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  1. Mine does that at 1:00 every afternoon. But I...

    Mine does that at 1:00 every afternoon. But I don't believe it has the ability to see the static pressure on the far side of the filter -- only the input and output sides of the fan. So it wouldn't...
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    Not really. With an MCA of 57 amps, I was able to...

    Not really. With an MCA of 57 amps, I was able to use #6 copper at its 75C rating (which is only 2 amps over its 60C rating). But voltage drop should be calculated from the actual load and not the...
  3. Hmmm, didn't think it worked that way. I've done...

    Hmmm, didn't think it worked that way. I've done some things to my evolution system since it was installed to lower static pressure and it has never complained. Did some other things that increased...
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    I don't believe there is a limit of 60A branch...

    I don't believe there is a limit of 60A branch circuits (residential or otherwise). But there is a requirement for many things with heating elements to have their loads subdivided into 48A segments...
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    Or was the flow hood round so its 12.6 sq...

    Or was the flow hood round so its 12.6 sq inches...

    Back to the original question. Who knows if the system is balanced. If you calculated the heat loss/gain on a per room basis, you should then...
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    And don't forget about air velocity in the trunk...

    And don't forget about air velocity in the trunk too. Even if the pressure loss is low, there is a speed limit for air. Once you know the CFM of the trunk between each takeoff, you can choose the...
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    In general, yes the total return pressure drop is...

    In general, yes the total return pressure drop is the same whether the filter is at the furnace or the return grill. But if you're trying to filter micro particles, putting the filter at the grill is...
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    Update. It was cold again this morning so I could...

    Update. It was cold again this morning so I could try another test. I confirmed that cycling the power on just the air handler will make the unit defrost one time after the 30 minute timer goes off....
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    Its a 698B. Outside air temp was 37F and coil was...

    Its a 698B. Outside air temp was 37F and coil was 26F when I reset the defrost to 30 minutes. After 30 minutes it was down to 11F coil temp, and 10F after an hour. Never went into defrost that entire...
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    Private Messaging

    I didn't see a help on how to use forum, so I'm posting here. How do you get private messaging to work? Other forums, and the FAQ here, say that "Send a Private Message" should appear when you click...
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    I think only the board was replaced and not the...

    I think only the board was replaced and not the sensors, but the reported temperatures seem to always make sense. I left you a Visitor Message. Can't seem to get PM's to work unless Visitor Messages...
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    Outside air temperature was 37F, so I'm well...

    Outside air temperature was 37F, so I'm well below that limit. Since the defrost board was replaced, what else could be wrong? It seems it has to be one of the inputs to the defrost board or somehow...
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    Infinity/Evolution Defrost

    I'm having a problem with my Bryant Evolution heat pump failing to defrost. The tech replaced the "defrost and temp sensor board" in the heat pump because there were temperature range errors logged...
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    Does your thermostat give any indication of when...

    Does your thermostat give any indication of when those heat strips are on (it could light up the emergency heat light, it could have an aux heat indicator, or it could tell you nothing)? You need to...
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    Here's my spreadsheet as a Word document (can't...

    Here's my spreadsheet as a Word document (can't upload a .xls file). It's kind of embarassing, but it tells me what I need to know. An online energy calculator would be better.

    This sheet assumes...
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    I made a spreadsheet a while back that compares...

    I made a spreadsheet a while back that compares fuel costs. At about 7 cents per kw-hr, gas would be cheaper if it was less than $1.10/therm. Since yours is higher than that, electricity will be...
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    It is not a concern, but it is an ignored factor...

    It is not a concern, but it is an ignored factor which would affect the calculated result versus the actual result. I think it is right to ignore it for heating. But the OP asked why his actuals and...
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    I believe another factor ignored by Manual J (and...

    I believe another factor ignored by Manual J (and perhaps HVAC Calc, haven't used that), is the heat generated by electrical appliances in your house. They do have a factor for that in cooling, but...
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    I measure static pressure by reading it off the...

    I measure static pressure by reading it off the thermostat... (Bryant Evolution). Before I had that system installed, I bought a Dwyer magnehelic kit, which I think was about $30. Using it, I felt my...
  20. There is nothing wrong with exposed NM cabling,...

    There is nothing wrong with exposed NM cabling, that is a permitted use. It needs to be protected from damage, and what constitutes that is up for the inspector to decide (and their interpretations...
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    Unless you want freezing air coming out all the...

    Unless you want freezing air coming out all the ducts during defrost (about 10 minutes of every hour all winter long), install the 10 KW strip. Here in Seattle, my HP frosts very easily when the...
  22. It is in the definition of relative humidity....

    It is in the definition of relative humidity. Lets say your winter outside air at 0F has 50% humidity. When you heat that air, it is able to hold more moisture. But unless you add some moisture, its...
  23. Note that the airflows to the 1st or 2nd floors...

    Note that the airflows to the 1st or 2nd floors relate to heat loss or gain and not volume. Perimeter length and amount of windows have the most influence. Also, the second floor has losses through...
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    Windows can make a huge difference. Changing them...

    Windows can make a huge difference. Changing them made a heat pump possible for me (reduced heat loss by over 12000 BTU). The difficulty is knowing what the U value and SHGC are. When my new windows...
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    The nameplate value will correspond to the...

    The nameplate value will correspond to the running amps of the heatpump. However, if the nameplate says "minimum circuit ampacity" or MCA, then there is a 125% factor for continuous use. I'd take the...
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    Can you explain why that is? I have a situation...

    Can you explain why that is? I have a situation where a 10x24 trunk needs a 6" branch at the end. This is in a basement and 2 feet short of the end of the wall. The easiest thing to do is put a 6"...
  27. That is an excellent suggestion too, especially...

