New answers tagged energy-efficiency
Use rigid foam. You can cut it with a circular saw, or with a utility knife. Buy a 2 inch sheet that's R13, you an always double it up to get R26. Measure the size you need and cut with a circular saw, it cuts like butter. Make 2 and then attach to each other and the door with silicone. You will still possibly have issues with air leakage around the door, ...
One recommendation is to use rigid foam insulation attached with caulking, liquid nails, or silicone.
A rigid foam (or ductboard) box in the attic which sits over (is larger than) the door opening. When you open the door, the box is still there. When you enter the attic you lift the box out of the way. When you are done in the attic, you lift the box back into position over the door, then close the door.
The EER (energy efficiency ratio) is a lovely mashup of units (BTU/h)/Watts (ie, 12500/1275 in the questioned case) that will tell you (part of) what you need to know. The rest is up to how much you run it. It uses 1.275 KWh/h (1275 watts) and that costs you 14.07 cents/hr at 11.04 cents/KWh Compare to whatever you think you might replace it with - you'd ...
The true answer is that it takes more energy to remove heat from a space than it does to add heat to a space. For every watt of heat you want to remove, you have to expend an additional 2 to 3 watts of heat just to carry that first watt away from the area. So, insulation will always be biased towards preventing heat ingress.
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