Another question I’ve been pondering: is it worth the trouble and expense to insulate the ceiling of our (essentially unheated) cellar– i.e., under the floor of our kitchen/living room/guest room?At first this seems like a no-brainer: we have nothing but a couple layers of wood slats between the (relatively) warmest part of the house, and the potentially coldest part. But that doesn’t necessarily mean it’s worth doing.
Consider: unlike the outdoors, which around here has the potential to get down to -15º at various times, the cellar last year never went below 34º. Whether that’s because the cellar is 2/3 underground and draws in geothermal heat, or because it draws some heat down through that uninsulated floor, or both, I don’t know– but if the cellar ever did start to head towards the freezing mark, we’d have to start heating it intentionally– so, conceivably, a result of insulating the top of the cellar might be that I have to turn on a heater in the cellar.
Consider also: unlike most homes, where the living room might often be at 68º, 70º, or higher, ours is rarely above 64º, and averages closer to 55º. So, the differential between cellar and living space is typically going to be less than 30º. Consider further: the boundary between the cellar and living space, being a horizontal plane, exists at the highest point of the cellar and the lowest point of the living area– thus, likely, at the warmest level of the cellar and the coldest level of the living area. So that probably narrows the maximum temperature differential still further, maybe to 25º (I could measure this, I suppose).
So, after considering all that, is it worth buying 600 sq. ft. of insulation ($250?) and spending a day of my life getting covered in fiberglass to install it? I think the answer may be this: insulate under the guest room only.