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Does Determining Insulation R-Values Make You Sweat?

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Have your Manual J8® practitioners ever called you with questions on a home that does not match any construction option in the Manual J Tables? If you have ever fielded R-value related questions on older homes, ACCA now has additional guidance for you. A new 2013 Technical Bulletin (TB) entitled Determining Insulation Values In Existing Homes has been developed for members. The TB provides strategies for determining viable insulation values for common types of thermal insulation. HVAC contractors can use information contained in the bulletin to accurately calculate heating and cooling loads for older homes and for new home construction with unique or cutting edge insulating features.

Manual J practitioners all have experience with numerous types of insulation. However, few can properly identify all of the materials they have encountered or know what the actual insulating value is per inch for all of the different materials they have seen. This makes some Manual J load calculations more difficult to complete accurately. The TB contains illustrations and notes on various categories and types of insulation and building materials found in homes throughout the U.S. to aid those who want to perform the most accurate Manual J possible where unusual building envelopes are involved.

The first step is to identify the construction method and materials used, and amount of insulation present in the home. To aid practitioners, the TB has two R-value tables for residential and light commercial applications. The first table contains R-values for common insulation materials. The second table provides R-values for common and not so common building materials. In the bulletin, R-value tables are used to establish Manual J compatible U-values for unique building assemblies. Those U-values are then plugged into Manual J load calculations. Additionally, for future use, the assembly U-values can be named with materials designation comparable to the descriptors in Manual J Table 4.

Knowing a walls insulating value solves one problem. However, for years, Manual J practitioners have wished they had Superman’s X-ray vision so they could evaluate how well the existing insulation was installed. Now there is a RESNET non-destructive procedure that can be used as a second step in the evaluation of existing

insulation. This industry accepted procedure utilizes thermal imaging to evaluate the level of fill for existing insulation. The TB includes a sample problem showing how to use this procedure.

Many HVAC contractors have seen opportunities for expanding their company’s market base by developing whole home performance capabilities. This TB can provide their staff with a useful field tool. Once accurate loads based on a Manual J are established for any home they can be used to recommend home performance upgrades. Thus, HVAC contractors can use their Manual J load calculations as a home improvement performance evaluation tools. Homeowners can be shown how home performance upgrades will affect HVAC equipment sizing requirements and lead to energy savings for the life of their new HVAC equipment.

Don Prather

Posted In: ACCA Now, Technical Tips

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