How To Install A Portable Air Conditioner Venting Thru A Casement Crank Window

Discussion in 'HVAC Heating & Cooling' started by chuck b, Jun 30, 2013.

  1. chuck b

    chuck b sea-bee

    Messages:
    75
    Location:
    levering, michigan
    How can you vent a one or two vent hose from a portable room air conditioner thru a casement crank style window providing a water tight seal. Window is in a upstairs bedroom.

    Are the two vent line for windows better than a single hose (one for exhaust and one for emitting fresh air and air balance)?

    Any brands recommended.

    If not practical would a portable room dehumidifier help some? Michigan, where summer temps hit 85-100. Have central air. Tried closing some 1st floor vents to help push air upstairs but not much help. Will also try a floor vent booster fan to see if it helps.

    Casement window width is only 25" and using a small regular a/c would present an even harder sealing problem.

    Thanks for advice in advance.

    Have heard closing off 1st floor cold air returns might help????
    Our first floor very comfortable. Attic well insulated with ridge vents.
    Last edited: Jun 30, 2013
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    Setting the fan control (if you have one) to ON may help, since constant circulation tends to even out temperatures. Combined heating/cooling with ducts and registers is usually a compromise...with heat, in the floor with the natural lighter, hot air rising works well, but it is lousy for a/c, since that cool air pools near your feet. In an ideal world, you have both floor and high wall or ceiling registers, and depending on the season, you shut one or the other off. Dumping cool air from up high works much better than trying to force it up from the floor or lower wall. Similar thing with the return - in the winter, you want to collect the cold air near the floor and return it to be heated, but sucking the cold air from the floor and replacing it with colder air at the floor does little to make the vertical space a constant temperature, so a high return works better to suck the hot air out at the top. I have a relatively open floorplan, and have a return at the top of my staircase to the second floor (which actually has a skylight well going up to the roof at the actual skylight)...I suck the hot air from there, and tend to open the ceiling vents upstairs, and partially close off the vents downstairs, which forces more cold upstairs, which falls down. With probably R-60 in the attic now, to balance things, I can have the vents nearly even, upstairs and down and maintain 1-2 degrees difference between the floors. If you want to use a window type a/c for an upstairs problem area, you may want to look into a sleeve, and put it through the wall instead of through the window. This would also allow you to locate it higher up on the wall.
  3. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    What Jim says about ducts always being sub-optimal when used for both heating & cooling is true. Even with a well insulated attic there will be a measurable heat gain through the roof itself, though windows usually dominate the number.

    Closing off ducts invariably increases air-handler driven room to room pressure differences which in turn drives outdoor air infiltration, increasing the indoor humidity (for lower comfort levels) and increases the energy use. If the ducts are not mastic sealed and insulated, doing so would marginally improve the cooling & heating effiency, but wouldn't solve the cooling season upstairs/downstairs balance issue.

    If you're looking for a more permanent and well-sealed solution that doesn't take up window space, a ductless mini-split (even a cheap no-name version) makes more sense than portable AC, and many come with pre-charged linesets for making DIY installation reasonable. A high-efficiency name-brand (Daikin, Mitsubishi, Fujitsu, etc.) 3/4 ton will run you about $1100-1400, for a cooling-only version add a hundred or two for a high efficiency cooling + heating version. A 1-ton is a couple hundred more. But for code-min SEER 13 second-tier manufacturers (LG, Sanyo) you can get usually get cooling-only 3/4 tonners for under $900, heat pump versions for under a grand. Yes, that's a lot more money than a $500 1-ton portable, but it'll be quieter & more comfortable, and the SEER numbers understate the efficiency of the modulating variable speed (sometimes called "inverter drive") mini-splits compared to any single-speed AC by quite a bit.

    To the extent that cooling the upstairs efficiently takes the load off the central AC, an upstairs ductless will often become by default the primary air conditioning unit for the house, and it may be worth the money to go for a higher efficiency model. If you're heating with propane or heating oil it's usually cheaper to heat with a mini-split heat pump too (and there are models fully rated for -15F cold temp operation now), so keep those things in mind as you explore this route- it's sometimes worth paying substantially more for a high-efficiency heating + cooling version if you're getting substantially more benefit & use out of it than just auxiliary AC for a few weeks out of every summer.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    FWIW, cooling often means moving more air than required for heat, plus, that higher air speed may help you feel cool when doing it (course, it's best to avoid those big drafts from the air outlets). Too high of a fan speed in the winter can be detrimental to comfort. Plus, the ducts typically need to accommodate that higher air volume for cooling, where you could get by with smaller ones for heat. To get it right is much more than someone making a WAG. High air speeds are more problematic when using a heat pump, as the outlet temp often isn't as high as when using a burner or resistance heating. Bottom line, the CFM capacity of the ductwork, fan, and heating/cooling unit must all be matched for best comfort and low noise levels.
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