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  1. #1
    Join Date
    Apr 2008
    Posts
    4

    contractors give different tonage quotes

    We are replacing the HVAC unit in our townhouse in Washington DC and are getting quotes on a dual fuel system from 3 contractors. All 3 levels of the building total 1200 sq ft. Depending on who you ask , calculated Heat loss is any where from 17,500 to 21,000 and Heat Gain is from 9,200 to 12,500.

    Contractor 1: 1.5 ton 15 SEER
    Carrier Furnace and Heat pump

    Contractor 2: 3 ton 15 SEER
    York (Luxaire Acclimate 9V series) Furnace and Heat pump

    Contractor 3: awaiting his quote.

    My questions are:
    Why such a discrepancy between tons for quotes 1 & 2?

    Is tonage a random concept and assigned by the manufacturer or does it refer to an absolute measurement? In other words could one of these quotes be configured incorrectly?

    Thanks

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,765
    one of them is waaay off

  3. #3
    Join Date
    Aug 2006
    Location
    Chelmsford MA
    Posts
    1,518
    Quote Originally Posted by t527ed View Post
    one of them is waaay off
    I agree, did anyone take all the measurements of the home and do a manual J? That is the only way to tell. Sounds like someone is using rule of thumb...
    We only want to do it, if we can do it right.

  4. #4
    Join Date
    Apr 2008
    Posts
    4
    I take it from your responses (nashobasales & t527ed) so far that tonage is an absolute.

    We purchased software from the link above and ran the numbers so that we might compare it to their results. Software support walked us through a couple of issues but it was determined that we had 17,500 heat loss and 9,200 heat gain.

    Contractor 1 said his was at 21,000 loss and 12,000 gain. Contractor 2 did not provide any numbers. Maybe his was the "rule of thumb" as nashobasales suggested.

    Thanks for your input guys. I'll keep you posted when quote #3 arrives.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    I'd bet #1 is correct.Nobody wants to install an undersized system,so I guess he has the load calc to back it up,meaning he knows he has sized it right.


    If the company is Cropp-Metcalf ,you are in good hands.

  6. #6
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by dash View Post
    I'd bet #1 is correct.Nobody wants to install an undersized system,so I guess he has the load calc to back it up,meaning he knows he has sized it right.


    If the company is Cropp-Metcalf ,you are in good hands.
    Dash what makes you say that?

  7. #7
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,611
    I used to live in a 1200 sq ft townhouse, inside unit. 1.5 ton A/C, could hang meat in there even in upper 90s weather. There's a 3 story townhouse community across from our office, most have 2 ton units though they don't need it. When I run a calc, I get about 11K. Got another neighborhood we work in, 50k furnace is oversized, 1.5 ton air. They are 2 story 1200 sq ft, lots of windows.

    Sounds to me like #1 is on it. 1.5 ton heat pump, the smallest gas furnae you can find. Wonder if a 7kw electric furnace might be better?

    #2 is out of his friggin' mind.

    Be interesting to see what #3 says.

  8. #8
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    I live in that general area and have a good recommendation for you if you're interested. I know this company can do heat load calculations. My email is in my profile. They are in MD but I don't think you will be too far away--I could be wrong, though.

  9. #9
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    rmvd

    what is your electric rate?

    you will never be able to properly size a gas furnace.

    what size is your existing AC condenser?

    IMO

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by second opinion View Post
    Dash what makes you say that?
    First part ,that's what we do ,size them ,and often find customer questio that what we propose is too small.

    Second part,I've known Mitch Cropp for many years.

    Why did you ask??

  11. #11
    Join Date
    Dec 2007
    Posts
    132
    First of all how is anyone sizing ant thing without r values ,window sizing and ratings contruction materials ect,ect,ect,. The 2 nd bidder might be quoting a 3 ton to get the heating btu's needed for the heat side of heat pump, sometimes you dont nessisaraly need it on the cooling but have to upsize to get the heat side right. The other issue is just because a manual j is done does not mean it is the bible ANYONE can buy and TRY to calculate losses and gains and loads BUT remeber you only get out what you put in, so any joe blow can fudge a manual j to make their system look like ie is sized correctly.

  12. #12
    Join Date
    Apr 2008
    Posts
    4
    It is very much like Baldloonie described. Long party walls and windows and doors facing north and south. We purchased the property and are gutting it. House will be fitted with new low-e glass windows, insulation to code and all energy star rated appliances and equipment.

    I didn't want to overload you guys with too much detail. It was the statement that #2 made about manufacturers configure their systems differently so a 3 ton from one can be equal to a 1.5 ton from another that made me wonder.

    A few weeks ago I attended a seminar from EarthCraft (Energystar and LEED) where they essentially said what Baldloonie did which is if you "seal the envelop" you can get away with a heat coil in your AC unit. My concern is if it isn't enough heat how expensive and troublesome will it be to retrofit a gas furnace if we go the heat coil route. Anyway sorry for the long post. Again it was #2's statement that drove me to this site. Which is great by the way.

  13. #13
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by dash View Post
    First part ,that's what we do ,size them ,and often find customer questio that what we propose is too small.

    Second part,I've known Mitch Cropp for many years.

    Why did you ask??
    Mutual acquaintance

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