Central Air conditionner 1 1/2 ton vs 2 ton

Discussion in 'HVAC Heating & Cooling' started by Hyrules, Mar 28, 2014.

  1. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    Hi everyone,

    I am currently shopping for central air conditioner for the house and I was wondering what was the difference between a 1 1/2 ton vs 2 ton.
    Some salesperson want to sell us a 2 ton some 1 1/2. The house is a standard basement and groundlevel house 24 x 40 or 960 sqft.

    Thanks.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,995
    Location:
    New England
    It's sort of like the difference between 200Hp and 300Hp engines...if you NEED a bigger one to say pull a trailer, then you need one, but it will use more fuel even when it isn't. Having too big of an a/c means it will turn on and off, and never stay on very long. Just like a car is better at cruzing down the highway rather than stop and go through the city, an a/c unit that is sized properly for your house will be more efficient AND more comfortable. Without knowing more about the house - amount of insulation, windows, orientation, and normal weather (for the design temp), you are just guessing at what size you need. In fact, you might be able to get by with a smaller one.

    The only way to know, save the most money, and be the most comfortable is to actually calculate the needs. Guessing by square footage is not very accurate. Since the new ones can last for a very long time, you don't want to go too big, or, for most of the time, the house may be the set temperature, it will only run a short time. An a/c unit needs to run most of the time to draw out the humidity (like a dehumidifier). Nothing worse than being cold and clammy! You'll be more comfortable with a smaller one that runs all of the time when it is really hot, drying out the house, even if it can't quite keep the temp down verses a bigger one that does, and the humidity level is way up there, almost as bad as outside.
  3. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    Thanks for the answer it makes a lot of sense.
    Last edited: Mar 29, 2014
  4. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    Most of the salesperson that came to the house for evaluation never calculated anything. They just gave us the amount of ton. Those thing I know : House orientation is more or less EAST / WEST , Windows are oriented east west as well and there are 3 windows in front and 2 in the back plus a sliding door. Normal temperature we are near ottawa some sites says zone 5. As for the amount of insulation i really dont know.
    Last edited: Mar 29, 2014
  5. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,121
    Location:
    Houston, TX
    Anyone that installs in your area should know about your requirements, for a house like yours.

    Many manufactures rate their units differently.

    I would go for a better brand (That You can get parts for) in either a 1.5 or 2 ton, and the one with the best warranty.

    The only difference in the two, may just be the way they are rated. And that will depend on where they are made.


    Close enough for government work.
  6. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    Yes we already made our choice on the brand. Ruud. Parts are widely available here and the warranty is really good. They where both recommended by different salesperson and on the web. We just wanted to know which one we should take.
    Last edited: Mar 29, 2014
  7. Reach4

    Reach4 Active Member

    Messages:
    2,229
    Location:
    IL
    Consider whether you like to keep the AC on pretty much all of the time when the weather is hot, or whether you often turn it warmer when you are away and want a faster cool-down upon return. Consider whether you like the AC cooler or warmer than most people.
  8. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,121
    Location:
    Houston, TX

    Looking at things like Compressor type is good.

    A multi speed compressor and fan motor may work better for any install. There are more parts to go bad, when it comes to how it works, but it can adjust to your needs using a good Thermostat.


    Good Luck.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,995
    Location:
    New England
    A proper analysis would need to know the size of the windows, their U-factor, and the insulation R-ratings, then surface area, things like 8' or other ceiling heights. If nothing else, you can probably see what type and amount of insulation is in the attic. How thick the walls are would give you an indication of the max possible insulation (like are they 2x4, 2x6, or other construction.

    The only time a bigger a/c unit is useful is if the whole house is heat soaked, and you want fast cool down. A smaller one will be more comfortable if you turn it on at the beginning of a heat wave (or like I do, at the beginning of the season!), and leave it on. The whole house can absorb a lot of moisture, and it takes awhile to dry it out. Makes it worse if you open the windows at night - it may be cool, but you're adding back lots of moisture into the structure that you have to remove the next time you turn on the a/c unit.

    A unit a little small may mean it will run all of the time, but it will also be drying out the air much better than one that turns on and off. In the first case, it may get a little warmer in the house, but it will be dry, and most people will still be comfortable. A cool, damp house is just not comfortable. There is no one right answer - each house is a bit different, and the use pattern may be different. A two-stage compressor can be a help, as it can act like the big one to cool things down fast, then switch to slower speed to maintain it. A variable speed fan on the furnace or air handler can make a big difference, too, as those tend to start out slow, which pulls more moisture out of the air, and at the end of the cycle, ramp down to extract all of the coolness in the coils.

    Without a good heat load analysis, most places tend to opt for a bigger one, but that may not be the best choice...they cost more to buy and run, and if not needed, aren't as comfortable.
  10. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    thank you all for your input. It will help alot in the decision. I'm currently tipping to the 1.5 ton version. It's smaller but I believe it should do the job. If my estimate is right it should do the job properly. We had 2 window air conditioner for a couples of year one was a 6500 btu and the other one was a 12500 btu which give 19000btu total. a 1.5 ton is about 18000btu which is enough to cool the whole house without a problem. More or less 1000btu will mostlikely not do a lot in difference.
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,995
    Location:
    New England
    That still may be too big, but it's harder to find smaller ones.
  12. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    Unless this house has a lot of west-facing window area picking up a lot of solar gain late in the day, even the 1.5 ton unit is probably going to be oversized for the load, but it would be a better choice than a 2- ton.

    The crude rule of thumb for code-minimum houses in Florida & Georgia these days is about 1 ton per 1000 square feet of conditioned space, and even that is sometimes a bit oversized. For houses with single-pane windows little or no wall insulation that also leak a lot of air, one ton per 500 feet of floor area usually works. I would be willing to bet that almost no houses in Quebec is built that way, but that's about where you would be with a 2-ton system.

    Windows in Quebec are likely to have somewhat higher solar gain than those used in the southern US, but during the middle of the day the angle of the sun is high, and a good potion of the heat gets reflected off the outer window pane. With a modest amount of roof overhang or small awning even that gain can be dramatically reduced. It's the west-facing glass that drives the peak loads up, because the gain occurs late in the day when the whole house has been baking in the sun all day, and the outdoor temperatures are higher, and very little of the heat/light is reflected due to the lower sun angle. Exterior shades or shutters work well on west facing windows though.

    If it is a fairly open floor plan with the doored-off rooms mostly on the north or east sides of the house, a better-class 3/4 ton or 1-ton mini-split would probably do a better job, since it modulates with load. It would run almost continuously while using very little power. but only the room with the interior coil unit is cooled directly. The good ones are also VERY quiet compared to any ducted system- quieter than your refrigerator.

    There are now mini-split heat pumps that can work at reasonable efficiency for heating in a Quebec climate too, which is much cheaper than heating with propane, heating oil, or electric baseboards, but may be more expensive than heating with natural gas. (It depends on your local electricity and gas rates.)
  13. Hyrules

    Hyrules New Member

    Messages:
    16
    Location:
    Quebec
    The house is oriented more or less east west. The front being west. During summer time alot of heat comes from the front windows as the sun is almost straight in front during the hotest hours of days. Temperature can get around 28 - 29ºC if the blinds are not closed in the living room that's when the oven in the kitchen is not running. Both are in a big open room ( combo living room / kitchen / Dinning Room) I believe a 1.5 ton will not be too much for those times. Anyway it's practically impossible to get less than that.
    Last edited: Mar 31, 2014
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