Exponential . . .you've got potential

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ISeeDeadBTUs

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Somewhere between Anectdotal and empirically driven, I'm postulating that as outside temps go up 10 degrees, the heat load must decrease exponentially-kinda like the tornado F-scale. Prolly one of you science types can quantify that with a heat loss formula, but I can't. Lately, though, I have been amazed at how I need to cut back on the quantity of wood for a load.

Oh! and side point for the RMND units. . . overloading (now much easier to do with higher outside temps) on succesive loads can turn coal beds into unburned charcoal/ash heaps. I find it's best to resist the temptation to load until the entire bed is below the bottom of the air inlets.
 
Most of the heat loss calculators are just spreadsheets that tally up all the various heat conduction paths to the outside. Walls, windows, ceiling, etc.

But I've seen blower door tests that demonstrate that at high temp differences the air just leaking out through the cracks can be more than 1/3 the total load. That air leakage increases with temp difference and wind.

I don't know if it's exponential but most houses could lose more air than you might think just by heat loss calculator estimates due to this increasing air infiltration as the weather get colder out.
 
Technically heat loss is determined with differential equations. It's not exponential but it is a curve (non-linear).

Heat loss calc's generally used in heating/cooling are very rough approximations. The folks that really care about heat transfer let sophisticated computer programs do the real number crunching based on inputs including types of material, ambient temp, temp difference, humidity, etc. and so on...

Heat transfer is an entire four (4) credit course for undergrad engineering geeks...
 
I know, I know, but we want to tend the fire!!
 
You have a good guess there.

Folks who want to analyze this stuff will look at three heat transfer mechanisms and come up with some sort of model (I am probably one of them). However, vapor movement (a non heat transfer element) can become a significant factor and make the amount of heat loss to look exponential.

Vapor movement or vapor loss is the direct exchange of inside air with outside air. Just like having some of the windows open, just a small amount can really chill a room.
 
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