duct to my finished basement, don't know about all the heat on one level.

    Is the $200/mo a january figure? a six mo average, or a 12 mo average?

    All I can say is that if ~25% of your heating degree days are >40°F, and the COP = 3 for the heat pump, then you will save 67% of 20%, or about 16% on the heating portion of your electric bill, relative to running the baseboards. If you have a sense of how much you are paying for elec heat, then you can compute your payback.

    Why did you rule out mini-split again?
  9. thinkxingu

    thinkxingu Minister of Fire

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    woodgeek,
    I ruled out mini-split because I've only got one end with a flat wall. The other side of the house is a bedroom, which obviously wouldn't work with the door shut.
    $200/month is our yearly budget. Our regular electric (during the summer) is about $100, so we pay approximately $150/mth to heat. Of course, that's higher during cold months and lower during shoulder. I think I'm just worried that, with a split level and all the heat coming to this one area where the return will be, that most of the warmth will be recycled.

    S
  10. thinkxingu

    thinkxingu Minister of Fire

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    OK, spoke to the second to last installer and we worked out a deal that would be less expensive. So, we're comparing the following two contractors--the major difference is one would use Trane and one would use York. The top estimate lists three intakes, whereas the second would only do one--but he said there'd be three different filters, and I'm not sure if that's right or not. Still not sure on heat pump, but it's about $300 more in my case. Thoughts?

    $5850 ($300 more for variable handler--see end):
    INSTALL 2.5 TON 13 SEER 410A AIR CONDITIONING SYSTEM COMPLETE
    INCLUDES:YORK 2.5 TON CONSENSER,COMPOSITE PAD,LINESET TO BE
    COVERED BY SLIMDUCT GUTTER SYSTEM,DRAIN,WET SWITCH,SECONDARY
    PAN,AIR HANDLING UNIT HUNG FROM RAFTERS,YORK CONVENTIONAL MULTISPEED
    2.5 TON AIR HANDLER, SUPPLY DUCT TRUNK WORK,THREE RETURNS WITH FILTER
    RACKS,SUPPLY DIFFUSSERS(MV PVC TYPE),HONEYWELL PRO300 DIGITAL T STAT.ALL
    LINE VOLTAGE WIRING BY OTHERS.ONE YEAR LABOR WARRANTY, FIVE YEARS MAJOR PARTS.
    CHANGE AIR HANDLER TO YORK VARIABLE SPEED AIR HANDLER.THIS UNIT ONLY
    AVAILABLE WITH THREE TON COIL AND TXV .A/H WOULD REQUIRE RETROFIT TO 2.5 TONS.


    $5975 (I think $600 more for variable handler, 2.5 ton would be $200 more)
    Trane 2-ton AC XB 13 SEER condenser and TAM4 A.H


    S
  11. woodgeek

    woodgeek Minister of Fire

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    Don't know the York/Trane hardware...I would still get the variable speed handler.

    The filters are right at the return grate...three returns, three filters. You were thinking it was at the handler?

    $300 for the HP version seems a no brainer....if it only covered 15% of your seasonal load, you would make it back in what, a year or two? If you didn't like it for some reason (noise/comfort), IMO unlikely, you are out only $300.

    Are they going to mastic all the ducts in the attic prior to wrapping??
  12. thinkxingu

    thinkxingu Minister of Fire

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    Ok: one guy will use liquid mastic, the other mastic tape. As for the return, the guy with three said it would be simple enough just to run three flex runs together (I think) whereas the other said more than one return would require a second trunk with the filter at the handler. As for the hp, I'm not sure what other costs there are other than the condenser.

    S
  13. woodgeek

    woodgeek Minister of Fire

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    In the setup we are discussing, there is no difference to the ducting, so the only difference is the compressor, a tstat that can operate it (with a couple extra wires in the low voltage wiring) and some (cheap) valving in the airhandler. You seem convinced that a HP won't work for you...above 40°F it adds very little complexity and similar ducting/sizing from an AC will be fine. Instead of coolth from the registers in the summer, you will get warmth spring and fall, at a 70% discount per BTU versus your baseboards.

    Think of it this way--you are sinking a chunk of $$ into all this AC hardware that will not run so many hours per year in your climate. For the cost of a couple valves, a nicer tstat and hooking up a couple wires, maybe a 5-10% markup you will be putting otherwise idle hardware to work for you to save you money.
  14. thinkxingu

    thinkxingu Minister of Fire

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    Alright, I think we're close, but one last question: variable speed vs. multi-speed handler. Sounds like VS would be quieter, more efficient, and better at dehumidifcation (important to us) but more expensive to repair. Thoughts?

    And a summary of where we're at:
    Trane XB13 (no heat pump, since no returns at lower level)
    Trane Handler (VS or MS, depending)

    S
  15. gtjp

    gtjp New Member

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    How does it work in our 80-deg winter days?

    Definitely agree returns in all doored-rooms , not bath nor too close to kitchens..
    and NOT LOW unless in the south of KY...even there design a 'ZONE return air chase with dual purpose damper... GREAT for church-style buildings to have damper-high/low returns.
    if heating is significant...

    double ceiling 16x30's are possible ret grilles now

    Central return is fine WITH room returns, I believe.
    Getting down to 11 btuhs / sq ft requires great return systems.
    Thanks Paul Doty of Heat Controller, Century Heating, WeatherKing, FLA: 1981 seminar.
  16. heat seeker

    heat seeker Minister of Fire

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    I have a VS air handler, and like it. It's very unobtrusive unless the demand is high - at startup in a warm house, or really hot days. Then it really moves a lot of air, and you can hear the air coming out of the vents. The compressor is a two speed, so they work together. I believe that helps with the dehumidification, which can be significant here in New England in summer. I have no data on repair costs, but if they are higher than a single speed, I think it's worth it.

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