Intelligent Use of Energy: Cut Heat Losses With Insulation
Richard R. Vaillencourt, PE,
Canterbury Engineering Associates LLC
Editor’s Note: This is the fourth in a series of articles on
intelligent energy use in buildings by consulting engineer Richard Vaillencourt. We hope you’ll find them helpful as you work to optimize
your building’s energy use.
GInsulation is the least expensive but most important part of your
energy equipment. Unfortunately, it is also often the most ignored. Any
money spent on energy that doesn’t get to where it is supposed to go is
wasted. Anytime the energy that you bought doesn’t hang around, but
quickly exits the building, you are spending more money than you need
Paradoxically, insulation does not stop heat flow! But it does present a
major restriction to the flow of heat. No matter how much insulation is
in place, heat will always be lost. If lost heat isn’t replaced by your
heating system, the inside temperature eventually will equal the outside
temperature. The temperature will remain constant only if you replace
energy in the space as fast as it is lost. Having insulation slows the
rate of energy losses and therefore the rate at which energy needs to be
replaced. Your goal should be to lose the least amount of energy
possible over time.
The most important thickness of insulation is the first inch. Adding a
covering of 1-inch-thick fiberglass insulation to a bare steam pipe will
have an amazing effect on heat loss. A bare 4-inch pipe carrying 15 psig
steam at 250 degrees F will lose about 530 Btu per hour per linear foot.
Add just 1-inch-thick fiberglass pipe insulation, and the heat loss
drops to 57 Btu/hr per linear foot. This is a heat loss reduction of 473
Btu/hr per linear foot – or close to 90 percent. Adding a second inch of
thickness will bring the heat loss down by only 20 more Btu/hr per
linear foot to approximately 37 Btu/hr per linear foot.
Insulation is equally effective on flat surfaces. If the temperature is
70 F on one side of a wall and 0 F on the other, a wall without
insulation will lose approximately 117 Btu per hour per square foot.
Adding 3.5 inch of fiberglass insulation (R-11) will reduce that heat
loss by about 95 percent down to only 6 Btu/hr per square foot. Adding
an additional 2 inches to R-19 will bring the heat loss down by only 2.5
more Btu/hr per square foot to about 3.5 Btu/hr per square foot.
These examples should bring home two truths about insulation:
1. Always insulate.
2. If you can only afford to use thin insulation, do it.
Straight pipes are the easiest and cheapest to insulate. But don’t just
insulate the pipes: insulate all the fittings, valves, etc. (except
steam traps). The irregular shapes of fittings and valves dramatically
increase the heat losses. As a rule of thumb, the heat loss from a
4-inch valve will be two to three times greater than that from one foot
of 4-inch pipe.
In the past, insulating fittings was a very expensive thing to do. The
insulation was custom-made from rigid, castable insulation for each
valve or fitting. This made the insulation hard to remove when
maintenance was required on the fittings and easily damaged every time
it was handled. The current practice is to purchase a blanket that is
very flexible, durable, wire-tied around the valve or fitting and is
easy to remove and reinstall.
Once insulation is in place, there is almost no maintenance involved.
All that is necessary is to protect it from damage. Insulation works by
creating multiple layers of air spaces. These air spaces can be lost if
crushed or filled with water. Do not let anyone walk on insulation –
whether on pipes, ducts or just in the ceiling. If the insulation gets
wet from roof or pipe leaks, it is virtually useless and must be
So the bottom line is insulate. No matter what you do, it is going to
make a difference.