jeff-4
10-06-2006, 02:34 PM
Hi! I have posted here before and received lots of good advice. I have one simple question (and read on for other advice you can give me!):
Could someone please let me know what Manual J, Version 8, lists as the design conditions for a heating calculation for a home in Minneapolis, MN?
I understand the indoor temperature is to be set to 70 F. I need to know the outdoor value (which I believe is listed in Table 1A). I do not own a copy of Manual J.
Why am I asking? I'll try to be brief. I ran into a lot of installation issues with the contractor who installed a Ruud Modulating furnace in my home last February. People here were very helpful to me (Thanks again!). Even after the installation issues were resolved, I still felt that my house was very slow to heat up in the morning. Talking over the summer with a friend who is an HVAC professional, he feels that the installed furnace is too small. After I carefully measured floors, windows, etc., in my home, he did a Manual J calculation for me (using indoor 70 F and outdoor -12 F) that showed that the furnace is too small. The calculations showed that the furnace was about 6% undersized. So, the furnace is not dramaatically undersized, but my feeling is that, living in Minnesota with a furnace for the next 18+ years, I want to have enough capacity to keep the house warm during an extreme cold snap. I can provide lots of details but will spare you of them at the moment.
I contacted my contractor with the issues, politely suggesting that the furnace may be undersized and offering the data and claculations, and faxed them to him. I told him that, if the furnace was indeed too small, I would willingly pay the cost differential of the hardware but I expected that he would have to bear the re-installation costs. He had his own guy do the "same" calculations, which of course showed the furnace to be adequately sized, and declared that my guy was incompetent. My HVAC friend doesn't want to ruffle feathers and wants his name kept out of the issue (a condition I agreed to). So, its a me versus them issue at present. I'd rather resolve the issue with the contractor than immediately think about litigation (but I will do this, if need be).
There are several suspect items in my contractor's heat load computation. First, they set the indoor temperature to 68 and the outdoor temperature to +17 F. I objected that this was not representative of the "worst-case" design scenario, but he insisted that the computations were done "by the book, version 8 of Manual J," including the +17 F outdoor temperature. Hence the one question above. Second, only the gross summaries of the computations were sent to me. There was no detail page withe the numbers that went into the computation. So what other things were assumed to make their computation come out with a smaller heat load? Finally, when I said that the sizing criterion should be as follows: needed furnace size (in input BTUs) >= the computed heat load (under worst-case conditions) divided by furnace efficiency (AFUE), he almost blew a fuse, stating something like "it's far more complicated than that."
So, first admonish me for not more carefully choosing a contractor and not demanding a heat load computation up front (although these guys may have simply fudged it anyhow for their own purposes).
But next, could anyone provide advice? I'd be willing to pay someone to become involved, with the understanding that these numbers might have to be carried to small claims court. Are ther other alternatives?
Thanks in advance to all who respond!
Could someone please let me know what Manual J, Version 8, lists as the design conditions for a heating calculation for a home in Minneapolis, MN?
I understand the indoor temperature is to be set to 70 F. I need to know the outdoor value (which I believe is listed in Table 1A). I do not own a copy of Manual J.
Why am I asking? I'll try to be brief. I ran into a lot of installation issues with the contractor who installed a Ruud Modulating furnace in my home last February. People here were very helpful to me (Thanks again!). Even after the installation issues were resolved, I still felt that my house was very slow to heat up in the morning. Talking over the summer with a friend who is an HVAC professional, he feels that the installed furnace is too small. After I carefully measured floors, windows, etc., in my home, he did a Manual J calculation for me (using indoor 70 F and outdoor -12 F) that showed that the furnace is too small. The calculations showed that the furnace was about 6% undersized. So, the furnace is not dramaatically undersized, but my feeling is that, living in Minnesota with a furnace for the next 18+ years, I want to have enough capacity to keep the house warm during an extreme cold snap. I can provide lots of details but will spare you of them at the moment.
I contacted my contractor with the issues, politely suggesting that the furnace may be undersized and offering the data and claculations, and faxed them to him. I told him that, if the furnace was indeed too small, I would willingly pay the cost differential of the hardware but I expected that he would have to bear the re-installation costs. He had his own guy do the "same" calculations, which of course showed the furnace to be adequately sized, and declared that my guy was incompetent. My HVAC friend doesn't want to ruffle feathers and wants his name kept out of the issue (a condition I agreed to). So, its a me versus them issue at present. I'd rather resolve the issue with the contractor than immediately think about litigation (but I will do this, if need be).
There are several suspect items in my contractor's heat load computation. First, they set the indoor temperature to 68 and the outdoor temperature to +17 F. I objected that this was not representative of the "worst-case" design scenario, but he insisted that the computations were done "by the book, version 8 of Manual J," including the +17 F outdoor temperature. Hence the one question above. Second, only the gross summaries of the computations were sent to me. There was no detail page withe the numbers that went into the computation. So what other things were assumed to make their computation come out with a smaller heat load? Finally, when I said that the sizing criterion should be as follows: needed furnace size (in input BTUs) >= the computed heat load (under worst-case conditions) divided by furnace efficiency (AFUE), he almost blew a fuse, stating something like "it's far more complicated than that."
So, first admonish me for not more carefully choosing a contractor and not demanding a heat load computation up front (although these guys may have simply fudged it anyhow for their own purposes).
But next, could anyone provide advice? I'd be willing to pay someone to become involved, with the understanding that these numbers might have to be carried to small claims court. Are ther other alternatives?
Thanks in advance to all who respond!