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  1. #1
    Join Date
    Sep 2002
    Posts
    12,195

    How would you size this job ?

    Guy calls and says that he wants to get off propane heat. He has a 2 ton AC and a 50K propane furnace.

    Over the telephone I suggest a heat pump, we talk about the why's of it all and so forth, and he agrees.

    I do the load calcs and come up with 13,200 cooling and 24,350 heating. So the closest I can do is an 18,000 BTU system which give about 18,000 heating as well. New coil, cond, air handler, 7.5KW electric heat.

    He and I go over the various numbers (real nice old guy) and talk about it.

    The guy says: Well, why not just install a 2 ton? That will give me 24,000 BTU's for heating and I'm happy with the 2 ton AC I have now. And that will have me using the backup heat less and so saving money by running the heat pump more.

    So at first I argue and talk about how important it is to have the AC sized correctly and so forth. But after a while - I start to see it his way: The 2 ton HP Will heat his house better and cheaper than the 1.5 ton. And, as he says; he is perfectly happy with the short cycling 2 ton AC.

    BTW: He keeps it on 80 degrees - which isn't helping the short cycling any. <g>

    I did think again about my two speed heat / one speed cooling idea. <g> Install two speed two ton and have the 24K heating he needs and the 12K cooling as well. But he doesn't want to spend the money for the two speed. Says he won't live to see it pay. He's 90. <g>

    So . . . . . what do you all suggest?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #2
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,847
    Rule # 1. The customer is always right. I know it's not right, you know it's not right. Give the old timer what he wants or someone else will. He's right, no way will he live long enough to see a return on his investment.

  3. #3
    Join Date
    Mar 2001
    Location
    North Carolina
    Posts
    428
    What is the location used for heat load? design temps?

  4. #4
    Join Date
    Sep 2002
    Posts
    12,195

    Locations -

    He's in Gloucester County NJ. (exit two in jersey-speak)

    I used 70 degrees for heating - (0 - 70) I used 20 degrees for cooling (100-80).
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,722
    On heat pumps, 25&#37; over sizing on cooling load is allowed in Manual J.
    Contractor locator map

    How-to-apply-for-Professional

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

  6. #6
    Join Date
    Sep 2002
    Posts
    12,195

    Yes, but -

    The cooling load is barely over 13K. The smallest residential system I can buy is 18K. 27% oversized instead of 25% - which is still pretty close. So yes; I am fine with that.

    But . . . . the 18K leaves me short on the heating side, the customer knows it, and wants to favor heating.

    A few years back I mentioned that his oversized AC (2 ton) would work better if he ran a dehumidifier in the house. So ever since he has had one running non-stop with the AC. It's set to 40% and sitting on a plank over his washing machine. When the washing machine is full - he washes his clothes in the distilled water. <g>

    He says that he's happy with that arrangement - so why should be go light on the heating side now? And then have to make up the difference with more expensive electric heating? And plus; not get all the "heat pump savings" that he could get by installing the 2 ton heat pump. Which was my whole 'selling point' to him in the first place - he's using my own logic to justify his position - which make it hard to argue against it effectively. <g>

    It seems to fly in the face of my in-grained 'accurate sizing is everything' training, but . . . . I'm really starting to agree with him. <g>

    That's why I wanted to bounce some ideas around with you.

    PHM
    ---------



    Quote Originally Posted by beenthere View Post
    On heat pumps, 25% over sizing on cooling load is allowed in Manual J.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  7. #7
    Join Date
    Sep 2002
    Posts
    12,195

    And BTW:

    I did not factor any of the extensive tree shading into the cooling load calcs. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  8. #8
    Join Date
    Mar 2001
    Location
    North Carolina
    Posts
    428
    What does the expanded ratings for the equipment say for 95 degree outdoor with 63 degree wetbulb @ 600 cfm? your 18k unit may only give you 12k sensible might want to check.

  9. #9
    Join Date
    Aug 2007
    Location
    WI
    Posts
    1,105
    The guy is 90. Give him what he wants. As long as he knows the pros and cons let him decide.

  10. #10
    Join Date
    Mar 2001
    Location
    North Carolina
    Posts
    428
    Quote Originally Posted by DesMech View Post
    The guy is 90. Give him what he wants. As long as he knows the pros and cons let him decide.
    Don't know about your area but here if you do the install and it is not right, when the 90 year old guy passes on, who ever gets the house may not be happy with it and you could find yourself correcting the problem outta your own pocket no matter what the previous owner wanted.

  11. #11
    Join Date
    Aug 2007
    Location
    WI
    Posts
    1,105
    Quote Originally Posted by obxtech View Post
    Don't know about your area but here if you do the install and it is not right, when the 90 year old guy passes on, who ever gets the house may not be happy with it and you could find yourself correcting the problem outta your own pocket no matter what the previous owner wanted.
    Around here, a lot guys would just slap in a 3 ton, "just to be sure". Manual J calcs on existing homes are virtually unheard of around here. You can disagree, but I would not consider what the op is talking about to be "over sizing". He is simply sizing the unit to cover the heat loss, because cooling is less of a concern. I did a geothermal job a couple of years ago, and the homeowner did not care one bit about air conditioning, but he wanted the lowest heating bill possible. We sized the unit to cover the heat loss. This meant the unit is about double the size needed to cool the home. He was very aware of the drawbacks, but ultimately, he made the decision, and he is very happy with his heating bills. By the way, I did not care about future homeowners, because I designed the system for the one who has to pay the bill now.

  12. #12
    Join Date
    Dec 2003
    Location
    Citrus County, Florida
    Posts
    1,488
    I thought that oversizing was supposed to be 15% or less. yes---no??
    Doug

  13. #13
    Join Date
    Sep 2002
    Posts
    12,195

    His neighbors have a 2.5 and a 3 ton <g>

    So it must be fairly common around here too. <g>

    He mentioned that to me originally: "How can I need a 1.5 ton system when I have a 2 ton Now and my neighbors all have 3 tons?"

    Which is why I showed him all my load calcs and went on to discussing the numbers and what they mean and why.

    Of course then he used my own heat pump logic right back on me. <g>

    I was just curious about how you all felt about it. And I'm happy to see you are willing to discuss it; the various pros and cons, and so forth.

    PHM
    --------


    Quote Originally Posted by DesMech View Post
    Around here, a lot guys would just slap in a 3 ton, "just to be sure". Manual J calcs on existing homes are virtually unheard of around here. You can disagree, but I would not consider what the op is talking about to be "over sizing". He is simply sizing the unit to cover the heat loss, because cooling is less of a concern. I did a geothermal job a couple of years ago, and the homeowner did not care one bit about air conditioning, but he wanted the lowest heating bill possible. We sized the unit to cover the heat loss. This meant the unit is about double the size needed to cool the home. He was very aware of the drawbacks, but ultimately, he made the decision, and he is very happy with his heating bills. By the way, I did not care about future homeowners, because I designed the system for the one who has to pay the bill now.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

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