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Adding insulation to a small chest freezer

Post in 'The Green Room' started by peakbagger, Oct 19, 2012.

  1. peakbagger

    peakbagger Minister of Fire

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    Northern NH
    I picked up a new small (5.3) cubic foot chest freezer a few months back and finally had a chance to run a dedicated outlet to it. I plugged it in and let it run overnight. It has 3" walls and 3" flip up top. I had a piece of 3" isoboard foam sitting around the size of the top lid and figured I would set it on top of the lid and see if I detect a temp difference between the top of the lid and the top of the foam. There definitely is a noticable difference. As the freezer isnt going to be opened very often I am going to wrap the sides with the same foam (left over from another project) and then rabbet in a top cover that will attached to the top lid. The compressor exhaust air out the side of the unit so the unit will not be completely wrapped. I dont plan on sealing it tight so the big issue will be if there are any condensation issues.

    Since the foam is free it will be interesting to see if the kwh drops.

    With this small size, a energy star unit was avaiable but it was special order and considerably more expensive for marginal reduction in energy usage.

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  2. midwestcoast

    midwestcoast Minister of Fire

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    I'm interested to see how that comes out. We bought a chest freezer last winter & I really like having it. I went for the highest efficiency I could find but was lucky to get a big discount on a scratch/dent floor model.
    I would agree that condensation may be a concern. Years ago my father covered the lid & upper sides of their (huge & way less efficient) chest freezer with a few layers of thick blanket. Rust did start to form on the lid after a year or 2. That was back when the freezers were only insulated with fiberglass though.
    How did you measure the temp differences? I see little difference on the freezer vs ambient temp in my basement with an IR thermo except a cold spot around the seal. I do wonder if the IR reads accurately on the white metal surface though.
  3. peakbagger

    peakbagger Minister of Fire

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    I didnt set up a thermocouple but its very noticable to the touch. Isoboard is waterproof so if I like the results I will probably attach it with Liquid Nails and run a bead along the outer edges. Wont look pretty but who cares.

    The exterior surface will generally equalize with the surroundings so an IR thermo will tend to read the temp of the air space.


    As an aside I helped someone empty out a large freezer that had been used on their farm for many years. It had been plugged in continuously and was pretty beat up. Once we emptied it out we could just barely move it. Once it warmed up, it started melting and there was water dripping out of the casing for a week. I expect for many years the only insulation was a block of ice in the walls of the unit.
  4. btuser

    btuser Minister of Fire

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    Depending on how it's built I wouldn't do what you're supposing.

    Where are the refrigeration lines? I've got two chest freezers, one about 10yr old and one brand new. Both have the liquid/vapor refrigeration coils placed on the inside and outside of the foam, just under the metal skin. The cold line circulates on the inside to cool the freezer and the exterior line set uses the outside to dissipate the heat. I'm sure you could add insulation to the top (or a weight to make sure the gasket is tight) but by adding a layer of insulation to either side will screw with the design of the freezer, making it much harder to dump heat or cause the compressor to cycle constantly.

    My 10 year old freezer is now my beer cooler/lagering chest and combo root cellar. I put a new thermostat on it and now it holds at about 33F and costs about $10/yr to run. I looked into building what is called a "keezer" (kegerator) and was warned that you can severely hamper the unit's performance (kill it in short order) by covering the sides with even a layer of 3/8" plywood. If your chest freezer doesn't have a fan (residential vs commercial) running to blow off heat then it will need air flow on the metal skin to get rid of it.

    Don't wrap it. It's already super- efficient compared to just about everything.

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