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  1. #14
    Join Date
    Jul 2008
    Location
    RTP North Carolina
    Posts
    81
    Quote Originally Posted by bostonguy View Post
    I laughed at this. My older brother likes to have his thermostat at 69 in the summer, guess we are just one hot, sweaty family.

    At 72 it does not feel that cold to me. Again could be that my current unit is oversized so that 72 is not actually cold but that is the setting I need to get the humidity out? Just wondering.
    Heh, Im glad ya didn't take offense, its just my night off and I've had a few (too many?) beers and I'm feeling a bit saucy. Anyways, yes you are correct. If your system is oversized then it will not run long enough too pull the relative humidity down to an acceptable level. 72 degrees with a high RH could be uncomfortable. Just keep in mind if your new system is smaller, then it will generally run longer, and this is a good thing.

  2. #15
    Join Date
    Jul 2008
    Posts
    20
    Quote Originally Posted by JohnnyValvecore View Post
    Heh, Im glad ya didn't take offense, its just my night off and I've had a few (too many?) beers and I'm feeling a bit saucy. Anyways, yes you are correct. If your system is oversized then it will not run long enough too pull the relative humidity down to an acceptable level. 72 degrees with a high RH could be uncomfortable. Just keep in mind if your new system is smaller, then it will generally run longer, and this is a good thing.
    No offense taken, I laughed when I read it. Hope you are enjoying your time off because you guys work hard and deserve your time when you can get it. I understand that a smaller system will run longer and is better. That's why I'm trying to make sure I make the right decision by reading and posting here.

  3. #16
    Join Date
    Sep 2005
    Location
    Texas
    Posts
    2,793
    a blood thinner prescription could help tremendously

  4. #17
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,699
    ROFL.

    When its 20°F outside. I'll be outside working in a Uniform shirt, and a Tee shirt.
    I keep a jacket in the truck in case it gets cold out.
    In the summer, my place is 72°F, and 48% RH.

    I like it cold. I don't think blood thinner would help me.

    Yes indoor design temp can effect the load calc.
    One may be using a higher infiltration rate then the other.
    They may be using different load programs. Or different versions of Manual J, one may be using version 7, the other ver 8.

    Ask them to put in writing, what temp it will maintain, and what %RH it is sized to maintain while running.
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  5. #18
    Join Date
    Mar 2008
    Posts
    87
    I agree with you Beenthere. When we are home it is normally on 72*. If it is decently warm outside I can easily keep it in the high 40's%RH. I was kind of misled by my contractor and this site as far as lowering the humidity to keep it comfortable. I was set on leaving it 75*. Now that I have had the system for a little bit, I leave it at 75* when not at home and 72* when I am there. Lower humidity helps, but I still like it cold. Maybe it’s a northern US thing? (I am in Northern, NY). During the winter anything above 68* starts to feel too warm to me.

    Teddy

  6. #19
    Join Date
    Jun 2008
    Posts
    80
    bostonguy,

    I can give you the reverse experience and live in a climate very similar to yours.

    I have a 2 ton York HP that is undersized. My manual j says I may need 2.5 tons, but a contractor I like and will probably use when this unit goes tango uniform says I need 3 tons.

    On hot days it struggles to reach 77 degrees and so runs a lot. Consequently my RH gets down to 38% - 40%, or so says my Carrier Performance Series tstat.

    I really, really like beenthere's suggestion of saying to put in writing what min temp and min RH they will guarantee.

  7. #20
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,699
    I've had my place at 75° 44%RH, it still didn't feel as good as 72° 48%RH.

    Comfort is a perceived thing. So many of the people here(including myself), are telling you at what temps and conditions, they perceive their comfort at.
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  8. #21
    Join Date
    Jul 2008
    Posts
    20
    Quote Originally Posted by beenthere View Post

    Ask them to put in writing, what temp it will maintain, and what %RH it is sized to maintain while running.
    I will ask about this, thanks for the suggestion.

  9. #22
    Join Date
    Jul 2008
    Posts
    20
    I have a couple of questions if those that have contributed to my thread happen to see this. The contractor that I am seriously considering gave me the following info for things that were suggested earlier in this thread.

    1. For design temperatures he said that he used outdoor temp of 95 degrees, indoor temp of 70 degrees and RH of 50%. Sounds reasonable to me, any thoughts or comments.

    2. When I asked what values he used for wall insulation in the load calc he said in order to determine wall insulation he would have to poke a hole in the wall to see what is there. My house was built in 1969 and he said that houses built back then used little in the way of wall insulation so he said that he assumed worse case and used zero for wall insulation value. I thought that I had read somewhere that you can take the wall temperatures of an exterior wall and an interior wall and the temp difference would give an idea of insulation in the wall. Am I totally misunderstanding this? The contractor does seem knowledgeable so if he is usung a zero value for wall insulation should I be concerned?

  10. #23
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,699
    I would be wondering.

    He can pull a wall plate and check for insultaion.

    I don't think your design temp in the summer is anywhere near 95.
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  11. #24
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,306
    Is 70* the temp you want to maintain? If it's 72* thats a Hank R. do not do.
    I would cut a hole in my sheetrock and check R values before I would assume no insulation in my calcs.
    What does Manual J use for your area? don't add degrees to YOUR design temp!
    Go here and read Proctor info,http://www.proctoreng.com/articles/better.html

  12. #25
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    Quote Originally Posted by beenthere View Post
    One may be using a higher infiltration rate then the other.
    Infiltration is always an "educated guess" at best. I'm always surprised when people expect that load calculations are such an exact science. It is very difficult to know if a house has 0.5 or 1 air changes per hour or anywhere in between or above or below - and that makes a big difference in load! In fact, infiltration often drives the load more than any other factor - including wall insulation! If you want the load calc to be that dead on - pony up for a blower door test!

    It places an element of trust in your contractors experience, in my opinion. We are here in our office chairs - your bidding contractors have seen the house - maybe your windows are new - maybe they suck, we don't know. No-one can tell you what size is right form where we sit.

    My house was built around 1962, and it has no wall cavity insulation. But it has a continuous layer of homasote, covered by cedar siding, covered by vinyl insulation (with integral Styrofoam insulation), and lots of shading on the southern exposure. My cooling load is diddly squat - but it would be hard to predict without "knowing the house" - or at least seeing it!

  13. #26
    Join Date
    Jul 2008
    Posts
    20
    Quote Originally Posted by beenthere View Post
    I would be wondering.

    He can pull a wall plate and check for insultaion.

    I don't think your design temp in the summer is anywhere near 95.
    You have no idea how I wish I could find a contractor like you or any of the professional contributors to this forum.

    Do you know what the Manual J design temp should be for the Boston area?

    I'll also suggest that a wall plate be pulled and see what the response is.

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