Page 1 of 11 12345678 ... LastLast
Results 1 to 13 of 131
  1. #1
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,739

    Ton to Square Foot rule of thumb?

    Many ask if there is a tonnage to sf rule of thumb, afraid that if equipment gets too small they will sail off the edge of the earth. Kinda like happened to explorers up until Columbus magically reshaped the earth from a pancake to a globe.

    That reshaping is occurring now in our industry. (of course stupid setback strategy thing needs to be weeded out of the public consciousness to really succeed).

    Well, there are some using this rule of thumb in reverse. If your equipment is more than 1 ton per 1000 square feet, the HERS guys suspect crappy work and pull out the magnifiers.

    Here's a GREAT article on the subject...
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  2. #2
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,157
    Here is a quote from the article.
    HVAC contractors doing their own load calculations are afraid to come out with a cooling load that's too low. They're afraid of call-backs from clients who can't keep their homes cool.
    Maybe AC Bad Dog is onto something when he talks of contractors making certain numbers come out of a manual J?

    Good article BTW.

  3. #3
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    996

    Figures

    don't lie, but liars can figure. And now, I think I'll have a drink

  4. #4
    Join Date
    Jun 2008
    Location
    Fort Worth,TX
    Posts
    56
    Quote Originally Posted by chuckcrj View Post
    Here is a quote from the article.

    Maybe AC Bad Dog is onto something when he talks of contractors making certain numbers come out of a manual J?

    Good article BTW.
    Judging by the area I am in this summer, 27 days straight of over 100 degree temps. I have 4 neighbors that did the energy audit and did the recommended. Guess what ! Not one of them can hold less than 85 in the house with the units running 24/7. Expensive lesson in electricity usage and equip cost.

    So much for design temps..

  5. #5
    Join Date
    Jan 2008
    Location
    In the work truck
    Posts
    3,029
    Quote Originally Posted by MLeonhardt View Post
    Judging by the area I am in this summer, 27 days straight of over 100 degree temps. I have 4 neighbors that did the energy audit and did the recommended. Guess what ! Not one of them can hold less than 85 in the house with the units running 24/7. Expensive lesson in electricity usage and equip cost.

    So much for design temps..
    Yea I hear that. I work in the heat all day, when I come home I want it cool. Last week it was 110* in NJ. Thats quite a bit over the design of 95*..

    It's been 73 in here.. sooo nice..
    Gotta have the right tool for the job!

    Where is all the stuff MADE IN THE USA?

    "Thats what we do Troy. Incredible, Invisible, Imbelivable things. We are an Unseen, Unknown, Unvincible fraternity of craftsman.."

  6. #6
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,739
    Quote Originally Posted by chuckcrj View Post
    Here is a quote from the article.

    Maybe AC Bad Dog is onto something when he talks of contractors making certain numbers come out of a manual J?

    Good article BTW.
    Yeah, Allison does good stuff.

    I think the problem is homeowners have very selective listening habits. And don't we all get tired of repeating themselves over and over on off clock time. I'm completely sympathetic to that.

    "My ac won't shut off"
    "I got home from work over an hour ago, and the ac hasn't shut off yet".
    "I think my ac is undersized, it seems to be running continuously, you better come check it out under warrantee"
    "rolleyes"

    Mam, let the equipment do it's thing. If the house is too cold for sleeping, bump the temp 1-2f.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  7. #7
    Join Date
    May 2000
    Location
    Urbandale IA. USA
    Posts
    4,939
    It just varies from location to condition.

    Examples:
    1. 2000sf South Florida or Texas
    2. 2000sf Northern Minnesota or Alaska
    3. 2000sf NO windows
    4. 2000sf ALL glass.

    Each example is different, but the sf is still the same....
    You CANNOT use rule of thumb.... !
    .
    Those who dance, appear insane to those who do not hear the music.
    Those who believe, appear ignorant to those who do not know God.

