Page 2 of 2 FirstFirst 12
Results 14 to 22 of 22

Thread: Short cycling

  1. #14
    Join Date
    Feb 2006
    Posts
    91
    Originally posted by thorton
    Originally posted by jeffshvac
    i wonder if a load calc was ever done 45,000 btu furnace with a nearly 2000 sq ft home?sounds a little undersized.
    Certainly does sound undersized. A furnace that small in a 2000 sq ft home should be running almost all the time, right?

    Thorton
    Then how can it be undersized? If it is undersized, it will not be able to meet the demand at the design conditions, will run continously and not get the temperature to what the theromstat is asking for. If it is oversized, then it will short cycle.

    For what it's worth, I have a 1950 square foot house in a much colder climate (average 7560 degree days per year). The house is old (108 years) and not too well insulated by today's standards. At the design temperature of 14F outside, 69F inside, the heatpump runs continuously and supplies about 40kbtu/h. I'm always astounded at the seemingly massive furnaces people talk about installing here - it's almost as though there's some macho pride in saying "yeah, I have a 185kbtu/h furnace". All that says to me is either their house has crappy insulation and/or they've wasted their money on equipment which is completely mis-matched to the task at hand.

    Paul.

  2. #15
    Join Date
    Aug 2002
    Posts
    1,649
    Jack,

    Check to see if the location of the thermostat is too close to a supply registar or if the hole for the t-stat wire is not sealed behind the t-stat...

    Good luck
    J

  3. #16
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,214
    Originally posted by pyropaul
    Originally posted by thorton
    Originally posted by jeffshvac
    i wonder if a load calc was ever done 45,000 btu furnace with a nearly 2000 sq ft home?sounds a little undersized.
    Certainly does sound undersized. A furnace that small in a 2000 sq ft home should be running almost all the time, right?

    Thorton
    Then how can it be undersized? If it is undersized, it will not be able to meet the demand at the design conditions, will run continously and not get the temperature to what the theromstat is asking for. If it is oversized, then it will short cycle.

    For what it's worth, I have a 1950 square foot house in a much colder climate (average 7560 degree days per year). The house is old (108 years) and not too well insulated by today's standards. At the design temperature of 14F outside, 69F inside, the heatpump runs continuously and supplies about 40kbtu/h. I'm always astounded at the seemingly massive furnaces people talk about installing here - it's almost as though there's some macho pride in saying "yeah, I have a 185kbtu/h furnace". All that says to me is either their house has crappy insulation and/or they've wasted their money on equipment which is completely mis-matched to the task at hand.

    Paul.
    Obviously, something else is wrong if a furnace this size short cycles in a house this size!!!

    Thorton

  4. #17
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,305
    On pretty much on all Honywell I set it at 3 (High Eff.) CPH.

    Sounds like it's on 5 cph right now.

    Mine some how at one time got changed to that, and it did the same thing as you were saying. it was at 5.

    If it was undersized, it would be running non stop and not keeping up to temp.

  5. #18
    Join Date
    Sep 2003
    Location
    Ocean County, N.J.
    Posts
    487
    I appreciate all your posts, and found the advice to be useful as this isn't the end. The homeowner is going to follow it through. I really need to know how the CPH is set up in this particular t/stat: T8112D 1005. Honeywell 5+2 programmable.

  6. #19
    Join Date
    Oct 2004
    Posts
    3,400
    Originally posted by jack david
    I appreciate all your posts, and found the advice to be useful as this isn't the end. The homeowner is going to follow it through. I really need to know how the CPH is set up in this particular t/stat: T8112D 1005. Honeywell 5+2 programmable.

    I hope this helps:

    http://customer.honeywell.com/Techli...0s/69-0917.pdf

  7. #20
    Join Date
    Sep 2003
    Location
    Ocean County, N.J.
    Posts
    487
    I would like to thank all of you again for your time, and bawl2, that was the iceing on the cake. Thanks.

  8. #21
    Join Date
    Oct 2004
    Posts
    3,400
    Originally posted by jack david
    I would like to thank all of you again for your time, and bawl2, that was the iceing on the cake. Thanks.
    Sometimes, even a blind hog finds an acorn.

    You're welcome!


  9. #22
    Join Date
    Jan 2006
    Posts
    32
    For what it's worth, I have a 1950 square foot house in a much colder climate (average 7560 degree days per year). The house is old (108 years) and not too well insulated by today's standards. At the design temperature of 14F outside, 69F inside, the heatpump runs continuously and supplies about 40kbtu/h. I'm always astounded at the seemingly massive furnaces people talk about installing here - it's almost as though there's some macho pride in saying "yeah, I have a 185kbtu/h furnace". All that says to me is either their house has crappy insulation and/or they've wasted their money on equipment which is completely mis-matched to the task at hand.

    Paul. [/B][/QUOTE]

    Totally agree ! How can anyone make that determination without seeing the house ? Especially when short cycling is the problem, not running flat out ? I have a 4500 sq. ft. house with a 59000 Gross output Buderus gas boiler. We have 3750 degree days where I live and on a 14F design day the heat loss (measured by boiler run time) is 21000 BTU. My boiler is way oversized for space heating, but when you add a 40 gallon buffer tank, it runs 20 mins every 60 mins on design day. That's 1 cph. Sounds like some people here would like to put a 185kbtu furnace into our house just based on square footage, but ignoring the fact that it's about 60% more effcient than an R2000 house.
    Heat load calcs are really easy to make in an existing house. Just clock the boiler over 1 hour and if you know it's gross output, you know what your heat loss is.

Page 2 of 2 FirstFirst 12

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