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“Engineering is the science of economy, of conserving the energy, kinetic and potential, provided and stored up by nature for the use of man. It is the business of engineering to utilize this energy to the best advantage, so that there may be the least possible waste.”
William A. Smith, 1908
Energy savings, of course, will vary depending on energy prices. The payback afforded by additional insulation or investment in energy conservation measures is the average amount of time it will require for the initial capital cost to be recovered as a result of the savings in energy bills. A payback of 3 to 5 years might be economic, because the average homeowner stays in a home that long. However, payback criteria can vary by individual, and renters, for example, often face the dilemma of not wanting to make improvements for which they may not be able to fully realize the benefits. Described below are a few insulation alternatives.Reduce indoor air temperature by 4°F (-16ºC) in the afternoon.
Lower the ceiling temperature, perhaps by more than 15°F (-9.4ºC). Insulation [radiant barrier] can reduce ceiling temperatures from 101°F (38ºC) in bright sun on Oahu to 83°F (28ºC) (Figure 13.2).
Reduce or eliminate the need for an air-conditioner.
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Table 13.1. Cost-effective Insulation R-values for Existing Homes [a;1]
In a climate that is… | And a heating system that is…[b] | Insulate to these levels in the… | Ducts (e] in unheated/uncooled… | ||||
Ceiling | Wood-frame wall [c] |
Floor | Basement or crawl space walls[d] | Attic | Basement or crawl space | ||
Warm, with cooling and minimal heating requirements [f]
|
Gas/oil or heat pump | R-22 to R-38 | R-11 to R-15 | R-11 to R-13 | R-11 to R-19 | R-4 to R‑8 | None to R-4 |
Electric resistance | R-38 to R-49 | R-11 to R-22 | R-13 to R-25 | R-11 to R-19 | R-4 to R‑8 | None to R-4 | |
Gas/oil or heat pump | R-38 | R-11 to R-22 | R-13 to R-25 | R-11 to R-19 | R-4 to R‑8 | R-2 to R-8 | |
Mixed, with moderate heating and cooling requirements [g] | Electric resistance | R-49 | R-11 to R-28 | R-25 | R-11 to R-19 | R-4 to R‑8 | R-2 to R-8 |
Cold, with mainly heating requirements [h] | Gas/oil | R-38 to R-49 | R-11 to R-22 | R-25 | R-11 to R-19 | R-6 to R-11 | R-2 to R-11 |
Heat pump or electric resistance | R-49 | R-11 to R-28 | R-25 | R-13 to R-19 | R-6 to R-11 | R-2 to R-11 | |
(a) Adapted from the U.S. Department of Energy 1997 Insulation Fact Sheet available at (800)-DOE-EREC and Modera et al., Impact of Residential Duct Insulation on HVAC Energy Use and Life Cycle Cost to Consumers, ASHRAE Transactions 96-13-4. (b) Insulation is also effective at reducing cooling bills. These levels assume your house has electric air conditioning. (c) R-values may be achieved through a combination of cavity insulation and rigid board insulation and are for insulation only (not whole wall). (d) Do not insulate crawl space walls if crawl space is wet or ventilated with outdoor air. (e) Use the lower R-value for return ducts and higher R-value for supply ducts. (f) Florida and Hawaii; coastal California; southeast Texas; southern Alabama, Arkansas, Georgia, Louisiana, and Mississippi. (g) Idaho, Kentucky, Missouri, Nebraska, Oklahoma, Oregon, Virginia, Washington, and West Virginia; southern Indiana, Kansas, New Mexico, and Arizona; northern Alabama, Arkansas, Georgia, Louisiana, and Mississippi; inland California; and western Nevada. (h) Great Lakes area, mountainous areas [e.g., Colorado, Wyoming, Utah, etc.]), New England, New York, northern Midwest, and Pennsylvania. |
Table 13.2. R-Values
of Roof Components [3]
Component | R-Value |
Inside air film | 0.92 |
Steel deck | 0.00 |
2" polyisocyanurate (5.56 x 2) | 11.12 |
3/4" perlite (2.78 x 0.75) | 2.09 |
Smooth built-up roof | 0.24 |
Outside air film in winter | 0.17 |
TOTAL | 14.54 |
Table
13.3. Floor Insulation [5]
R-Value | Batt Thickness |
R-19 | 6 1/4 inches |
R-22 HD | 5 1/2 inches |
R-22 | 7 1/2 inches |
R-25 | 8 1/2 inches |
R-30 | 10 inches |
R-30 HD | 8 1/2 inches |
R-38 | 12 inches |
R-38 HD | 10 inches |