    That is an excellent suggestion too, especially for very cold areas. I considered that for myself also, since I already had the oil infrastructure. But my tank is buried and 40+ years old, and I...
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    There is also a FPM limit for each type of pipe....

    There is also a FPM limit for each type of pipe. I'm not sure why (noise, turbulence, duct abrasion...), but Manual D lists these limits. Smooth metal duct has the highest limit, and flex the lowest....
  29. If the blower has enough force to overcome the...

    If the blower has enough force to overcome the static pressure, does it really matter? If one design is a little lossier than the others, up the pipe size and now it is less. Yes, it will be slightly...
  30. Thread: CFM & Others

    by suemarkp
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    You can't violate physics (go back to the...

    You can't violate physics (go back to the equation I posted). At 1000 CFM and a dT of 34, this is 36,700 BTU. A 10K strip will be close to this (34,120 BTU), so that value must be for the strip...
  31. Thread: CFM & Others

    by suemarkp
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    Yes, by Td I mean delta temp (which can be rise...

    Yes, by Td I mean delta temp (which can be rise or drop).

    Hopefully, this is the manual you're looking at (specifically page 5):
    http://www.goodmanmfg.com/Portals/0/Goodman/Specs/SS-GAEPF.pdf
    ...
  32. Your situation is very similar to my own, as I...

    Your situation is very similar to my own, as I changed from oil to a heat pump 2 years ago. The biggest factor between oil and heat pumps is the size heater you can buy. The largest residential heat...
  33. Thread: CFM & Others

    by suemarkp
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    1,670

    You should be able to cross check some things if...

    You should be able to cross check some things if you know the CFM, BTU, and/or Td. Use this equation to see how things fit:

    BTU = 1.08 * Td * CFM

    If you're getting a 14.7F rise at 1050 CFM,...
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    Show me any residential breaker that is listed...

    Show me any residential breaker that is listed for 100%. I don't know of any. Even if the air handler is 100% rated, the panel supplying it won't be. So you need the 125% factor added in, and you're...
  35. The calculation is not trivial (you can't just...

    The calculation is not trivial (you can't just read a chart), but its not rocket science either. To see where the economic trade off is on costs, you compare the cost per BTU for electricity and gas....
  36. Thread: CFM & Others

    by suemarkp
    Replies
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    1,670

    Your air is way too fast for a heat pump,...

    Your air is way too fast for a heat pump, especially if that is the minimum airflow and you're running on the first stage. You need a way to slow the blower down with only one stage of heating, but I...
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    Not always, there is a major exception for motors...

    Not always, there is a major exception for motors and compressors where the breaker can be much larger than the ampacity of the wire. You pick the wire by ampacity requirements (MCA nameplate value)....
  38. Thread: CFM & Others

    by suemarkp
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    1. Depends on how hot you want the air coming out...

    1. Depends on how hot you want the air coming out to be. My 4 ton heat pump runs at 300 to 350 CFM/ton in heating mode (300 for "comfort", 350 for "efficiency"). I know the CFM because it tells me...
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    It means you're most likely not even flowing this...

    It means you're most likely not even flowing this much air. A rule of thumb is 400 CFM/ton for air conditioners and 350 CFM/ton for heat pump heating. If you have more air flow than this, the "hot...
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    How can you say its too small? Did he specify the...

    How can you say its too small? Did he specify the CFM of the system?

    You would rarely get more than 100 CFM through a 6" duct, and most likely will have less than that on some runs. If all 11...
  41. I'm interested in the answer because I have this...

    I'm interested in the answer because I have this same problem (10 degrees too hot in summer, 5 degrees too cold in winter). I know the second floor is not getting enough airflow (it needs to at least...
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    Yes you can use a 20A on #14 wire too, if you...

    Yes you can use a 20A on #14 wire too, if you meet one of the specific sections of table 240.4(G). I thought you knew about 240.4(G) as you indicated in your previous posting. That is your permission...
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    I don't totally agree -- why do you think #12 is...

    I don't totally agree -- why do you think #12 is only good for 20A? Table 310.16 is the primary ampacity table electricians use, but it does also have derating factors. The breaker can be sized by...
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    Agreed. Another thing many people (including some...

    Agreed. Another thing many people (including some electricians) don't know is that the 60C ampacity of #12 copper wire is 25 amps. So as long as the MCA of the AC compressor is 25 or less, you can...
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    Bryant version

    I have the Bryant Evolution control which I thought was identical to the Infinity control. However, all I can find for adjusting humidity is a bar graph that has no numbers -- I can just go higher or...
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    I'm betting the problem is the service to your...

    I'm betting the problem is the service to your house. The circuit to the AC will make the dimming last longer if it is undersized, but your #6 wire is fine if its copper (and you're not near the...
  47. I had oil and its a slam dunk that a heat pump is...

    I had oil and its a slam dunk that a heat pump is cheaper than oil. I can not get gas at my house (unless I pay for a 1500 foot trench). Since I don't have gas I don't know what the gas rates really...
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    I'm going to be a dissenter here, and you may not...

    I'm going to be a dissenter here, and you may not know me from anyone, but your installation is fine and you're wasting your contractors time to come fix it. NEC 240.4(D) is the rule that normally...
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    I'm not so sure even Manual D provides the...

    I'm not so sure even Manual D provides the answer. Adding elbows adds an equivalent length to that run. I think an elbow is something like 50' of length. The register boot is usually the worst at...
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    I don't think there is one. Locked Rotor Current...

    I don't think there is one. Locked Rotor Current (LRA) or the Rated Load Amps (RLA) are directly related to the size of the motor compressor. But as compressor and system efficiencies go up, you...
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