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Water Heater Insul Jackets


Jerry Simon
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Kurt has a couple of insightful posts on this forum that explain how insulating jackets actually decrease efficiency.

I freely admit to stealing his thoughts in the recent past to make myself appear brighter.

As for locating the posts, you're on your own.

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Originally posted by Bain

Kurt has a couple of insightful posts on this forum that explain how insulating jackets actually decrease efficiency.

I freely admit to stealing his thoughts in the recent past to make myself appear brighter.

As for locating the posts, you're on your own.

Found it...thanks...you're right, it was that Kurt nut.

Insulation acts in a linear fashion fir heat transfer through the material. In math terms, H=kxT, or heat loss equals the thermal constant (U value) times the thickness of the insulation times the Temperature difference between inside and outside. More simply – if you double the thickness of the insulation, you cut the heat loss in half. This, we pretty much all know intuitively. But it’s only true for flat surfaces. There’s a lot of simplification that goes on to get to that simple formula.

When you start insulating cylinders, you can’t ignore the effect of curvature. If the insulation is thin, the effects of curvature are small, and the formula above works fine. But as the insulation gets thick, the surface area of the outside increases with the square of the thickness while the surface area of the inside stays constant. Effectively, the heat has more “pathwaysâ€

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I don't buy it either.

At one time, I proposed a simple experiment to address this theory (myth?).

Start with several identical 5-gallon buckets full of hot water.

Place each on an identical sheet of foam insulation board.

Wrap each in a different thickness of fiberglass insulation.

Place another piece of insulation board on top of each one.

Monitor the temperature of each bucket over a period of several hours.

I predict that if you were to plot the results, you'd see a linear relationship between insulation thickness and heat retention.

Maybe this winter. Better yet, get Mythbusters on the phone . . .

- Jim Katen, Oregon

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