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Thread: Will an air to air ductless heat pump on house cause too much vibration?

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    DIY Junior Member rgs's Avatar
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    Default Will an air to air ductless heat pump on house cause too much vibration?

    I'm planning to install a Mitsubishi mini split ductless air to air 18,000 BTU heat pump with the outside unit hung on an outside wall and I'm wondering if anyone has experience with this type of installation and can tell me if it will cause too much vibration in the house. Installer says he can mount it on rubber brackets.
    Thanks,
    Richard
    Last edited by rgs; 12-03-2013 at 05:37 AM.

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    In the trades Dana's Avatar
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    These things have scroll compressors- you can barely hear the sucker even when standing next to it- even the blower is hard to hear unless it's going at max speed.

    If you're mounting it on the side of the world's crummiest trailer with 2x3 studs 24" o.c. it may be enough of a tympanic surface to hear it while indoors, but on any framed housing it would be tough. You can use heavier duty vibration isolating rubber mounts between the unit and the bracket if you like, but most people just use whatever mounts the bracket kit comes with (usually ~6-10mm thick rubbery pads.)

    Last edited by Dana; 12-03-2013 at 09:55 AM.

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    DIY Junior Member rgs's Avatar
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    Thanks very much, Dana. And thanks very much too for all the rest of your very interesting posts on heat pumps. They've been very informative and useful.
    Richard

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    DIY Junior Member rgs's Avatar
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    One other question, if you don't mind. I saw this photo of a mini split installation on another site. I have a similar unheated sun porch with panels around the side that we open in the summer but usually close in the winter. I'm thinking if I install the heat pump in this way, it will draw it's air from inside the sun porch (though in my case it would be on the north side of the porch) where the temperature is usually a few degrees warmer than it is outside and thus be more efficient. I wonder if it's worth doing or whether the air flow might be a bit too constricted.

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    The compressor for this Kennebunkport, Maine, home is set up high on a stand on the south side of the house. It draws air from a three-season porch that has glass panels installed in the winter, pulling air up through the gaps in the floorboards. A protective roof will be installed as well.
    Last edited by rgs; 12-03-2013 at 10:53 AM.

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    In the trades Dana's Avatar
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    The volumes of air going through the outside unit (even at low speed) are HUGE, and it matters not one bit which side of the house it's located. At high speed a 1.5 ton like the -FE18 will be moving something like 4000-5000 cubic feet per minute, and yes, there's quite a rush of air standing right in front of the fan! There's a big whoosh and some hum, at high speed, but not the propeller-blast vibe of a light plane on a takeoff roll. (They designed them to be tolerably quiet even at max-speed in dense urban environments.)

    Pay attention to the clearance specifications- if you make it too tight to the wall you can impede air flow- the way it's boxed in from the sides in that picture looks way out of spec. It looks like they were in the middle of building a shed roof/awning over the top of the unit, which is good practice for protecting it from eave-cornice falls and roof avalanches, etc, but this one looks too restricted.

    If there is room to install it completely under the deck or very open crawl space or pier-foundation, that usually provides enough protection from both snow-drift and roof avalanches, etc. I've seen an under-deck installation work pretty well at a ski-condo in Smuggler's Notch, VT where they get deep snowfalls fairly often (deeper than at sea level in the marittimes, but maybe not quite as deep as the Gaspe' highlands.)

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    DIY Junior Member rgs's Avatar
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    Thanks again, Dana. I see there's no point in trying to draw the air in from inside the porch with that much air demand. There's only some 2,000 cubic feet of air on the porch at any one time.

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