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Storage container Heat loss

Jellis Member Posts: 226
Howdy folks!
I am trying to size a heating and cooling unit for a storage container to be used as conditioned storage.
40x8x8 and 20x8x8
will use 2" of open cell spray foam on walls and ceiling,
container will be sitting on slab.
No windows, 1 exterior door
interior desired temp 70°F outdoor heating temp -4°F
I've tried a few different tools and have come up with a fair difference in BTU requirements.
Curious if anyone has had any luck with this.


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,326
    Open cell foam has an R value of 3.8 per inch. I'm guessing the only infiltration is the door?
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  • Jellis
    Jellis Member Posts: 226
    @Robert O'Brien
    yes indeed. just the door.
  • Jamie Hall
    Jamie Hall Member Posts: 15,858
    Don't overthiink it. You have 2 inches of foam at R 3.8 per inch. That gives you a total R of 7.6. Then your heat loss rate is your delta T (74) times your area -- whatever that is -- divided by your R value.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,175
    The floor is a big variable being uninsulated. Without that factor, my calc says 11,000 at design for the 40ft container. I would estimate that to double if the floor were factored in, but my program doesn't seem to want to cooperate
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,141
    Can you lift the container enough to insulate under the floor? A forklift or a couple of bottle jacks may be able to get you enough room to spray some foam under there. Then all you would need is a couple of candles every other day. That sounds like you might need Air Conditioning in the summer too. A ductless mini-split HP might do both zones if they are close enough to each other.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • neilc
    neilc Member Posts: 1,300
    what you doing in these boxes?
  • bitcohen
    bitcohen Member Posts: 4
    edited May 4
    5000 BTU would cool the whole container IF it is all insulated. Shading from the sun is very good also
    With a 2" gap under the door, some cold air will filter out to the larger area and somewhat condition the air but don't expect a lot of cool especially with the container not insulated.
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