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“Doghouse” efficiency

Austin G | Posted in General Questions on

I built, inside my garage, an enclosed area of about 100 sq ft with a 5’ ceiling for my dogs.  I used 2x6s, insulated with 6” rock wool, and then sheathed the structure with poly iso and housewrap tape.  It is not exposed to the weather, but I wanted to efficiently heat/cool the area.

My problem is, not wanting to spend the money on a 6k btu mini split this very moment, used the smallest portable a/c I could find – a 5500 btu hisense portable.  The structure also has the best dog door I could find, a double flapped insulated opening with magnets to hold each flap shut.  Many see where this is going… the negative pressure created by the a/c in a tightly sealed small space is pulling the flaps open, effectively rendering my attention to detail pointless.

What would be the best way to combat this?

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  1. Walter Ahlgrim | | #1

    How many hoses does your portable AC unit use? If your unit had 2 hoses going outdoors you should not change the pressure in the garage.

    When looking for you new AC unit search for "dual hoses"


    1. Austin G | | #4

      It’s just a single hose. That makes sense, I’m not well versed in this type of a/c. Haven’t had a window unit since I was a kid and used nothing but mini splits in my own homes. May have to look for a dual hose

  2. Steve Knapp CZ 3A Georgia | | #2

    You could buy a smaller "doghouse" AC ( But I would consider cutting a ventilation hole to allow some air exchange. You could use a hole saw set and keep enlarging the hole until the door closes.

    1. Austin G | | #5

      That’s similar to what I was thinking. Maybe make the vent down low in the garage to hopefully intake as cool of air as possible.

      Just sucks to cut a whole in an enclosure I meticulously air sealed haha

      1. Andrew C | | #8

        wrt cutting a vent hole down low in the garage -
        Where would this intake come from, inside or outside the garage? In a typical garage, inside intakes would mean the dogs would be sucking on exhaust and gas fumes, fertilizer/pesticides, paint, the garbage, etc. Not exactly good IAQ.
        Clearly if you're spending this amount of effort on your dogs you care about them. Hopefully if you have to cut a vent hole it will draw air from the outside.

        I spent time over the years trying to make comfortable accomodations for our dogs outside, but my spouse solved the problem by just letting them inside. I didn't really complain, but we only have one dog.

        1. Austin G | | #13

          While admittedly I didn’t think about this, my garage is pretty much just storage and parking for my wife’s car. It’s a PZEV, that should help right? Haha, no idea if that’s true, but any hazardous supplies are kept in the barn. My though was air drawn in from low in a shaded building would be cooler than outside. May not be enough to even matter

  3. Jon R | | #3

    A window air conditioner would be more efficient in terms of excess outside air.

    1. Austin G | | #6

      Do window units not create negative pressure also? I don’t have any windows in the enclosure but could certainly cut and frame in a window unit into a wall.

      1. Jon R | | #9

        My understanding is that most can control how much outside air you want to enter the room. None is an option (but not a good idea).

  4. Steve Knapp CZ 3A Georgia | | #7

    Depending on your climate zone, you might want to install a heat pump water heater in the garage. I have one in mine, and it does a pretty good job of cooling and dehumidifying the space.

  5. Expert Member
    Dana Dorsett | | #10

    >"Many see where this is going… the negative pressure created by the a/c in a tightly sealed small space is pulling the flaps open, effectively rendering my attention to detail pointless."

    A doghouse of that size that is THAT tight is a problem for the health of the occupants, unless there is active ventilation.

    Got a ZIP code (or at least an IECC climate zone)?

    How many lbs of dog (cumulative, if multiple dogs) would be spending 8 hours or more in there?

    1. Austin G | | #12

      I sit RIGHT on the border of zone 4 and 5.

      Three dogs of varying extremes haha. 130 pounds, 75 pounds, and 10 pounds.

      The middle dog is never inside, the big dog refuses to be inside in the winter, and the small dog refuses to be outside in the winter.

      My assumption was the doggy door would be leaky enough to be sufficient. But I didn’t want it to be so leaky it stayed open. I don’t think I want to put an ERV in a doghouse lol, but I’d love to if I hit the powerball!

      1. Expert Member
        Dana Dorsett | | #14

        With all three of them (215lbs of dog) in the space at once it would need something like 10-15cfm continuous ventilation to keep the CO2 levels from rising. Clearly with just the 10 pounder the air leakage alone is going to be enough. Panasonic makes some 10-20 cfm supply-only ventilators.

        A heated dog bed on the floor is probably a better solution than maintaining room temp with a thermostat controlled mechanical system. Even short-haired dogs are pretty OK with a 50F space if they have an 80-90F pad to lie on. The heat emitted by the 75lb dog plus the electrically heated dog bed would probably be more than enough to keep the space north of 40F when it's 0F outside.

        Is the 130lber one of those Bernese Mountain dogs or St. Bernard or something?

        >"Do window units not create negative pressure also? I don’t have any windows in the enclosure but could certainly cut and frame in a window unit into a wall."

        That's correct. Window units take outdoor air and blows it through the condenser coil is on the exterior of the building. The evaporator coil is taking in indoor air and blowing just as much air as it's sucking in back to the indoors. This isn't the case with 1-hose portables.

        The 1-hose portables the condenser coil is robbing air from the conditioned space, heating it up and ejecting it to the exterior, depressurizing the space. The evaporator coil's air output is only a fraction of the total air being pulled into the unit- half or more is being blown outdoors through the condenser coil. As the cooling load rises, the less efficient it is, since it's sucking in more outdoor air into the conditioned space.

        This gives it lower-than advertised efficiency & capacity, since it's forcing unusually high ventilation/infiltration rates, which becomes an increasing fraction of the total cooling load. The hotter it is, the less net capacity it has. You won't run out of capacity for cooling your doghouse, but it does depressurize the space, pulling garage air 0r outdoor air into the dog house. A window unit won't do that.

  6. Jon R | | #11

    Perhaps useful (on Amazon):

    Midea U Inverter Window Air Conditioner 8,000BTU

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