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  1. #27
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,244
    In our area, 80 & pump is cheaper heat than 95 and A/C. So if you are going to look at 80, I'm still saying do dual fuel. Your climate is similar to ours, I imagine your juice rates are too.

  2. #28
    In our area, 80 & pump is cheaper heat than 95 and A/C. So if you are going to look at 80, I'm still saying do dual fuel. Your climate is similar to ours, I imagine your juice rates are too.......BaldLoonie
    ________________________


    I meet with the rep. Monday morning. I'll ask him about a HP. I agree, our climates are probably quite similar.

    Thanks,

    Mike

  3. #29
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Quote Originally Posted by mikeinomaha View Post
    "My only suggestion - get a XV95, jeesh."......larobj63
    _________________________


    I get the feeling you're indicating the XV95 is a "no-brainer".<very big grin>

    Trying not to be too dense, but why specifically? The cost difference would not be insignificant and there's a 50/50&#37; chance dear wife and I may have to move in 5-7 years. In addition, fresh air/vent run to the outside is more complicated (more cost) due to a finished basement. Obviously, high-efficiency is nice, but initial cost and potential lack of return on invested dollars can't be ignored. In your expert opinion, considering the above, would you still spend the extra cash?

    I'm not trying to challenge...just honestly don't know. I will have the rep. run the numbers with the XV95, though.

    And by the way, thanks,

    Mike

    Yes - it's just the way I think, and I guess I'm slightly un-apologetic about it. The material cost-up isn't that large - but you will need to direct vent the 95 like you say. If the furnace is in a finished area, you're certainly right - running the new vent and supply won't be trivial. I wasn't considering that aspect of the install because I "ass"umed the furnace was in an accessible spot where hooking it up would be easier.

    The whole "move in 5-7 years" - well - there are two types of people, those that are staying forever (built their dream house, the minority), and the rest of us. Everybody's got the 5-7 year plan, ya know? If everyone had that mentality - everyone would buy an 80% efficient appliance, and here's the zinger - the world be worse off for it.

    I have an XV95 and will be getting a XL15 heat pump. I'll also probably be moving in "5-7 years". Not trying to be righteous - just letting you know I wouldn't point the finger if I hadn't ponied up for the better equipment myself.

    From an economic POV - my equipment will be lucky to pay for itself (incremental cost difference, even) in the time we're at this house. But the equipment will continue to be high efficiency for the next family - and I really think in 5-7 years, high efficiency equipment will be the norm, and that 80% furnace will stick out as a dinosaur.

    I usually don't present such subjective arguments, but there you have it.
    Last edited by larobj63; 09-14-2008 at 09:50 AM.

  4. #30
    From an economic POV - my equipment will be lucky to pay for itself (incremental cost difference, even) in the time we're at this house. But the equipment will continue to be high efficiency for the next family - and I really think in 5-7 years, high efficiency equipment will be the norm, and that 80&#37; furnace will stick out as a dinosaur.......larobj63
    __________________________________


    Actually, IMHO you make a very reasonable case....if not environmental, at least economical.

    If, as you suggest, in 5-7 years the 80% furnace might stick out as a dinosaur (possibly due to painful increases in natural gas prices), what I thought I was saving today may be erased at sale time when at my potential buyers want to reduce the sale price of my home because of "that dinosaur" of a 80% furnace. Dunno, but the point can't be ignored.

    Of course my other concern, both on a cost basis and conservation basis is trying to size this new system accurately. I'm obviously not an expert but I see a Man. J stating I have a heat gain of 35044 Btuh (3.2 ton) (SHR 0.70). The ARI certificate states a cooling capacity of 42000, EER 11.50, SEER 14.20 (all cooling).

    According to several articles referenced here on this forum, the authors state that the Man J overstates the cooling requirements (an inherent built-in fudge factor) and that "rounding up" is a uneconomic bad idea.

    Does this coil-a/c match-up meet the Man J numbers for sizing? Clearly, an oversized unit could be more expensive both initially and ongoing than the incremental cost of a high-efficiency unit.

    Thanks for your thoughts.

    Mike

  5. #31
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    What was the indoor summer design temp.

    An A/C, is only at its rated capacity at 95&#176; outdoor temp, and an indoor temp of80&#176;DB, and 67&#176;WB.

    At an indoor condition of 70&#176;F 50&#37;RH, that 3.5 ton may lose 10,000 BTU's of its sensible capacity.
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  6. #32
    What was the indoor summer design temp.

    An A/C, is only at its rated capacity at 95&#176; outdoor temp, and an indoor temp of80&#176;DB, and 67&#176;WB.

