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  1. #14
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    dele

  2. #15
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Quote Originally Posted by Airmechanical View Post
    why do you think 95% of all systems are designed with the coil on the supply side of the blower?
    95% of gas furnace systems, sure. Air handlers for heat pumps where duel fuel is not implemented are virtually always coil first. But then you must know that, so I'm a bit perplexed by your replies.

  3. #16
    Join Date
    Nov 2007
    Location
    Livermore, Ca
    Posts
    163
    Quote Originally Posted by airtime View Post
    3 tons for 1100 sq. ft.? No insulation? Around here most houses that size use 1/2 that tonnage, but they are well insulated. Is 3 tons what the load calc called for?
    I'm feeling ya. I got whacked by a hack. He didn't do a calc. Says, "3 ton.. A little large but should be OK." wtf. I didn't know calc's existed until I came across this site.

    I have R13 in walls R30 in ceiling. Crawl space with no insulation. Dual pane winders. 3/12 pitch on the rafters. Wood siding.

    The more I learn the deal, the more pissed I get at the installing contractor.
    Bordering legal action if this keeps up.

    My calc's came out to 2 ton and 56k heat

    I can't yet enjoy this HP to tell if I even like them or not.

    I can't fully enjoy this system to even find out if I like HP's or not. Third season like this. Stop the pain. Oh the humanity.

  4. #17
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    Quote Originally Posted by regis101 View Post
    Greetings.

    If I remember correctly, when using a HP, the evap coil is on the return side of the blower? So as to act like a draw-thru?

    If so, why is this? Perhaps so that it doesn't get affected by aux heat?

    Secondly, If someone wanted to just use a HP as only AC, using a gas furnace as the primary heat source, would the evap coil then go on the supply side of the furnace? Disabling the HP function.

    Just researching options

    Thanks, Regis
    Here's my understanding - it depends on your backup heat mode. If your backup heat is gas, then the coil can go anywhere - either the furnace is running, or the heat pump is running. Not both.

    If your backup source is electric, then the coil HAS to be on the return side. Otherwise, the HP can't add heat to the air (it needs to add it's heat first).

  5. #18
    Join Date
    Nov 2007
    Location
    Livermore, Ca
    Posts
    163
    Thanks for the clarification, Waterloo.

  6. #19
    Join Date
    Mar 2007
    Location
    Quebec, Canada
    Posts
    56
    Always better to put the coil in the return
    Why?
    - Heat stages will work together. They can't if coil is in the supply because head pressure rise.
    - Coil isn't exposed to Aux heat
    - No need to cycle aux heat during defrost cycle

    Very very very common with electric stips as Aux.

    oil or gaz furnace :
    Always put the coil in the supply
    Why?
    - Condensate on oil pot, corrosion, Leak if in the return.
    - Must use a plenum sensor to cycle the aux heat during defrost

  7. #20
    Join Date
    Nov 2007
    Location
    Livermore, Ca
    Posts
    163
    I'm having an "A-ha" moment. Thank you

  8. #21
    Join Date
    Apr 2006
    Posts
    143

    return

    That 14" return to the 3ton HP is waaaaaay short of required. Some installers will run 16" flex to a 3ton HP thinkin thier ductulator is also a flexulator...still not enough air usually

  9. #22
    Join Date
    Nov 2007
    Location
    Livermore, Ca
    Posts
    163
    I recently put EfficientComfort.net on my fav's list. They have a nice "rule of thumb" for duct systems. Lots of other good info, also.

    For metal supply trunks with 3 tons it says 16". For flex returns it says a 14 and a 12. Oh my gawd

  10. #23
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    This thread reminds me of a system I found at our local ambulance service....

    In order the air goes through the system.....

    Face grille, return duct, evaporator coil, filter rack, furnace, supply duct


    All electric heat pump
    the coil is in the same cabinet as the blower assembly and heater assembly
    Air enters coil first, then blower, then electric heat strips
    Allows for more even air distribution across coil

    Dual fuel system or regular air conditioner with furnace for heat
    Furnace then coil
    blower is in the furnace

    if the coil is put before, the heat exchanger cells would become cold
    while in cooling mode. This will cause the inside of the heat exchanger cells
    to sweat.
    Since alot of furnaces are in attics... the sweating heat exchanger could in fact form enough condensed water to drain onto the ceiling

    you also intensify the effect the heat exchanger has on adding heat to the air stream in the summer.
    75 degree air going across a 120 degree heat exchanger gains some heat
    55 degree air going across a 120 degree heat exchanger gains more heat
    (would be equal to 75 degree air moving across a 140 degree heat exchanger.)
    technically... the heat exchanger would not be 120 inside it... even though the attic is 120... but the concept remains the same... I just simplified it for discussion


    aside from that
    I think the real question should be....
    how do you find a tech that can do the job correctly
    Try contractor locators on various brand name sites....
    ie Trane,
    Carrier,Rheam, and so on

    Getting late... will let you look up the other links
    Try Nate and ACCA as well

    Check with your power and light company... see if they have a heat pump program (we have one through TVA)

  11. #24
    Join Date
    Nov 2007
    Location
    Livermore, Ca
    Posts
    163
    I had a , new to my area, Rheem contractor/tech come and look a short time ago. Gave me the "tsk tsk" story. Didn't even charge me for the service call because he felt sorry for us. I mailed him a check anyway. Karma thing, I suppose.

    He verified that 2 ton is all I need and that the 14" duct system would work. A 16" return would be better and adding two more registers would be helpful.

    Last year I had a, close to my area, Rheem contractor/tech revise my ducting to ~work using the 3 ton, on paper. Still does not make the system right for the house being that it's a bit large. But liveable.

    On a side note, both of these contractors seem to think that for our geographic area, forced air is better. But that's another debate.

  12. #25
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

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    Quote Originally Posted by Irascible View Post
    95% of gas furnace systems, sure. Air handlers for heat pumps where duel fuel is not implemented are virtually always coil first. But then you must know that, so I'm a bit perplexed by your replies.

    your right, i did not mean to post that i must of hit send by mistake!

    but more than 50% of residential systems have the coil on the supply side of the blower!



    .

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