Page 1 of 2 12 LastLast
Results 1 to 13 of 24
  1. #1
    Join Date
    Jul 2006
    Posts
    151

    Manual J question

    I have a copy of a manual J done on my house. If I am reading it correctly, the heating load is 43351 and cooling is 25503. CFMs = 1234
    SQ Feet = 1933

    A 3 ton system was recommended based on these numbers. (This also happens to be the size of the current system.)

    Here is the system and it's performance numbers. The cooling numbers are close to a full 3 tons, but the heating numbers seem low. Especially if the heating load is 43351. Will this heat pump have any trouble heating my house until the temp gets low enough for the propane furnace to kick in?

    XR-13 4TWR3036A
    90% TUX1B080A9421A (74K BTU)
    4TXCB036BC3

    SEER 14.00 (35200 cooling)
    HSPF 8.50 (31000 at 47* / 19600 at17*)
    EER 11.80

    Thanks.

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    They will set it up to switch at the temperature needed ,no worries,I hope.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,384
    I see some issues!

    First is the ratings. Not sure where you got yours but AHRI Directory says that HP with that coil and standard blower is 13.00 SEER and 8.20 HSPF. Heating output is low as usual with A-S/Trane.

    Now, if your heat loss is 43K, you don't need that big furnace. The appropriate furnace would be the AUX2B060. Grossly oversizing a furnace means your actual efficiency would be reduced. You could have short cycling and you could cycle on the furnace's limit if the duct system isn't rather large.

    If you like it ice cold, a 3 ton for just over a 2 ton load may be OK but the calcs if done right reflect the desired indoor temp. But the appropriate cooling (HP) unit would be 2.5 ton. Going nearly 50% oversized means short cycles and high humidity. And your 13 SEER will be effectively lowered due to constant cycling in mild weather.

    As for changeover, I set A-S systems to change to gas 5° warmer than brands with good heating figures.

    Personally I wouldn't want that system and hope our salesmen wouldn't suggest a system like that with those kind of gain/loss numbers.

  4. #4
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    What was the sensible and what was the latent loads?

  5. #5
    Join Date
    Jul 2006
    Posts
    151
    Quote Originally Posted by sparksandfan View Post
    What was the sensible and what was the latent loads?
    It appears to me those fields are blank. There is a scan of the manual J below.

    Bald, could you give me the ARI reference number for the match you are getting? Thanks.



  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,755
    2421 Latent?

    What area are you in again.
    Contractor locator map

    How-to-apply-for-Professional

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

  7. #7
    Join Date
    Jul 2006
    Posts
    151
    Triad area of NC. Winston-Salem.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,755
    Latent load sounds low.
    Strange how it works out to require a 3 ton to get that sensible. Almost like the load calc was done to require the size you already have.
    Contractor locator map

    How-to-apply-for-Professional

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

  9. #9
    Join Date
    Jul 2006
    Posts
    151
    Quote Originally Posted by beenthere View Post
    Latent load sounds low.
    Strange how it works out to require a 3 ton to get that sensible. Almost like the load calc was done to require the size you already have.
    I could be wrong, but I don't believe this salesman ever checked the size of my old AC unit or asked me what size it was. I dunno.

  10. #10
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,350
    Was the salesman possibly trying to achieve 1200 CFM, thus suggesting a 3-ton unit?

  11. #11
    Join Date
    Jul 2006
    Posts
    151
    Quote Originally Posted by RyanHughes View Post
    Was the salesman possibly trying to achieve 1200 CFM, thus suggesting a 3-ton unit?
    I have no idea about that. He looked at the furnace in the garage and took measurements of it and noted the BTUs. Then we walked outside to look at the AC unit. I don't remember him looking on the back of it to get the size. Then we came back inside and he took measurements of all the rooms and windows and noted the window type (I have some old and some new). He checked where the supply and return vents were. And checked the attic insulation. He asked when the house was built and took a guestimate on the wall insulation. I don't recall him doing anything else, but it's possible I may be forgetting something.

    I know NOTHING about manual J's, so I don't know what looks strange or not.

  12. #12
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    Latent load sounds like a very tight house was assumed, but I see that the sheet says average construction.

    If the sensible load is as stated, then as BaldLoonie said, a 2.5 ton air conditioning would more closely match. It would still have latent capacity for your area.

    Is there a lot of wind wash in the winter? Are you on a hill or open pastures? High air change rate in winter?

  13. #13
    Join Date
    Jul 2006
    Posts
    151
    Quote Originally Posted by sparksandfan View Post
    Latent load sounds like a very tight house was assumed, but I see that the sheet says average construction.

    If the sensible load is as stated, then as BaldLoonie said, a 2.5 ton air conditioning would more closely match. It would still have latent capacity for your area.

    Is there a lot of wind wash in the winter? Are you on a hill or open pastures? High air change rate in winter?
    I think average would be accurate, definitely not "very tight". House is brick, split foyer. Faces southwest. Has a large window area in the foyer area (about 41 sq ft) This glass is single pane. I have put some "tinting" on it to help some. And front porch overhang also blocks some afternoon sun.

    Not on a hill or open area. Not unusually windy that I'm aware of.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event