  8. #8
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,739
    Did you read the article? He's not using it as a sizing mechanism, he's using it as a flag to catch when contractors aren't sizing properly.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  9. #9
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,837
    Actually, most of the complaints could be dismissed if the load was calculated using the diversification method and using zone controls. Manual 'J' without diversification assumes the entire house is under the same load all day long. But in reality, often there are large windows facing east or west that are not subject to high loads all day long. Using diversification the size of the system can often be reduced but with use of an appropriately divided zone control system, there need be no loss of comfort.

  10. #10
    Join Date
    Dec 2006
    Location
    Litchfield,Il
    Posts
    565
    Thanks for the article Tedd! Why is there a rule of thumb in the first place?? Every single house has its issues and if you do run into a "perfect" envelope well, you need to play the lottery quick! With all the varibles on what is allowing heat to escape and make its way into the home, how can any HVAC contractor just put a rule of thumb on Sqft to Equipment size. I use a heat load cal. program and I still at the end wonder if I was correct on selecting the type of exterior wall insulation. I know I put in the correct window and door specs but I also see the worn out and missing caulking and how a improper door installation leaves a slight crack at the frame. All these items allows leakage , so when I do the Heat load cal. and it recommends a 3 ton I sit there and think "Are these customers going to think Im crazy when I say the 3 ton will keep you comfortable IF you address these other issues with your home" ? Sad part is they have instantly thought I was doubting my calculations and was wanting to blame their house issues in the process. Maybe I don't need customers like this but I have found more like this than not.
    If your not getting the results you desire then change. People change from either desperation or inspiration.

  11. #11
    Join Date
    Jul 2006
    Posts
    1,091
    So he has a RULE of THUMB too.

  12. #12
    Join Date
    Jul 2011
    Posts
    354

    Smile

    Quote Originally Posted by luskys a/c View Post
    Thanks for the article Tedd! Why is there a rule of thumb in the first place?? Every single house has its issues and if you do run into a "perfect" envelope well, you need to play the lottery quick! With all the varibles on what is allowing heat to escape and make its way into the home, how can any HVAC contractor just put a rule of thumb on Sqft to Equipment size. I use a heat load cal. program and I still at the end wonder if I was correct on selecting the type of exterior wall insulation. I know I put in the correct window and door specs but I also see the worn out and missing caulking and how a improper door installation leaves a slight crack at the frame. All these items allows leakage , so when I do the Heat load cal. and it recommends a 3 ton I sit there and think "Are these customers going to think Im crazy when I say the 3 ton will keep you comfortable IF you address these other issues with your home" ? Sad part is they have instantly thought I was doubting my calculations and was wanting to blame their house issues in the process. Maybe I don't need customers like this but I have found more like this than not.
    rule of thumb, in northern NJ you have 3 popular types of houses, ranch,cape,colonial, if your in a area and do all the same houses w/o major tightening up. i.e. serious insallation, total upgrades of windows,heavy duty sealing, unless that's the case you know how many BTU's per sq. ft. you need! if you go to a house in the same area but have heavy glass,sky lights,what ever , then you go with the load calc. that's where the
    rule of thumb comes from. i'm seeing some people when doing load calcs spec 25 degree temp, diff, because on those 97 degree days they want it 72, 77 degrees isn't cutting it. now do to new laws and new construction, load calcs are becoming a requirement in some states and localities. one quick ex. one time in 1995, i went to a ladies house, 800 sq. feet, i said your looking at 1 1/2 tons, she wanted 2. no problem, IMHO a 1/2 is NO big deal, i'm not a purist, plus on those 97 days people like it. having said that another co. came in at 4 tons!! yep 4 tons! you heard it 4 tons! that's 4 tons for a 800 sq. ft. house, very well insulated. so that's why you need load calcs, every ines rule of thumb may be differant. by the way that house with the 2 ton 800 sq.feet cools great for the last 15 yrs.

  13. #13
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,072
    Quote Originally Posted by thes View Post
    one quick ex. one time in 1995, i went to a ladies house, 800 sq. feet, i said your looking at 1 1/2 tons, she wanted 2. no problem, IMHO a 1/2 is NO big deal, i'm not a purist, plus on those 97 days people like it. having said that another co. came in at 4 tons!! yep 4 tons! .
    4-tons? maybe they thought she was one hot Momma.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

Page 1 of 11 12345678 ... 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