Jeremy Felt

Thermodynamics of a house roof spoiler

I hope the title of this is not “thermodynamics of a house roof spoiler” when I’m finished and if so, then I apologize for not being more creative.

I woke up this morning to a house that was slightly chilled: 66°F rather than 68°F. The boiler wasn’t able to keep up even though the low temp last night was somewhere in the neighborhood of 32°F. The boiler is old, likely 30 years, but in general it does okay as long as the outside temperature is 27°F or above.

One thing different was the sustained 15-20mph winds that seemed to last the entire night. That made me wonder how much wind could affect the transfer of heat from inside the house. A quick search later and I was reading a nice answer on the physics Stack Exchange that explains wind’s impact on Newton’s law of cooling.

𝑑𝑄 / 𝑑𝑡 = ℎ𝐴Δ𝑇(𝑡)

According to that answer, h is the heat transfer coefficient in that equation and “blowing cool air over a hot object has the effect of increasing h.”

So, given that our house is the object containing heat in this scenario, that h is probably much higher than normal, and that the surface area (𝐴) is large because it’s a house, I have to assume that deflecting the wind to reduce h in some way may help.

This is where things are going to get silly.

A rough sketch of a house on a hill with arrows representing wind.
I swear that’s a house.

Our house sits on a hill. If you could see wind, you could probably see it hurtling toward the house from miles away across Eastern Washington. When the wind blows from West to East, as it often does, it hits the back of the house.

The house has a flat roof where a second level bedroom was added years ago. That roof then shifts to sloped in the front.

This morning, as I was walking around the chilly house, wondering why the boiler wasn’t keeping up, I started thinking about the roof, how it was flat, and how it offered a nice opportunity for the heat inside the house to just keep moving along.

I then wondered what would happen if we put a spoiler on the roof. I hadn’t had my coffee yet, though it’s much later now and I’m still writing this post so I can’t really blame the coffee.

A rough sketch of a house on a hill with a highlighted spoiler of sorts.
Look at that fancy spoiler on this not so fancy sketch of a house.

So my thermodynamics question for the month—and I’m hoping the person I wrote this for doesn’t laugh too hard—is: would a spoiler do anything to reduce the amount of heat exchanged due to high sustained winds? 💨

I’m guessing the answer is that improving the insulation in the roof is a much better bet, but blogging is fun, so there.

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