    At an indoor condition of 70&#176;F 50&#37;RH, that 3.5 ton may lose 10,000 BTU's of its sensible capacity..............beenthere

    ________________________________

    On my Man. J, the Summer Design Conditions were listed as:

    Outside db................92&#186;F
    Inside db..................75&#186;F
    Design TD................17&#186;F
    Daily range...............M
    Relative humidity.......50%
    Moisture diff..............39 gr/lb



    In reality, the actual temps my wife would like maintain in the summer is an indoor temp of 70&#186;! She'd kill me if she read this but she's getting hot flashes and to stay out of the "doghouse", I try to do as she wishes. :-) Of course the flashes won't last forever....it just seems like it. :-)


    Thanks,

    Mike


    P.S. Is there a data field entry in the 8th edition of the Man. J that accounts for menopause??? :-)

  7. #33
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    That will be in ver 10.

    That extra 5&#176; your wife wants, will most likely need it to be a 3.5 ton instead of a 3 ton.
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  8. #34
    That will be in ver 10.

    That extra 5° your wife wants, will most likely need it to be a 3.5 ton instead of a 3 ton.

    beenthere...

    ____________________________

    LOL!!! My wife thinks ver 10 should account for husbands that are full of hot air!


    Anyway, thanks for the reply.

    Do I understand you correctly that (ignoring the 70ºF inside temp stuff), that a 3 ton might be the proper size for 75ºF?

    I get the feeling my contractor might want to "be on the safe side" and round up. He may not subscribe to the belief that the Man. J inherently oversizes a/c's (assuming that it's true, and I've only read that it does).

    Or, are my concerns much ado about nothing and either 3 ton or 3.5 ton will suffice since the Man. J numbers include guesses such as infiltration, etc.?

    Honestly, I won't drive y'all crazy nitpicking. If this proposed system is in the correct range based on margin of error, I'd be satisfied.

    Thanks, again.

    Mike

  9. #35
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    I think he's going to 3.5 tons, to cover for those days that the OD temp exceeds 92&#176;.

    The 3.5 ton, if set up for 350CFM per ton, you should be ok.
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  10. #36
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Quote Originally Posted by mikeinomaha View Post

    Or, are my concerns much ado about nothing and either 3 ton or 3.5 ton will suffice since the Man. J numbers include guesses such as infiltration, etc.?
    I'm impressed you get this concept. For all the glory that Manual J or any other sizing program is - there is still educated guesswork being done by the operator/engineer/installer - mainly infiltration, as you mentioned. Other variables that are tough to get really, really right include shading and even orientation. Does that house front facade face South, or is it South-West, or is it South-South-West? You get my point.

    Like beenthere said - if the manual J was done at 75 deg design indoor temp, the extra 1/2ton will likley be put to good use bringing it down to 70 on design day (92, 95 whatever outdoor temp). And also like beenthere said, at those indoor conditions, the sensible capacity will be less than if it were 75 Indoor.
    Last edited by larobj63; 09-14-2008 at 07:12 PM.

  11. #37
    Gentlemen, one and all...thanks a million for your patience and expertise.

    You all are very kind to provide such help. I (like most) had NO earthly idea what HVAC professionals have to deal with every day. Had I not tried to get some limited insight through this forum, I still would've thought the profession to be fairly straight forward.

    It's quite impressive the amount of knowledge and experience necessary to function adequately and safely in this field. And to think residential is just one facet of HVAC. It seems you need to know physics, math, chemistry, biology, weather, and also have manual skills as well. Add to that working in cramped, hot, filthy attics and dirty basements....as a consumer, I hate to say, you don't make enough money.

    So far I've learned just enough HVAC to know I've barely scratched the surface and really don't know hardly anything. I'm happy to leave it to the professionals.

    Thanks again.

    Mike

  12. #38
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by mikeinomaha View Post
    Gentlemen, one and all...thanks a million for your patience and expertise.

    You all are very kind to provide such help. I (like most) had NO earthly idea what HVAC professionals have to deal with every day. Had I not tried to get some limited insight through this forum, I still would've thought the profession to be fairly straight forward.

    It's quite impressive the amount of knowledge and experience necessary to function adequately and safely in this field. And to think residential is just one facet of HVAC. It seems you need to know physics, math, chemistry, biology, weather, and also have manual skills as well. Add to that working in cramped, hot, filthy attics and dirty basements....as a consumer, I hate to say, you don't make enough money.

    So far I've learned just enough HVAC to know I've barely scratched the surface and really don't know hardly anything. I'm happy to leave it to the professionals.

    Thanks again.

    Mike
    that's a nice comment Mike!



    .

  13. #39
    Join Date
    May 2008
    Location
    Last moon off of Pluto
    Posts
    49
    Mike you're the Man...

    I say come on back anytime!

    Thanks,

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