One of the best things about becoming a homeowner is the amount you learn about construction. Of course, that also means you learn about design. The older house that I live in has a relatively centrally placed forced-air furnace with ducts that are also centrally located. This system is similar to how houses were designed when the main heat source was a wood-burning stove or a fireplace.

With a stove it makes sense to have one big stove in the middle of the house. The result though is that the center of the house is warmer than the outer perimeter. It turns out that this arrangement is not the best for forced-air furnaces. A better approach, used on more modern homes, is to have the ducts on the outer perimenter of the house, blowing hot air inwards. This provides a more even heating of the home’s interior.

Obviously, when forced-air furnaces were introduced, the first designers of these heating systems looked to fireplaces and wood stoves for inspiration. But, the situation was different. And, it took a while for people to make things better. (Cost is another issue; it is a lot cheaper to run ducts that travel a short distance from the heat source.)

Solving problems involves dealing with constraints. Assumptions are self-imposed or guessed at constraints. There is nothing wrong with having constraints and making assumptions. What is wrong is not looking at them carefully to see whether they are valid. A great design based on a wrong assumption is at best a theoretical exercise, at worst it is a blunder.

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